Chapter 69. Monitored Anesthesia Care and Anesthesia Outside the Operating Room

1. Many patients who are scheduled for monitored anesthesia care (MAC) are considered high risk for general anesthesia, and MAC is mistakenly presumed to be safer than general anesthesia.

2. MAC does not describe the continuum of depth of sedation; rather, it describes a specific anesthesia service in which an anesthesiologist has been requested to participate in the care of a patient undergoing a diagnostic or therapeutic procedure.

3. Many patients who are considered for minimally invasive procedures out of the operating room (OR) are considered high risk for traditional surgical procedures.

4. For deep sedation/MAC, proper choice of sedatives and their dosing can optimize patient safety, recovery, and discharge times.

5. The same monitoring and equipment, preprocedure evaluation, NPO (nothing by mouth) status, and recovery room standards used in the OR apply to remote locations.

6. The length and type of procedure, airway considerations, and remoteness of the location should all be considered when choosing the anesthetic technique.

7. Patient safety should supersede any other considerations in remote location anesthesia.

8. Open communication between the anesthesiologist and the proceduralist is key to safety and favorable outcomes.

9. Propofol sedation is classified as deep sedation in many circumstances. It may result in significant changes in airway anatomy and cardiopulmonary physiology. Therefore, propofol should be administered only by clinicians qualified to rescue patients from any level of sedation, including general anesthesia.

10. Involvement of the anesthesiologists in institutional sedation policy and in planning and developing remote anesthesia locations is essential.

Recent advances in medical practices such as imaging and minimally invasive diagnostic and therapeutic procedures have led to an exponential growth in the need for anesthesia services outside of the operating room (OR); so-called remote anesthesia. Each area presents unique challenges for the anesthesia care team (eg, the patient population served, the nature of the location, the procedures performed). The trend of expanding the range of procedures outside of the OR will continue, and the demand for anesthesia services in these locations will grow. For these reasons, anesthesia care teams must become involved in the care of patients and in the details of the procedural area into which they are called to provide their services. This includes ensuring that the same standards and codes that govern the OR and the recovery of patients from anesthesia are present in these remote locations before administration of an anesthetic.1

A variety of anesthetics have been successfully used for these procedures. A very commonly used technique is monitored anesthesia care (MAC). This chapter reviews the concept, definitions, and details of the MAC technique; the common procedures performed out of the OR, which often require the expertise of trained anesthesia personnel; and the specific challenges faced by the anesthesia care team in remote areas. Because these issues have been of great interest to anesthesia providers in general and anesthesiologists in particular, the American Society of Anesthesiologists (ASA) has issued many relevant and useful position statements and practice guidelines related to MAC and remote anesthesia care; this chapter also reviews these.

Definitions

Monitored Anesthesia Care

Monitored anesthesia care does not describe the continuum of depth of sedation; rather, it describes a specific anesthesia service in which an anesthesiologist has been requested to participate in the care of a patient undergoing a diagnostic or therapeutic procedure.2

Monitored anesthesia care was defined by the ASA in 2008 as a specific anesthesia service for a diagnostic or therapeutic procedure.3

Indications for MAC include the nature of the procedure, the patient's clinical condition, or the potential need to convert to a general or regional anesthetic. MAC includes all aspects of anesthesia care: a preprocedure evaluation, intraprocedure care, and postprocedure anesthesia management. During MAC, the anesthesiologist provides or medically directs a number of specific services, including but not limited to:

• Diagnosis and treatment of clinical problems that occur during the procedure
• Support of vital functions
• Administration of sedatives, analgesics, hypnotics, anesthetic agents, or other medications as necessary for patient safety
• Psychologic support and physical comfort
• Provision of other medical services as needed to complete the procedure safely

Monitored anesthesia care may include varying levels of sedation (Table 69-1), analgesia, and anxiolysis as necessary. The provider of MAC must be prepared and qualified to convert to general anesthesia when necessary. For instance, if the patient loses consciousness and the ability to respond purposefully, anesthesia care must then convert to a general anesthetic, regardless of whether airway instrumentation is used or not.

Moderate Sedation (Conscious Sedation)

Moderate sedation is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.2

Deep Sedation

Deep sedation/analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully after repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.2

General Anesthesia

General anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive-pressure ventilation may be required because of depressed spontaneous ventilation or drug-induced depression of neuromuscular function. Cardiovascular function may be impaired.2

Guidelines and Statements

The ASA issued a statement on granting privileges to a non-anesthesiologist practitioner for personally administering deep sedation or for supervising deep sedation by individuals who are not anesthesia professionals.4 It should be noted that because of the significant risk that patients who receive deep sedation may enter a state of general anesthesia, privileges to administer deep sedation should be granted only to practitioners who are qualified to administer general anesthesia or to appropriately supervised anesthesia professionals.

Another important ASA statement issued on granting privileges to a non-anesthesiologist practitioner for administering moderate sedation5 expressed genuine concern that individuals, however well intentioned, who are not anesthesia professionals may not recognize that sedation and general anesthesia lie on a continuum and thus deliver levels of sedation that in fact represent general anesthesia; however, they lack the training and experience to recognize this state and respond appropriately. Because of this concern, the ASA suggested a framework for granting privileges that would help ensure competence of individuals who administer or supervise the administration of moderate sedation. The aim of this statement is to assist health care organizations develop a program for granting privileges for providing moderate sedation.

Additional important points from the statement:

Only physicians, dentists, or pediatrists who are qualified by education, training, and licensure to administer moderate sedation should supervise the administration of moderate sedation. These practitioners should have completed formal training in the safe administration of sedative and analgesic drugs and in rescuing patients who exhibit adverse physiologic consequences of a deeper-than-intended level of sedation. Additional stipulations are that practitioners:

• Have the skills necessary for obtaining the patient's medical history and performing a physical examination to assess risks and comorbidities.
• Be able to assess the patient's risk for aspiration of gastric contents.
• Understand the pharmacology of all sedative and analgesic drugs the practitioner requests privileges to administer and their pharmacologic antagonists, vasoactive drugs, and antiarrhythmics.
• Understand the benefits and risks of supplemental oxygen.
• Be proficient in airway management with facemask and positive-pressure ventilation.
• Monitor physiologic variables.
• Document the drugs administered and at regular intervals monitor the patient's level of sedation and physiologic condition.

Fasting Guidelines

Because it is frequently not easy to predict the level of a patient's responsiveness to sedatives and because the sedation is a continuum, in which deeper levels of sedation might end up with a state of general anesthesia, it is recommended that the same NPO (nothing per os) guidelines for general anesthesia be followed in MAC cases. In urgent or emergent cases, the risk of pulmonary aspiration should be considered when determining the required level of sedation.

Preprocedure Evaluation

Preprocedure evaluation of the patient is crucial in determining the risk factors related to the patient's condition and also to anesthesia.

Some MAC cases are treated outside ORs; therefore, preprocedural evaluation of the place where the planned procedure will be performed is also of great importance. In many instances, patients undergoing interventional procedures are deemed to be at high risk for surgery because of multiple comorbid conditions or a specific life-threatening condition. Nevertheless, regardless of the anesthetic technique planned, these patients should receive the same level of attention given to patients being prepared for a surgical procedure in the main OR (MOR) pavilion. Focused history (major illnesses, medication allergies, NPO status, and previous anesthesia complications) and physical examination (mainly cardiovascular, respiratory, and airway) are mandatory. Relevant laboratory studies and other investigations (eg, electrocardiography [ECG], chest radiographs) should be reviewed. Patient counseling before the start of the procedure is vital to the success of the planned procedure and the anesthesia care. A patient who is well informed of the entire plan regarding MAC and who knows what to expect regarding the level of consciousness and awareness during the procedure is a more satisfied patient. Not all patients are candidates for MAC. The preprocedure visit is also important to determine candidacy for MAC.

Candidacy for Monitored Anesthesia Care

Procedures performed under MAC primarily depend on the patient's cooperation and motivation, as well as on the nature of the procedure being performed.

Mild to moderate sedation can actually disinhibit a patient's response to painful stimulation; therefore, if adequate local or regional anesthesia is unavailable for a patient who must undergo a painful procedure, MAC cannot be implemented successfully.

Although MAC carries no absolute contraindications, it may be unsuitable for the following patients and under the following conditions:

• Pediatric patients
• Patients without full mental capacity
• Intoxicated patients
• Patients with a condition that inhibits them from lying still for the period of time needed for the procedure
• Language barrier between the patient and the provider
• Psychotic or uncooperative patients
• Medically unstable patient, such as a patient with congestive heart failure, who is scheduled for an emergency procedure that requires supine position and the patient has orthopnea and cannot lie supine, although the procedure requires a supine position
• Patient with a suspected or known difficult airway; for instance, the airway may be difficult to monitor because of the position required or the nature of the procedure
• Excessively long procedures
• Procedures performed in an uncomfortable position. (eg, prone, lithotomy, kidney rest, and kneeling positions)
• Procedures in which a large volume blood loss or cardiorespiratory instability is expected
• Procedures in which even minor movement could be hazardous to the patient.

Intraoperative Monitoring

Standards for intraoperative monitoring of cases performed under MAC should be identical to those performed under general or regional anesthesia. These standards would naturally extend to providing anesthesia in settings outside the ORs as well.

Monitoring Depth of Sedation during Monitored Anesthesia Care

Accurate assessment of sedation depth is important in minimizing the risks of MAC and procedural sedation both inside and outside the OR. Many patients, particularly the elderly and very ill patients, may rapidly move from a plane of light sedation to obtundation. Practitioners should have the means to effectively monitor depth of sedation. Because the direct effect of sedatives and hypnotics on the brain cannot be measured, clinicians usually rely on indirect measures of the level of sedation, such as frequent patient stimulation (eg, Observer's Assessment of Alertness/Sedation Scale (OAA/S), Table 69-2) to measure the depth of sedation. These techniques, however, require persistent patient cooperation and are subject to testing fatigue. Additionally, there are procedures and cases during which periodical patient movement and speech might preclude the successful completion of the procedure. Also, clinicians traditionally have relied on subjective measures or autonomic signs of patient responsiveness to judge depth of sedation and analgesia. However, changes in autonomic signs (eg, hypertension and tachycardia) do not reliably predict awareness and discomfort during general anesthesia.6-8

An objective measure of sedation depth theoretically could decrease the incidence of patients being undersedated and oversedated, reduce anesthetic wastage, and shorten recovery and discharge times. Because the brain is the target of anesthetic action, and electrical activity of the cerebral cortex can be measured via electroencephalography (EEG), most depth-of-anesthesia monitors have focused on measuring changes in the EEG. The Bispectral Index Scale (BIS) was the first clinically available depth-of-anesthesia monitoring device. The BIS is a proprietary algorithm (Aspect Medical Systems, Newton, MA) that generates a linear dimensionless number ranging from 0 to 100 that decreases in proportion to increased anesthetic depth. The BIS does not correlate with movement, heart rate, or blood pressure. Although the BIS has been used more commonly during general anesthesia, it has been evaluated measuring the depth of sedation with propofol,9,10 midazolam,8 and even sevoflurane.11 During propofol-induced sedation, the BIS was shown to correlate with OAA/S scores,10,12 loss of response to verbal commands,9 suppression of learning,13 and propofol blood concentrations.13 Gan and colleagues14 demonstrated faster recovery times and decreased propofol usage with the addition of the BIS monitor, although formal cost-effectiveness studies during MAC or regional anesthesia have not been undertaken. Furthermore, BIS monitoring accurately and objectively measures patient sedation level during endoscopy15 and during procedural sedation in the emergency department (ED).16 In contrast to the targeted BIS readings for patients undergoing general anesthesia (BIS values 40-60), BIS readings of 60 to 80 are targeted during MAC. BIS values approaching 60 are associated with a low probability of recall.9,10,17 However, recall is impaired at much higher BIS values than is response to command.18 It is important to realize that BIS measurements are slightly dependent on the type of anesthetic agents used. Several authors have shown higher BIS values for loss of consciousness when opioids were added to an anesthetic.11,18,19 This phenomenon, which extends to other agents (eg, ketamine, nitrous oxide), exists because noncortical structures underrepresented in the EEG contribute to the mechanism of hypnosis and sedation with opioids.20 It should be noted that ketamine can cause loss of response to verbal command in doses as low as 0.25 mg/kg without altering BIS measurements.21 It also has been suggested that spinal and epidural anesthesia may affect BIS measurements independently of other anesthetics.22,23 Morley and colleagues22 demonstrated a small but detectable EEG suppression in patients receiving spinal anesthesia without concomitant intravenous (IV) sedation. The mechanism appears to be related to decreased afferent stimulation of the reticular activating system and is independent of block level.

A priori, the authors believe there is a selective subset of patients undergoing MAC in whom BIS monitoring is a valuable adjunctive clinical monitor to standard clinical evaluation. BIS monitoring would probably be particularly beneficial during procedures in which patients should not move or speak, procedures of prolonged duration, and procedures involving patients of advanced age or ill health. Whenever possible, patients should be monitored via behavioral methods (eg, continual assessment of response to commands) in addition to the BIS. Because both the general public and many non-anesthesiologists have difficulty distinguishing between deep levels of sedation and general anesthesia, it is advisable to discuss patient concerns about "awareness" or "being awake" during the patient's preanesthetic assessment and interview. Patients insisting on guaranteed amnesia and hypnosis for procedures under MAC should be offered general anesthesia if feasible.

Space Allocation and Equipment Needs

The ASA has published a statement that includes the following24:

• Availability of a reliable oxygen source and delivery method (nasal cannulas, face masks), along with backup supply of oxygen in the form of a full E cylinder
• Availability of adequate suction
• Ability to scavenge waste gases when inhaled anesthetic agents are required
• Presence of a self-inflating resuscitator bag that can administer at least 90% oxygen and deliver positive-pressure ventilation in the event of respiratory distress
• Adequate anesthetic drugs, monitoring equipment, and supplies for the duration of the case
• Adequate lighting and electrical outlets for proper visualization and operation of anesthesia equipment
• Availability of sufficient space for the anesthesia provider and any other necessary personnel, as well as unobstructed access to the patient, anesthesia equipment, and emergency supplies
• Emergency cart with a defibrillator and emergency drugs for cardiopulmonary resuscitation
• Observance of all applicable building codes and facility standards
• Availability of adequately trained staff for immediate assistance of the anesthesia provider, as well as reliable two-way communication with which to request additional assistance
• Provision of adequate postanesthesia care, which should include appropriately trained staff and equipment that ensures safe transport of the patient to the designated recovery area

After these conditions have been met, the anesthesia caregiver can focus on the actual care of the patient undergoing the proposed procedure.

An ideal sedative should have the following properties:

• Easy titration
• Potent sedative and amnestic agent with analgesic properties
• Rapid onset with predictable pharmacodynamics and pharmacokinetics
• Rapid recovery with no residual effect
• High safety profile with cardiorespiratory stability
• Painless injection

Unfortunately, this sedative has yet to be discovered, although the commonly used sedatives posses some but not all of these properties.

Propofol

Propofol is the most commonly used agent for IV induction of general anesthesia in the United States. It is also commonly used for maintenance of general anesthesia, for sedation in MAC cases, and for sedation of critically ill patients in intensive care units (ICUs). Because sedation is a continuum, it is not always possible to predict how an individual patient will respond. Accordingly, agents such as propofol require special attention because of the potential for rapid, profound changes in sedative and anesthetic depth, and the lack of antagonist medications. Even if moderate sedation is intended, patients receiving propofol should receive care consistent with that required for deep sedation. Propofol has the advantages of rapid onset and short recovery time,25-27 easy titration, and antiemetic action. However, it may inhibit hypoxic ventilatory drive and depress the normal response to hypercarbia; moreover, at higher doses, it can cause apnea and inhibit airway protective reflexes. Additionally, it has a hypotensive effect and may induce pain on injection, and prolonged infusion may result in propofol infusion syndrome.28 This syndrome is of greater concern in the ICU than in the procedural sedation setting.

Benzodiazepines

Midazolam, diazepam, and lorazepam are the three benzodiazepines commonly used in anesthesia. The benzodiazepines are used primarily for anxiolysis and amnesia as well as for moderate sedation in MAC cases. Midazolam can be administered orally, intranasally, intramuscularly, or intravenously. It can be used as a bolus IV dose or continuous IV infusion. The onset of action as well as duration of action of midazolam depend on its route of administration as well as the dose given; it is also affected by concurrent administration of other medications. Several studies pointed out the effectiveness of midazolam in the prevention of nausea and vomiting.29-31 However, midazolam has no analgesic properties, so it is generally used with other opioids during MAC cases.

After a single dose of IV midazolam, the peak effect is reached in 2 to 3 minutes, and the duration varies depending on the dose and on the age and condition of the patient. Incremental doses of 0.5 to 1 mg of IV midazolam are usually given every 2 to 3 minutes to reach the desired level of sedation. The oral dose is 5 to 15 mg for adults and 0.5 to 0.75 mg/kg for pediatric patients. Midazolam can be used as a continuous infusion with a dose 1 to 2 mcg/kg/min.

Among midazolam's many advantages are that it causes less respiratory depression than with other sedatives at the desired levels of sedation; has a reliable anxiolysis and amnestic action; prevents nausea and vomiting; and elevates seizure threshold, which increases the safety of local anesthetics used.

Opioids

Opioid analgesics have been the mainstay of pain control for thousands of years; they mimic the effects of endogenous substances known as endorphins. Because of the unreliable amnestic effect of opioids, they are usually used in conjunction with other sedatives such as benzodiazepines in MAC cases. In MAC cases, opioids play an important role in providing analgesia in conjunction with local anesthetics. Opioids exert their analgesic action at the brain 32 as well as at the spinal cord levels.33 The peripheral analgesic effects of opioids have also been described (Table 69-3).34,35 Opioids may cause pruritus, nausea and vomiting, and respiratory depression even in doses too small to disturb the level of consciousness. More importantly, they can induce chest wall rigidity that is severe enough to compromise respiration; however, this can be treated by induction of general anesthesia and muscle relaxation.

Individual Opioids

Morphine

Morphine has a delayed onset and prolonged duration of analgesia. These two properties may render morphine a poor choice for MAC cases in which rapid titration to effect is desired. Morphine in small doses intraoperatively administered may be suitable to provide prolonged postprocedure analgesia if significant pain is anticipated postoperatively.

Meperidine

Meperidine 50 to 100 mg IV together with diazepam were commonly used agents in procedure sedation in the early days of gastrointestinal (GI) endoscopies when sedation was ordered by the endoscopist and administered by the nurse.36 Meperidine was the most commonly used medication in the GI suite about 20 years ago.37 However, in today's practice, when anesthesiologists are more involved in the care of these patients and the number of MAC cases has increased, meperidine is used less often, and other opioids with faster onsets and shorter durations of action (eg, fentanyl, remifentanil, alfentanil, and sufentanil) are being used more often. Meperidine has an atropine-like action, inducing tachycardia, which can confuse the picture during sedation because it might be interpreted as patient discomfort. Also, its central cholinergic actions are undesirable. On the other hand, the advantage of meperidine lies in its anti-shivering action, which can be beneficial in MAC cases. Meperidine in a dose of 12.5 to 25 mg IV is effective for the relief of shivering.

Fentanyl

Fentanyl is still one of the most commonly used analgesics in MAC cases. Fentanyl can be used as a bolus dose or as a continuous infusion. Fentanyl's safety and potency as an analgesic and as a sedative rendered it an attractive choice for anesthesiologists as well as non-anesthesiologists for procedural sedation in the ED,38-40 radiology, and endoscopy suites. Fentanyl has the advantage of easy titration if given in repeated boluses (0.5-1 mcg/kg) or as a continuous infusion (0.01-0.05 mcg/kg/min).

Remifentanil, Alfentanil, and Sufentanil

Relatively newer rapid-onset, short-acting synthetic opioids have gained a place in modern anesthesia in general anesthesia as well as MAC cases. These newer agents have the advantage of easy titration as well as potency. The relative potency ratios for fentanyl, sufentanil, alfentanil, and remifentanil, to each other are approximately 1:12:0.0625:1.2, respectively.41

Usually, these potent short-acting opioids are used as continuous infusion with or without an initial bolus dose. Remifentanil was evaluated as a sole agent for procedural sedation and resulted in good patient and practitioner satisfaction,42 but patients' recall of the procedure was high, although not usually unpleasant, and respiratory depression was common. Remifentanil usually is used in combination with other sedatives such as propofol or midazolam, and much experience has been documented with these combinations.43,44 Remifentanil is usually given in a bolus dose of 0.5 to 1 mcg/kg, a dose that can be repeated, and the continuous infusion rate is usually 0.05 to 0.1 mcg/kg/min.

Alfentanil is significantly less potent than fentanyl or remifentanil and has been successfully used for sedation when combined with propofol. It is another rapid-onset, short-acting medication that can be administered in bolus doses or continuous infusion. The usual bolus dose of alfentanil is 5 to 10 μ/kg, which can be repeated in 1.5-μ/kg increments. The infusion rate for alfentanil sedation is usually 0.25 to 1.0 μ/kg/min.

Both remifentanil and alfentanil are associated with significant postprocedure pain because of their short durations of action, so traditionally, another longer-acting analgesic is recommended to be given during the procedure, especially when significant postoperative pain is anticipated.45

Sufentanil is the most potent synthetic opioid. It is approximately 5 to 15 times more potent than fentanyl and has a similar onset of action. Both sufentanil and fentanyl are formulated with the same concentration (50 mcg/mL), and an overdose resulting in severe respiratory depression could occur if sufentanil were mistaken for fentanyl. Sufentanil can be given as a bolus (0.1-0.5 mcg/kg) or infusion (0.005-0.01 mcg/kg/min) during MAC. Bailey and colleagues46 compared the effects of sufentanil and fentanyl on volunteers and showed that sufentanil produced longer lasting analgesia but less depression of ventilation than did fentanyl. Few other studies have focused on sufentanil in the setting of MAC, particularly since the advent of alfentanil and remifentanil. One possible reason for the dearth of studies lies in the unpredictable cardiovascular depression associated with sufentanil use, including bradycardia and hypotension, especially because these effects do not appear to be dose dependent.47

Ketamine

Ketamine is a phencyclidine derivative that produces profound analgesia, amnesia and sedation, and bronchodilatation. It usually preserves spontaneous breathing, cardiovascular stability, and airway reflexes. However, in larger doses, ketamine can produce hypoventilation and even a short period of apnea.48 When added to N2O and fentanyl, ketamine produces a state of dissociative anesthesia, a form of general anesthesia characterized by catalepsy, catatonia, and amnesia but not necessarily involving complete unconsciousness.

In low doses, ketamine elevates the pain threshold, causing analgesia. Ketamine's analgesic action lasts through the postprocedure period. The IV induction dose of ketamine is 2 mg/kg; below this dose (0.2-0.8 mg/kg), ketamine has a sedative and analgesic effect. After a single IV dose of ketamine, its onset of action is 30 to 60 seconds, and its peak effect occurs in 1 minute, with a 15-minute duration of action. The use of ketamine was limited because of the high incidence of emergence phenomena (10%-20%)49 in which there is postoperative disorientation, sensory and perceptual illusions, and vivid dreams. Emergence reactions can be prevented or attenuated by the coadministration of a benzodiazepine, barbiturate, or propofol with ketamine during sedation.50-52 In addition, ketamine increases salivation, intracranial pressure, intraocular pressure, and myocardial oxygen consumption.

Newer Sedatives

Dexmedetomidine

Dexmedetomidine is a highly selective α2-adrenergic agonist with sedative and analgesic properties. The Food and Drug Administration (FDA) approved dexmedetomidine in 1999 for short-term use (<24 h) for mechanically ventilated patients in the ICU, but since then, it has gained popularity in procedural sedation and MAC cases. Dexmedetomidine is used as a continuous infusion at a rate of 0.2 to 1 mcg/kg/h with or without an initial loading dose of 0.5 to 1 mcg/kg over 10 to 20 minutes.

After a bolus dose of dexmedetomidine, the onset of action is within 5 to 10 minutes with a peak effect in 15 to 30 minutes and a duration of action 60 to 120 minutes that is dose dependent.

Dexmedetomidine has the unique property of maintaining respiratory stability.53,54

Patients sedated with dexmedetomidine are easily arousable and maintain their ability to cooperate with the anesthesia provider, especially during airway instrumentation and awake fiberoptic intubation.55 It also has moderate analgesic,56 limited amnestic,57,58 and antisialagogue properties.59

Bradycardia after administration of α2-agonists is well documented.60,61 Blood pressure response to dexmedetomidine infusion is reported to be biphasic, with initial brief hypertension followed by more prolonged hypotension.57 Cardiovascular side effects are more profound in elderly patients, especially with bolus doses and higher infusion rates. A slower onset and delayed recovery compared with propofol were also reported.62,63

Fospropofol

Fospropofol is a water-soluble prodrug of propofol. Fospropofol liberates propofol by the enzyme alkaline phosphatase. One milligram of fospropofol liberates 0.54 mg of propofol. Because of the conversion of the prodrug to propofol, the time to peak of propofol concentration after a bolus and the elimination of propofol after infusion is longer than for propofol formulated in a lipid emulsion. The recommended fospropofol dose is 4.9 to 6.5 mg/kg IV bolus for individuals who weigh between 60 and 90 kg followed by supplemental doses of 0.25 of the initial dose administered no more frequently than every 4 minutes as needed to achieve desired level of sedation. Patients who weigh less than 60 kg are dosed as if they weigh 60 kg, and those who weigh more than 90 kg are dosed as if they weigh 90 kg. Fospropofol has the advantage over the traditional propofol preparation by being less painful with IV injection as well as no lipid load when prolonged infusion is required.

Side Effects of Fospropofol

Side effects of fospropofol include:

• Pruritus (incidence, 8%-28%), including genital, perineal, and generalized pruritus
• Paresthesia (incidence, 52%-74% percent), including perineal discomfort or a burning sensation
• Mild risk of hypoxemia, headache, and hypotension

Clinical experience with fospropofol remains limited, but the safety margin is apparently good.

The FDA-approved package insert of fospropofol states as follows64: "Lusedra [fospropofol disodium] should be administered only by persons trained in the administration of general anesthesia and not involved in the conduct of the diagnostic or therapeutic procedure. Minimal requirement for MAC applies here as well."

Antiemetics and Antinausea Medications

Postprocedure nausea and vomiting are less likely to occur with MAC cases because the effects of inhalational anesthetics are absent. However, nausea and vomiting may occur because of the stress of the procedure, the procedure itself (such as GI endoscopies and ophthalmic procedures), or the sedatives or analgesics (opioids) used. Postprocedure nausea and vomiting might explain patient dissatisfaction as well as a delayed discharge.

Commonly used medications for the prevention and treatment of postprocedure nausea and vomiting are dopamine antagonists, histamine antagonists, serotonin antagonists, anticholinergics, neurokinin antagonists, and dexamethasone. These medications can be used before, during, or after the procedure, depending on the relative risk of a patient to develop postoperative nausea and vomiting. Care should be taken with the sedative properties of some of these agents, especially in elderly patients.

Analgesics

A postprocedure pain control plan should be considered during MAC cases to provide analgesic coverage when the effect of the local anesthetic used for the procedure, as well as the sedatives and analgesics used during the procedure, wear off. Opioids as well as nonsteroidal anti-inflammatory drugs are good agents for controlling postprocedure pain.

Intermittent Bolus Technique

Different techniques have been used in MAC to administer sedatives and analgesics. Of these, the simplest and most commonly used is the intermittent bolus technique in which the medications are intermittently administered by the anesthesia provider to titrate to a desired level of sedation.

The advantage of this technique lies in its simplicity; however, that might not be the case with the newer agents with higher potencies and short durations of action, which can result in over- or undersedation. This technique is suitable for minor procedures of short duration when relatively longer-acting sedatives such as benzodiazepines and opioids are used; it is also suitable for use in younger healthy patients for whom the safety margins with medications are wider than for chronically debilitated elderly patients who may be oversensitive to the load of a bolus medication.

Continuous Infusion Technique

Conventionally, IV anesthetics have been administered as a large bolus or by multiple intermittent doses during a procedure. However, clinical studies have demonstrated that IV anesthetics given by variable-rate continuous infusion provide certain advantages over intermittent bolus techniques. They include (1) improved cardiopulmonary stability, (2) more predictable plasma drug concentrations, (3) reduced need for supplemental anesthetics or vasoactive drugs, (4) faster recovery times, and (5) lower total drug doses used.65,66

Target-Controlled Infusions

In 1983, Schuttler and colleagues67 used a computer-assisted infusion system to administer a constant plasma concentration of alfentanil and etomidate for surgical anesthesia. At the time, the concept was novel because drugs usually were dosed at a constant infusion rate regardless of expected changes in plasma concentrations over time. Many research groups have since developed their own systems for a variety of anesthetics. By delivering a target concentration of a drug rather than a target infusion rate, these target-controlled infusion (TCI) systems can effectively and rapidly achieve, maintain, and adapt plasma concentrations of drugs to changing patient and surgical needs.

A TCI device is a computerized infusion pump in which the selected drug is administered according to its known therapeutic window, the patient response, and the predicted (via computer modeling) drug concentration. The computer is programmed with a pharmacokinetic model as well as pharmacokinetic data. The computer automatically controls the infusion pump to maintain the target plasma concentration. Target concentrations can be increased or decreased over time based on clinical need.68

Pharmacokinetic data used in TCI systems have generally been derived from the literature, and the effectiveness and accuracy of TCI systems depend on such data. Most of these pharmacokinetic parameters are derived from small sample sizes of healthy individuals.69

There is considerable interpatient variability in both pharmacokinetics and pharmacodynamics. Compared with standard infusion pumps, TCI systems allow the incorporation of patient covariates (eg, weight, age, hepatic function, cardiac output) into dosing models that would otherwise be impossible to replicate without TCI systems.

Anesthetics used during MAC should permit rapid recovery with minimal or no residual cognitive or psychomotor impairment. At the same time, each patient care facility should develop recovery and discharge criteria that are suitable for its specific patients and procedures. Recovery and discharge criteria for MAC should be no different from those for general or regional anesthesia.70

Physicians should be able to assess home readiness in a simple, clear, reproducible manner. Medicolegal considerations mandate that physicians have evidence that the patient's discharge criteria were met (Tables 69-4 and 69-5) and that all discharge instructions have been signed by the patient and documented in the medical record. Patients should be duly informed that home readiness does not confer the ability to drive a car or return to work.

Although MAC is generally believed to be much simpler and safer than general anesthesia or regional anesthesia, this perception is unfounded, according to the ASA Closed Claims study published in 2006.71 The study was based on 7000 claims obtained from 35 professional liability insurance companies in the United States over a period of almost 20 years. Of 1952 claims for surgical anesthesia in the analysis, 121 claims (6%) were associated with MAC, 1519 (78%) were associated with general anesthesia, and 312 (16%) were associated with regional anesthesia. Patients who had undergone procedures under MAC were older and sicker (Table 69-6) compared with those who had undergone procedures under general anesthesia or regional anesthesia.

Interestingly, the proportion of claims for death and permanent brain damage was less in regional anesthesia compared with MAC (14% vs 33% for death and 8% vs 7% for brain damage, respectively). In contrast, the severity of injury was similar between MAC claims and those associated with general anesthesia (27% death and 10% brain damage; Fig. 69-1). Respiratory events were in similar proportions for MAC (41%) and general anesthesia (44%) claims but were much smaller for regional anesthesia claims (6%) (Table 69-7). Of these events, inadequate ventilation or oxygenation was the most common respiratory event in MAC cases, in which the patients were heavily sedated with a combination of sedative, hypnotic, and analgesic agents; the most common combination was propofol, midazolam, and fentanyl. About 50% of the cases involved procedures performed around the head and neck, which deprived the anesthesiologist of direct access to the patient's airway. Contributing factors entailed inattention to monitors, poorly functioning monitors, or inactive alarms, which caused delay in the recognition of problems and thus failure to intervene in adverse respiratory events. The standard of care was judged by reviewers to be appropriate in only 59% of the MAC claims, which was thus no different from general anesthesia claims. Payment frequency and amounts were similar for all types of anesthesia.

Electroconvulsive therapy (ECT) is used for treatment of bipolar affective disorder, major depressive episodes, and schizoaffective disorders, which are resistant to medical therapies. Overall, ECT is a relatively safe procedure with a very low incidence of major cardiovascular complications. It involves the induction of generalized seizure activity by introduction of an electrical stimulus through electrodes placed along the temporal area, either unilaterally or bilaterally. Often these procedures are performed in the morning in the postanesthesia care unit (PACU) because this area lies close to the OR, is well equipped, has monitored beds, and is staffed with nurses who are very familiar with anesthesia procedures and recovery from it.

Because of the nature of the therapy and the associated physiologic responses to generalized seizures, general anesthesia is required. Many patients have comorbid illnesses in addition to their psychiatric disorders. Although the overall number of procedures performed in the United States is large, morbidity and mortality associated with ECT are surprisingly low. These low rates result primarily from the use of standard monitors during the course of treatments as well as recent advances in pharmacologic agents used for anesthetic management and control of hypertensive and cardiac responses to seizure activity. A large retrospective review by Nuttall and colleagues72 reported a low incidence of complications associated with anesthesia for ECT. The most notable complications associated with ECT were prolonged seizures, which in this study were successfully treated with benzodiazepines. The goal of the anesthesia provider in the anesthetic management for ECT is to institute adequate airway support, suppress any recall or awareness of the session, and attenuate the physiologic responses to the stimulus. When the patient is ready to begin the session, the appropriate monitors are placed, and oxygen is delivered to the patient via face mask. General anesthesia is induced via an IV induction agent. When the patient loses consciousness, a muscle relaxant, generally succinylcholine, is administered in preparation for the induced seizure. For patients with a pseudocholinesterase deficiency or any contraindications to succinylcholine, a suitable nondepolarizing muscle relaxant is used in place of succinylcholine. When general anesthesia has commenced, the patient's airway and breathing are supported via face mask and positive-pressure ventilation.

The anesthesia provider continues to support respiratory function until the return of spontaneous ventilatory effort by the patient. In some instances, other forms of airway intervention may be necessary, such as endotracheal intubation for patients with severe gastroesophageal reflux disease. Because the ECT treatment course can last from several days to several weeks, any difficulties with the airway should be duly noted for any subsequent sessions and appropriate arrangements made.

Methohexital has been the most widely used induction agent in recent times. All hypnotic agents cause some reduction in seizure activity, but methohexital affects such activity to a lesser degree than the other agents. However, methohexital alone fails to prevent the resulting tachycardia and hypertension associated with ECT. The hemodynamic effects of ECT have been well studied in animal models with brief initial parasympathetic stimulation followed by sympathetic stimulation. Similar cardiovascular effects have been reported with humans. In ECT patients, brief episodes of bradycardia followed by significant tachycardia associated with hypertension may occur. Whereas the parasympathetic response is mediated by the vagus nerve, the sympathetic response reflects hippocampal activity as well as circulating catecholamines. The increase in systolic blood pressure and heart rate immediately after the stimulus may be as much as 30% to 40% and 20%, respectively.73 In patients with known cardiovascular disease or significant risk factors, these responses should be kept to a minimum to prevent any untoward cardiac events during the course of treatment. Several studies have been performed to determine which agents or combinations of agents best suppress this hyperdynamic response to ECT stimulation. A study by Gazdag and colleagues74 examined the difference in duration of seizure activity and hemodynamic response to ECT between methohexital and propofol. Although propofol significantly lowered the duration of seizure activity compared with methohexital, the clinical efficacy of the treatment was not diminished, and the resultant lower mean arterial pressure associated with propofol could be beneficial to patients who demonstrate a higher cardiovascular risk profile. Other studies investigated anesthetic regimens that included methohexital with adjuvant therapies. Locala and colleagues75 performed a prospective, randomized, double-blind study on the use of methohexital alone and remifentanil supplemented with a dose of methohexital sufficient to suppress recall. Patients who received remifentanil demonstrated a significant reduction in systolic blood pressure and heart rate associated with ECT. In addition to the ability of remifentanil to suppress the sympathetic response to seizure activity, some reports in the literature have indicated that it may increase the duration of seizure activity, making it an attractive agent in the anesthesia provider's arsenal.76

Other means of attenuating the hemodynamic response to ECT in patients with cardiovascular disease include the use of antihypertensive medications, most notably β-blockers. A study by Zhang and colleagues77 examined the effect of different doses of nicardipine administered before induction of seizure activity. They discovered that a dose of 40 mcg/kg IV of nicardipine in addition to 0.15 mcg/kg of labetalol sufficiently blunted the hyperdynamic response without a significant decrease in seizure duration or postprocedural hypotensive effects.

On the other hand, asystole is very rarely reported in association with ECT. It has been suggested that asystole results from multiple factors, including the use of bilateral versus unilateral electrode placement, history of atrioventricular blockade, higher doses of succinylcholine, the use of thiopentone as an anesthetic agent, history of significant coronary artery disease, administration of β-blockers as a premedication, and subconvulsive electroshock.78 These factors alone or in combination may increase the risk of bradydysrhythmias and asystole. Premedication with glycopyrrolate has been proposed to prevent bradyarrhythmias; however, it has not gained popularity because of its side effects and the fact that sympathetic response is more commonly seen than parasympathetic response.

In the authors' clinical practice, they have found that this postseizure hemodynamic turbulence is very short lived, and in most patients, no treatment is necessary and one need only to "wait it out." However, for cardiac patients, especially those who exhibit symptoms of ischemia on their ECG, the use of short-acting agents such as esmolol to treat tachycardia or nitroglycerine IV boluses to treat hypertension may be of value.

Most patients who present for ECT either are currently taking or have taken antidepressants or other psychiatric agents. Historically, the agents of most concern with regard to anesthesia have been the monoamine oxidase (MAO) inhibitors. According to previous recommendations, these medications were to be discontinued 2 weeks before any elective procedure.79 However, in a series of case reports presented by Dolenc and colleagues,80 patients experienced no adverse effects from general anesthesia with concurrent use of an MAO inhibitor.19 Furthermore, no difference in hemodynamic response to ECT sessions was noted in patients either currently receiving or not receiving an MAO inhibitor. Perhaps then, more important that discontinuation of MAO inhibitors is avoidance of any known contraindicated drugs, such as indirect-acting sympathomimetics and meperidine.

The number of diagnostic and therapeutic procedures performed in gastroenterology suites has increased greatly as the benefit of early screening for and treatment of both benign and malignant conditions have been established. The majority of cases use some form of anesthesia, either moderate sedation administered by the gastroenterologist or deep sedation and general anesthesia administered by the anesthesia provider. The anesthesia team usually becomes involved in the more complicated or emergent cases. To that effect, most patients who present to an anesthesia provider for periprocedural care often are elderly or tend to have multiple comorbid conditions that should be addressed before commencement of the anesthetic.

The most common procedures performed in the gastroenterology suite are upper endoscopy, colonoscopy, sigmoidoscopy, and endoscopic retrograde cholangiopancreatography. Each of these procedures carries its own unique challenges for anesthesia providers. Colonoscopy traditionally is performed either without sedation or under moderate sedation administered by the endoscopist. A deeper lever of anesthesia is required in some patients because of their increased apprehension or severe discomfort experienced during the procedure. Important considerations for the anesthesiologist during colonoscopy include hemodynamic instability caused by dehydration from a preparatory bowel regimen and uncompensated anemia from severe GI bleeding. During upper endoscopy procedures, patients usually are placed in the extreme lateral or prone position (Figs. 69-2 and 69-3). The combination of patient positioning and the nature of the procedure itself limit access to the head and consequently the airway. Airway obstruction and apnea during sedation may develop, so the endoscopist and the anesthesia provider must have a clear understanding between them that emergency management of the airway supersedes continuation of the procedure until the situation has been safely controlled. Bradycardia or other arrhythmias can result from distension of the GI tract or from probe insertion.81 Other complications include bleeding, perforation, aspiration, and infection.82 To block the gag reflex during gastroscope insertion, a topical anesthetic spray is usually used. Most GI physicians use IV sedation, usually midazolam and an opioid (meperidine or fentanyl), for the patient's comfort. Some procedures require the use of more potent agents because the procedures are longer and more complex and necessitate a high degree of patient cooperation.83 Propofol, with its potent amnestic properties and rapid recovery time, has become an ideal choice for these procedures. It can be titrated to produce any level of anesthesia, from anxiolysis to general anesthesia. Its tendency to produce deep sedation with subsequent loss of protective airway reflexes at standard doses has limited its use to anesthesiologists and other individuals trained in airway management.84 The level of sedation needed to successfully complete endoscopic procedures varies among populations. In general, elderly patients tolerated these procedures well at propofol concentrations associated with moderate sedation, but younger patients typically required larger doses (deep sedation) to suppress the somatic response to endoscopy.85 Although most GI procedures can be completed successfully under MAC (see Fig. 69-2), general anesthesia with endotracheal intubation (see Fig. 69-3) may be necessary, for example, in patients who have a difficult airway, undergoing a relatively long procedure, or are at high risk for aspiration. The need for intubation should be addressed with the endoscopist because the presence of an endotracheal tube may make the procedure difficult to perform.

There has been exponential growth in procedures for interventional pulmonology as a result of the proliferation of these procedures and the new indications for them (Table 69-8). Many traditional thoracic surgical procedures (eg, mediastinal staging) are now minimally invasive and can be performed as outpatient procedures.86 Increased demand has led to the establishment of specialized interventional pulmonology centers outside of the ORs.

New Procedures

Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration

Through endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA), the structure of the tracheobronchial wall and adjacent structures can be well visualized. This is an accurate, safe, and cost-effective technique that allows biopsy of mediastinal lymph nodes and peribronchial lesions.87,88

Complete Mediastinal Staging Using Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration

EBUS-TBNA has proved valuable for mediastinal lymph node staging of lung cancer.89

Electromagnetic Navigational Bronchoscopy

Electromagnetic navigational bronchoscopy is designed to enable the pulmonologist to biopsy lesions within the periphery of the bronchial tree. The system uses computer software that converts computed tomography (CT) scan images into three-dimensional virtual lung reconstruction. This setup allows navigational guidance within the lungs to endobronchially invisible targets and subsequent biopsy, almost in the same fashion as stereotactic brain biopsy or brain surgery.9

Procedures under Investigation

Bronchoscopic lung volume reduction is a technique by which unidirectional endobronchial valves are inserted through a flexible bronchoscope aimed at deflating existing bullae. This procedure is indicated in managing terminal chronic obstructive lung disease as an alternative technique for surgically removing diseased lung tissue, the so-called "lung-volume reduction surgery."

Bronchial thermoplasty includes heat that is applied endobronchially to reduce the mass of the airway smooth muscle as a treatment for patients with poorly controlled asthma.90

Anesthetic Care

Preoperative Evaluation

The extent of preoperative evaluation depends on whether the procedure is elective or emergent and how stable or critical the airway is. Preoperative assessment is usually conducted in the customary fashion with special attention to the following:

• Airway evaluation and symptoms of compromise
• Review of the pulmonologist's evaluation of the size of the lesion or tumor, its location with the bronchial tree, and its extent
• CT scans of the neck and chest to rule out airway abnormalities and mediastinal masses

Judicious use of premedication sedatives and anxiolytics is advised because of the compromised respiratory status of these patients. The majority of uncomplicated and routine diagnostic bronchoscopic procedures can be performed under light sedation. However, when the lung is compromised or when the procedure entails more than a simple diagnostic bronchoscopy, deep sedation MAC and general anesthesia by an anesthesiologist is needed. In these situations, many sedatives (eg, midazolam, fentanyl, morphine, remifentanil, alfentanil, or propofol) have been traditionally and successfully used. More recently, dexmedetomidine and fospropofol have become acceptable choices.55,91,92

A total IV anesthetic technique (TIVA), usually an infusion of propofol, is preferred over an inhalational anesthetic technique for the following reasons:

1. It ensures continuous delivery of anesthesia compared with an inhalational anesthetic technique because the integrity of the airway conduit for delivering inhalation anesthetic to the patient is not guaranteed for the whole duration of the operation because of the nature of the procedure.93

2. It prevents pollution of the OR by inhalational anesthetic agents when leaks occur during airway instrumentation, thereby avoiding the risk of sedating OR personnel.

Muscle relaxants are commonly used in these procedures to facilitate endotracheal tube insertion. Relaxation of the jaw muscles makes it easier and safer for the rigid bronchoscope to be inserted. Muscle relaxants also improve overall lung compliance by eliminating the chest wall component. Finally, they provide a motionless patient, which is advantageous because unexpected patient movement can have serious consequences, as in lasering airway lesions. It is wise to restrict all administered fluids to the minimum needed for these patients because many of them present with a very limited lung reserve, and pulmonary congestion may aggravate their condition.

Many anesthesiologists and surgeons use corticosteroids, in particular dexamethasone, as a prophylactic measure to decrease airway edema after airway surgery so that residual postoperative swelling of the vocal cords can be avoided. Steroids are also used in cases of extensive surgical tracheobronchial tissue trauma. However, this practice is defended only on the basis of its putative clinical advantage because evidence of its real advantage is controversial at best.94-97

Management of the Fraction of Inspired Oxygen

Administering a fraction of inspired oxygen (FIO2) of 1.0 in such procedures is very common. However, it is usually necessary to maintain FIO2 at the lowest tolerable level (<0.4) during airway laser usage or electrocautery. Periods of extended apnea and complete airway obstruction can be expected during more challenging cases. Complete airway occlusion frequently occurs during the critical phase of removing the stent or stent fragments or the inflated balloon dilators used for tracheobronchial dilation. Therefore, it is always advisable to return to ventilation with 100% oxygen before extraction of the stent before exchange of airways and before extubation. Finally, during any part of the procedure, if the patient cannot tolerate lower oxygen levels, it may be necessary to defer treatment temporarily and ventilate with higher oxygen concentrations.

Airway Management Choices

No Airway

This is a popular technique because relatively short procedures are performed in a remote bronchoscopy suite where an anesthesia machine and capnography are unavailable. Great emphasis should be placed on airway topicalization to ensure that a patient can tolerate the bronchoscope without needing deeper planes of sedation, that may add to their concurrent risks.

Endotracheal Tube

Intubation with a large-diameter endotracheal tube (eg, size 8.5) facilitates ventilation around the relatively large-diameter flexible bronchoscope, and when it is cut short, it facilitates navigation of the fiberoptic bronchoscope. A short large-bore endotracheal tube could be used via an existing tracheotomy with flexible bronchoscopic instruments. Use of a fiberoptic swivel adaptor will allow continuous ventilation, thereby avoiding circuit disconnection during flexible bronchoscopy.

Rigid Bronchoscope (Figure 69-4)

Because of the size and noncompressible material in silicon stents, a rigid bronchoscope is preferred for insertion and removal of silicon stents, for removal of granulation tissue and large tumors invading the tracheobronchial tree, and in some instances to support airway patency in the face of a large mediastinal mass compressing the airway. When a rigid bronchoscope is used, ventilation could be accomplished through either attaching the anesthetic circuit to the bronchoscope side port or through jet ventilation where the jetting device is attached through a special adaptor to the bronchoscope side port. Leaks around the rigid bronchoscope are common but can be easily remedied by maximizing the fresh gas flow and packing the mouth with saline-soaked gauze.

Supraglottic Airway

In cases in which the tracheal lesion is subglottic, a supraglottic airway (SGA) (eg, a laryngeal mask airway) can be effective98,99 because it allows access to the subglottic lesion with the flexible bronchoscope, and offers a means of ventilation as well. However, it does not guarantee reliable protection against aspiration.

The techniques described above require clear communication between the anesthesiologist and the pulmonologist. Most of the procedures described above are performed as outpatient procedures; patients are discharged the same day. However, extremely sick patients undergoing a complicated resection or lasering of endotracheobronchial lesions may benefit from overnight admission. This compares favorably with that of invasive thoracic surgery, which requires postoperative ICU admission and a prolonged hospital stay.

Potential complications of bronchoscopic surgery are numerous, ranging from hypercarbia and minor levels of hypoxemia on the one hand to major bleeding, tracheal rupture, and loss of airway integrity on the other.

Stent removal provides an example of a risky pulmonologic intervention. Potential complications include retention of stent pieces, mucosal tears with bleeding, reobstruction, the need for postoperative mechanical ventilation, pneumothorax, damage to the pulmonary artery, and death.93 The jet ventilation technique can lead to barotrauma, including pneumothorax, necessitating chest tube insertion. Laser airway fire, although rare, is also a very serious complication.

The key to favorable outcomes lies in deep understanding of the underlying lung pathology; open two-way communication between the anesthesiologist and pulmonologist; understanding the nature of the procedure; and above all, vigilance and preparedness.

An increasing number of patients are undergoing invasive cardiology procedures that require the presence of trained anesthesia providers. In the past, certain procedures, such as placement of pacemakers/defibrillators, were performed in the OR by a cardiothoracic surgeon with a cardiac anesthesiologist in attendance.100 Recently, however, implantation of these devices is being performed by the interventional cardiologist in the cardiac/electrophysiology laboratory with the assistance of a noncardiac anesthesiologist. The physiologic status of patients presenting for placement of implantable cardioverter-defibrillators (ICDs) varies from young, otherwise healthy individuals with supraventricular dysrhythmias (Wolff-Parkinson-White syndrome) to elderly patients with significant coronary artery disease or congestive heart failure who have survived a life-threatening arrhythmia (ventricular tachycardia, ventricular fibrillation). Many have severe ventricular dysfunction. The extent of their cardiac disease should be assessed preoperatively by the anesthetist, and appropriate consultations should be obtained from the cardiologist responsible for the patient's care.

Anesthetic management for these cases ranges from sedation to general anesthesia with an endotracheal tube. Complicated cases of pacemaker or ICD wire extraction are typically performed under general anesthesia. In the case of automatic ICD implantation, after the device has been implanted, a device check is performed, consisting of induction of ventricular tachycardia or ventricular fibrillation, recording detection of the arrhythmia by the device, and treatment of the arrhythmia. This process can be quite uncomfortable to the patient, especially if multiple cycles are necessary. When sedation is used, the anesthesia provider must be prepared for a brief period of general anesthesia to allow for such device testing.101 Antiarrhythmic drugs and an external defibrillator should be present at all times in case the device fails to restore normal sinus rhythm. Along with standard monitors, an arterial line is usually used for this purpose. However, central venous catheters, providing ideal access for injecting vasoactive drugs, are reserved for sicker patients scheduled for more invasive procedures. A postprocedural chest radiograph should be obtained to rule out pneumothorax or pericardial effusion and to confirm lead placement. Patients may recover in the cardiac laboratory recovery room if the nurses are trained and qualified to recover patients from anesthesia; otherwise, they should recover in the main hospital PACU.

Electrical cardioversion is used to convert patients to normal sinus rhythm. The usual indications are atrial fibrillation, atrial flutter, and supraventricular tachycardia. Cardioversion can be performed either emergently (hemodynamically unstable arrhythmias) or electively (failed medical therapy). Because of the physical discomfort and psychologic distress caused by the procedure, electrical cardioversion is performed either under deep sedation or general anesthesia. For emergent cases, patients should be treated as having "full stomach" and appropriate aspiration precautions taken. In elective cases, a brief period of general anesthesia using an induction dose of etomidate, propofol, or methohexital for the actual delivery of the stimulus is sufficient. It is usually so brief that ventilatory support is generally unnecessary.102 However, patients with difficult airway may require a SGA or endotracheal tube for ventilatory management during the procedure. The induction dose should be adjusted cautiously; sedatives received by the patient should be considered if the procedure is to follow a transesophageal echocardiography, so as to avert atrial thrombus before the cardioversion. The postprocedural recovery time is generally brief.

Interventional radiology is currently exhibiting unprecedented growth, from state-of–the-art imaging studies to placement of vascular stents. As interventional radiologists continue to expand their scope of practice to the limits of modern medicine, the role of anesthesiologists in this medical odyssey has become increasingly prominent. Initially, the majority of interventional procedures were performed with local anesthesia and minimal sedation administered by a radiologist. However, as the nature of the procedures became increasingly complex and the need for total patient compliance became necessary, the level of sedation required to successfully perform these interventions gradually began to rise. The frequent need for deeper sedation coupled with the increasing number of high-risk patients presenting for these "minimally invasive" procedures has led to the growing involvement of trained anesthesia personnel in perioperative management in the radiology suite. The radiology community generally believes that the presence of a separate anesthesia provider responsible for sedation/anesthesia, pain control and continuous resuscitation during technically challenging procedures, especially in critically ill patients, should be mandatory.103 A wide variety of cases are performed in the radiology suite, many of which involve the services of an anesthesiologist. This section focuses on the most common and clinically demanding procedures and their complications as they relate to the anesthetic management.

Radiofrequency Ablation

Radiofrequency ablation (RFA) is a widely used noninvasive treatment for primary and metastatic tumors and painful bone and neural lesions. One limitation of this form of therapy has been the relatively small area of tumor destruction achieved in a single treatment. However, recent technologic advances in this modality have allowed for destruction of larger lesions (>5 cm in diameter) during a given session.104 This improvement has led to the expanded use of RFA in the treatment of many malignant tumors, including pulmonary, hepatic, bone, and renal cancers.

Radiofrequency ablation entails placement of either a single electrode or multiple electrodes contained in a single needle into the lesion targeted for ablation. Once in place, tissue coagulation is induced through an electromagnetic source within the electrode.105 Correct positioning of the electrode into the lesion of interest is accomplished through guidance from imaging techniques, which include ultrasonography, CT, CT with fluoroscopy, or magnetic resonance imaging (MRI). Although CT is the preferred modality, the choice of imaging depends on the availability of the technology at a particular center and on the technical expertise of the interventionalist performing the procedure.42 Anesthetic management of RFA depends on the size and location of the tumor. For most cases, MAC is sufficient and is generally well tolerated by patients. For larger lesions or lesions near vascular structures, general anesthesia with placement of endotracheal tube may be required to prevent patient movement during critical portions of the procedure. Complications of RFA include hemorrhage, pneumothorax, hemothorax, thermal injury, electrical shock, and hyperthermia because the patient may exhibit significant increases in body temperature in response to direct heating of large masses.106 Patients can recover in the hospital PACU or in the recovery area of the interventional suite, if appropriate.

Cryoablation

Cryoablation is a minimally invasive technique for treating lung, liver, breast, kidney, and prostate masses. It uses liquid nitrogen or gaseous argon for cooling, which results in tissue destruction through direct freezing and in denaturation of tissue. Both MAC and general anesthesia have been used successfully for these procedures, depending on patient characteristics and the size and location of the mass.

Interventional Neuroradiology

Perhaps one of the most challenging and exciting fields of interventional medicine is the area of interventional neuroradiology. Noninvasive treatment of neurovascular disease has evolved significantly. The most common treatments are embolization or sclerotherapy of tumors and arteriovenous malformations (AVMs), angioplasty for cerebral vasospasm, embolectomy for acute stroke, and coil embolization of cerebral aneurysms. In most of these cases, general anesthesia is the preferred method of anesthetic management because patients are often required to remain motionless for extended periods. Each of these procedures carries its own patient and risk profiles, which the anesthesia provider should consider in formulating a management plan. Common complications of interventional neuroradiologic procedures include cerebral ischemia, hemorrhage, catheter displacement, and pulmonary embolism.107 The goals of perioperative management in these procedures are no different from those set for any neurosurgical case: maintenance of hemodynamic stability, preservation of cerebral blood flow and cerebral perfusion pressure, and rapid emergence after completion of the procedure to assess the patient's neurologic status.108

Arteriovenous malformations are vascular structures in which one or more aberrant arteries feed into a nidus that is then drained by coexisting aberrant veins. In the past, embolization of AVMs was performed before surgical resection of the abnormality. However, many of these lesions are now being treated by embolization alone in light of the availability of experienced neuroradiologists.109 Embolization is accomplished by deploying thrombosing coils or permanent balloons or by injecting sclerosing agents, glues, or particulate material. Complications after embolization include cerebral hemorrhage or edema resulting from sudden reperfusion into areas that previously were underperfused.110

Careful management of arterial blood pressure and thus cerebral perfusion pressure is important. This is best accomplished under general anesthesia with the use of muscle relaxation to avoid the sudden increase in blood pressure and intracranial pressure associated with coughing or involuntary paroxysmal movement. Some patients may require preoperative and intraoperative pharmacologic agents to assist in controlling blood pressure during the procedure. Propranolol, in addition to its known hemodynamic effects, has been shown to possibly reduce cerebral metabolic rate and cerebral blood flow without significant impairment of metabolism–flow coupling.111 Invasive blood pressure monitoring is recommended for patients for whom deliberate hypotension is planned. Placement of other invasive monitors will depend on the current physical status of the patient and on the need for postprocedural hemodynamic monitoring.

The endovascular approach via coil placement is gaining popularity in the treatment of unruptured aneurysms.112 The basic goal of this approach is obliteration of the aneurysm sac through the placement of coils.113 Possible complications associated with coil embolization include hemorrhage, thromboembolism, and vasospasm, which is most notably problematic in the case of aneurysm rupture. Nimodipine remains the agent of choice for prevention or continued treatment of vasospasm. Additionally, hypervolemia–hypertension–hemodilution (triple H) therapy remains popular for treating cerebral arterial spasm. Patients who undergo these procedures are admitted to the ICU for postprocedural monitoring of their neurologic status.

Carotid artery stenting is another minimally invasive procedure that is being performed in place of the traditional carotid endarterectomy because it is believed to improve outcomes.114 Although it could be performed under MAC or general anesthesia, MAC has the advantage of allowing the assessment of neurologic status and the detection of changes in mental status.115

Transjugular Intrahepatic Portosystemic Shunting

Transjugular intrahepatic portosystemic shunting (TIPS) is a technique that involves the creation of a shunt through the liver between one of the hepatic veins and either the right or left portal vein.116 TIPS traditionally has been used to treat esophageal varices, but its uses have been expanded to include the treatment of several other hepatic conditions, such as portal vein thrombosis and Budd-Chiari syndrome. TIPS can be performed under MAC or general anesthesia, depending on the patient's physical and mental status and the practitioner's familiarity and experience with the technique. Patients who present for TIPS may have a large amount of ascites or other complications of hepatic disease, pleural effusions, intrapulmonary shunting (which can restrict ventilatory effort and decrease oxygenation),117 cirrhotic cardiomyopathy, encephalopathy, coagulopathy, and hepatorenal syndrome. Patients who have a significant amount of ascites or who have experienced a recent episode of GI bleeding are at increased risk for aspiration. The procedure itself may require several hours to perform, which requires a cooperative and stable patient. Often, TIPS is preceded by paracentesis to relieve some of the increased intra-abdominal pressure. All of these factors must be taken into consideration when choosing an appropriate anesthetic method. Standard monitors usually are sufficient, but more invasive monitors may be required in emergent cases and in hemodynamically unstable patients (exhibiting active bleeding, severe cardiomyopathy, and acid–base disturbances). Adequate IV access in the form of a large-bore catheter should be established because hemorrhage is one of the complications of the procedure, and the patient may experience hemodynamic instability. Recovery usually takes place in the PACU or ICU.

The previous section discussed therapies in the radiology suite that involve some type of invasive technique. For many of these procedures, the need for sedation or anesthesia is self-explanatory. However, the services of the anesthesia providers may also be required for various noninvasive diagnostic modalities. This section discusses the most frequently performed examinations, MRI and CT scan.

Magnetic Resonance Imaging

Magnetic resonance imaging is a diagnostic imaging tool that uses both static and magnetic field gradients, the strength of which ranges from 0.15 to 3.0 Tesla. MRI entails certain risks, the most serious of which stem from ferromagnetic objects or equipment near the magnetic field. Many of the reports of injury or fatality are related to these objects, which become projectiles when exposed to the strong magnetic field. Furthermore, patients who have any indwelling metallic device, such as a pacemaker, ICD, aneurysm clip, or infusion pump, are generally contraindicated for MRI.118 However, MRI can be performed on a limited bases for patients who have implanted devices such as a deep-brain stimulator or vagal and phrenic nerve stimulators. Monitors should be attached to patients with care; MRI-compatible ECG pads should be used, and the monitor wires should be prevented from coiling because coiling may result in patient burns.119 Finally, risks may occur that are associated with contrast material, such as the increased risk of nephrogenic systemic fibrosis when gadolinium is administered to patients with acute or severe renal insufficiency.119

Quenching

Anesthesiologists should become familiar with this process, which entails rapid helium evaporation and the loss of superconductivity of the current-carrying coil. The loss may occur unintentionally from accidentally pressing the emergency button or intentionally turning off the scanner to release a ferromagnetic object that became attached to it in a superconducting magnet. As the superconductive magnet becomes resistive, heat is released that can lead to the boiling of liquid helium in the cryostat. This event may pose a hazard if it has not been expected and properly planned for. The evaporated coolant requires emergency venting systems to protect patients and operators. Cryogenic liquids and their associated cold vapors can produce effects on the skin similar to those of a thermal burn and can cause frostbite. In addition, prolonged breathing of extremely cold gases may damage the lungs. Finally, unprotected skin can stick to very cold metal (eg, metal cooled by liquid helium) and then tear when pulled away.

Quenching can cause total magnet failure, which cannot be reversed. MRI systems are designed so that all of the escaping cryogenic gas is directed out of the building. If pipes are blocked, helium gas will be released into the scanner room, creating a large white cloud of chilled gas and displacing oxygen. Under such circumstances, it is essential that the scanner room be evacuated because displacement of oxygen under such extreme conditions could lead to asphyxiation and death. The force of quenching can be strong enough to destroy the walls of the scanner room or the MRI equipment. Access to the scanner room during quench may prove to be impossible because the high pressure created by escaping gas may make it difficult to open the doors. In addition, magnetic fields may persist after a quench, necessitating continued caution in approaching the area with ferromagnetic materials or equipment.120

Because of the need for absolute immobility and the length of some types of scans, some patients, most notably pediatric patients, require deep sedation or general anesthesia for successful completion of the study (discussed further in Chapter 63). In the adult population, claustrophobia, chronic back pain (which precludes lying still within the scanner, a condition that allows good image quality), and movement disorders are the most common reasons that call for anesthesia services. Studies have shown that a fairly large percentage of adults (14%-20%) require some anesthesia in order to tolerate MRI.121 In these cases, anesthetic techniques range from moderate sedation for adults with mild claustrophobia or anxiety to general anesthesia for patients in whom airway issues are expected (eg, patients with obstructive sleep apnea). One of the more effective and popular techniques is TIVA with propofol as the drug of choice or inhalational anesthetic when an MRI-compatible anesthesia machine is available. Whatever the preferred method, the presence of MRI-compatible airway equipment is essential during any anesthetic in this location. Ideally, an MRI-compatible anesthesia machine and monitors should also be available. Additional anesthetic considerations for MRI include limited access to the patient and decreased visibility.122 Most institutions have a window or video equipment with which to view the patient throughout the examination, as well as an intercom with which to talk to the patient who is mildly sedated. Technicians or other personnel in the area should clearly understand that the scan should be halted if any issue arises. If designated space and trained personnel are available, patients may recover in the radiology area.

The ASA issued a practice advisory in 2009 regarding the MRI and practice safety in that environment; this is a very useful resource for clinicians who care for MRI patients.120

Surgical Magnetic Resonance Imaging Suite

This is a fully equipped OR with an integrated imaging system that includes both MRI and a C-arm for pre-, intra- and postoperative imaging for diagnosis, intervention, and postoperative follow-up. It is typically used for cranial and spine surgery. This complex system requires special OR and anesthesia equipment that is MRI compatible, and the same precautions and practices that apply to MRI are valid here as well. General anesthesia is the modality of choice in these cases, and the anesthesia team should receive formal in-service training on how to manage cases in such an environment before they embark on taking care of patients there.

Computed Tomography Scans

Computed tomography scans are generally of shorter duration than MRI scans and rarely require the presence of an anesthesia provider. Access to the patient undergoing a CT scan is limited because of the ionizing radiation being used to produce the required images. However, use of specialized anesthesia equipment is unnecessary, and the patient is much more visible to the anesthesia provider because the patient is not completely enclosed in a cylinder. Propofol is the drug of choice because the procedures often are short, and lingering sedative effects are undesirable. Patients who receive oral contrast should be intubated and the contents of their GI tract suctioned before extubation. The recovery time usually is short, depending on the agent used. Many patients can bypass the PACU and recover on site if they are stable.

In this era of rapid medical changes, more complex procedures are being performed outside the ORs, especially in endoscopy, radiology, and electrophysiology suites and in cardiovascular catheterization laboratories. A significant number of these procedures are being performed under MAC. One report estimates that charges to Medicare for anesthesia for colonoscopy increased by 86% (to $80,000,000)123 between 2001 and 2003. These numbers are probably even greater now. In response to the rapid increase in anesthesia services, payment for anesthesia in these cases has been thoroughly examined. Most payors distinguish between high- and average-risk cases. In general, payors have allowed charges for anesthesia in high-risk patients. Payment policies for average-risk patients are evolving; however, there are differences among Medicare contractors.36

Monitored anesthesia care cases take place in surgical/ambulatory centers, radiology suites, endoscopy suites, or even physicians' offices. Because of the broad range of cases, the availability of a dedicated anesthesia team to provide MAC is generally considered a financial challenge for anesthesia providers. Scheduling plays a major role in the financial success of providing these services, especially when they are provided outside OR complexes. Cases requiring the service of an anesthesiologist should be grouped together when possible to increase the likelihood of financial viability for that provider. If the volume of sedation cases is large enough, an anesthesiologist may dedicate the entire day to a specific location. Otherwise, the anesthesia provider probably will spend part of the day providing sedation in one location and the other part of the day providing anesthesia in another location.

As more minimally invasive procedures replace conventional surgeries, the demand for MAC will increase, and anesthesiologists' role outside the OR will expand. Accelerating this trend are new developments in the field of natural orifice transluminal endoscopic surgery (NOTES) in which access is gained through the mouth, rectum, vagina, and possibly urethra, and no incision is needed. As a result, anesthesiologists must leave the familiar environment of the operating room pavilion and venture into the unfamiliar territory of hospital policy and procedures to ensure that our non-OR patients receive the same high standard of care that is available to them in the OR. Successful safe delivery of remote anesthesia care requires a well-thought-out plan and organization (Table 69-9). Anesthesiologists' specialized training, airway management skills, and thorough knowledge of the physiologic effects of anesthetic agents in various disease processes give us a distinct advantage over many of the personnel who currently provide sedation services in these remote areas. Although an increasing amount of literature regarding our role and current practices in non-OR locations is available, even more studies are necessary if we are to maximize patient safety through better training and better use of technology and pharmacology. Enhanced knowledge will enable us to strengthen our efficiency in this field and accommodate the growing number of patients and specialists requiring our services.

• Abdelmalak B, Makary L, Hoban J, Doyle DJ. Dexmedetomidine as sole sedative for awake intubation in management of the critical airway. J Clin Anesth. 2007;19:370-373.
• Alspach D, Falleroni M. Monitoring patients during procedures conducted outside the operating room. Int Anesthesiol Clin. 2004;42:95-111.
• American Society of Anesthesiologists. Continuum of Depth of Sedation: Definition of General Anesthesia and Levels of Sedation/Analgesia. Approved by the ASA House of Delegates on October 27, 2004, and amended on October 21, 2009.
• American Society of Anesthesiologists. Practice advisory on anesthetic care for magnetic resonance imaging: a report by the American Society of Anesthesiologists Task Force on Anesthetic Care for Magnetic Resonance Imaging. Anesthesiology. 2009;110:459-479.
• American Society of Anesthesiologists. Statement on Nonoperating Room Anesthetizing Locations. Approved by the ASA House of Delegates on October 15, 2003 and amended on October 22, 2008.
• American Society of Anesthesiologists Task Force on Postanesthetic Care. Practice guidelines for postanesthetic care: a report by the American Society of Anesthesiologists Task Force on Postanesthetic Care. Anesthesiology. 2002;96:742-752.
• Doyle DJ, Abdelmalak B, Machuzak M, Gildea TR. Anesthesia and airway management for removing pulmonary self-expanding metallic stents. J Clin Anesth. 2009;21:529-532.
• Kelhoffer ER, Osborn IP. The gastroenterology suite and TIPS. Int Anesthesiol Clin. 2003;41:51-61.
• Osborn IP. Anesthetic considerations for interventional neuroradiology. Int Anesthesiol Clin. 2003;41:69-77.