Chapter 50. Airway Management of the Obstetrical Patient with an Anticipated Difficult Airway

The patient is a 32-year-old black woman G1P0 at 31-weeks gestation. Her medical history is notable for mild obesity (102 kg; BMI 39), a suggestion of sleep apnea (a report of significant snoring and periods of apnea while she sleeps), and treatment for chronic hypertension for the past 6 years.

Five days prior to admission, the patient's hypertension and peripheral edema worsened, and she developed new-onset proteinuria. A 3.0 kg weight gain during the 7 days prior to admission was also noted. At the time of admission, the patient had a blood pressure of 168/102 mm Hg, a heart rate of 85 beats per minute (bpm), a short neck, large breasts, an airway classified as Mallampati Class IV, a 3 cm mouth opening with prominent incisor teeth, a thyromental distance of 2.0 cm, and a limited range of motion of her neck. She was placed on strict bed rest and treated aggressively with atenolol and furosemide.

Twenty-four hours prior to delivery, a non-stress test demonstrated little or no reactivity and late decelerations with the few contractions she was having. The decision was made to induce labor and deliver the fetus. In the 8 hours preceding her induction, her hematocrit rose from 32% to 41% and her platelet count fell from 178K to 75K × 109 /L. The patient was placed on a magnesium sulfate intravenous infusion. She was noted to become increasingly edematous and somnolent.

With induction of labor, the patient has developed regular contractions of appropriate strength for some 12 hours. She has progressed to 10 cm cervical dilation and has been pushing for 3 hours. The baby has remained at −1 station and does not appear to be descending. Because of the risk of inadequate coagulation, the patient has been managed throughout labor with a systemic opioid. A decision has been made to perform a cesarean section. The fetus is stable at the present time.

50.2.1 What Are the Physiological Changes of Pregnancy that Impact on the Airway Management of This Patient?

This patient is at considerable risk of rapid oxygen desaturation because of her pregnancy-associated increase in oxygen consumption, decrease in FRC, increase in closing volume, and increase in alveolar-arterial oxygen gradient. She is also at risk for aspiration because of pregnancy-related decreased gastroesophageal sphincter tone, increased gastric acid production, and decreased gastrointestinal motility. Therefore, this patient must be pretreated with a nonparticulate antacid and perhaps an H2 receptor blocker. If the patient is rendered unconscious before her airway is secured, a rapid-sequence induction with cricoid pressure must be employed to minimize the risk of gastric content reflux and aspiration.

50.2.2 What Is the Most Likely Diagnosis for This Patient?

This patient has chronic hypertension, with superimposed severe preeclampsia, that is, severe hypertension, edema, and proteinuria. She has been given magnesium sulfate for both seizure prophylaxis and blood pressure control. In addition, she has developed thrombocytopenia and a likely associated platelet dysfunction. Regional anesthesia, while preferred, is considered contraindicated under these circumstances.

50.2.3 What Is Preeclampsia?

Preeclampsia is a term that describes a subset of pregnancy-induced hypertension accompanied by proteinuria, low plasma oncotic pressure, generalized capillary leakage, and edema, including the airway, after the 20th week of gestation. While edema is commonly present, it is no longer a required criterion for diagnosis of preeclampsia.1 Preeclampsia is more dangerous if onset is prior to 34 weeks.

Preeclampsia can be mild or severe. Severe preeclampsia is defined by the presence of at least one of the following: blood pressures ≥160 mm Hg systolic or 110 mm Hg diastolic; proteinuria ≥5 g/24 h; headache; blurred vision; epigastric or right upper quadrant pain; and pulmonary edema.

Because thrombocytopenic coagulopathy frequently complicates preeclampsia, general anesthesia is usually employed, if an operative delivery is required.

50.2.4 What Are the Consequences of Preeclampsia on the Parturient Airway?

The possibility of severe upper airway edema constitutes a major concern with preeclampsia.2 Any suggestion of stridor or dyspnea should particularly alert the practitioner to the possible hazards of a difficult airway. However, extreme difficulty may be encountered in preeclamptic patients who are asymptomatic. The airway of a preeclamptic patient will be edematous and friable, and thus very unforgiving if multiple attempts at intubation are required. In addition, there have been observations of pharyngeal narrowing that could contribute to difficulty in blind intubating procedures.

50.2.5 What Is the Impact of Weight Gain and Obesity on the Parturient?

Weight gain is a natural consequence of pregnancy, however in recent years the proportion of women gaining greater than the recommended weight has increased.3 This patient has experienced a rapid weight gain of greater than 3.0 kg in the week prior to intervention, primarily as a result of generalized edema. This patient is of particular concern because her preeclampsia was preceded by significant obesity.

Obesity places the parturient at greater risk for hypertension, diabetes, preeclampsia, difficult labor, increased likelihood of instrumental delivery, and postpartum hemorrhage. All of these conditions frequently require surgical intervention.4-6 Difficult mask ventilation, as well as increased volume and acidity of gastric contents, are also associated with obesity. Indeed, there is a documented association of obesity with airway difficulty and maternal mortality.7-10

50.2.6 Does Labor Have Any Effect on the Parturient Airway?

The incidence of Mallampati Class IV airways increases by as much as 34% as pregnancy progresses from 12 to 34 weeks' gestation.11 In addition, airway status can deteriorate significantly as labor proceeds.12,13 This suggests that the dynamic airway status should be examined repeatedly throughout labor, particularly in those patients where initial concerns of a possible difficult airway exist.14

50.2.7 Does This Patient Have a Worrisome Airway?

The patient, as described, is likely to be difficult at laryngoscopy and intubation. While no single measurement is sufficient to predict a difficult laryngoscopy, this patient certainly has more than two of the usual predictors. The Mallampati Class IV assessment indicates that oral structures are large in relation to mandibular size. The short thyromental distance and prominent incisors correlate with difficulty in placing a laryngoscope blade.15 All of these, in association with a short thick neck, limited range of motion of the neck, and large pendulous breasts, suggest that laryngoscopic intubation would be very difficult.

In addition to an unfavorable anatomical presentation, the patient's obesity and potential sleep apnea would suggest potential difficulties with mask ventilation.16 The combination of potential difficult mask ventilation and difficult laryngoscopic intubation drastically limit the options available for oxygenating this patient. If this patient's fetus was experiencing a significant distress, management of her airway would be even more problematic.

50.3.1 What Initial Preparations Should Be Made with the Obstetricians as Induction of Labor Is Undertaken?

One of the most important things that an anesthesia practitioner must do is to communicate with the obstetricians, the nurses, the patient, and the patient's family. The health care team and the patient/family must understand that every effort would be made to avoid the necessity for an urgent induction of general anesthesia. The reasons underlying this plan must be clearly and frankly explained. Nevertheless, all equipment must be readied for urgent induction, and obstetrically relevant protocols should be reviewed by all caregivers. Algorithms used on the obstetrical floor are quite different from the ones used in the general operating room (see Chapter 49).

50.3.2 What Anesthetic Technique Would Be Most Appropriate for a Surgical Delivery of a Parturient with an Anticipated Difficult Airway?

Some form of regional anesthesia (epidural, spinal, continuous spinal, or combined spinal/epidural) would be the preferred management technique for a parturient with an anticipated difficult airway. However, this patient's developing coagulopathy precludes the use of a regional technique. While it is very unusual for a successful regional technique to require conversion to general anesthesia, there are reports of failed regional techniques, and circumstances may arise, necessitating induction of general anesthesia. Therefore, backup plans for induction of general anesthesia, should the need arise, must be formulated in advance.

50.3.3 What Specific Equipment Should Be Available in Caring for This Patient: A Parturient with an Anticipated Difficult Airway, Short Thick Neck with Anatomy Distorted by Edema and Obesity, and at Considerable Risk for Bleeding and Excessive Secretions?

The operating room (OR) should be readied—the OR bed should be ramped (see Section 18.3.2) and the difficult airway cart (see Chapter 59) should be immediately available at the induction site.

While there are a number of alternative intubating techniques under general anesthesia, the authors believe they all have limitations. Rapid-sequence induction with direct laryngoscopy, under any circumstance, is dangerous. Techniques requiring transillumination are technically very difficult in obese patients with a short neck, or excessive neck tissue and edema. Poor neck anatomy greatly hinders rescue techniques such as transtracheal jet ventilation, cricothyrotomy, or tracheotomy. Blind nasotracheal tube placement will inevitably lead to considerable bleeding in a pregnant preeclamptic patient; and blind placement of the endotracheal tube using an Eschmann tracheal introducer, or its equivalent, requires at least some visualization of the epiglottis. There is some enthusiasm for the elective utilization of an LMA in a pregnant patient at term,17 but such advocacy is usually limited to healthy non-obese patients and is very rarely used in North America. Laryngeal mask airways such as the LMA-ProSeal™ (LMAP), or the disposable LMA-Supreme™, with incorporated esophageal vents, have the potential advantage over the LMA-Classic™ of providing some protection against the aspiration of gastric contents. Unfortunately, there are case reports of gastric regurgitation and aspiration during their use,18,19 particularly if the LMAP is not properly placed in the hypopharynx. An intubating LMA (ILMA or LMA-Fastrach™) might also be considered; however failure with these devices is not unknown.

In recent years there has been a profusion of video laryngoscopic devices introduced on the market. Numerous studies, in non-obstetric patients with difficult airways, report improved laryngoscopic views and intubation success rates compared with direct laryngoscopy.20-22 There are also some published reports of improved laryngoscopic views, and intubation success rates, in morbidly obese patients using video laryngoscopes. However, the results are inconsistent and vary according to particular devices and skill set of the anesthesia practitioner.23-25 There are no published reports of the success rates of these devices in obstetric patients.

An awake technique is probably most appropriate for this patient. A number of practitioners employ an awake look technique. That is, the airway is topicalized, or anesthetized using laryngeal nerve blocks, and then examined under direct vision using a laryngoscope. However, evidence exists of poor correlation between airway visualization in an awake patient and patients who are subsequently anesthetized and paralyzed.26

For this patient, the authors would choose awake intubation using a flexible bronchoscope. Sedatives and hypnotics will usually be required to facilitate an awake intubation and consideration will be required in regard to unusual sensitivity to these agents in pregnant patients, and patients with sleep apnea. In addition, potential impact of drugs and techniques on the newborn will require consideration. Pharyngeal and laryngeal structures must be anesthetized adequately for awake bronchoscopic intubation to be successful, and topicalization of the airway in edematous airways is usually difficult and requires patience. Some practitioners advocate laryngeal nerve blocks in this instance. However, in the edematous obese neck, nerve blocks are both difficult and frequently not successful.

50.4.1 What Precautions Must Be Taken When the Case Ends?

The difficult airway case does not end with intubation. One must be equally cautious with the extubation. There are certainly many occasions in which one might consider leaving the obese preeclamptic patient intubated for several hours after surgery, to allow time to remobilize some of the edema fluid, and improve airway conditions. The preeclamptic patient is invariably on magnesium for seizure prophylaxis and if non-depolarizing neuromuscular blocking agents have been used, complete reversal of these agents must be ensured. Prior to extubation, the patient must be fully awake and capable of protecting her airway from aspiration. In many instances, one might consider checking for an air leak (a leak test) around the deflated cuff of the endotracheal tube, to further ensure that the patient's airway will be patent after extubation. Consideration should also be given to extubation over an airway exchange catheter which may be left in situ and be used as a conduit for reintubation.27

The obese preeclamptic patients with an anticipated difficult airway can be exceedingly challenging to manage and are best cared for in a team effort. Thorough understanding of the pathophysiology of preeclampsia is critical in providing the optimal anesthetic care for these patients. Their care cannot be rushed, and decisions must be made in a logical and methodical manner. In addition, the practitioner must continue to review the difficult airway algorithm and make a concerted effort to remain facile with those devices that may be needed in difficult airway scenarios.