52.3.1 What Is Unique About Managing the Airway Urgently in the Traumatic Brain-Injured Patient Who Also Happens to Be a Near-Term Parturient?
As discussed earlier, the practitioner must deal with competing priorities: the patient has features suggestive of difficult intubation, specifically, difficult bag-mask-ventilation (BMV) and difficult extraglottic device (EGD) use—secondary to the suspicion of blunt trauma injury to the thorax. Additionally, she needs to have her airway managed atraumatically and quickly in the presence of traumatic brain injury, and a greatly increased aspiration risk. Adherence to the Difficult Airway Algorithm (see Chapter 2) may result in some delay, while resorting to rapid-sequence induction (RSI) runs the risk of inducing and paralyzing a patient at high risk for aspiration and difficult airway.
The practitioner has time to call for help and a difficult airway cart, as the SaO2 is acceptable, while borderline, and the FHR is normal. The airway practitioner should begin denitrogenation quickly using a mask with a rebreathing bag, and 15 L·min−1 of flesh gas flow with oxygen.
Assisted ventilation may be required, taking care to avoid inflating the stomach, and the rapid respiratory rate makes this a challenge. If the practitioner is not confident of tracheal intubation, or his/her capacity to provide gas exchange using BMV or EGD, an awake look with a laryngoscope may help with the decision to move to a surgical airway, or to embark on an RSI pathway. As the status of the cervical spine (C-spine) stability is unclear, the collar is gently removed and airway evaluation and management is performed while maintaining in-line stabilization.
Should RSI be selected in the setting of a patient with acute severe head injury, the patient ought to be pretreated with an opioid, lidocaine, and defasciculating agent, although some would argue that pretreatment with an opioid, or even lidocaine, will further compromise respiration in a patient who does not have a secured tracheal tube. The selection of an induction agent and the dose employed will be guided by the degree of hemodynamic stability, and in this case, is likely to be etomidate at a reduced dose (eg, 0.2 mg·kg−1). The dose of the neuromuscular blocker, such as succinylcholine, is never modified and is 1.5 mg·kg−1.
Alternatively, an awake look to determine intubatability may be performed. This patient has a GCS of 5 and may not require sedation (eg, etomidate titration). However, patients with acute severe head injury may present with a clenched jaw, prohibiting an awake look. If this occurs, the only options are RSI and cricothyrotomy.
Induction and neuromuscular blocking agents must be prepared prior to securing the airway. A selection of intubation and rescue airway devices familiar to the airway practitioner must also be prepared. In this case, laryngoscopic intubation is judged to be highly likely (Plan A). Plan B is to use an intubating LMA (ILMA), and Plan C is a surgical airway should both fail. Following denitrogenation with 100% oxygen, pretreatment, induction, paralysis, and the application of cricoid pressure by an experienced assistant are undertaken. A third person maintains manual in-line stabilization of the neck, and the trachea is successfully intubated. After carbon dioxide detection confirms tracheal placement, the endotracheal tube is secured. An orogastric tube may be placed to reduce the risk of aspiration.
As a cautionary note, despite the advances that are continuously made in airway management, the incidence of the failed or difficult airway in an obstetrical population remains higher than that seen in the general population. A recent Australian multi-institution audit conducted to assess practice of general anesthesia for cesarean section confirmed an incidence of failed intubation of 1:274, and difficult intubation of 1:30.5 These numbers are generally quoted in the literature.
It is recognized that the concept of difficult intubation in pregnancy is not without controversy. Some have argued that the difficulty is self-imposed: by anxiety with the urgency of situation; use of junior anesthesia practitioners on labor units; and the lack of opportunity to practice skills; and as a consequence of the high use of regional anesthesia in obstetrics.6,7 This reservation notwithstanding, the possible loss of an airway, with a resulting period of hypoxia, and the increased possibility of acid aspiration, put both the mother's and her fetus' life in peril. Furthermore, her status of an unclear C-spine carries additional risk of injury, if a difficult intubation is encountered.
If, on assessment of this mother, there is any element of doubt about one's ability to efficiently and safely place a tracheal tube, a strong argument could be made for a surgical airway (without paralysis or sedation), by a skilled practitioner. She may well need a tracheotomy for prolonged ventilation at any rate.
52.3.2 How Would You Secure the Airway If Three Attempts at Laryngoscopic Intubation Failed Despite Laryngeal Manipulation?
While maintaining cricoid pressure, ventilation should be provided by BMV with 100% oxygen. Gradual relaxation of cricoid pressure may be indicated if it is felt to hinder the ability to ventilate. If, at any point, the ability to maintain oxygen saturation is lost, an immediate surgical airway is indicated. As preparations for the surgical airway are underway, an ILMA can be inserted. Should this reestablish adequate ventilation, tracheal intubation through the ILMA can be considered.
Oxygen desaturation and hypotension are associated with poor outcomes in patients with acute severe head injury.
52.3.3 What Specific Concerns Related to the Airway Do You Have If This Patient Needs to Be Transported to the Radiology Suite for Diagnostic Imaging?
This patient will require ongoing sedation, paralysis, and mechanical ventilation during transport to diagnostic imaging to maintain oxygenation and to keep her PaCO2 within her physiologic range (between 30 and 32 mm Hg). Although hypocapnia has traditionally been considered an important part of the management of head injury in pregnancy, a reduction in PaCO2 below 30 mm Hg can be associated with a harmful reduction in uterine and cerebral blood flow with compromise to fetal perfusion.8 Following the acute resuscitation phase, PaCO2 levels should be monitored continuously by capnometry/capnography, or periodically by arterial blood gas sampling.
The endotracheal tube should be properly secured, as movement from stretchers to radiology tables increases the risk of accidental extubation. In addition, appropriate equipment and personnel to manage reintubation should be immediately available, including drugs (both induction agents and neuromuscular blocking drugs), laryngoscopes, endotracheal tubes, and rescue devices (including an Eschmann Tracheal Introducer and an LMA).
52.3.4 Are Sedating Drugs and Muscle Relaxants Safe in Pregnancy?
The duration of action of agents, such as vecuronium and rocuronium, may be prolonged in the pregnant state, and therefore, in non-resuscitation situations, dosing should be titrated using a neuromuscular block monitor.9 Although small amounts of non-depolarizing muscle relaxants are known to cross the placenta to the fetus when administered as a bolus, there are no reports of adverse fetal effects. The effects of prolonged (>24 hours) neuromuscular blocking drug administration on a fetus are unknown. It has been shown, however, that the fetal-maternal ratio of vecuronium increases significantly with prolonged induction to delivery times.10 In a scenario such as this, personnel should be available to ventilate or intubate the trachea of a neonate should the need arise.
All patients intubated as part of an emergency resuscitation effort ought to receive sufficient sedation and muscle relaxation to facilitate mechanical ventilation and attenuate the stress responses (increased airways resistance, ICP, blood pressure, and heart rate). This is particularly important in patients with poorly controlled elevated ICP, such as in this patient. Drug selection in pregnancy is somewhat problematic, as few of the available drugs are approved for use in parturients. The US Federal Drug Administration has created a classification structure for drugs administered to women during pregnancy.11 This five-level system of classification categorizes agents from safe to use, with well-controlled studies (category A—no risk to the fetus), to those which are clearly contraindicated (category X).
Most anesthetic and sedating agents fall into the category C group, in which risks cannot be ruled out (often due to the lack of controlled studies). It is recommended that category C agents be used only if the potential benefit to the mother justifies the potential risk to the fetus. Although the key teratogenic period is from 31 to 71 days postconception, fetal brain and organ development continues throughout gestation, rendering them susceptible to the adverse affects of agents administered to the mother.
The prevailing wisdom in the decision-making process is to bear in mind that the general health and well-being of the fetus is entirely dependent on the survival and well-being of the mother. As a general principle, drugs with a known safe history of use in pregnancy, such as thiopental and fentanyl, can be used. There is a growing body of evidence that propofol is also safe, although the experience is substantially less than those for thiopental and fentanyl. The fact that propofol is commonly used in the care of adult patients with neurotrauma would suggest its favorable application in this case. Despite traditional cautions in regard to possible teratogenic effects of benzodiazepines, recent evidence indicates that these agents are not proven human teratogens.12 The safety of etomidate in pregnancy has not been established. The drug crosses the placenta and has been shown to produce a fall in serum cortisol in the fetus lasting for about 6 hours. The significance of this finding is unclear. The selection of etomidate in this case was driven by the considerable hemodynamic instability noted in the mother.
By and large, there is little evidence that a single dose of any currently available IV induction agents is harmful to the fetus.