Chapter 52. Airway Management in the Pregnant Trauma Victim

A 35-year-old pregnant woman, at approximately 36 weeks gestation, is admitted to the emergency department (ED) following a motor vehicle crash. She has a closed head injury, bilateral femoral fractures, and possible abdominal trauma. Her Glasgow coma score (GCS) is 5; she does not open her eyes (1); there is no audible vocalization (2); and she is showing decorticate rigidity (3). Her heart rate is 135 beats per minute (bpm), blood pressure 85/40 mm Hg, and respiratory rate is 40 breaths per minute and shallow. Fetal heart rate (FHR) is 110 bpm. The oxygen saturation (SaO2) is 90% on a non-rebreathing oxygen mask. A cervical collar is in place and Thomas splints are being applied to the legs.

52.2.1 What Are the Immediate Evaluation and Management Priorities in This Patient?

Initial evaluation and management priorities for the near-term parturient are no different than any trauma victim—assessment of airway, breathing, and circulation (ABCs), followed by a secondary survey, including assessment of the abdomen and fetus.

Unique considerations related to the pregnancy, such as supine hypotensive syndrome and the significant capillary engorgement of the nasal and oropharyngeal mucosa, may impact positioning, hemodynamics, and airway management.1

Immediate attention is directed toward the airway. Her GCS and oxygen saturations mandate endotracheal intubation and ventilation. She is not a crash airway, and therefore an evaluation for difficulty is performed employing the MOANS, LEMON, RODS, and SHORT mnemonics (see Sections 1.6.1, 1.6.2, 1.6.3, and 1.6.4). In this particular patient, difficulty should be anticipated and an approach as suggested in the Difficult Airway Algorithm (see Chapter 2) adopted, recognizing that parturients at term have a substantially elevated risk of aspiration, particularly in this circumstance where protective airway reflexes are compromised.

Following airway management, attention is directed to an assessment of breathing. Her lung fields must be evaluated for presence, equality, and quality of breath sounds. This evaluation, coupled with a stat portable chest x-ray, may uncover a pneumothorax and/or hemothorax that could require treatment.

In pregnancy, minute ventilation is normally increased by approximately 45%, largely through an increase in tidal volume. This increased minute ventilation results in a fall in PaCO2 to approximately 30 mm Hg. Therefore, one should initially moderately hyperventilate this patient empirically. Ventilation may be guided by arterial blood gases, once resuscitation has been established.

During pregnancy, an increase in gastric acid production results not only in an increased volume but a decrease in the pH. Coupled with a decrease in the competency of the lower esophageal sphincter, a greatly enhanced risk of reflux is present. The most effective protection against aspiration in this situation is the presence of a cuffed endotracheal tube in the trachea.

The final step of the primary survey is directed to the evaluation and management of the circulation. This patient is hypotensive. Positioning to minimize supine hypotensive syndrome (or aortocaval compression syndrome) and volume resuscitation should be undertaken. A wedge should be placed under the right hip to create 30 degrees of left uterine displacement. This will reduce aortocaval compression and improve systemic and placental perfusion.2 Large-bore IV cannula and fluids must be initiated as the parturient can lose 30% of her blood volume before demonstrating cardiovascular changes.3 There is a strong correlation between hypotension and negative outcome for both an injured brain, and a fetus in utero.

Relative anemia (approximately 11 g/dL or 6.9 mmol·L−1), related to an enhanced blood volume, is a physiologic response to pregnancy. In a healthy near-term parturient, blood pressure may remain at near-normal values until greater than 1000 mL of blood loss occurs. In addition to the usual sources of blood loss in a trauma victim, the uterus can be a source of significant hemorrhage, for example, both placental and uterine abruption may be associated with blunt abdominal trauma, such as lap belt injury.

Now the attention can be turned to the secondary survey focusing on her head injury, the abdomen, and the stabilization of her fractures. Her GCS of less than 7 indicates a significant head injury at risk of further decompensation at any time. Securing an airway in a timely fashion may be critical in limiting hypoxic brain injury and avoiding surges in intracranial pressure (ICP) related to elevations of PaCO2.4

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.

52.4.1 What Fetal Monitoring Is Required in This Situation?

Fetal monitoring during trauma resuscitation is often challenging because of limited access to the abdomen. Continuous fetal monitoring is possible from about 18 weeks gestational age, although it is technically difficult to perform transabdominally early in gestation. FHR variability as an indicator of fetal well-being is usually not established until 25 to 27 weeks of gestation. Additionally, sedating agents affect FHR variability, further limiting its usefulness.13 Therefore, persistent and marked fetal bradycardia may be the only true indicator of fetal distress in early pregnancy or in pregnant patients receiving sedating medications.

Blunt or perforating abdominal trauma place the fetus directly at risk due to the potential for placental abruption, or uterine hypoperfusion, related to maternal hemodynamic instability.

As indicated earlier, it is reasonable, therefore, to use continuous fetal monitoring in a pregnant trauma victim if it is physically possible. This assumes that personnel skilled in fetal heart trace reading are available, and a plan to deliver the fetus if there is evidence of fetal compromise. The American College of Obstetricians and Gynecologists supports a position of individualizing the use of monitoring in these situations as a team approach, so as to optimize the safety of both the mother and the fetus.14 After 35 weeks gestation, delivery results in minimal morbidity to the fetus.

52.4.2 What Findings Would Lead to a Decision to Expedite the Delivery of the Fetus?

Evaluation of the pregnant trauma victim involves the evaluation of two patients, the mother and the fetus. Assessment and stabilization of the mother is always the first priority. Occasionally, the resuscitation of the mother requires the delivery of the fetus. The classic example is during maternal cardiac arrest. If the fetus is older than 24 weeks, and if it has not been possible to resuscitate the mother after 4 minutes of cardiopulmonary resuscitation (CPR), the fetus should be delivered by emergency cesarean section. This is done to improve both fetal outcome and the effectiveness of maternal CPR, by removing any aortocaval obstruction.

In cases where the mother is hemodynamically unstable secondary to hemorrhage and possible placental abruption, delivery of the fetus may be necessary as part of maternal resuscitation. Immediate induction of anesthesia with airway management is mandated.

A more common scenario is that of a hemodynamically stable mother, with a fetus demonstrating signs of terminal fetal distress (severe fetal bradycardia). This situation parallels any other emergency cesarean section for fetal distress. As in all situations where anesthesia induction agents and muscle relaxants are used, a strategic plan (Plans A, B, and C) must be in place for management of the failed intubation.

The management of trauma in a parturient often provides significant challenges to practitioners. The physiologic changes of pregnancy must be considered when one interprets vital signs, response to resuscitative maneuvers, and laboratory investigations in these trauma victims. The fetus adds a second dimension to the resuscitation, although maternal well-being and safety should remain the primary concern.

The benefit of left uterine displacement as part of the resuscitation must be recognized. Airway protection is a critical part of management, as these patients are at higher risk of aspiration due to the physiologic and mechanical changes of pregnancy. The value of Airway Management Algorithms in crisis situations, such as the resuscitation of the parturient, cannot be overemphasized.