A 25-year-old primigravida at 39-week gestational age presents to the case room with ruptured membranes and frequent uterine contractions. She does not want to have epidural analgesia because of a story she heard about an epidural complication suffered by one of her distant relatives. After 14 hours of labor, augmented with oxytocin, and now 2 hours of pushing, she is urgently taken to the operating room for emergency cesarean section because of prolonged late decelerations. She weighs 253 lb (115 kg) and is 5′3″ (160 cm) tall, giving her a BMI of approximately 45 kg·m⁻². Airway examination on admission revealed a Mallampati II and a thyromental distance of 4 cm. She has a full neck extension with normal dentition and a normal mouth opening. On arrival in the operating room her Mallampati score was now assessed to be III. She has large gravid breasts. Her blood pressure is 128/68 mm Hg, heart rate 100 beats per minute (bpm), respiration rate 20 breaths per minute, and SaO₂ of 99% on a 100% O₂ rebreathing face mask. On arrival in the operating room, the fetal heart rate is 80 bpm.

What Are the Anesthetic Options for Cesarean Section in This Patient?

An emergency cesarean section is mandated to deliver the fetus with persistent bradycardia (late deceleration), while minimizing potential/preventable risk to the mother. Anesthesia risk factors for airway management in this patient include her BMI (45 kg·m⁻²), potential for airway edema after 2 hours of pushing and infusion of oxytocin and enlarged breasts. Although regional anesthetic techniques have become the standard of anesthetic care for operative delivery in obstetrics,¹ this patient has refused the regional approach.

The concerns for emergency cesarean section under general anesthesia include securing the airway, minimizing the risk of aspiration, reducing the sympathetic response to laryngoscopy and intubation, ensuring adequate fluid resuscitation, and the potential of blood loss due to volatile-agent-induced uterine atony. With respect to the first of these concerns, all labor and delivery facilities must have a difficult airway cart and contingency plans for failed laryngoscopic intubation.¹

What Are the Airway Considerations in Pregnant Women?

Pregnancy is associated with fluid retention and weight gain.² Mallampati Class III and IV airways seem to be more prevalent in parturients at the beginning of labor (28%) than in the general adult population (7%–17%), suggesting that an increase in tongue volume may be one of the physiologic changes of a normal pregnancy.³ Structurally, the pharyngeal airway is surrounded by soft tissues, such as the tongue and soft palate, which are enclosed by bony structures such as the mandible and spine. The size of the airway space is determined by the balance between the bony enclosure space and soft tissue volume when the tone of pharyngeal muscles is attenuated or eliminated by general anesthetics and muscle relaxants. Pharyngeal edema, presumably due to fluid retention during pregnancy, and pharyngeal swelling that develops acutely during labor, increases the soft tissue volume surrounding the airway narrowing the pharyngeal airway in parturients.² Many have hypothesized that changes in airway anatomy in the parturient include such factors as weight gain during pregnancy, fluid administration during labor, and the length of the first and second stage of labor.

A recent study from France by Boutonnet et al.⁴ demonstrated an increase in the incidence of Mallampati Classes III and IV beginning in the eighth month of pregnancy, extending to the beginning of and during labor, and that this change was not fully reversed for up to 48 hours after delivery. Moreover, these changes occurred irrespective of any increase in body weight, duration of first and second stages of labor, or volume of IV fluid administered. In their study, they made observation at four time points: at 8 months of gestation (not in labor); when the epidural was placed; 20 minutes after delivery; and finally at 48 hours after delivery. They found no changes in Mallampati score in 38.8% of their patients. However, in the remaining women, significant changes were observed in the interval between the first nonlaboring assessment, at 8 months and at placement of the epidural; and between placing the epidural and delivery. Figure 53–1 illustrates their findings of a progressive increase in Mallampati Class III and IV airway.

Similar results were observed by Kodali et al.⁵ As with the Boutonnet et al.⁴ study, no correlation was observed between airway changes during labor and duration of labor, or fluids administered during labor.

Research related to the pathophysiology of upper airway obstruction has revealed a significant reduction of lung volume in patients with pharyngeal narrowing.⁶ Obese parturients, a high-risk group for perioperative airway catastrophe, are prone to develop progressively narrower pharyngeal airways due to increased soft tissue volume surrounding the pharyngeal airway resulting in a decrease of lung volume during pregnancy. Lung volume reduction during general anesthesia is known to be more prominent and prolonged in obese patients. The assumption is that FRC is decreased further contributing to the more rapid desaturation following induction seen in these patients.

The assessment of the pregnant patient must specifically address features that increase the risk of difficult laryngoscopic intubation, including receding mandible, limited mouth opening, short neck, limited neck movement, high Mallampati grade (III and IV), etc. Taken together, these features are known to increase the likelihood of a difficult laryngoscopic intubation.⁷ Using the airway assessment strategies as described in Chapter 1 (MOANS, LEMON, CRANE, RODS, and SHORT), this patient’s airway assessment suggests possible difficult bag-mask-ventilation (BMV), factors suggestive of a difficulty with direct and indirect (video) laryngoscopy, possible difficult use of an extraglottic device (EGD), and possible difficult surgical airway.

The standard of care in obstetrical anesthesia demands that the airway of this patient be secured in such a manner that the risk of aspiration is minimized, leaving the airway practitioner with two choices in this case, rapid sequence induction (RSI), or an awake technique. An awake technique reduces the risk of a failed airway in an anesthetized and paralyzed patient. The decision to perform an awake intubation technique, rather than an RSI, should be based on clinical findings and the experience of the practitioner. In either case, contingency plans (Plans B and C) must be in place in the event that these techniques fail. One of the contingency plans must be a surgical airway, or cricothyrotomy.

How Should the Anesthetic be Conducted in This Patient?

Aspiration prophylaxis using oral 0.3 M sodium citrate (30 mL) and intravenous ranitidine 50 mg (±metoclopramide 10 mg) should be given, following the placement of an intravenous catheter. Appropriate intravenous anesthesia induction agents (propofol 2 mg·kg⁻¹ or thiopentone 3–4 mg·kg⁻¹, and succinylcholine 1.5 mg·kg⁻¹) are prepared. A designated assistant with experience in applying cricoid pressure during the RSI must be available if an awake technique is not employed.

The patient is placed in a left tilt (at least 15 degrees) to minimize the risk of aortocaval compression syndrome (supine hypotensive syndrome). In addition, the thorax, shoulders, neck, and head of this morbidly obese parturient should be elevated (ramping) to bring the anatomical axes of the oral, pharyngeal, and laryngeal structures into alignment (see Figures 20–2 and 51–2). Evidence suggest that placing the patient in a 20 to 30 degree head-up position improves ventilation and denitrogenation, reduces interference with laryngoscope insertion by large breasts, improves the view at laryngoscopy, and may reduce gastroesophageal reflux.⁸ A polio handle (short handle) laryngoscope may facilitate blade insertion in the face of large breasts. Alternatively, an assistant may be designated to retract the breasts caudally during laryngoscopy.

In all circumstances, a difficult airway cart with appropriate airway devices must be immediately available. Denitrogenation is crucial. Though some have noted that modified shorter-duration denitrogenation techniques may suffice and be effective,^9,10 standard techniques and durations are recommended as is the addition of high-flow nasal oxygen (10–15 L·min⁻¹) for the duration of the induction/intubation sequence (see Chapter 7).¹¹

Following an RSI with cricoid pressure, direct laryngoscopy, using a #3 Macintosh blade, reveals a Cormack–Lehane (C/L) Grade 4 view (only the hard palate is visible). A second attempt at laryngoscopy using a #3 Miller blade also fails to reveal any identifiable glottic structures, despite laryngeal manipulation. Following the second attempt at laryngoscopic intubation, the patient’s O₂ saturation falls to 85%, her heart rate is 120 bpm, and her BP is 180/120 mm Hg.

What Does One Do If One Cannot Visualize the Cords on Second Attempt of Laryngoscopy?

There should be no delay in summoning additional assistance and informing all team members of the gravity of the situation. It is necessary to analyze why the attempts were unsuccessful by recalling the six factors that affect the success of the attempt: the practitioner, optimum head and neck position, optimum paralysis, best external laryngeal manipulation, type of laryngoscope blade, and length of blade (see Chapter 9).

Various laryngoscope blades, rigid fiberoptic laryngoscopes, and video-laryngoscopes (with modified curved and straight blades) can be considered, if the practitioner possesses a degree of expertise in their use. Improperly applied cricoid pressure can make visualization of the glottic opening more difficult, necessitating guidance by the practitioner. The use of cricoid pressure has become a source of controversy; however, to date, it remains as a recommendation in most obstetric airway algorithms.¹² Backward, upward, and right side pressure (BURP) on the thyroid cartilage can also be guided by the practitioner, and may help to improve the laryngeal view. An Eschmann Tracheal Introducer is useful if the epiglottis can be visualized, otherwise it has a limited role. In the environment of a rapidly developing crisis, and a glottis that is difficult to visualize, a flexible bronchoscopic intubation would likely be inappropriate.

How Does One Apply the Failed Airway Algorithm in This Situation?

The rapid oxygen desaturation after the second intubation attempt is likely related to the decrease in functional residual capacity (FRC) and increase in O₂ consumption (basal metabolic rate) seen in the gravid state.¹³ This patient’s respiratory reserve is further compromised by her obesity, and by being placed in the supine position. In addition, repeated attempts at intubation are likely to lead to upper airway trauma, particularly in the parturient, where the airway is edematous and the submucosal capillaries are fragile.

Because of these factors, and in the face of unacceptable oxygen saturations after the second attempt, it is imprudent to proceed to a third laryngoscopic attempt, without first attempting BMV while maintaining cricoid pressure. Adopting a Failed Airway Algorithm approach at this point must be considered. If BMV is successful, provided the fetal distress has resolved, awakening the patient ought to be considered, followed by an awake technique to secure the airway (see Chapter 51).

In the presence of fetal distress, if BMV is possible with cricoid pressure, a decision should be made about proceeding. Factors to be considered in this decision include: the availability of extra hands, the expected duration of the surgery, the skill of the obstetrician, the availability of equipment and skill to execute a definitive plan for securing the airway, and an assessment of the potential intraoperative complication this patient may pose (such as hemorrhage). A plan must be in place for securing the airway if a decision is made to proceed.

If BMV is unsuccessful, even by easing the cricoid pressure, a rescue device should be inserted. The ASA Difficult Airway Algorithm¹⁴ recommends that a laryngeal mask airway (LMA) should be inserted as a rescue device for ventilation and oxygenation in a “can’t ventilate, can’t oxygenate” (CICO) situation. Failing that, the ASA algorithm recommends a surgical approach. It is the opinion of the authors and editors that a sequential approach in an airway emergency is imprudent, and a concurrent approach is advocated (see Failed Airway Algorithm in Chapter 2).