Chapter 51. Unanticipated Difficult Airway in an Obstetrical Patient Requiring an Emergency Cesarean Section

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, for prolonged late decelerations. She weighs 253 lb (115 kg) and is 5 ft 3 in (160 cm) tall, giving her a BMI of approximately 45. Airway examination reveals a Mallampati Class III and a thyromental distance of 5 cm. She has a full neck extension with normal dentition and a normal mouth opening. 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.

51.2.1 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) 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, reducing the sympathetic response to laryngoscopy and intubation, 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

51.3.1 What Are the Airway Considerations in Pregnant Women?

Pregnancy is associated with fluid retention and weight gain.2 Mallampati Class III and IV seem to be more prevalent in parturients at the beginning of labor (28%) than in the general adult population (7%-17%), suggesting that tongue volume increase maybe 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. Size of the airway space is determined by the balance between the bony enclosure space and soft tissue volume, when pharyngeal muscles are inactivated by general anesthetics and muscle relaxants. Pharyngeal edema, presumably due to fluid retention during pregnancy, and pharyngeal swelling acutely developed during labor, increases the soft tissue volume surrounding the airway, narrowing the pharyngeal airway in parturients.2 Many have hypothesized on predictors of this event including weight gain during the 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 demonstrated an increase in the incidence of Mallampati Class III and IV from the eighth month of pregnancy to the beginning of labor, and during labor, and this incidence was not fully reversed up to 48 hours after delivery.4

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 score in 38.8% of their patients, however, in the remaining women, significant changes were observed both in the interval between the first nonlaboring assessment, and at placement of the epidural, and between placing the epidural and delivery. As illustrated in Figure 51-1, a progressive increase in Mallampati Class III and IV airway was seen.

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

Recent extensive research on the pathophysiology of upper airway obstruction revealed a significant role of lung volume reduction in pharyngeal narrowing.6 Obese parturients, a high-risk group for perioperative airway catastrophe, are prone to develop progressively narrower pharyngeal airways due to increase of soft tissue volume surrounding the pharyngeal airway, and decrease of lung volume during pregnancy. Lung volume reduction during general anesthesia is known to be more prominent and prolonged in obese 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, and high Mallampati Grade (III and IV). 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, RODS, and SHORT), this patient's airway assessment suggests possible difficult bag-mask-ventilation (BMV), possible difficult use of extraglottic device (EGD), and possible difficult surgical airway. But there are no other predictors of a difficult laryngoscopy and intubation.8,9

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.

51.4.1 How Should the Anesthetic Be Conducted in This Patient?

Reflux/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.

The patient is placed in a left tilt (at least 15 degrees) to minimize the threat of aortocaval compression syndrome (or 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 18-2 and 49-2). A polio-handle (short handle) laryngoscope may be required during intubation to facilitate laryngoscope blade insertion, in the face of large breasts. Alternatively, an assistant may be designated to retract the breasts caudally during laryngoscopy. A difficult airway cart with appropriate airway devices must be immediately available. Denitrogenation is achieved. It should be noted that modified shorter duration denitrogenation techniques may suffice and have been shown to be effective.10,11

Following an RSI with cricoid pressure, direct laryngoscopy, using a #3 Macintosh blade, reveals a Cormack/Lehane (C/L) Grade IV 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.

51.4.2 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 blade, and length of blade (see Section 1.6.2).

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. These include the McCoy, Shikani, Bullard, GlideScope, and McGrath laryngoscopes. Improperly applied cricoid pressure can make visualization of the glottic opening more difficult, necessitating guidance by the practitioner. 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.

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

The rapid 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.12 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 49, Figure 49-4).

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 Algorithm recommends that a laryngeal mask airway (LMA) should be inserted as a rescue device for ventilation and oxygenation in a cannot ventilate, cannot intubate (CICV) situation.9 Failing that, the ASA algorithm recommends a surgical approach. It is the opinion of the authors and editors that this sequential approach in an airway emergency is imprudent, and a concurrent approach should be advocated (see Failed Airway Algorithm, Chapter 2).

As the parturient has an increased aspiration risk, an LMA-ProSeal™ or a disposable LMA-Supreme™ with an esophageal vent may be a more appropriate rescue device, as long as the practitioner is familiar with its placement. Anecdotal reports have demonstrated success with its use in similar circumstances, with better seating and ventilation, and a reduced risk of aspiration related to the venting of contents through the gastric port.13,14 On the other hand, an intubating LMA (ILMA) has the advantage of serving as a conduit to secure the airway with an endotracheal tube. Placement of the tracheal tube can be achieved blindly through the ILMA device,15 or can be facilitated using a flexible bronchoscope (FB),16 or a lightwand device.17 The use of an FB allows visualization of the cords, facilitating the placement of the endotracheal tube under indirect vision and avoiding potential trauma from a blind technique.

Placement of the LMA, LMA-ProSeal™, or ILMA may be hindered by cricoid pressure. It has been suggested that relaxing cricoid pressure, briefly, may allow higher placement success rates.18,19 Cricoid pressure has also been shown to reduce tidal volumes and increase airway pressures.20 These difficulties have served to highlight recent studies, questioning the efficacy of cricoid pressure in the prevention aspiration and its hindrance in airway management.21,22 Others, however, have not demonstrated such disadvantages.23

51.4.4 If One Is Successful in Providing Ventilation and Oxygenation with an LMA, Should One Proceed with the Cesarean Section?

When an airway cannot be secured with an endotracheal tube, devices, such as the LMA are effective rescue aids. Following the insertion of the LMA, proper placement should be confirmed by end-tidal CO2 (ETCO2) detection, an unobstructed ETCO2 trace pattern (if capnography is employed), and adequate chest and abdominal excursion during ventilation.

While the LMA has been shown to be effective and safe in providing ventilation and oxygenation to healthy, non-obese, fasted parturients for elective cesarean section,24 it is generally accepted that the LMA should be used only as an emergency device for airway management in the parturient when tracheal intubation is unexpectedly difficult.25 The decision to proceed with cesarean section with an LMA in place should be based on the risk–benefit assessment on the effectiveness of oxygenation with the LMA, the condition of the fetus, the ability to expedite the delivery of the fetus, and ultimately, the safety of the parturient (context sensitive).

Actions that may lead to regurgitation and aspiration must be minimized if one proceeds with an LMA as the airway. Coughing related to light anesthesia may lead to regurgitation and must be avoided. High intragastric pressure, and incompetence of the lower esophageal sphincter, likewise predispose to regurgitation. There is evidence that gastric insufflation leading to elevated intragastric pressure is reduced by the application of cricoid pressure,26,27 and the avoidance of increased intragastric pressure may permit ventilation of the patient at a lower peak airway pressure.28 Finally, the obstetrician should be advised to minimize fundal pressure, if possible, during delivery of the baby.29

Should there be a serious doubt with regards to the safety of the mother in regard to difficult airway scenario options, the parturient should be awakened despite the presence of fetal distress. An alternative means of intubation (such as a flexible bronchoscopic technique), or of anesthesia (regional or local anesthesia), should then be undertaken.

51.4.5 If a Combitube™ Is Used to Secure the Airway, What Other Management Issues Should Be Considered?

The Combitube™ is an alternative, double-lumen airway device that is designed to be inserted blindly into the esophagus with over 80% success on the first attempt. It is commonly used among emergency medical services personnel with limited intubation experience.30 It may also be employed as a rescue airway device. If placed properly, it permits gas exchange and probably provides a measure of protection against aspiration (see The Combitube™, Section 12.6, for a detailed description of the device and how it is used). Little information on the use of this device in the obstetric population exists. A theoretical disadvantage may be the potential for trauma (bleeding) in an already engorged airway during its insertion.

51.4.6 When Should One Proceed with a Surgical Airway? Who Should Do It? What Equipment Should Be Immediately Available on the Labor Unit?

A surgical airway in a parturient is performed when the patient's airway can neither be intubated nor ventilated (CICV airway). Clinically, the oxygen saturation declines rapidly due to increased metabolic rate and diminished FRC in the pregnant woman. Delay in recognizing a CICV failed airway contributes to adverse outcomes and increased maternal mortality.31 Surgical and nursing support must be immediately available to assist as necessary.

Commercially available cuffed cricothyrotomy kits are standard tools that must be available in all maternal suites, and their use should be regularly reviewed. Chapter 13 provides a detailed description of the commercial kit recommended, and the techniques of surgical airway management.

It should be emphasized that the recognition of the potential difficult airway, avoiding delay in recognizing the CICV situation, and regular practice of a failed intubation drill will contribute toward improving the outcome. Although both surgical and anesthesia practitioners should be conversant with this procedure, the onus is on the anesthesia practitioner to perform the procedure if indicated. With the risk of the failed airway being 10 times more common in the parturient than in the general surgical population, it is mandatory that those who provide anesthesia care in the labor ward be trained in the use of these devices and techniques.32

51.5.1 Having Secured the Airway, How Does One Manage This Patient Postoperatively?

The likelihood of successful extubation is based on several factors, and guided by the condition of the patient's airway, but must err on the side of caution. In situations in which airway edema is anticipated to increase, such as significant fluid resuscitation, or an already edematous airway having suffered trauma during intubation attempts, the prudent course is to ventilate the patient for 12 to 24 hours postoperatively in a 15 to 30-degree head-up position.

Consideration should also be given to the effect of residual sedatives, or the likely need for further sedatives or analgesics, in the postoperative period. The pharyngeal airway is a collapsible tube and its patency is regulated by upper airway dilating muscles. Increase in the dilating muscle activity acts to maintain the narrowed pharyngeal airway in awake patients with obstructive sleep apnea, and similar neural mechanisms, presumably compensate the progressive upper airway narrowing in parturients. Preservation of these neural regulatory mechanisms is, therefore, crucial for parturients with a high Mallampati class. The neural compensatory mechanisms become weaker during general anesthesia, sedation, and sleep with residual anesthetics. It is important to stress that the size of the airway space is determined by the balance between the bony enclosure size and soft tissue volume (anatomical balance), when pharyngeal muscles are inactivated by general anesthetics and muscle relaxants.3 General anesthesia for emergency cesarean delivery in obese parturients, during or immediately after labor, may tend to exaggerate upper airway swelling and lung volume dependence. This is in addition to impairment of neural compensatory mechanisms, and is, therefore, a potential worst-case scenario for upper airway maintenance.

A trial of extubation may only be attempted if the patient is fully awake, muscle relaxation fully reversed, and preparations are in place for immediate reintubation. The Frova Introducer, or other tracheal tube exchanger (see Section 11.2.2), may be placed through the tracheal tube, prior to its removal, to serve as a reintubation guide should it be required. The patient usually tolerates these small diameter devices reasonably well, if local anesthetic is instilled down the endotracheal tube prior to placement. These devices have a hollow lumen, providing limited gas insufflation capacity if reintubation over the guide proves difficult or impossible. Employing a laryngoscope to straighten the angle of approach aids tracheal placement over a guide, as do smaller tracheal tubes that are less likely to become impinged on the laryngeal structures. Increasing obstruction, significant respiratory effort, or increasing acidosis are early indications of extubation failure.

The incidence of the CICV failed airway is more than 10-fold in the parturient at term, compared to a general surgical population. The obstetrical anesthesia practitioner must be prepared to manage the difficult and failed airway. Regular rehearsal of a failed airway plan of action along with the obstetric team, maintaining skills in the use of a rescue device (eg, the intubating LMA), and ensuring that surgical airway devices are immediately available are essential components of that preparation.