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The Unanticipated Difficult Intubation in Obstetrics

Mhyre, Jill M. MD; Healy, David MD

doi: 10.1213/ANE.0b013e31820a91a6
Obstetric Anesthesiology: Focused Review Article
Chinese Language Editions
Continuing Medical Education

In this focused review, we discuss an algorithm specifically for the unanticipated difficult intubation in obstetrics. This generic algorithm emphasizes a standardized and prespecified sequence of interventions to provide safe, efficient, and effective airway management for the emergency obstetric surgical patient. Individual institutions and anesthesia providers are encouraged to use this framework to select specific pieces of equipment for each step, and to create regular opportunities for all obstetric anesthesia providers to become facile with each airway device and to integrate the algorithm under simulated conditions.

From the Department of Anesthesiology, The University of Michigan Health System, Ann Arbor, Michigan.

Supported by the Department of Anesthesiology, The University of Michigan Health System, Ann Arbor, MI.

The authors declare no conflicts of interest.

Address correspondence and reprint requests to Jill M. Mhyre, MD, Department of Anesthesiology, The University of Michigan Health System, L3622 Women's Hospital, 1500 E. Medical Center Dr., SPC 5278, Ann Arbor, MI 48109-5278. Address e-mail to jmmhyre@umich.edu.

Accepted November 24, 2010

Approximately 1 in 300 obstetric patients who undergo the induction of general anesthesia will have a failed intubation with standard direct laryngoscopy.13 The most effective strategy to manage the difficult airway in obstetrics is to avoid it. However, once rapid sequence induction of general anesthesia is selected, the anesthesiologist should have a preformulated strategy to manage the unanticipated difficult intubation.4 Although comprehensive difficult airway algorithms are available,5,6 a well-rehearsed algorithm specific for the obstetric patient may be more useful in this setting.712Figure 1 is a suggested algorithm that synthesizes existing documents in a concise format. This focused review expands on the algorithm and discusses the rationale behind it.

Figure 1

Figure 1

Before the anesthetic induction, practitioners should consider aspiration prophylaxis and optimize patient and table position, oxygen administration, operator, medication dosing, and equipment. For most women, particularly those who are obese, the optimal position is ramped with left uterine displacement. The ideal ramp aligns the external auditory meatus with the xiphoid process in a horizontal plane.13 Optimal oxygenation is essential to achieve the longest possible duration of apnea before desaturation, and requires 3 to 5 minutes of tidal volume breathing with 100% oxygen14 or 8 deep breaths over 60 seconds.1416 Equipment should be immediately available for the entire airway management algorithm. Table 1 presents a suggested list of basic equipment that should be prepared on the work surface of the anesthesia machine before inducing any obstetric anesthetic. Remaining equipment should be stored in a portable storage unit located in the obstetric operative suite.4

Table 1

Table 1

The anesthetic induction drug should be selected based on availability and overall clinical condition of the patient. Succinylcholine provides better intubating conditions more rapidly than rocuronium, with an average recovery time of <10 minutes.17 Gentle mask ventilation before laryngoscopy may be considered in fasted patients.18 To maximize oxygenation and minimize gastric insufflation, any attempt at ventilation should be an optimized attempt, characterized by oral airway insertion, jaw thrust, cricoid pressure adjustment, and a well-fitting facemask.

For the first intubation attempt, priorities include speed, a high rate of success, and minimal airway trauma. Standard direct laryngoscopy to insert a styletted small-diameter endotracheal tube remains the gold standard for tracheal intubation in obstetrics. Cricoid pressure is controversial and discussion of its use is beyond the scope of this review. However, cricoid pressure should be reduced, adjusted (BURP: backward, upward, rightward pressure), or released if necessary to facilitate intubation or ventilation.1921 Success rates for each intubation attempt may be further improved by gum elastic bougie insertion, a smaller-diameter endotracheal tube, and minor head position adjustments.

If intubation fails, mask ventilation is recommended to oxygenate the patient, assess the ease of ventilation, and provide time to set up equipment for the second intubation strategy.15,16,18 A 2-handed technique may improve gas exchange if mask ventilation is difficult. For patients who remain well oxygenated, it may be appropriate to move immediately to the second intubation attempt.

The backup intubation strategy should include familiar equipment, with options listed in Table 2. The specific strategy is less important than expertise in deploying it. Videolaryngoscopy is becoming the rescue strategy of choice, and some authors even advocate it as the primary laryngoscopic technique. However, at this time, comparative studies among obstetric patients are not available. Three small series describe obstetric airway management with an Airtraq22,23 or a GlideScope.24 Comparative studies among non-obstetric patients with predicted difficult intubation do not favor any particular videolaryngoscope,25 but speed, simplicity, reliability, and efficiency are desirable characteristics.

Table 2

Table 2

Although each potential device might be optimal under select circumstances, the obstetric patient with failed intubation will be served best by clarity of purpose and action. Therefore, the institutional algorithm should select specific techniques and equipment for each step of the general algorithm.26 Each institution should establish a program by which all personnel responsible for obstetric patients become facile with each airway device, and are able to integrate the series of techniques into the difficult airway algorithm.26,27 The true cost of each device will include not only the cost of use for each emergency, but also the cost of training all providers to a level of proficiency, and maintaining the equipment in an ongoing state of readiness. An effective device may be considered cost saving if it avoids the medical, legal, and emotional consequences of just one failed airway.

Help should be requested as soon as difficulty is anticipated or encountered. The response will depend on institutional resources. At a minimum, the institutional difficult airway algorithm should specify the appropriate responders and an efficient means to contact them.

Oxygenation and ventilation take priority over intubation when the hemoglobin saturation decreases below 90%, cyanosis develops, or after 2 intubation attempts fail. Each attempt entails one insertion of the relevant airway equipment by a single provider, and should be completed in <1 minute. A review of the American Society of Anesthesiologists obstetric closed claims data suggests that repeated attempts at intubation may result in progressive difficulty in ventilation that ultimately leads to complete airway obstruction.28

If intubation fails, then positive pressure ventilation with either a facemask or an extraglottic airway may be used to await, and then support, spontaneous ventilation. Once adequate ventilation is established, the decision to proceed with surgery or awaken the patient weighs the risks of maternal aspiration and subsequent failed ventilation against the maternal and fetal consequences of delayed delivery.

Extraglottic airway options are listed in Table 3. The most important characteristic of an extraglottic airway used for airway rescue is rapid, reliable insertion. An esophageal drain, high sealing pressure, and features that facilitate intubation are desirable. Several case reports document successful airway protection in the setting of copious gastric contents removed through an esophageal drain.2932 Retropharyngeal tube airways, such as the Laryngeal Tube, have a relatively narrow profile, and may be preferred in the setting of significant oropharyngeal edema.12,33

Table 3

Table 3

A number of case reports and small series have described successful obstetric airway rescue with a Classic laryngeal mask airway (LMA),2,3436 ProSeal LMA,2,35,3740 LMA FasTrach,2,41 Combitube,42 and Laryngeal Tube-S.31 The Classic LMA has been used electively in a series of 1067 scheduled cesarean delivery patients managed under general anesthesia.43 LMA insertion was successful on the first attempt in 98% of patients and effective within 3 attempts for all but 7 patients, with no cases of regurgitation or aspiration in the entire series. Cricoid pressure release is recommended to facilitate extraglottic airway insertion, and may be reapplied once adequate ventilation is established.4345

To avoid aspiration with an extraglottic airway, it is necessary to ensure proper siting of the device, select a device with an esophageal drain or an esophageal balloon or both, maintain cricoid pressure as ventilation permits (releasing and reapplying briefly during insertion), ask the surgeons to limit fundal pressure during delivery, and maintain adequate anesthesia. Intraoperative coughing can precipitate regurgitation and dislodge the device.46 In the event of regurgitation with an extraglottic airway, experts recommend positioning the patient head down and on her side if possible, leaving the airway in place, suctioning the esophageal drain, inserting an orogastric tube to empty the stomach contents, and consideration of fiberoptic intubation and bronchoscopy.46

For emergent cesarean delivery with an unsecured airway, it is probably best to wait until the neonate has been delivered to consider additional attempts at definitive airway management. Even after delivery, if ventilation is adequate and the surgery is straightforward, attempts at intubation or surgical airway access may carry more risks than benefits. If intubation is essential, then an optical guidance technique may help to limit further airway trauma with repeated blind attempts.

If ventilation becomes impossible at any point, then the patient's neck and head should be repositioned, and equipment prepared for a surgical airway. In the case of impossible mask ventilation, a single attempt to insert an extraglottic airway could be completed while an assistant prepares equipment for needle or cannula cricothyrotomy. Further noninvasive airway management should be completed by a second provider while the surgical airway is secured without delay.10,47

Multiple invasive airway techniques have been compared with varying results and are beyond the scope of this review. All invasive airway techniques may introduce morbidity; frequent training is thought to facilitate efficiency, effectiveness, and safety. Proficiency with the Melker percutaneous cricothyrotomy dilational set (Cook Medical Inc., Bloomington, IN) may require as few as 5 insertion simulations48; however, performance seems to decline within 3 months, and frequent retraining is necessary.a Regardless, review of closed claims data for injuries attributed to invasive airway access suggests that the most serious complication of any emergent invasive airway technique is a failure to apply the technique early enough, before the consequences of significant hypoxia develop.49

Failed oxygenation resulting in maternal cardiac arrest in a patient >20 weeks' gestational age mandates perimortem cesarean delivery within 5 minutes of the arrest to optimize the effectiveness of chest compressions for maternal resuscitation.50,51

General anesthesia continues to have an essential role in obstetrics whenever neuraxial anesthesia is contraindicated or fails, or surgical urgency demands it. Usually, airway management is uneventful, but unanticipated difficult intubations do continue to occur. To prepare, anesthesiologists should select and verify appropriate airway equipment, establish reliable systems for equipment maintenance, and ensure comprehensive training in the use of these devices according to a succinct airway algorithm.

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DISCLOSURES

Name: Jill M. Mhyre, MD.

Role: This author helped review the literature and write the manuscript.

Attestation: Jill M. Mhyre approved the final manuscript.

Name: David Healy, MD.

Role: This author helped review the literature and write the manuscript.

Attestation: David Healy approved the final manuscript.

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ACKNOWLEDGMENTS

The authors acknowledge with appreciation Mary Lou Greenfield, MPH, MS, Lauren Cook, and Syed Shabbir for their work on this project.

a Prabhu A, Correa R, Wong D, Chung F. Cricothyroidotomy: learning and maintaining the skill for optimal performance. Difficult Airway Society Annual Scientific Meeting, Oxford, UK, 2001.
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