Airway Management in Obstetric Patients

Key Points

• Anesthesia is a leading cause of maternal mortality and ranks seventh in the United States and eleventh in the United Kingdom. Airway-related complications during general anesthesia (GA) for cesarean delivery (CD) feature as a predominant cause of anesthesia-related maternal morbidity and mortality and are preventable.

• Pregnancy-related anatomic and physiologic changes are not the sole reason for difficulty with intubation, ventilation, and extubation. Other reasons include lack of preanesthesia assessment and preparedness, inadequate communication, loss of situational awareness, and lack of clinical airway management skills.

• Early preoperative assessment for patients undergoing labor and delivery must include a thorough airway history and examination and a rescue plan for potential failed tracheal intubation (TI). Appropriate airway equipment and personnel must be immediately available in labor and delivery suites to manage the difficult airway (DA).

• Although regional anesthesia (RA) is safe in most patients undergoing CD, in certain exceptional situations an awake TI is considered the safest choice in cases of anticipated or known DA in a patient undergoing nonurgent CD. Awake TI can be performed using flexible scopes or video laryngoscopes. Appropriate topical anesthesia of the airway and judicious sedation (with minimum adverse effects on the fetus) can enable any of these techniques to be used successfully. Video laryngoscopy for awake intubation is associated with shorter intubation time; it has a success rate and safety profile comparable to flexible bronchoscopy.

• Adequate preoxygenation, left uterine displacement (LUD), head-elevated positioning and use of ramp, and supplementary high-flow oxygen via nasal cannula enhance oxygenation and prevent early desaturation.

• Video-assisted laryngoscopy should be the first line laryngoscopy.

• In a cannot intubate/cannot oxygenate (CICO) critical airway scenario, invasive airway access is a high priority. A scalpel-bougie surgical cricothyrotomy technique must be considered in the critical airway with increasing hypoxemia situation.

• Extubation airway-related problems have emerged as the most common cause of airway-related maternal mortality in recent reports from the United States and the United Kingdom.

• Simulation-based training during residency training is essential to address the declining use of GA for CD.

• High-fidelity simulation training with formal instruction in management of failed TI, difficult ventilation, and cricothyrotomy skills should be taught and practiced.

Introduction

Anesthesiologists in active obstetric anesthesia practice uniformly agree that general anesthesia (GA) for cesarean delivery (CD) should be reserved for special circumstances, such as emergent delivery for a life-threatening (mother or baby) situation, when regional anesthesia (RA) is contraindicated, or in complicated cases. Evidence-based literature from the United States and United Kingdom has demonstrated that complications of airway management, which include difficult laryngoscopy (DL), difficult or failed tracheal intubation (TI), and inability to ventilate or oxygenate following induction of GA for CD are major contributory factors leading to significant maternal morbidity and mortality. ^, Thus, the anesthesiologist involved in obstetric airway management respects the gravity of GA for CD. The trend in obstetric anesthesia clinical practice in industrialized countries has shifted significantly toward RA for most operative obstetric surgical procedures leading to a decline in GA for CD. Despite the decline in GA, it remains an enigma as to why the incidence of failed intubation in obstetric patients has not changed in the last four decades. Prediction of difficult airway (DA) in obstetric patients is not always reliable, yet proper airway assessment and evaluation are required. Based on published literature, the focus priorities include the following:

• 1.

  Readiness and appropriate preparation for GA in an obstetric patient;

• 2.

  Formulate strategies to manage DA and difficult intubation (DI);

• 3.

  In the event of failed intubation, outline strategies to establish ventilation;

• 4.

  In a critical airway situation with hypoxemia, the emphasis is on optimizing oxygenation to support safe outcomes for both mother and baby;

• 5.

  A strategy to manage safe extubation in a patient with known DA;

• 6.

  Availability of airway devices in an obstetric suite; and

• 7.

  Maintenance of advanced airway management (AAM) skills.

Common Obstetric Practices and Concerns

The common practice in obstetric anesthesia is to accomplish intubation using a single dose of succinylcholine when anesthetizing for CD under GA. From an obstetric anesthesia perspective, a DI is defined as when an experienced provider cannot successfully accomplish intubation within the timeframe of the initial induction. The increased use of RA and the significant decline in GA for operative procedures raises three concerns: clinical, patient safety, and educational:

The clinical concerns center on the changing demographics among the obstetric patient population. As the prevalence of high-risk obstetric patients with comorbidities (particularly pregnant patients with congenital heart disease, advanced maternal age, morbidly adherent placental abnormalities requiring cesarean hysterectomy) and morbid obesity continues to increase, anesthesia providers will encounter clinical scenarios in which neuraxial anesthesia may be contraindicated or impossible, making airway instrumentation and management both necessary and challenging. Approximately one-third of obstetric general anesthetics are now administered after failed neuraxial anesthesia.

Because of the declining GA experience of anesthesia trainees and the inability to acquire airway management skills in pregnant patients, the educational concern has resulted in educators opting for simulation-based training to enhance anesthesia trainees’ cognitive, technical, and nontechnical skills. This includes clear communication during a simulated obstetric emergency on a high-fidelity patient simulator. An emphasis on critical airway management skills and front-of-neck access cricothyrotomy techniques is essential.

Incidence of Difficult or Failed Intubation and Cannot Intubate/Cannot Oxygenate in Obstetrics

A literature review of obstetric failed intubations from 1970 to 2021 shows that the incidence of failed intubation in obstetric patients has not changed in 40 years. It remains unchanged at 2.6 per 1000 anesthetics (1 in 390) for obstetric GA and 2.3 per 1000 GA (1 in 443) for CD ( Table 37.1) . Maternal mortality from failed intubation was 2.3 per 100,000 GAs for CD (1 death per 90 failed intubations). Maternal deaths were secondary to aspiration, and hypoxemia events were secondary to airway obstruction or esophageal intubation.

Over the years, maternal morbidity and mortality secondary to airway-related complications have declined. However, the incidence of DI during CD has remained unchanged because of the altered anatomic and physiologic changes of pregnancy and failure to predict DI in two-thirds of the cases. ^, A retrospective study performed at Baylor College of Medicine in 2017 found that the incidence of failed intubation was 1:232, which is comparable to previous studies. All the failed intubations were rescued by the laryngeal mask airway (LMA). As compared with the incidence of failed intubation in obstetrics, the incidence of failed intubation in surgical patients averages 1:2230. Therefore, there is a nearly eightfold increased risk for failed intubation in obstetric patients. Interestingly, in countries with a high GA usage rate during CD (i.e., South Africa), a lower failed intubation rate of 1 in 750 is reported.

Anesthesia-Related Maternal Mortality

Recent reviews on anesthesia-related maternal mortality have heightened anesthesiologists’ awareness of potential airway problems in obstetric patients. Despite the increased use of RA and advances in airway management, difficult or failed intubation cases are still reported when RA is converted to GA during CD, because of either pain or hemorrhage. Concerns for rapid delivery of the fetus often lead to time pressure, which may result in poor preparation, inadequate planning, gaps in nontechnical communication, and substandard performance of technical tasks in the majority of CD under GA. ^,

US Data on Anesthesia-Related Maternal Mortality

Anesthesia-related maternal mortality ranks seventh among the leading causes of maternal deaths in the United States ( Fig. 37.1 ). The first landmark study of anesthesia-related maternal mortality in the United States was reported in 1997. It revealed a 16.7 relative risk ratio increase in mortality in mothers who received GA compared with those who received RA. A total of 82% of the deaths occurred during CD and mainly resulted from difficult or failed intubation, inability to ventilate and oxygenate, and pulmonary aspiration and respiratory complications. The death rates during GA for CD increased from 20 per million between 1979 and 1984 to 32.3 per million between 1985 and 1990. The relative risk ratio of GA-associated deaths was 2.3 times higher than RA-related deaths. This evidence-based data ushered in a significant change in anesthesia practice for pregnant patients who moved away from GA to predominantly RA for CD, demonstrating the death rate for RA during the same time had declined from 8.6 to 1.9 per million ( Table 37.2 ).

Table 37.2

Case Fatality Rates and Rate Ratios of Anesthesia-Related Deaths During Cesarean Delivery by Type of Anesthesia: United States (1979–2002)

		Case Fatality Rates (deaths per million, general or regional anesthetic)
Year of Death		General Anesthetic		Regional Anesthetic		Rate Ratios
1979–1984		20.0		8.6		2.3 (95% CI 1.9–2.9)
1985–1990		32.3		1.9		16.7 (95% CI 12.9–21.8)
1991–1996		16.8		2.5		6.7 (95% CI 3.0–14.9)
1997–2002		6.5		3.8		1.7 (95% CI 0.6–4.6)

CI, Confidence intervalReproduced with permission from Hawkins, JL. Anesthesia-related maternal mortality in the United States 1979–2002. Obstet Gynecol. 2011; 117(1):71.

In a follow-up report, a reexamination of trends in anesthesia-related maternal deaths from 1991 to 1996 compared with anesthesia-related deaths from 1997 to 2002 showed the case fatality for GA declined from 16.8 to 6.5 per million. However, despite the changes in practice, 56 anesthesia-related deaths were primarily associated with complications during anesthetic induction, failure of TI (25%), respiratory failure (20%), or high spinal or epidural block (16%) followed by respiratory failure.

Maternal deaths following extubation and emergence from GA are another area of concern. A review of anesthesia-related maternal deaths during the perioperative period in Michigan (1985–2003) found that deaths occurred during emergence, extubation, or recovery from hypoventilation or airway obstruction. Obesity and race (that is, African American) were considered important risk factors for anesthesia-related maternal mortality. Currently, the anesthetic-related maternal death rate in the United States has stabilized to 1 out of 1 million live births. Although the reasons for the reductions in anesthesia-related deaths are not fully understood, there is reason to believe that the improved outcomes are a result of (1) the changing patterns of anesthesia practice, predominantly toward RA; (2) GA in elective obstetric cases being reserved for high-risk patients with comorbidities; (3) enhanced awareness and use of protocols and DA algorithms; and (4) use of alternate airway devices, particularly SGA, in DA management.

Obstetric Anesthesia Closed Claims Studies

The American Society of Anesthesiologists (ASA) database is a structured evaluation of adverse events from the closed claims files of 35 US professional liability insurance companies. Before 1990, maternal death and newborn death/brain damage were the most common obstetric anesthesia malpractice claims in the database. Obstetric anesthesia claims for injuries from 1990 to 2003 were compared to claims before 1990, and the proportion of obstetric anesthesia claims from 1990 or later associated with CD decreased. The proportion of claims related to GA from 1990 onward decreased, and the proportion of maternal death/brain damage and newborn death/brain damage also decreased. Malpractice claims from 1990 or later related to respiratory causes of injuries decreased to 4% from the pre-1990 level of 24%. Claims pertaining to inadequate oxygenation/ventilation, pulmonary aspiration of gastric contents, and esophageal intubation have also decreased. However, the claims related to DI after 1990 in comparison with pre-1990 have not changed.

UK Data on Anesthesia-Related Maternal Mortality

Anesthesia-related deaths in the United Kingdom rank as the 11th leading cause of maternal death. A new consortium formed in 2014—Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK)—initiated a collection of all medical records of all notified maternal deaths, including all maternal deaths from Ireland. The leading causes of death are listed in Fig. 37.2 . The reports show that since the early 1980s, there has been a dramatic reduction in anesthesia-related maternal deaths, with the maternal mortality rate for deaths attributed to anesthesia from 1952 to 2011 having fallen dramatically ( Fig. 37.3 ). A significant contributor to the success has been a result of a reduction in airway- and GA-related deaths. Between 2009 and 2012, 4 deaths were classified as directly because of anesthesia, a rate of 0.17 per 100,000 pregnancies. Increased use of RA, aspiration prophylaxis for CD, and improvement in airway training have likely contributed to this decrease.

The current UK Obstetric Surveillance System (UKOSS) of data collection found the incidence of failed TI in obstetric anesthesia to be 1 in 224. Advanced maternal age, obesity, and a Mallampati (MP) score >1 were significant independent predictors of failure. The Fourth National Audit Project (NAP4) of the Royal College of Anesthetists and the Difficult Airway Society (DAS) were designed prospectively to study the incidence of major complications of airway management in hospitals in the United Kingdom and to perform quantitative and qualitative data analysis. ^, In four cases, pregnant women had problems with intubation during emergency CD. These cases took place outside of regular working hours, involved complex patients, and were managed by senior anesthetists. The airway complications noted were aspiration, patient woken up followed by failed awake flexible scope intubation (FSI), a failed cricothyrotomy attempt, and a successful surgical airway. In NAP4 the most common recurring themes resulting in adverse airway-related outcomes are listed in Box 37.1 . All patients were admitted to the intensive care unit (ICU) and made a full recovery.

Box 37.1

The Fourth National Audit Project (NAP4): The Most Common Recurring Themes Resulting in Adverse Airway-Related Outcomes

Reproduced with permission from Cook TM, Woodall N, Harper J, Benger J, Fourth National Audit Project. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 2: Intensive care and emergency departments. Br J Anaesth. 2011;106(5):632–642.

Poor airway assessment

Repeated intubation attempts

Lack of preformulated strategy for management of the difficulty airway

Awake fiberoptic intubation indicated but not used

Obesity as a risk factor

High failure rate of emergency cricothyroidotomy and other rescue techniques

Adverse airway events during emergence and extubation

Adverse airway-related outcomes in the intensive care unit and emergency department

Trends in Obstetric Anesthesia

The heightened awareness among anesthesia practitioners regarding the risk for difficult and failed intubation in obstetrics along with the increased trend toward RA techniques have resulted in a marked decline in GA. The National Health Service maternity statistics show that the number of obstetric GAs for CD administered in the United Kingdom decreased from 50% to as low as 5%. Johnson and colleagues similarly found over the same period a marked decline in GA for CD, from 79% to less than 10%. In the United States, Palanisamy and colleagues compared data in their large-volume, tertiary care institutions and reported a dramatic decline in the use of GA from 4.5% (1990–1995) to 0.6% (2000–2005).

The current trend in the United States and the United Kingdom is to use GA mainly for the true emergency CD, especially if there is insufficient time or a contraindication to RA. Encountering a DI in the obstetric population continues to persist; therefore, the emerging problem of declining airway skills is important, given the unchanged rate of failed TI in the past four decades. The risk of failed TI is considerably higher for an emergency CD than for an elective CD, with 80% of airway-related fatalities occurring during an emergency CD (nights and weekends) and usually involving trainees. Because of the decreased use of GA for CD, the trend in the anesthesia trainees’ experience with GA in obstetric patients is also declining. ^{, ,}

Risk Assessment

Maternal, fetal, surgical, and situational factors contribute to the increased incidence and risk of failed intubation following GA for emergency CD. Anatomic and physiological factors alter the airway during pregnancy. In addition, the pulmonary, gastrointestinal, and cardiovascular changes associated with pregnancy place the parturient at risk for DMV, DI, DL, hypoxemia, and cardiorespiratory arrest. The anatomic and physiologic changes during pregnancy and associated risks are highlighted in Box 37.1 .

Obesity

Obesity is a significant risk factor for DI and is becoming an increasing concern in the obstetric population. In 2011–2012, the Centers for Disease Control and Prevention (CDC) reported that 34.9% of adults in the United States had a BMI above 30.32 kg/m ² (BM1 >30 kg/m ² is considered obese). The CDC also predicts that 50% of the population in the United States will have a BMI greater than 30 kg/m ² by 2025 ( Fig. 37.4 ). A definition of obesity specific to pregnancy does not exist, but the consensus is that a pregnant woman is considered overweight when her BMI is 25.0 to 29.9 kg/m ² and to have obesity when her BMI is 30 kg/m ² or greater. The incidence of DI in the population with obesity varies from 15.5% to a reported incidence of 33%.

In 2015, the National Health and Nutrition Examination Survey showed that 36.5% of women of reproductive age (20 to 39 years) in the United States had obesity. It is estimated that 15% of pregnant women in the United Kingdom have obesity, with 5% having a BMI greater than 35 kg/m ² . The prevalence of morbid obesity (BMI >40 kg/m ² ) in pregnancy has increased significantly over the past decade and now represents over 10% of Western women of reproductive age.

A review of anesthesia-related maternal mortality from Michigan showed that obesity was a significant risk factor for airway-related adverse events contributing to maternal mortality. A 6-year review of failed intubations in obstetric patients in a region of the United Kingdom reported 36 cases of failed intubation in women whose average BMI was 33 kg/m ² . In the confidential inquiries into maternal deaths in the United Kingdom from 2000 to 2002, 35% of all the women who died had obesity, 50% more than the general population. In the reports from 2003 to 2005, 4 of the 6 deaths directly attributable to anesthesia occurred in patients with obesity, two of whom had morbid obesity (BMI >35 kg/m ² ). The ASA obstetric anesthesia closed claims files indicate that damaging events related to the respiratory system were significantly more common among patients with obesity (32%), than without it (7%) patients. Further, mortality was more common among patients with obesity. These data stress the importance of increased vigilance when caring for the obstetric patient with obesity and necessitates immediate availability of resources, including DA equipment in the labor and delivery suite.

The American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin No. 156, “Obesity in Pregnancy,” recommends that an anesthesiologist should be consulted before delivery when a patient with obesity is identified. This allows adequate time for developing an anesthetic plan that addresses the availability of proper equipment for airway management, hemodynamic monitoring, appropriate venous access, and the influence of comorbid conditions such as sleep apnea.

The dosing of induction agents in the parturient with obesity should be based on ideal body weight rather than actual body weight. Thoughtful attention regarding the dose of neuromuscular blocking agents is also warranted. A 2006 study sought to identify the dose of succinylcholine that provided ideal intubating conditions in nonpregnant patients with obesity. The study compared doses of 1 mg/kg of ideal body weight, lean body weight, and total body weight. It concluded that dosing based upon total body weight was superior for providing optimum intubating conditions. Alternatively, rocuronium may be given to provide adequate intubating conditions at a dose of 1–1.2 mg/kg of ideal body weight. Sugammadex, a cyclodextrin, can be used to reverse neuromuscular blockade induced with rocuronium or vecuronium and is active in as little as 2 minutes. It has not been studied in parturients at this time, although its use has been documented with no ill effect to mother or fetus. An ideal dose has yet to be established.

Predictors of Difficult Mask Ventilation and Predictors of Difficult Intubation

Traditional airway assessment involves an attempt to predict the difficulty of glottic view at DL and, by inference, difficulty in intubation. However, such assessment is neither sensitive nor specific and may be unreliable. ^, Because of this, it is essential for the anesthesia provider to take a detailed history of the patient and perform a thorough airway assessment to identify any potential risk factors for a DMV or TI. While it is imperative to prepare for a suspected DA, it is just as crucial to be prepared for the unanticipated DA to avoid potential complications. Preparedness is crucial in a parturient since, similar to patients with obesity, a gravid uterus typically leads to a decreased functional residual capacity (FRC), increased oxygen requirements, and, therefore, a tendency to more rapidly desaturate.

A retrospective audit performed on all obstetric GAs, involving a total of 3430 cases over an 8-year period, found 23 DI patients, with an incidence of 1:156. DI was anticipated in 9 patients, 3 of whom underwent an awake FSI; in the remaining 6 patients with morbid obesity, senior trainees or consultants managed the DI, and unanticipated difficulties occurred in 14 patients (61%). The study showed a zero incidence of esophageal or failed intubation. Preoperative assessment was either not recorded in 6 cases or was poorly documented in 8 cases.