The practice of obstetrics carries a high medical liability risk; the 2006 American College of Obstetricians and Gynecologists (ACOG) on professional liability reported a “continuing negative trend” that professional liability was having on the practice of obstetrics and gynecology. The survey data showed that 89.2% obstetricians who responded had at least one professional liability claim during their career or an average of 2.62 claims per OB/GYN doctor (20). Similarly, obstetric anesthesia also carries high liability (5). The trend continues, similarly in the 2012 ACOG Survey on professional liability also showed that 77.3% OB/GYN practitioners experienced at least one professional liability claim filed against them during their professional careers with an average of 2.69 claims per OB/GYN (21).

The ASA Closed Claims Project is a structured evaluation of adverse events from the closed claim files of 35 United States professional liability insurance companies. Maternal death and newborn death/brain damage were the most common obstetric anesthesia malpractice claims in ASA closed database before 1990 (5). The liability profile changed, as the trends in obstetric anesthesia have changed dramatically in the last three decades. Obstetric anesthesia claims for injuries from 1990 to 2003 were compared to obstetric anesthesia claims for injuries before 1990. Compared to pre-1990 claims, the proportion of obstetric anesthesia claims from 1990 or later associated with cesarean delivery decreased; the claims associated with GA decreased (p < 0.01), the proportion of maternal death/brain damage and newborn death/brain damage decreased (Fig. 24-1). Malpractice claims from 1990 or later related to respiratory causes of injuries decreased from 24% (pre-1990) to 4%; claims (1990 or later claims) related to inadequate oxygenation/ventilation and pulmonary aspiration of gastric contents and esophageal intubation also decreased. However, despite the decrease in claims, the most common anesthetic causes of maternal death/brain damage in claims associated with general anesthesia were difficult intubation and maternal hemorrhage. The seven difficult intubation injuries occurred between 1991 and 1998, mostly upon induction (six of seven cases). The airway-related claims involved multiple attempts at tracheal intubation leading to progressive difficulty with ventilation. In two of the claims, tracheal intubation was assessed to be difficult preoperatively, with a backup plan to awaken the patient and perform fiberoptic intubation. However, progressive airway difficulties occurred while attempting to awaken the patients, thus resulting in adverse outcomes. The claims related to DI after 1990, as compared to claims pre-1990 have not changed (5) (Table 24-4). The overall improvement in the closed claims statistics and decline in anesthesia-related maternal mortality in the past few years and overall risk ratio between GA and RA can be attributed to the practice guidelines introduced by ASA including the ASA Practice Guidelines in Obstetric anesthesia. These initiatives include implementation of minimum standard of care requiring the use of respiratory system monitors (pulse oximetry and capnography) during anesthesia; enhanced awareness of the risk of pulmonary aspiration of gastric contents in the obstetric patient (22); decreased utilization of GA in obstetric practice and the heightened awareness of the ASA difficult airway algorithm (10). During the past two decades, anesthesiologists have focused on improving their management of difficult/failed intubation management and gaining experience with the laryngeal mask airway and other airway devices (10).

Similarly, the Doctors Insurance Company reported on 22 anesthesia malpractice closed claims between 1998 and 2006, filed after maternal cardiac arrests in the labor and delivery suites (23). Adverse events resulted in 10 maternal deaths; 11 had anoxic brain damage with only one patient surviving neurologically intact. Of the 22 malpractice claims, only one case involved GA and failed intubation. Thirteen cases were regional anesthesia-related respiratory arrests after epidurals
with unintentional intrathecal injections and five high spinals during cesarean delivery. Seven patients were moved to the operating room for resuscitation due to lack of airway equipment in the labor and delivery suite. Five arrests occurred during spinal anesthesia for cesarean delivery in the operating room. However, none of the operating rooms had audible alarms on the monitors at the time of arrest (23). The details of airway management were not outlined.

The hormonal influences of pregnancy and, in particular, the effects of estrogen resulting in an increase in the ground substance of the airway connective tissue, increased blood volume, an increase in total body water, and an increase in interstitial fluid, result in hypervascularity and edema of oropharynx, nasopharynx, and respiratory tract thus contributing to soft tissue airway edema. Airway changes with an increase in the Mallampati (MP) scores have been shown to occur during pregnancy, labor, and delivery (47). Further, the incidence of MP classes III and IV increases during labor compared to the prelabor period, and these changes are not reversed by 48 hours after delivery (48). Therefore, it is absolutely necessary to examine the airway of a parturient in labor prior to administering anesthesia for a CD (48). Excessive weight gain during pregnancy, preeclampsia,
iatrogenic fluid overload, bearing-down efforts during labor with increases in venous pressure, all may lead to an increase in upper airway mucosal edema. Additional upper airway change includes tongue engorgement during pregnancy leading to decreased mobility of the floor of the mouth (49) and changes in the MP score (50). Several published reports describe difficulties in intubation secondary to development of airway edema during labor and delivery, preeclampsia, and status-post massive fluid and blood transfusion resuscitation following postpartum hemorrhage all resulting in higher MP scores (51).

Difficulties with tracheal intubation due to facial and laryngeal edema in patients with preeclampsia and eclampsia have also been described, including instances of rapid development of airway edema (52). Due to the increased vascularity, engorgement of the mucosa and swelling of the airway, the parturient is not only at increased risk for epistaxis following manipulation of nasopharynx with nasotracheal intubation, but also vulnerable to increased trauma with repeated attempts at intubation (53). Avoiding manipulation of nasopharynx, using smaller-sized tracheal tube, and strict adherence to no more than two attempts at orotracheal intubation, are important to avoid airway management–related trauma, bleeding, edema and further complications, and catastrophes (53).

The gravid uterus displaces the diaphragm cephalad with progression of the pregnancy and leads to a 20% decrease in functional residual capacity (FRC); this decrease will be exacerbated to a significant degree in the supine position. In the supine position, the FRC is 70% of its normal capacity measured in the upright position. In an obese parturient, the supine position can result in airway closure and an increase in alveolar–arterial gradient during normal tidal respiration, predisposing the parturient to lower partial pressure of oxygen (54). At the same time, oxygen consumption is increased by 20% secondary to the metabolic needs of the growing fetus, uterus, and placenta. Chest wall compliance is decreased and the effect of the anatomical changes imposed by the pregnancy is a 50% increase in the oxygen cost of breathing. Ventilatory drive is increased by progesterone during pregnancy, giving rise to hyperventilation to meet the increased oxygen demands of the pregnant mother. Both the oxygen consumption and carbon dioxide production are increased by 20% to 40% at term. The decrease in FRC coupled with increased oxygen utilization shortens the safe apnea time after induction of anesthesia (55). The time to desaturation and hypoxemia is much faster, than the recovery from the time needed to recover from the apnea produced by the succinylcholine (56).

Preoxygenation also plays a critical role in maximizing the safe duration of apnea. The purpose of preoxygenating a patient before induction of general anesthesia is to provide the maximum duration that a patient can safely tolerate apnea so that airway interventions may be undertaken at the lowest threat to the patient, even in situations where unanticipated difficulties arise. This issue on preoxygenation is discussed in the section on preoxygenation.

The gravid uterus compresses the inferior vena cava in the supine position resulting in a decrease in venous return and cardiac output. The reduction in cardiac output and elevated oxygen consumption can further decrease the oxygen saturation. The decrease in cardiac output, and the ensuing hypoxemia, during a difficult intubation, failed intubation, or CICV situation predisposes the mother to the risk for myocardial hypoxemia, cardiovascular arrest, and compromised uteroplacental perfusion, which can also place the fetus’ well-being at risk. Maintaining left uterine tilt, establishing an airway with adequate ventilation and oxygenation in a timely manner, maintaining adequate perfusion in mother and baby, and cardiovascular stability become extremely important in order to ensure safe outcome for both.

Gastrointestinal changes which include hormonal, anatomical, and physiologic changes during pregnancy are recognized risk factors for gastric regurgitation and pulmonary aspiration during a general anesthetic. The decrease in gastric pH and an increase in intragastric pressure associated with an increasingly incompetent gastroesophageal sphincter raise a concern about a “full stomach” in obstetrical patients; further, with the onset of labor there is also a delay in gastric emptying. Aspiration-related deaths during pregnancy occur from complications associated with induction problems such as difficult intubation, esophageal intubation, and inadequate attempts at ventilation (1,8,57).

During the last two decades, obesity has become a global epidemic with more than one billion overweight adults worldwide (58). In the United States, the Centers for Disease Control (CDC) trends by states, from 1985 to 2009, show that during the past 20 years, there has been a dramatic increase in obesity with 33 states, having a prevalence equal to or greater than 25%, and in 9 states with a prevalence of obesity greater than 30% (59). Obesity in pregnancy has increased in accordance with the increased prevalence of obesity in the general population, with the prevalence of obesity during pregnancy varying from 6% to 28% (60).

A body mass index (BMI) greater than 25 kg/m² is considered overweight and a BMI greater than 30 kg/m² is considered obese. In the nonobstetric population, a BMI greater than 26 kg/m² results in a three-fold increase in the incidence of difficult mask ventilation (61). Several review articles support an association between obesity and DI in the obstetric and nonobstetric patients (62).

On the basis of an analysis of 20 years of data from a large tertiary Canadian maternity center, McKeen has recently reported that maternal age >35 years, weight 90 to 99 kg, and the absence of active labor were associated with an increased risk for DI (46). Although these findings are concerning, due to the increasing prevalence of obesity in the maternal population and the larger number of women delaying conception, they are also difficult to apply clinically.

Both prepregnancy obesity and excessive weight gain during pregnancy are associated with comorbidities such as hypertension or preeclampsia with intrauterine growth retardation, diabetes and macrosomia, and dysfunctional labor, thus increasing the incidence of operative CD. The incidence of postpartum hemorrhage is also higher in these obese patients leading to an increased likelihood of a general anesthetic intervention.

Weight gain during pregnancy results from the increasing size of the uterus and fetus, increased blood and interstitial fluid volumes, and deposition of new fat. There is a correlation between weight gain and an increase in the Mallampati score (63). The weight gain and obesity are associated with an increase in the Mallampati score; the incidence of partially obliterated oropharyngeal space in an obese parturient is doubled
compared to nonpregnant patients (64). Obesity compounds the effects of pregnancy on the increase in breast size and engorgement. In the supine position, the enlarged breasts can encroach into the neck area impeding effective application of cricoid pressure and cause difficulty with laryngoscope blade insertion. An increase in neck circumference is an added risk factor for DI and difficult MV (65). These aforementioned changes, the breast engorgement, along with anthropometrical difference between patients, create a risk for difficult laryngoscopy, difficult tracheal intubation, and difficult mask ventilation (33). DI is encountered more frequently in morbidly obese parturients weighing more than 130 kg (62). In obesity, the respiratory-related changes of pregnancy are even more significant, with marked decrease in FRC such that the closing capacity exceeds FRC during tidal breathing, thus leading to a decrease in arterial oxygen tension and predisposing the parturient to a much higher risk of hypoxemia during a difficult tracheal intubation or difficult mask ventilation encounter (66).

In the obese parturient, a thorough preoperative assessment, review of comorbidities, and previous anesthetic history for difficulty with tracheal intubation is essential so as to allow for proper preparation and appropriate interventions. The “ramped position” in obese parturients prior to induction of general anesthesia becomes critical so as to facilitate ventilation and improve the laryngoscopic visualization of the glottis for tracheal intubation. The aim is to achieve the “best alignment” of the three axes, (oral, pharyngeal, and laryngeal) in the obese patient.

The cornerstone in prevention of airway catastrophes in obstetric patients is firstly, to attempt to predict which obstetric patients are at risk for difficult laryngoscopy, DI, and difficult mask ventilation.

Numerous investigators have attempted to predict the difficult airway by using simple bedside physical examination. There are numerous publications using univariate or multivariate predictors of difficult intubation in the nonobstetric patients and a handful of publications utilizing multivariate predictors in predicting the difficult airway in obstetric patients (70). Yentis (70) describes the problems with many studies examining the prediction of difficult airway; therefore, it is appropriate to delineate the terms used to describe the accuracy or predictive power of the tests. The various tests used to predict a difficult airway in the general population as well as the obstetric population will also be described in this section.

A test to predict difficult intubation should have high sensitivity, so that it will identify most patients in whom intubation will be truly difficult. It should also have a high positive predictability value, so that only few patients with airways actually easy to intubate are subjected to the protocol for difficult airway management (64).

It is also of paramount importance to recognize the predictors for “difficult to mask ventilate” in obstetric patients. Successful mask ventilation (MV) provides anesthesia practitioner with a rescue technique during unsuccessful attempts at laryngoscopy and unanticipated difficult airway management situations. Pregnant women become hypoxemic more rapidly during episodes of apnea as detailed in the section on respiratory changes during pregnancy. Computer modeling of the rate of arterial oxyhemoglobin desaturation in fully oxygenated patients suggests that this process occurs significantly more rapidly in moderately ill and obese patients compared to healthy individuals (56) (Fig. 24-2). Similarly, utilizing a computer model, it is observed that there is reduced tolerance for apnea in pregnant patients particularly in the Trendelenberg position (54). These studies emphasize the importance of recognizing early that one is in a difficult intubation scenario, and strategizing how to oxygenate and ventilate the mother.

Although there is an extensive body of literature addressing predictive factors for difficult laryngoscopy and grading its view, investigations that focus on difficult MV are limited (69). A four-point scale to grade difficulty in MV has been identified (Table 24-7). Encountering a clinical situation with either a grade 3 MV (inadequate, unstable, or requiring two providers) or a grade 4 MV (impossible to ventilate) with a difficult intubation (DI) represents the most feared airway outcomes; a patient in whom establishing tracheal intubation is difficult and the primary rescue technique of conventional
MV is also challenging. Therefore, it is important to predict this situation thus allowing the practitioner to be prepared with alternative tools, that is, laryngeal mask airway, video laryngoscopes, and so forth.

In an observational study of 22,660 attempts at MV in nonobstetric patients, the criteria that correlated with grade 3 or 4 MV and DI may be applicable to the obstetric population, include independent risk factors, such as (1) limited or severely limited mandibular protrusion, thick or obese neck anatomy, (2) a history of sleep apnea, (3) a history of snoring, and BMI of 30 kg/m² or greater (72). This study supported and was able to demonstrate the value of the mandibular protrusion test in predicting difficult MV and DI as suggested by Takenaka et al. (73).

The IID by itself is not a reliable predictor of difficult tracheal intubation in either general or obstetric patents (74). The maximal mouth opening is influenced by the degree of atlanto-occipiatl joint extension (75). Even though Savva et al. found that the IID was not a useful independent test in identifying difficult tracheal intubation (74), in the Australian Critical Incident Monitoring Study (76), the four variables associated with difficult intubation were limited mouth opening, obesity, limited neck extension, and lack of a trained assistant. Limited mouth opening along with limited jaw protrusion often ranks high in composite scores such as the Wilson Risk Sum (77) (weight, head and neck movement, interincisor gap, mandibular jaw protrusion, receding mandible, buck teeth), and the Arne Risk Index scores (28) (history of DI, pathologies associated with DI, clinical symptoms, TMD <6.5 cm, restricted head and neck movement, Mallampati scores 2 to 4, IID <5 cm, jaw protrusion class B or C) are used to predict difficult tracheal intubation.