14: Anesthetic Complications due to Airway Management/Aspiration

INTRODUCTION

The term difficult airway most commonly refers to difficulty in placing an endotracheal tube through the vocal cords with the use of direct laryngoscopy. However, it can also refer to difficulty in providing adequate mask ventilation.¹ Despite advances in airway management and rescue, the incidence of airway difficulty encountered in the pregnant population resulting in inability to intubate is still estimated by some to be 1 in 300, a value eight times higher than that seen in the general population.^{2, 3, and 4} In the past, aspiration was considered a major cause of maternal morbidity and mortality.⁵ It follows that complications of airway management and failed or difficult intubation after induction of general anesthesia in near term pregnant women may be significant contributors to anesthesia-related maternal complications, and avoidance of difficult airway scenarios be of paramount concern to the obstetric anesthesiologist. Indeed, failure to intubate was the leading cause of anesthesia related maternal mortality from 1979 to 1990.⁶ Historically, this has led anesthesiologists to reduce the use of general anesthesia and thus the rate of airway catastrophe at the time of induction of general anesthesia for cesarean delivery. More recently, however, because of improved difficult airway protocols and rescue equipment, including the use of the laryngeal mask airway, increased use of regional anesthesia, and overall increased awareness, the maternal death rate from airway complications, particularly at induction of general anesthesia, appears to be decreasing.^7,8 The following discussion focuses on airway and gastrointestinal changes in pregnancy, managing the difficult airway, and aspiration.

UPPER AIRWAY AND RESPIRATORY MECHANICS

Pregnancy, labor, delivery, and the puerperium induce significant changes in upper airway anatomy and respiratory mechanics (Table 14-1). Higher levels of estrogen and an increase in maternal blood volume contribute to capillary engorgement, mucosal edema, and tissue friability in the parturient’s airway. This airway edema can be significantly worsened by preeclampsia, respiratory tract infection, expulsive efforts during the second stage of labor, and excessive fluid administration. Mallampati score increases during gestation and more so during labor.⁹ Because of these airway changes, it is generally recommended to use smaller sized endotracheal tubes for general anesthesia in pregnant women.⁴ Direct laryngoscopy should be performed carefully so as to minimize trauma and subsequent bleeding. Nasal endotracheal intubation should be used cautiously and with careful attention to vasoconstriction of the nasal mucosa.¹⁰

Respiratory physiologic changes during pregnancy relevant ...