Chapter 63: Aspiration

BACKGROUND

Aspiration of gastric contents can cause a chemical pneumonitis characterized by tachypnea, hypoxia, and fever, first described by Mendelson in 1946.¹ The incidence of mortality from aspiration during anesthesia for labor and delivery has declined over the recent decades. Data from Mothers and Babies—Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK), which is the most comprehensive database on maternal mortality, suggests aspiration has not been a contributing factor to maternal mortality since 2009.² The Serious Complication Repository Project in the United States evaluated 257,000 deliveries at 30 institutions between 2004 and 2009, found no reported cases of aspiration.³ This decline is likely due to:

• The greater use of neuraxial techniques for cesarean delivery

• The frequent use of chemical prophylaxis

• Rapid sequence intubation in the event of a general anesthetic

• Better anesthesia training

• Adherence to NPO (nothing by mouth) guidelines⁴

The true incidences of aspiration and aspiration pneumonitis are difficult to determine because of inconsistent criteria for diagnosis and lack of comprehensive data. However, it is known that morbidity varies according to ASA status of the patient, the type and volume of aspirate, the therapy administered, and criteria for diagnosis. This chapter will primarily focus on how to identify parturients at risk for aspiration and administer prophylaxis as indicated to reduce the risk of complications.

RISK FACTORS FOR ASPIRATION

Risk Factors for Aspiration⁵

• Inadequate fasting time

• Emergency surgery

• General anesthesia, especially with difficult intubation

• Gastrointestinal obstruction

• Previous gastrointestinal surgery

• Delayed gastric emptying (i.e., diabetes, active labor, opioids)

• Recent trauma

• Increased intracranial pressure

• Morbid obesity

• Use of nitrous during labor

• Cognitive neurological impairment

GASTRIC ULTRASOUND

• Gastric ultrasound has been studied, but not yet fully validated for assessment of aspiration risk in obstetrics.

• There may be a role for gastric ultrasound in cases of urgent cesarean delivery for women who have not met fasting guidelines.

• If a nonfasted parturient has a full stomach on ultrasound, delay surgery if possible, avoid general anesthesia if possible, and consider additional promotility agents.

PROPHYLAXIS

• If possible, adhere to NPO guidelines (see Chapter 36, “NPO Guidelines”).

• Use neuraxial anesthesia whenever possible, and advocate early labor epidural for high-risk parturients.

• For induction of general anesthesia, use rapid sequence induction and tracheal intubation.

• Under general anesthesia, empty stomach using orogastric tube prior to extubation and extubate awake after return of airway reflexes—risk of aspiration at extubation is equal to that of induction (Chapter 48, “General Anesthesia for Cesarean Delivery”).

• “Consider the timely administration of nonparticulate antacids, H2-receptor antagonists, and/or metoclopramide for aspiration prophylaxis”—ASA Practice Guidelines for Obstetric Anesthesia^6,7 (see Table 63-1).