According to Niederman, “The entity of aspiration pneumonia in pregnant patients is a familiar one: in the 1960s as many as 2% of all maternal deaths were the result of aspiration. The pregnant woman is physiologically predisposed to aspiration. Factors including elevation of intragastric pressure due to the gravid uterus, a relaxed gastroesophageal sphincter due to the circulating progesterone, and delayed gastric emptying that accompanies pregnancy, all contribute to the risk of aspiration. These physiologic factors, coupled with sedation and analgesia given in the labor room and vigorous abdominal palpation during examinations, greatly escalate the threat of aspiration.
Because acid aspiration is an important complication of obstetric anesthesia, some form of chemoprophylaxis is often given preoperatively to minimize the risk. Drug regimens include a combination of histamine type 2 (H2) receptor antagonist, a promotility agent such as metoclopramide, and sodium citrate. Omeprazole has also been studied in this setting, but there is no consensus that any one regimen is superior, reflected by the wide variations in practice seen from hospital to hospital. Aspiration in the pregnant patient will usually occur in the labor room at the time of delivery. Aspiration may involve bacteria present in the oropharynx (S aureus, gram-negatives or anaerobes), liquid gastric contents, or solid particulate matter from the stomach. Typically, pneumonic infection resulting from the aspiration of bacteria occurs at least 24 hours after the event. Particulate matter, when aspirated, will lead to acute bronchospasm, cough, and cyanosis. Aspiration of gastric fluid leads to a somewhat different set of clinical consequences, including tachypnea, bronchospasm, pulmonary edema, hypotension and hypoxemia, approximately 6 to 8 hours after the event. The pH of the gastric fluid is critical — acid pneumonitis rarely occurs unless pH is less than 2.5. Therefore, lung injury is minimal when aspirated gastric juice has a pH greater than 2.5.
The occurrence of respiratory failure in the postpartum period should always introduce a high index of clinical suspicion of aspiration. Supportive management is indicated, primarily in the form of supplemental oxygen, bronchodilators, and ventilatory support if needed. If signs of infection evolve, antibiotic therapy to cover gram-negatives, gram-positives, and anaerobes must be initiated, though not all aspirations lead to pneumonia. Prevention is the major thrust of management. Regional anesthesia is preferred over general. If general anesthesia is mandated then the patient must be NPO for a full 24 hours. Airway protection is paramount even with regional anesthesia, and cricoid pressure and rapid sequence induction must accompany endotracheal intubation. The importance of raising gastric acid pH has already been discussed.” Risk of failed intubation three to eleven times greater in pregnant than nonpregnant: Airway edema, high rate of emergency surgery, breast enlargement and weight gain.
Reduced barrier pressure or inability of lower esophageal sphincter to increase its tone due to progesterone.
Pregnancy alters the anatomic relationship of esophagus to diaphragm and stomach.
Gastric emptying appears normal in early labor, but becomes delayed as labor progresses.