Full stomach

A 37-year-old woman with small bowel obstruction but otherwise in good general health presented to the operating room for exploratory laparotomy, lysis of adhesions, and possible bowel resection. Her past surgical history was significant for cholecystectomy 3 years ago, under general anesthesia, and cesarean delivery 1 year ago with spinal anesthesia. Both procedures were without complication. She weighed 65 kg. In the preoperative holding area, her vital signs were heart rate, 97 beats per minute, blood pressure, 130/65 mm Hg, and respiratory rate, 12 breaths per minute. She was found to have acute abdominal tenderness, and she had a nasogastric tube in place. The tube was draining approximately 25mL per hour of bilious fluid. Her hematocrit was 39%.

What are the mechanisms a conscious person has to prevent regurgitation and pulmonary aspiration?

The lower esophageal sphincter (LES) is the primary barrier to gastroesophageal reflux. The LES is 2 to 5 cm long and moves upward with inspiration and downward with exhalation. On swallowing, the esophagus undergoes peristaltic contractions to allow the passage of food, and the LES relaxes. This sphincter traverses the diaphragm and has a resting pressure greater than gastric pressure. The difference in these pressures (LES pressure minus gastric pressure) is known as “barrier pressure.” In normal subjects, an increase in abdominal pressure triggers an increase in lower esophageal pressure, maintaining barrier pressure. Gastroesophageal reflux disease (GERD) occurs when the barrier pressure decreases. Reflux occurs when either the LES pressure decreases or the gastric pressure increases.

The angle where the esophagus meets the stomach also protects against GERD. If the angle is oblique, high gastric pressures are required to cause reflux. However, if the angle is small (as often occurs in patients with morbid obesity or a gravid uterus), reflux may occur at low gastric pressures.

Another protective mechanism is the diaphragmatic crura that tighten at the lower esophagus to prevent reflux. The upper esophageal sphincter (striated muscle that is not under conscious control) is a third mechanism to protect against regurgitation. Virtually all commonly used general anesthetics including muscle relaxants cause relaxation of this sphincter.

Finally, there are intrinsic airway reflexes that protect the airway against aspiration in the event of regurgitation. These include the cough reflex (a period of brief inspiration followed by a forceful expiration), the expiration reflex (expiration without inspiration), laryngospasm and apnea (closure of both the false cords and the true cords), and spasmodic panting (rapid shallow breathing) ( Box 32-1 ).

BOX 32-1

Mechanisms to Prevent Regurgitation and Pulmonary Aspiration

  • Lower esophageal sphincter

  • Gastroesophageal angle

  • Diaphragmatic crura

  • Upper esophageal sphincter

  • Airway reflexes

    • Cough

    • Expiration reflex

    • Laryngospasm and apnea

    • Spasmodic panting

Discuss the risk factors for regurgitation and pulmonary aspiration during general anesthesia.

General anesthesia is associated with loss of protective upper airway reflexes. A patient under general anesthesia who has regurgitation is at risk to aspirate the regurgitant. Any condition associated with an increase in intragastric volume, an increase in intragastric pressure, or a decrease in LES tone may result in regurgitation and pulmonary aspiration ( Box 32-2 ).

BOX 32-2

Conditions Associated with Regurgitation and Pulmonary Aspiration for which Rapid-Sequence Induction Should Be Considered

  • Obesity

  • Abdominal surgery

  • Depressed level of consciousness

  • History of gastritis or ulcer

  • Bowel obstruction

  • Pain or stress

  • Emergency surgery

  • American Society of Anesthesiologists Physical Status IV-V

  • Esophageal disorders or previous esophageal surgery

  • Recent meal

  • Diabetes mellitus, if associated with gastroparesis

  • Ileus

  • Trauma

  • Concurrent opioid administration

  • Symptomatic hiatal hernia

ASA, American Society of Anesthesiologists.

When can aspiration occur during the perioperative period?

Aspiration can occur at any time during the perioperative period. Specifically, it can occur at the following times:

  • Before induction

  • During induction before laryngoscopy

  • During mask ventilation

  • During laryngoscopy

  • During extubation

  • Immediately after tracheal extubation

  • In the postanesthesia care unit

However, most of the time, aspiration occurs at induction during laryngoscopy.

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Jul 14, 2019 | Posted by in ANESTHESIA | Comments Off on Full stomach
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