Gastric volume and pH in out-patients

Area of Science:

• Anesthesiology
• Gastroenterology
• Surgical Risk Assessment

Background:

• Gastric volume and acidity are critical factors influencing aspiration risk during anesthesia.
• Understanding pre-anesthetic gastric content is crucial for patient safety, particularly in ambulatory surgery.

Purpose of the Study:

• To compare gastric volume and pH in outpatients versus inpatients under general anesthesia.
• To assess the accuracy of gastric tube aspiration in determining gastric volume.

Main Methods:

• Gastric content volume and pH were measured in 21 outpatients and 21 inpatients post-anesthesia induction.
• Gastric volume was determined using a polyethylene glycol dilution technique and direct aspiration.
• Gastric fluid pH was measured directly from withdrawn samples.

Main Results:

• Outpatients exhibited a mean gastric volume of 69 mL (±17 mL) compared to 33 mL (±4 mL) in inpatients.
• Mean gastric pH was 1.8 (±0.2) for outpatients and 2.0 (±0.3) for inpatients.
• Four outpatients had >75 mL gastric fluid with pH < 2.0; direct aspiration underestimated gastric volume.

Conclusions:

• Outpatients under general anesthesia have larger gastric volumes and potentially higher aspiration risk than inpatients.
• Standard gastric tube aspiration is an unreliable method for estimating true gastric volume.
• These findings underscore the importance of vigilant pre-anesthetic assessment for outpatients to mitigate aspiration events.