A comparison of the volume and pH of gastric contents of obese and lean surgical patients

Anesth Analg. 1998 Jan;86(1):147-52. doi: 10.1097/00000539-199801000-00030.


Obese surgical patients are typically considered to be more likely than lean patients to possess high-volume and low-pH (HVLP) gastric contents after a standard preoperative fast, based on a study of a population predominately consisting of patients receiving intramuscular preoperative sedation. We revisited this issue in a study population of 256 fasted surgical patients, of which 232 received no preoperative antacid or gastric prokinetic drug. Immediately after endotracheal intubation, an 18-French sump tube was placed, and gastric contents were withdrawn. Subjects' gastric contents were defined as HVLP if they exhibited a combination of a volume > 25 mL and a pH < 2.5. Obesity was defined as a body mass index > 30. Among nonmedicated obese patients, the proportion with HVLP gastric contents was 20 of 75 (26.6%). The proportion of lean patients with HVLP gastric contents was 66 of 157 (42.0%). The difference between the HVLP proportions for these two groups was found to be significant (P < 0.05) using chi 2 analysis. Obesity seems to be associated with a significantly decreased risk of HVLP gastric contents among surgical patients with no history of gastroesophageal pathology after a normal interval of preoperative fasting.

Implications: Previous studies have shown that obese surgical patients have a greater volume of acidic stomach contents than lean patients, despite a routine preoperative fast. We have reexamined this issue and found that among otherwise healthy, fasted, obese surgical patients, there is a lower incidence of combined high-volume, low-pH stomach contents compared with lean patients.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Body Mass Index
  • Female
  • Gastric Acidity Determination
  • Gastrointestinal Contents*
  • Humans
  • Male
  • Middle Aged
  • Obesity / metabolism*
  • Pneumonia, Aspiration / metabolism
  • Surgical Procedures, Operative