Drinking 300 mL of clear fluid two hours before surgery has no effect on gastric fluid volume and pH in fasting and non-fasting obese patients

Can J Anaesth. 2004 Feb;51(2):111-5. doi: 10.1007/BF03018767.


Purpose: To determine whether, in obese [body mass index (BMI) > 30 kg.m(2)] patients, oral intake of 300 mL clear liquid two hours before elective surgery affects the volume and pH of gastric contents at induction of anesthesia.

Methods: A single-blind, randomized study of 126 adult patients, age > or = 18 yr, ASA physical status I or II, BMI > 30 kg.m(2) who were scheduled for elective surgery under general anesthesia. Patients were excluded if they had diabetes mellitus, symptoms of gastroesophageal reflux, or had taken medication within 24 hr that affects gastric secretion, gastric fluid pH or gastric emptying. All patients fasted from midnight and were randomly assigned to fasting or fluid group. Two hours before their scheduled time of surgery, all patients drank 10 mL of water containing phenol red 50 mg. Those in the fluid group followed with 300 mL clear liquid of their choice. Immediately following induction of general anesthesia and tracheal intubation, gastric contents were aspirated through a multiorifice Salem sump tube. The fluid volume, pH and phenol red concentration were recorded.

Results: Median (range) values in fasting vs fluid groups were: gastric fluid volume 26 (3-107) mL vs 30 (3-187) mL, pH 1.78 (1.31-7.08) vs 1.77 (1.27-7.34) and phenol red retrieval 0.1 (0-30)% vs 0.2 (0-15)%. Differences between groups were not statistically significant.

Conclusion: Obese patients without comorbid conditions should follow the same fasting guidelines as non-obese patients and be allowed to drink clear liquid until two hours before elective surgery, inasmuch as obesity per se is not considered a risk factor for pulmonary aspiration.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Anesthesia, General
  • Drinking / physiology*
  • Elective Surgical Procedures*
  • Fasting / physiology*
  • Female
  • Gastric Juice / chemistry
  • Gastric Juice / physiology
  • Gastrointestinal Contents* / chemistry
  • Humans
  • Hydrogen-Ion Concentration
  • Male
  • Middle Aged
  • Obesity*
  • Phenolsulfonphthalein / administration & dosage
  • Single-Blind Method
  • Time Factors


  • Phenolsulfonphthalein