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Gastric Fluid Volume and pH after Fentanyl, Enflurane, or Halothane-Nitrous Oxide Anesthesia with or without Atropine or Glycopyrrolate

*Professor and Chairman. Department of Anesthesia, Indiana University School of Medicine, Indianapolis, Indiana 46223.

Abstract

Gastric fluid volume and pH were determined immediately following the induction of anesthesia and again after 2 hours of anesthesia consisting of 60% nitrous oxide plus either fentanyl, enflurane, or halothane. Adult patients undergoing elective, but not upper abdominal, operations were subjects for this study. Preanesthetic medication included intramuscular morphine with or without either atropine (0.4 mg) or glycopyrrolate (0.2 mg). Gastric fluid volume after 2 hours of anesthesia was significantly less (p < 0.05) than immediately after induction of anesthesia. Gastric volume was similar for all anesthetics and was not influenced by the inclusion of anticholinergic drugs in the preanesthetic medication. Compared with control gastric pH (only patients with an initial pH less than 3.5 were studied) there was no change in pH after 2 hours of fentanyl anesthesia with or without either atropine or glycopyrrolate. Likewise, pH did not change during halothane anesthesia without anticholinergic drugs. Enflurane anesthesia with or without anticholinergic drugs and halothane combined with atropine or glycopyrrolate were associated with significant increases (p < 0.05) in gastric pH. Glycopyrrolate was associated with greater increases in pH than was atropine (p < 0.05). These data suggest that gastric fluid production is minimal during anesthesia irrespective of anesthetic drugs or preanesthetic medication. Halothane or enflurane, but not fentanyl, when combined with glycopyrrolate preanesthetic medication was associated with the greatest increase in gastric pH. However, the increased pH was not seen in all patients and often the increase was not sufficiently great to protect against pneumonitis should aspiration have occurred.

Key Words: GASTROINTESTINAL TRACT • stomach • ANESTHETICS • Volatile: halothane • ANESTHETICS • Volatile: enflurane • ANALGESICS • fentanyl.