Antacids as Preoperative Medication
  •  in adults: possibly, relatively high-risk of pulmonary complications if aspiration volume:
    1. > 25 ml and
    2. pH < 2.5
  • Antacids: neutralize gastric acid content
    • Single dose -- 15-30 minutes before induction: about 100% effective in increasing gastric fluid pH above 2.5
    • Sodium citrate (0.3M) --nonparticulate antacid-- commonly given before the procedure when an increase in gastric fluid pH is required
    • Nonparticulate antacids:
      • do not themselves produce pulmonary damage if aspiration of gastric fluid containing these antacids occur.
      • Colloid antacid suspensions: more effective than nonparticulate agents in increasing gastric acid pH
        •  Aspiration of gastric fluid containing particulate antacids produce significant/persistent damage even if gastric pH has been increased:
          •  Damage:
            •   pulmonary edema
            •   arterial hypoxemia
  • Onset: no "lag time"-- as seen with H2 receptor antagonists
    • Effective on fluid already present in the stomach
    • Good choice in emergency situations (assuming patients can take oral medication)
  • Other issues:
    • Antacids increase gastric fluid volume (unlike H2 receptor antagonists)
      • Most evident following repeated dosing -- e.g., during labor {concurrent opioid administration may promote gastric emptying delay}
    • Do not withhold antacids because of possible increases in gastric volume --increasing the pH is more important
  • Other drugs:
    • Omeprazole -- gastric acid suppression by inhibition of parietal cell proton pump
    • 40 mg IV (adult); 30 minutes prior to induction has been employed
    • 40-80 mg oral -- 2-4 hours before surgery is required
    • Duration of action of effects on gastric pH: about 24 hours
    • pH increases; variable effects on gastric volume with omeprazole and H2 receptor antagonists
Moyers, J.R., Preoperative Medication, Chapter 21, In: Clinical Anesthesia 3rd edition, (Barash, P.G., Cullen, B.F. and Stoelting, R.K., eds) Lippincott-Ravin, Philadelphia, New York, 1997, pp. 519-529