Nursing Pharmacology Chapter 27:  Gastrointestinal Drugs

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" which may be 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  delay gastric emptying.

  • 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.

    • Parietal cells H ion secretion depends on a H⁺,K⁺-ATPase pump-- promoting H-K exchange

    • H⁺,K⁺-ATPase located in apical membrane to and tubulovesicular apparatus of parietal cells

    • Luminal surface of the membrane enzyme: exposed to gastric luminal acid

    • Omeprazole and lansoprazole inhibit the proton pump, effectively irreversibly  thus requiring synthesis of new enzyme protein

    • Omeprazole and lansoprazole approved for treatment of:

      • Duodenal ulcer

        •  May be used in conjunction with triple therapy

      • Erosive esophagitis

        • Qadder MA Falk GW Acid Peptic Disorders (Cleveland Clinic:  Center for Continuing Education) http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/gastroenterology/acid-peptic-disorders/

      • Gastric acid hypersecretory states, including Zollinger-Ellison syndrome

    Friedman, L. S. and Peterson, W.L. Peptic Ulcer and Related Disorders In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., and Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp. 1597-1616.

  • IV 30 minutes prior to induction has been employed

  • 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