Antacids as Preoperative Medication
In adults: possibly, relatively high-risk of pulmonary complications if aspiration volume:
> 25 ml and
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
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:
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)
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
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:
May be used in conjunction with triple therapy
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