Reliable gastric tonometry after coronary artery surgery: need for acid secretion suppression despite transient failure of acid secretion

Objective:To study the need for suppression of gastric acid secretion for r eliable intragastric partial pressure of carbon dioxide (PCO2) tonometry by evaluating the effect of an oral dose of: sodium bicarbonate before and af ter administration of the H-2-blocker ranitidine to mimic CO2 generation fo llowing the buffering of acid by bicarbonate in patients after cardiac surg ery. Design: Prospective, open, non-randomized clinical study. Setting: Cardiothoracic intensive care unit at a university hospital. Patients: 10 patients after elective coronary artery bypass surgery. Interventions: An oral dose of 500 mg sodium bicarbonate before and after a cid secretion suppression by 100 mg ranitidine as an intravenous bolus give n at approximate to 3 h after surgery (day 0) and on the first postoperativ e day (day 1). Measurements ann results: Intragastric PCO2 (iPCO(2); tonometry), gastric j uice pH (aspirate) and arterial blood gas values were measured. On day 0, t he iPCO(2) was 25 +/- 5 mmHg before and 31 +/- 5 mmHg after the bicarbonate dose, 29 +/- 5 mmHg after ranitidine infusion, and 31 +/- 5 mmHg after the bicarbonate dose following the ranitidine infusion (NS). On day 1, the bas al iPCO(2) was 32 +/- 4 mmHg and it increased to. 56 +/- 25 mmHg following bicarbonate (p < 0.01). After ranitidine, the iPCO(2) was 33 +/- 4 mmHg bef ore and 40 +/- 14 mmHg after bicarbonate (NS). Basal gastric juice pH was > 4 in nine of ten patients on day 0 and > 4 in seven of ten patients on day 1. Conclusions: Pharmacological suppression of gastric acid secretion is m andatory for reliable iPCO(2) tonometry after cardiopulmonary bypass surger y, even when gastric acid secretion is transiently inhibited. In fact, gast ric acid secretion was inhibited immediately after surgery, but returned on the first postoperative day in most patients, as judged from the bicarbona te back titration of gastric acid, even when gastric juice pH was relativel y high.