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 reliable intragastric partial pressure of carbon dioxide (PCO2) tonometry by evaluating the effect of an oral dose of: sodium bicarbonate before and after administration of the H-2-blocker ranitidine to mimic CO2 generation following the buffering of acid by bicarbonate in patients after cardiac surgery. 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 acid secretion suppression by 100 mg ranitidine as an intravenous bolus given at approximate to 3 h after surgery (day 0) and on the first postoperative day (day 1). Measurements ann results: Intragastric PCO2 (iPCO(2); tonometry), gastric juice pH (aspirate) and arterial blood gas values were measured. On day 0, the 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 basal 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 before 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 mandatory for reliable iPCO(2) tonometry after cardiopulmonary bypass surgery, even when gastric acid secretion is transiently inhibited. In fact, gastric acid secretion was inhibited immediately after surgery, but returned on the first postoperative day in most patients, as judged from the bicarbonate back titration of gastric acid, even when gastric juice pH was relatively high.