Gastric tonometry during major abdominal surgery.

Objective: To investigate whether changes in gastric intramucosal pH (pH(im)) occur during major abdominal surgery, and if so, to determine the relationship between classic global indices of tissue perfusion such as mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), urine flow (UF) and arterial pH (pHa). Study design: Prospective descriptive study. Patients: Seven ASA2 patients undergoing major abdominal surgery. Methods: After induction of anaesthesia and endotracheal intubation, a tonometer nasogastric tube was positioned in the stomach, Measurements of ionometric PCO2 (PCO(2)ss), end-tidal PCO2 (PETCO(2)), PaCO2, bicarbonates [bicarb .], pHa, MAP, HR, CVP and UF were collected at baseline (H0), and one, two, three, and 24 hours (H1, H2, H3, and H24) after the beginning of surgery. Results: Haemodynamics did not significantly change during anaesthesia. During recovery HR increased and CVP decreased significantly. The pH(im) decreased significantly from 7.42 +/- 0.03 at H0 to 7.30 +/- 0.02 at H3. This was associated with a significant decrease in pHa (from 7.43 +/- 0.02 at H0 to 7.33 +/- 0.02 at H3) and in [bicarb .] from 22 +/- 1 mmol at H0 to 20 +/- 1 mmol at H3). The PaCO2 increased significantly from 33.5 +/- 1.5 mmHg at H0 to 39.5 +/- 2.8 at H3. On the other hand, pH(imcorr) (7.40 - (pHa-pH(im)) and Delta CO2 (PCO(2)ss-PETCO(2)) did not vary during anaesthesia. Postoperative organ failure did not occur in these patients. Conclusions: The pH(im) may decrease during anaesthesia without evidence of abnormal tissue perfusion. In order to avoid confounding factors such as PaCO2 and [bicarb .] we propose to monitor Delta CO2 or pH(imcorr) instead of pH(im).