Objective: To investigate whether changes in gastric intramucosal pH (pH i m ) 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 tonometric PCO 2 (PCO 2 ss), end-tidal PCO 2 (PETCO 2 ), PaCO 2 , 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 i m 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 PaCO 2 increased significantly from 33.5 +/- 1.5 mmHg at H0 to 39.5 +/- 2.8 at H3. On the other hand, pH i m c o r r (7.40 - (pHa-pH i m ) and ΔCO 2 (PCO 2 ss-PETCO 2 ) did not vary during anaesthesia. Postoperative organ failure did not occur in these patients.Conclusions: The pH i m may decrease during anaesthesia without evidence of abnormal tissue perfusion. In order to avoid confounding factors such as PaCO 2 and [bicarb.] we propose to monitor ΔCO 2 or pH i m c o r r instead of pH i m .Objectifs: Etudier les variations du pH intramuqueux gastrique (pH i m ) en perioperatoire chez des patients beneficiant d'une chirurgie abdominale majeure. Analyser celles-ci et les comparer aux donnees hemodynamiques usuelles que sont la pression arterielle moyenne (PAM), la frequence cardiaque (FC), la pression veineuse centrale (PVC), la diurese horaire (DH) et le pH arteriel (pHa).Type d'etude: Etude prospective pilote.Patients: Sept sujets de classe physique ASA 2, devant beneficier d'une chirurgie abdominopelvienne de plus de 180 minutes.Methodes: Apres induction de l'anesthesie generale et intubation endotracheale, un tonometre nasogastrique etait positionne dans l'estomac. Trente minutes apres l'induction, puis toutes les heures apres le debut de l'intervention, ainsi qu'une, 2 et 24 heures apres la fermeture parietale etaient mesurees la PCO 2 du serum sale (PgCO 2 ) ainsi que la PETCO 2 , la concentration arterielle en bicarbonates [bicarb.], la FC, la PAM, la PVC et la DH.Resultats: Les parametres hemodynamiques n'ont pas varie de facon significative au cours de l'anesthesie. Au cours de la phase de reveil, la FC a augmente et la PVC diminue de facon significative. Le pH i m a diminue de facon significative passant de 7,42 +/- 0,03 a H0 a 7,30 +/- 0,02 a H3. Cette variation etait associee avec une decroissance significative du pHa (de 7,43 +/- 0,02 a H0 a7,33 +/- 0,02 a H3) et des [bicarb.] de 22 +/- 1 mmola H0 a 20 +/- 1 mmol a H3. De meme, la PaCO 2 a augmente de facon significative de 33,5 +/- 1,5 mmHg a H0 a 39,5 +/- 2,8 a H3. Pourtant, le pH i m corrige (7,40 - (pHa - pH i m )) et le ΔCO 2 (PgCO 2 -PETCO 2 ) n'ont pas varie de facon significative au cours de l'anesthesie. Il n'y a pas eu de defaillance postoperatoire chez ces patients.Conclusions: Une baisse du pH i m peut survenir en cours d'intervention sans manifestations evidentes de perfusion tissulaire insuffisante. Afin d'eviter la confusion de facteurs tels que la PaCO 2 et les [bicarb.] nous proposons de remplacer la mesure simple du pH i m par le monitorage du ΔCO 2 ou le calcul du pH i m corrige.