Évaluation de la théorie de Stewart lors de l'acidose métabolique survenant après chirurgie cardiaque sous circulation extracorporelle

Abstract

Introduction According to the Stewart approach of acid-base regulation, chloride from either volume replacement or cardiopulmonary bypass (CPB) priming solution may induce metabolic acidosis. The alternative hypothesis stands in volume dilution with solutions free of bicarbonate. Objectives Evaluate the acid-base status of patients undergoing cardiac surgery with CPB priming containing chloride and bicarbonate. Material and methods Prospective study. Methods Twenty-eight patients were prospectively included. Priming of CPB contained 47.4 mmol/l of bicarbonate and 97.7 mmol/l of chloride. Arterial blood samples were taken at 3 timings: prior (T1) and after (T2) CPB, and on arrival in the ICU (T3). Following measurements were performed: Na +, K +, Cl -, Mg ++, Ca ++, phosphates, albumin, lactate and arterial blood gases. Results After CPB respiratory acidosis was observed. There was a significant increase of chloride with a decrease in apparent strong ion difference (SIDa). At the same time bicarbonate and base excess (BE) remained constant. A significant but weak correlation between BE and SIDa existed (r 2 = 0.06, p = 0.024). On the contrary, no correlation was found between variations of BE and SIDa. However, the correlation was stronger between values and variations of bicarbonate and BE (respectively r 2 = 0.605, p < 0.0001 and r 2=0.495, p < 0.0001). Conclusion No metabolic acidosis occurred after cardiac surgery when CPB was primed with bicarbonate. Therefore, it appears that chloride administration is not the main mechanism being involved in the acid-base regulation. This reinforces the hypothesis that metabolic acidosis during CPB may mainly be due to dilution of bicarbonate.