Role of pump prime in the etiology of cardio-pulmonary bypass associated acidosis.

The development of metabolic acidosis during cardio-pulmonary bypass (CPB) is a well recognized but poorly explained phenomenon. It has been hypothesized that it is purely a development after the delivery of pump prime. A retrospective study was conducted at our hospital on 68 patients who underwent elective coronary artery bypass grafting (CABG). Sampling of arterial blood was performed at three time intervals: (T(1)) Baseline, prior to induction; (T(2)) 5 minutes after initiation of CPB and prior to administration of cardioplegia solution; (T3) during rewarming prior to weaning the patient off CPB. Measurements of Na(+), K(+), Cl(-), pH, pCO(2), HCO(3) (-), Base excess, Anion gap, Strong ion difference at each collection point were performed. Results were analyzed in a quantitative manner. On delivery of pump prime, all patients' developed metabolic acidosis. However, it is very important to distinguish the metabolic acidosis as their management varies. Anion gap has been found to be useful in managing peri-operative metabolic acidosis.