Introduction: A wide range of acid base fluctuations are seen during Cardiopulmonary bypass (CPB) and the development of metabolic acidosis is well recognized. We conducted a study tocompare the metabolic effects of Ringer lactate and Plasmalyte-A as CPB prime in causing bypass associated acidosis in valve replacement surgeries. Methods: We performed a prospective, randomized controlled study on a total of 80 adult patients undergoing CPB for valvular heart surgeries. The patients were randomized into two groups: Group I (Ringer Lactate) and Group II (Plasmalyte-A). Arterial blood samples were taken before initiating CPB, 30 minutes after starting CPB, then every half hourly till termination of CPB and after half an hour stay in the ICU post operatively to analyze primarily H+ ions, bicarbonates, lactate and strong ion difference. Results and Discussion: The results were analyzed in a quantitative manner. In Ringer Lactate group, during CPB, there was reduction in pH from 7.428 ± 0.029 at T1 to 7.335 ± 0.06 ( P < 0.01) and 7.358 ± 0.06 ( P < 0.01) at T2 and T3 respectively. Mean bicarbonates decreased in Ringer Lactate group during CPB from 24.28 ± 1.65 mEq/L at T1 to 20.98 ± 2.97 mEq/L at T2 ( P < 0.01). In Plasmalyte-A group, mean pH, bicarbonate, strong ion difference (SID) were comparable at all time intervals ( P > 0.05). In Ringer Lactate group, maximum surge in mean blood lactate levels was seen from 0.85 ± 0.35 mmol/l at T1 to 4.29 ± 1.78 mmol/L ( P < 0.01) and 4.17 ± 1.28 mmol/L ( P < 0.01) at T2 and T3, respectively. Such surge was not seen in Plasmalyte-A group. The mean SID decreased during the CPB in Ringer Lactate group from 41.102 mEq/L at T1 to 35.66 mEq/L ( P = 0.033) at T2 implying metabolic acidosis. Numbered patients having hypotension and arrhythmias were also higher in Ringer Lactate group again indicating higher acidosis. Conclusion: The different composition of Plasmalyte-A and Ringer Lactate have different metabolic implications for patients undergoing cardiac surgery. Patients who received Plasmalyte-A as cardiopulmonary bypass prime developed less metabolic acidosis. Hence we conclude that Plasmalyte-A is the preferred cardiopulmonary bypass prime in adult patients undergoing valve replacement surgeries.

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