OPTIMAL FLOW-RATES FIX RETROGRADE WARM CARDIOPLEGIA

Retrograde delivery of warm blood cardioplegia may improve nutrient ca rdioplegic Bow beyond coronary obstructions, but may not adequately pe rfuse the right ventricle and the posterior left ventricle. To determi ne the optimal flow rate for warm retrograde cardioplegia, we assessed 62 patients undergoing elective coronary artery bypass in two studies . In the low flow study, administration of 50 ml/min (n = 9), 75 ml/mi n (n = 11), or 100 ml/min (n = 7) was associated with high lactate pro duction and oxygen extraction during cardioplegic administration. At 5 0 minutes of cardioplegic arrest, the coronary venous effluent pH was low in all groups In the high flow study, 30 patients all received flo w rates of 100, 200, and 300 ml/min in randomized order during the cro ssclamp period. In addition, five patients received cardioplegia at a rate of 500 ml/min for the duration of the crossclamp period. Administ ration of 200 ml/min or higher minimized lactate production and mainta ined coronary venous pH within the physiologic range, but flows of 300 ml/min or higher did not increase oxygen use or reduce lactate or aci d production. Patients in the low flow groups had significantly greate r myocardial lactate release during cardioplegic infusion and after re moval of the crossclamp than the high flow group. Warm retrograde card ioplegia should be delivered at Bow rates of at least 200 ml/min durin g elective coronary artery bypass operations.