Cold continuous antegrade blood cardioplegia: high versus low hematocrit

Objective: Cold continuous antegrade blood cardioplegia (CCABCP) is used with different hematocrit values. We investigated the consequences of CCABCP with low hematocrit (LH: 20–25%) versus high hematocrit (HH: 40–45%). Methods: Anesthetized open chest pigs (25 kg) were placed on cardiopulmonary bypass (CPB). The hearts were arrested for 30 min by 6°C CCABCP with either LH or HH (n=8, each): After an initial 3 min application of high potassium (20 mEq) BCP the hearts were arrested for subsequent 27 min by normokalemic 6°C cold blood delivered continuously antegradely. Thereafter the hearts underwent perfusion with warm systemic blood for an additional 30 min on CPB. Biochemical cardiac data (MVO2 (ml min−1 100 g−1), release of creatine kinase (CK; units min−1 100 g−1)) and lactate (mg min−1 100 g−1)) and the coronary vascular resistance index (CVRI (mmHg ml−1 min g)) were measured during CPB. Total tissue water content (%) and left and right ventricular stroke work indices (LV-and RV-SWI (g m kg−1)) were assessed 30 min after discontinuation of CPB and compared to pre-CPB controls. Results: The hearts of the LH group had no biochemical or functional disturbance. The HH group showed marked CK leakage (0.6±0.2* vs. 0.1±0.1, *P≪0.05 for comparison of LH vs. HH with Student's t-test for unpaired data), impaired initial oxygen consumption (4±1* vs. 7±1) after cardiac arrest, an increased CVRI (82±12* vs. 50±8), the formation of myocardial edema (81.0±1.3* vs. 77.5±1.2), and poor functional recovery (LVSWI 0.2±0.1* vs. 1.0±0.1; RVSWI 0.1±0.1* vs. 0.5±0.1). The absence of lactate production in both groups was in accord with the non-ischemic protocol. Conclusions: CCABCP with a low hematocrit of 20–25% is cardioprotective. In contrast, CCABCP with a high hematocrit of 40–45% jeopardizes the heart despite avoiding ischemic periods, and should be avoided.