Hypocalcemia in Piglets Reduces Cardiac and Pulmonary Vascular Disturbance after Hypoxemia and Reoxygenation during Cardiopulmonary Bypass

Abstract

Background: Placing cyanotic newborns on cardiopulmonary bypass (CPB) and performing abrupt reoxygenation affects myocardial Performance. This study tests the hypothesis that hypocalcemia is benefical in this circumstance of reoxygenation. Methods: Twenty-one newborn piglets (anesthetized, openchests) were placed for one hour on CPB. Seven piglets under normoxic and normocalcemic conditions were the controls. The other piglets underwent hypoxemia and subsequent reoxygenation, for periods of 30 minutes each, under normo-calcemic (Normo-Ca⁺⁺, n = 7) or hypocalcemic conditions (Hypo-Ca⁺⁺, n = 7). Thirty minutes after discontinuation of CPB, the hemodynamic function was assessed taking into account stroke work indices (SWI), end systolic elastance (EES), pulmonary vascular resistance index (PVRI), cardiac release of conjugated dienes (CD) and creatine phosphokinase (CK), and myocardial oxygen consumption (MV02). These parameters were expressed as a percentage of the pre-CPB value. The endogenous antioxidant reserve capacity (AORC) of ventricular wall specimens was determined by in-vitro lipid peroxidation forming malondealdehyde (nmol MDA/g protein). Results: After one hour of CPB the cardiac Performance returned to normal range without any functional or metabolic disturbance. The normocalcemic condition resulted in a hardly impaired cardiac performance (42%**SWI; 67%**EES), an augmented PVRI (more than 4-fold**), and highly elevated release of CD and CK (3-fold * * each). The Normo-Ca⁺⁺ group's MV02 (95 ±14%) was unaltered. The hypocalcemic condition improved the myocardial function to near control value (85 % SWI; 91 % EES) and attenuated the augmentation of the PVRI (n.s. vs. Control group) down to 64% of the Normo-Ca⁺⁺ group's level. The release of CD and CK in the Hypo-Ca⁺⁺ group (both n.s. vs. Control group) only minimally increased. The Hypo-Ca⁺⁺ group's MV02 improved (137±8%*). The MDA formation was worse (344±38**) in the Normo-Ca⁺⁺ group, but unaltered in the Hypo-Ca⁺⁺ group (203±9; n.s. vs. Control group (218±20)). * = p<0.05 vs. Controls and Normo-Ca⁺⁺, ** = p<0.05 vs. Controls and Hypo-Ca⁺⁺, using ANOVA. Conclusions: Hypocalcemia during hypoxemia and subsequent reoxygenation highly attenuates myocardial and pulmonary vascular disturbance in newborn piglets. This condition of low blood calcium protects cardiac function and metabolism as well as the pulmonary vascular tone due to diminished myocyte membrane damage, reduced cellular membrane lipid peroxydation, and improved endogenous antioxidant reserve capacity.

Key words

Cardiopulmonary bypass - Hypoxemia - Newborn piglet - Hypocalcemia - Reoxygenation injury