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
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