Proper timing of blood cardioplegia in infant lambs: superiority of a multiple-dose regimen

Propofol protects the immature rabbit heart against ischemia and reperfusion injury: impact on functional recovery and histopathological changes

The general anesthetic propofol protects the adult heart against ischemia and reperfusion injury; however, its efficacy has not been investigated in the immature heart. This work, for the first time, investigates the cardioprotective efficacy of propofol at clinically relevant concentrations in the immature heart. Langendorff perfused rabbit hearts (7–12 days old) were exposed to 30 minutes' global normothermic ischemia followed by 40 minutes' reperfusion. Left ventricular developed pressure (LVDP) and coronary flow were monitored throughout. Lactate release into coronary effluent was measured during reperfusion. Microscopic examinations of the myocardium were monitored at the end of reperfusion. Hearts were perfused with different propofol concentrations (1, 2, 4, and 10 μg/mL) or with cyclosporine A, prior to ischemic arrest and for 20 minutes during reperfusion. Propofol at 4 and 10 μg/mL caused a significant depression in LVDP prior to ischemia. Propofol at 2 μg/mL conferred significant and maximal protection with no protection at 10 μg/mL. This protection was associated with improved recovery in coronary flow, reduced lactate release, and preservation of cardiomyocyte ultrastructure. The efficacy of propofol at 2 μg/mL was similar to the effect of cyclosporine A. In conclusion, propofol at a clinically relevant concentration is cardioprotective in the immature heart.

Mechanisms of a reduced cardiac output and the effects of milrinone and levosimendan in a model of infant cardiopulmonary bypass

OBJECTIVES

A low cardiac output state is an important cause of morbidity after pediatric cardiopulmonary bypass. The objectives of our study were to define the early precipitants of the reduced cardiac output and to investigate the effects on these of milrinone and levosimendan in a model of pediatric cardiopulmonary bypass.

DESIGN

Experimental study.

SETTING

: Research laboratory at a university-affiliated, tertiary pediatric center.

SUBJECTS

Eighteen piglets.

INTERVENTIONS

Piglets, instrumented with systemic, pulmonary arterial, and coronary sinus catheters, pulmonary and circumflex arterial flow probes, and a left ventricular conductance-micromanometer-tipped catheter, underwent cardiopulmonary bypass with aortic cross-clamp and cardioplegic arrest. At 120 mins, they were assigned to control, milrinone, or levosimendan groups and studied for a further 120 mins.

MEASUREMENTS AND MAIN RESULTS

In controls, between 120 and 240 mins, cardiac output decreased by 15%. Systemic vascular resistance was unchanged, but pulmonary vascular resistance increased by 19%. Systemic arterial elastance increased by 17%, indicating increased afterload. End-systolic elastance was unchanged, and coronary sinus oxygen tension decreased by 4.0 +/- 1.7 mm Hg. In animals receiving milrinone cardiac output was preserved, and in animals receiving levosimendan cardiac output increased by 14%. Both drugs prevented an increase in arterial elastance and pulmonary vascular resistance after cardiopulmonary bypass. Systemic vascular resistance decreased by 31% after levosimendan, and end-systolic elastance increased by 48%, indicating improved contractility. Both agents prevented a decrease in coronary sinus oxygen tension.

CONCLUSIONS

Increased afterload, which is not matched by an equivalent elevation in contractility, contributes to the reduced cardiac output early after pediatric cardiopulmonary bypass in this model. This increase is prevented by milrinone and levosimendan. Both agents exert additional beneficial effects on pulmonary vascular resistance and myocardial oxygen balance, although levosimendan has greater inotropic properties.