Efeitos do sulfato de magnésio na hemodinâmica cardiovascular de cåes anestesiados com pentobarbital sódico / Effects of magnesium sulphate on the cardiovascular hemodynamics of dogs anesthetized pentobarbitone

ABSTRACT

Background and Objectives - A controversy exists in the literature regarding the effects of the acute administration of magnesium on the cardiovascular system of animals and humans. The purpose of this study was to evaluate the effects of hypermagnesemia on the cardiovascular hemodynamics of dogs. Methods - Sixteen mongrel dogs were anesthtized with pentobarbitone 30mg.kg-1 and submitted to volume expansion with Ringer's solution (0.4ml.kg-1.min-1) and mechanical ventilation with room air. In this model, the hemodynamic repercussions of the following drugs and doses were studied: pentobarbitone 5mg,kg-1 - Group 1, control - and the association of pentobarbitone and magnesium sulphate (MS), at the dose of 140 mg.kg-1, injected in 15 minutes, followed by an infusion of 80 mg.kg-1.h-1 - Group 2. The parameters studied were: heart rate, blood pressure, inferior vena cava pressure, cardiac index, systolic index and peripheral resistance index, evaluated at 5 different moments: 15(M1), 30(M2), 60(M3) and 75(M4) minutes after the first supplementary dose of pentobarbitone and 15 minutes (M5) after the second supplementary dose. In group 2, the moments M3, M4, M5 corresponded to 15, 30 and 60 minutes after the priming dose of magnesium sulphate. Results - Group 1 animals exhibited tachycardia since the beginning of the experiment. There was a decrease in the cardiac index, in the systolic index and an increase in the inferior vena cava pressure. group 2 animals also exhibited tachycardia, but heart rate decreased after MS infusion. The blood pressure and the peripheralresitance index decreased. The systolic index increased and the cardiac index decresead only at he end of the experiment. Conclusions - The antiadrenergic effects of Ms could have been responsible for the decrease in heart rate. The vasodilating effects of the magnesium induced the decrease in the peripheral resistance index. The vasodilating effects of the magnesium induced the decrease in the peripheral resistance index. The systolic index increased, showing that myocardial depression did not occur.