Efeitos do sulfato de magnésio na hemodinâmica e funçåo renal de cåes anestesiados com pentobarbital sódico / Effects of magnesium suplhate on the renal hemodynamics and function of dogs anesthezied with pentobarbitone

RESUMO

Background and objectives - The use of magnesium sulphate for the prevention of seizures in pre-eclampsia may induce hypermagnesemia. Clinical and experimental studies are not in agreement about the effects of magnesium on the renal hemodynamics and function. We therefore studied the effects of hypermagnesemia on the renal hemodynamics and function of dogs anesthetized with pentobarbitone. Methods - Sisteen mongrel dogs were anesthetized with pentobarbitone 30mg.Kg-1 and submited to extracellular volume expansion with Ringer's solution (0.4 ml.Kg-1.min-1) and mechanical ventilation with room air. The dogs were allocated into two groups of 8 animals, for the study of renal hemodynamics and following the administration of 5mg.Kg-1 of pentobarbitone (Group 1 - control) or pentobarbitone associated with magnesium selphate in the dose of 140mg.Kg-1, administered in 15 minutes, followed by 80mg.Kg-1.h-1 (Group 2). The parameters studied were PAH clearance, creatinine clearance, osmolar clearance, free water clearance, renal blood flow, renal vascular resistance, filtration fraction, urinary volume, plasmatic and urinary osmolarity, urinary and fractionary excretion of sodium and potassium, measured at five moments 15 (M1), 30 (M2), 60 (M3) and 75 (M4) minutes after the first supplementary dose of pentobarbitone and 15 minutes (M5) after second supplementary dose in Group 1. In Group 2, the moments M3, M4, M5 were 15. 30, and 60 minutes after the priming dose of magnesium sulphate and during the maintenance dose. Results - In Group 1 no significant changes were observed in renal hemodynamic parameters and creatinine clearance. The extracellular volume expansion increased urinary volume and decreased urinary osmolarity as a consequence of sodium, potassium and free water clearance. The fractionary excretion of sodium was maintained. The plasmatic osmolarity increased. In Group 2, renal hemodynamic parameters and creatinine clearance were also maintained. There was an increased in renal sodium clearance, as detected by the increased in the fractionary excretion of sodium. Conslusions - Magnesium sulphate did not produce significant changes in renal hemodynamics and facilitated the renal excretion of sodium in dogs anesthetized with pentobarbitone