CARDIOVASCULAR-RESPONSES TO EXPERIMENTAL INFRARENAL AORTIC CROSS-CLAMPING - MODULATING EFFECTS OF ISOFLURANE, SODIUM-NITROPRUSSIDE AND MILRINONE

Background: Pharmacological control of blood pressure is usually indic ated during aortic cross-clamping (AXC). The aim of this study was to analyze the modulation by isoflurane (ISO), sodium nitroprusside (SNP) and milrinone (MIL) of the systemic circulatory responses to a standa rdized infrarenal AXC. Methods: Chloralose-anaesthetized pigs were exp osed to AXC at control (no vasoactive drugs) and during the administra tion of each of the drugs. Results: During control, AXC increased mean arterial pressure (MAP, 17+/-4%) and systemic vascular resistance (SV R, 27+/-7%), but induced no significant changes in cardiac output (GO) , heart rate (HR), pulmonary arterial pressures, pulmonary vascular re sistance or central venous pressure. Low-dose ISO (0.7%) and investiga ted doses of SNP and MIL did not significantly alter this response. Hi gh-dose ISO (1.4% attenuated the AXC-induced increase in SVR, but not in MAP. All drugs decreased non-clamp MAP levels. Therefore, with low- dose ISO and with SNP or MIL, peak MAP during AXC was not significantl y different from control non-clamp levels (i.e. prior to pharmacologic al or surgical interventions), High-dose ISO was associated with a MAP during AXC that was below control non-clamp levels. Conclusions: The objective that during AXC MAP should not exceed control non-clamp leve ls was achieveable by ISO, SNP or MIL. The modulating actions of the d rugs on MAP during AXC were exerted mainly through reductions in non-c lamp levels. This systemic hypotension was associated with decreased C O and SVR during ISO, and with decreased SVR and increased HR during S NP and MIL. Attenuation of the AXC-induced increase in SVR was produce d only by 1.4% ISO.