Systemic vascular effects of isoflurane versus propofol anesthesia in dogs

Vascular effects of general anesthesia are usually described by changes in vascular resistance, which assumes a linear pressure-flow relationship passing through the zero-flow zero-pressure point, and neglects the pulsatile properties of the circulation. We compared the systemic vascular effects of isoflurane versus propofol anesthesia by measurements of aortic pressure-flow relationships, systemic vascular impedance (SVZ), and pressure transfer function (PTF). Eight mechanically ventilated dogs received isoflurane 1.4% end-tidal and propofol 18 mg.kg-1.h-1 in a random sequence. During both periods, pressure-flow data and SVZ data were obtained at baseline and after stepwise reduction of the cardiac output by inflation of a balloon in the inferior vena cava. Instantaneous pressure and flow were measured at the aortic root using a micromanometer-tipped catheter and an ultrasonic flow probe. Compared to baseline, low flow decreased the aortic pressure and increased the resistance, characteristic impedance, and oscillatory/total work ratio. Compared with isoflurane, propofol resulted in higher aortic pressure, lower characteristic impedance, and lower oscillatory/total work ratio. Low-frequency PTF moduli decreased at low flow and increased with propofol. We conclude that, compared with isoflurane, propofol better preserves aortic pressure and increases aortic compliance, and thus improves the energy transmission from the left ventricle to the arterial system.