Systemic haemodynamic and metabolic effects of deliberate hypotension with isoflurane anaesthesia or sodium nitroprusside during total hip arthroplasty.

Isoflurane (ISO) was examined as an alternative hypotensive agent to nitroprusside (SNP) in 16 patients (mean age: 60 years) anaesthetized for total hip arthroplasty. MAP was decreased to 50 per cent of the awake level by infusion of SNP in Group I (n = 8) and with ISO in Group II (n = 8). Fentanyl (10-16 micrograms X kg-1) was administered to both groups. Haemodynamic measurements were repeated in the lateral position before, during and after hypotension. Polygeline and fresh frozen plasma were infused throughout the study period in volumes sufficient to maintain pulmonary capillary wedge pressure in the 7-9 mmHg range. The MAP decrease was the same in both groups, as were perioperative blood replacement (mean 500 ml), and postoperative haematocrits. Total perioperative fluid replacement was higher (p less than 0.01) in Group I (mean 2500 ml) than in Group II (mean 1300 ml). Venous tone was more affected by SNP than by ISO. ISO decreased the systemic vascular resistance index and oxygen consumption (VO2) without any change in CI or in Qs/Qt, in contrast to SNP which increased CI, VO2 and Qs/Qt.