Hypotensive anaesthesia for spine surgery--nitroglycerin vs halothane

Thirty patients (ASA I or II) requiring spine surgery under general anesthesia were studied. To induce hypotension, halothane 0.5 to 2.5% (n = 15) or nitroglycerin infusion (1-2 micrograms/kg/min) (n = 15) was used. The parameters studied were blood pressure, blood loss, operating time and recovery score. The systolic blood pressure was maintained between 80-100 mmHg during surgery in both the groups. The blood loss with nitroglycerin was significantly less (202 +/- 114 ml) than halothane group (602 +/- 312 ml). All the patients were alert at the end of surgery in the nitroglycerin group (recovery score 9.8 +/- 0.76) as against the halothane group (7.98 +/- 0.9 p < 0.01). Tachycardia or tachyphylaxis was not observed with nitroglycerin. This study suggests that continuous intravenous infusion of nitroglycerin is effective and safe in reducing blood loss and operating time during spine surgery.