[Controlled hypotension during posterior vertebral arthrodesis; value of an isoflurane-nitroglycerin combination]

Eighteen young patients (mean age +/- SD 15.9 +/- 3.3) scheduled for operative treatment of idiopathic scoliosis (posterior spine fusion) were studied during surgery. Deliberate hypotension (MAP less than 60 mm Hg) of long duration (greater than 2 hours) was induced using isoflurane and nitroglycerin. Hypotension was effective in less than 15 min in all patients. The mean inspiratory fraction of isoflurane employed was 2.04 +/- 0.19% for the first operative hour, and 1.36 +/- 0.20% for the second operative hour. The difference between these inspiratory fractions is highly significant (p less than 0.001), while the rate of nitroglycerin infusion was unchanged (3 micrograms X kg-1 X min-1). Heart rate increases significantly at H1 and H2 when compared to preinduction values and the product of heart rate X systolic blood pressure decreases significantly with a mean of 30% versus preinduction values. A satisfactory operative field was obtained in all cases. Blood loss was dependent of the duration of surgery, of the total blood volume of the patient, of the length of spine fusion. For each patient, a slope of blood loss was established. The mean slope was 3.74 +/- 0.39 ml X kg-1 X h-1. The determination of the slope at the end of the first operative hour allows us to predict the total blood loss during surgery. Intra operative awakening was obtained 22.8 +/- 3.7 min after isoflurane was discontinued. Isoflurane and nitroglycerin produce a stable and safe hypotension with no major hemodynamic disturbances. Isoflurane has to be discontinued 20 min before the wake-up test.