DILTIAZEM REDUCES THE DOSE REQUIREMENT FOR NITROPRUSSIDE-INDUCED HYPOTENSION

The efficacy of diltiazem, a calcium channel blocker, for reducing the dose requirement for nitroprusside-induced hypotension was studied in 20 healthy patients during spine fusion for scoliosis. Anesthesia inc luded methohexital (3 mg/kg followed by 3 mg.kg-1.h-1 intravenously), nitrous oxide, and alfentanil (40 mug/kg, followed by 0.7 mug.kg-1.min -1 intravenously). Patients were assigned randomly to two groups, rece iving either nitroprusside alone or nitroprusside and diltiazem (bolus of 80 mug/kg with two consecutive infusions of 4.5 mug.kg-1.min-1 dur ing the first 30 min and then 1.3 mug.kg-1.min-1). Nitroprusside was u sed to maintain mean arterial pressure at 55-60 mm Hg in both groups. Hypotension was obtained in similar times, 4 min in the group receivin g nitroprusside alone (range, 1-8 min) and 2 min in the group receivin g nitroprusside and diltiazem (range, 1-8 min). Nitroprusside administ ration lasted 186 +/- 17 min (mean +/- SEM) in the group receiving nit roprusside alone and 214 +/- 26 min (mean +/- SEM) in the other group (NS). After hypotension, arterial blood pressure returned to its initi al value in a time of 7 min in the group receiving nitroprusside alone (range, 5-9 min) and 9 min in the group receiving nitroprusside and d iltiazem (range, 7-13 min) (NS). Cumulative doses of nitroprusside wer e larger in the group receiving nitroprusside alone (0.47 +/- 0.07 mg/ kg; mean +/- SEM) than in the other group (0.24 +/- 0.05 mg/kg; mean /- SEM) (P < 0.01). Significant increase in plasma thiocyanate concent ration, cardiac index, and heart rate was observed only in the group r eceiving nitroprusside alone, but no intergroup differences were found . We conclude that low-dose diltiazem decreases nitroprusside requirem ents. This drug combination allows nitroprusside to be used for delibe rate hypotension and probably reduces the risk of cyanide toxicity.