Nitroprusside vs. a nitroprusside-trimethaphan mixture for induced hypotension: hemodynamic effects and cyanide...

Changes in hemodynamic variables and whole blood cyanide and plasma thiocyanate concentrations associated with the infusion of sodium nitroprusside were compared with those during administration of a mixture of sodium nitroprusside (25 mg) and trimethaphan camsylate (250 mg) in a solution of 5% dextrose in water in twenty subjects who required deliberate hypotension for major orthopedic procedures. Subjects were randomly assigned to receive nitroprusside alone (group 1; n = 10) or the nitroprusside-trimethaphan mixture (group 2; n = 10). All subjects received a similar anesthetic technique, consisting of 5 mg/kg thiopental, 1 mg/kg succinylcholine, 1% halothane, 0.2 mg/kg metocurine, and 60% nitrous oxide in oxygen. Mean arterial pressure decreased and was maintained at 55 mm Hg for 258 +/- 4 and 266 +/- 8 minutes in groups 1 and 2. Arterial hypotension was associated with a rise in cardiac output and heart rate in group 1 but not in group 2. Subjects in group 2 required less nitroprusside than did those in group 1 (1.39 +/- 0.3 and 5.82 +/- 0.63 micrograms/kg/min) because of the synergistic or additive action of the combination. After 4 hours of hypotension, the whole blood cyanide level rose from 3.5 +/- 1.1 to 96.6 +/- 14.0 micrograms/dl (1.35 +/- 0.27 to 37.2 +/- 5.4 mumol/L) in group 1 and from 3.7 +/- 1.1 to 22.7 +/- 4.2 micrograms/dl (1.42 +/- 0.4 to 8.7 +/- 1.6 mumol/L) in group 2.(ABSTRACT TRUNCATED AT 250 WORDS)