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

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)