The synergistic effect of two different nondepolarizing muscle relaxants on intraocular pressure

Abstract

Study objectives: To evaluate the synergistic effect of neuromuscular blockade, produced by administering a priming dose of d-tubocurarine before or after pancuronium bromide, on endotracheal intubating conditions, intraocular pressure (IOP), and hemodynamic changes 1 minute following injection of intubating doses. To compare the results with equipotent doses of the individual muscle relaxants administered as a single bolus dose or in divided doses.

Design: Randomized study.

Setting: University medical center.

Patients: Ninety ASA physical status I and II inpatients (45 males, 45 females) assigned to one of six comparable groups (A-F).

Interventions: One hour after premedication, either normal saline (Groups A and B) or a priming dose of either d-tubocurarine (Groups C and F) or pancuronium (Groups D and E) was given intravenously (IV). Three minutes later, anesthesia was induced with 6 mg/kg of 2.5% thiopentone i.v. Then an intubating dose of pancuronium (Groups A, C, and E) or d-tubocurarine (Groups B, D, and F) was administered. The total dose given was equal to d-tubocurarine 0.4 mg/kg or pancuronium 0.07 mg/kg. Patients were intubated 1 minute after injection of an intubating dose of either relaxant.

Measurements and main results: IOP was measured with a Perkins applanation tonometer and blood pressure (BP) by a sphygmomanometer. Heart rate was derived from the electrocardiogram. Intubating conditions were scored according to given intubation criteria. Measurements were obtained at different times before and after intubation. In those patients given only one muscle relaxant for intubation either divided into priming and intubating doses or preceded by normal saline (Groups A, B, E, and F), there was a significant increase in IOP in response to intubation as compared with baseline (p < 0.05). In contrast, when d-tubocurarine was used as the priming drug for pancuronium blockade (Group C), IOP was significantly reduced in response to intubation, despite a concomitant increase in BP (p < 0.05). No significant change in IOP was observed when pancuronium was used as the priming drug for d-tubocurarine blockade (Group D). Although good to excellent intubating conditions were reported in Groups C and D, poor intubating conditions were reported when the priming muscle relaxant was the same as the relaxant used to intubate.

Conclusions: A smooth, rapid-sequence intubation with a concomitant reduction in IOP as required for open-eye, full-stomach patients can be achieved with a judicious mixture of nondepolarizing muscle relaxants as described for d-tubocurarine and pancuronium in Groups C and D.