The effects of thiopental sodium on fentanyl-induced muscle rigidity in a human model

To describe a safe human model in which to study the treatment of fentanyl-induced muscle rigidity and report on the efficacy of thiopental sodium for this purpose.

Randomized, observer-blinded comparison of regimens.

Inpatient surgery at a university-affiliated teaching hospital.

Thirty patients scheduled for elective surgery in whom the administration of high-dose fentanyl was felt to be appropriate and who experienced severe muscle rigidity in the chest, abdomen, and upper extremities after the fentanyl was administered.

One arm was isolated from circulation with a blood pressure (BP) cuff inflated to 100 mmHg above systolic blood pressure (SBP), after which fentanyl 25 to 50 micrograms/kg was administered intravenously (IV) at a rate of 1 mg/min in the contralateral arm. If severe muscle rigidity became apparent in three muscle groups (the chest, abdomen, and arms), patients were either (1) observed for 3.5 minutes without further intervention, (2) given thiopental sodium 1.5 mg/kg IV, followed 120 seconds later by succinylcholine 1 mg/kg IV, or (3) given succinylcholine 1 mg/kg IV, followed 120 seconds later by thiopental sodium 1.5 mg/kg IV.

A single observer, blinded to the technique, evaluated and recorded the degree of muscle rigidity present in the chest wall, abdomen, and upper extremities (one isolated from the circulation by a tourniquet) 90 seconds and 3.5 minutes after the onset of muscle rigidity in the control group and 90 seconds after the administration of either thiopental sodium or succinylcholine in the two experimental groups. The observer was the same individual in all instances. The muscle rigidity associated with the administration of high-dose fentanyl was clinically attenuated by the administration of thiopental sodium, especially in the extremities. Succinylcholine was more effective than thiopental sodium in producing muscle flaccidity in all muscle groups not isolated by a tourniquet. In no case did the muscle rigidity compromise our ability to oxygenate the patient adequately.

Thiopental sodium does blunt the degree of muscle rigidity induced by high-dose fentanyl, though not as effectively as does succinylcholine. One can safely isolate an extremity prior to the administration of high-dose fentanyl and a muscle relaxant, intubate the trachea, and ventilate a patient, while retaining the ability to study the effect of centrally acting drugs on fentanyl-induced rigidity in the isolated extremity.