British Journal of Anaesthesia, Vol 75, Issue 4 436-440, Copyright © 1995 by The Board of Management and Trustees of the British Journal of Anaesthesia
G. Audibert and F. Donati
To determine the influence of circulatory factors on onset of neuromuscular
block, we have measured twitch height in an arm with a tourniquet inflated
during onset and compared this with data from a control arm in 20 patients
under fentanyl-thiopentone-nitrous oxide- isoflurane anaesthesia. Patients
were allocated randomly to receive either vecuronium 0.1 mg kg-1 (n = 10)
or suxamethonium 1 mg kg-1 (n = 10). The EMG response of the first dorsal
interosseous to single twitch stimulation of the ulnar nerve every 10 s was
recorded in both arms. When neuromuscular block was 20% (i.e. twitch height
was 80% of control), the tourniquet was inflated to a pressure of 250 mm
Hg. It was deflated 5 min later. In the vecuronium group, the rate of onset
did not differ in both arms and mean maximum block was 95 (SD 4)% in the
tourniquet arm, which was not different from 99 (2)% in the perfused arm.
In the suxamethonium group, the presence of a tourniquet decreased the rate
of onset by 66%. Maximum block was only 74 (20)% in the tourniquet arm
compared with 97 (5)% in the perfused arm (P < 0.05). The difference in
maximum neuromuscular block between arms was 4 (3)% in the vecuronium group
and 22 (17)% in the suxamethonium group (P < 0.01). We conclude that
during onset, neuromuscular block continued to increase in spite of
interruption of blood flow, and this increase was greater with vecuronium
than with suxamethonium. These results suggest that redistribution of free
molecules of drug from extra-junctional to junctional areas is one of the
factors governing onset of action of neuromuscular blocking drugs.
CLINICAL INVESTIGATIONS
Onset of neuromuscular block after tourniquet inflation: comparison of suxamethonium with vecuronium
Department of Anaesthesia, Hotel-Dieu Hospital and Universite de Montreal, Montreal, Quebec, Canada
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