Target controlled priming for rapid onset of intubation dose: A new approach

To determine the pattern of onset of the intubating dose when given at a monitored target priming block in either phase of the priming drug effect.

Sixty consenting ASA I and II patients were premedicated by intramuscular buprenorphine (5 μg·kg^-1) 1h before surgery. Neuromuscular junction monitoring was done by stimulating the ulnar nerve at the wrist using Myotest and recording the adductor pollicis response on Myograph-2000. After stabilization of the twitch tension at the titrated supramaximal stimulus (1 Hz), double-burst stimuli (DBS) were given to monitor the priming effect of vecuronium bromide (Vb) (0.015 mg·kg^-1). The DBS ratio (DBSr=D ₂/D ₁) was calculated for the DBS response, repeated at 20s. Depending on the target priming block level (DBSr 0.8, 0.6, or 0.5) and the phase of the priming block to give an intubating dose of Vb (0.8 mg·kg^-1) injection, all patients were randomly assigned to six study groups: group 1 (DBSr 0.8), group 3 (DBSr 0.6), and group 5 (DBSr 0.5) during the priming block progression phase (before peakD ₁ suppression), and group 2 (DBSr 0.8), group 4 (DBSr 0.6), and group 6 (DBSr 0.5) during the priming block regression phase (after peakD ₁ suppression). Anesthesia was induced by thiopental (5-7 mg·kg^-1) just before the intubating dose. The effect of the intubating dose on twitch stimuli (1 Hz) was monitored.

We observed that in spite of significantly variable priming intervals for identical DBSr in two different phases, the onset time of the intubating dose to 0 response was identical in similar DBSr group patients; i.e., at 0.8 DBSr, 65.0±5.2s (group 1)vs 66.0±8.0s (group 2); at DBSr 0.6, 55.2±3.7s (group 3)vs 55.2±4.9s (group 4); and at DBSr 0.5, 43.5±4.8s (group 5)vs 43.5±4.2s (group 6). At 0 twitch response, the intubating conditions were comparable in patients of the six groups.

In conclusion, target controlled priming (DBSr) for administration of the intubating dose appears to be a useful double-vision sign to predict the onset of the effect of the intubating dose precisely.