The induction phase of neuromuscular block after suxamethonium and pancuronium: analysis of the time constant of single-twitch decay (tau T1).
The T1% (first unconditioned stimulus of train-of-four) decay was analysed in 55 patients paralysed with different doses of suxamethonium and pancuronium during minor elective ear and nose surgery. In patients given pancuronium, T1% decay is well described by a mono-exponential function: a semi-log plot of ln(T1%) versus time is in fact a straight line. Predicted values are quite comparable with mean and individual values recorded in patients. From these equations the time-constant of single-twitch decay, or tau T1, may be calculated easily: it is a good dynamic descriptor of the speed of onset of neuromuscular block. In patients paralysed with suxamethonium, the rapidly developing block makes it difficult to acquire a sufficient number of data for computation of regression lines: while T1% seems to decrease exponentially, as in the pancuronium groups, no definite conclusions are possible at present. The authors conclude that tau T1 may be a useful dynamic descriptor of neuromuscular block induced by non-depolarizing muscular blocking drugs. Two new concepts are introduced: (i) the time spent to overcome the 'margin of safety' of neuromuscular transmission, or T MOS; and (ii) the speed index, as a measure of the relative speed of the onset of block.
Romano
E
E
Università degli Studi di Trieste, Ospedale di Cattinara, Italy.
Molassi
M
M
Serra
L
L
D000200:Action Potentials / Q000187:drug effects; D000758:Anesthesia; D000769:Anesthesia, Inhalation; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects*; D010197:Pancuronium / Q000008:administration & dosage / Q000494:pharmacology*; D011897:Random Allocation; D011930:Reaction Time; D013390:Succinylcholine / Q000008:administration & dosage / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects; D013997:Time Factors
D013390:Succinylcholine; D010197:Pancuronium