CORRESPONDENCE RAPID TRACHEAL INTUBATION WITH NON-DEPOLARIZING NHUROMUSCULAR BLOCKING DRUGS: THE PRIMING PRINCIPLE

Sir,—Tracheal intubation can be performed within 1 min after the injection of suxamethonium chloride i.v. Suxamethonium, however, has unwanted side-effects and may cause serious com-plications. With reasonable doses of non-depolarizing neuromus-cular blocking drugs, suitable conditions for tracheal intubation cannot be achieved in less than 2-3 min. Furthermore, with the exception of vecuronhim, intubating doses of these drugs may have unwanted side-effects. In exploring various possibilities to farilimr rapid tracheal intubation, it was envisaged that this may be accomplished by the administration of a non-depolarizing neuromuscular blocker in divided doses. The first, a "priming " dote, administered to awake patients should be large enough to cause moderate inhibi-tion of neuromuscular transmission, indirflt'Tig greater than 75% occupancy of the endplate receptors (Paton and Waud, 1967), but small enough not to cause any unpleasant symptoms. The second, larger, "intubating " dose administered after the induction of anaesthesia would then rapidly increase receptor occupancy to 90%, necessary for profound neuromuscular blockade (Paton and Waud, 1967). Subsequently it was established with vecuronium that the "priming " dose should be 15-20 % and the "intubating " dose 50-60 % of the customary dose (lOOugkg-1) used to facilitate tracheal intubation and that the optimal time interval between the two doses should be6-8min. Using a 15-figkg~ ' "priming " and a 50-|tgkg~ ' "intubating " dose of vecuronium, excellent conditions developed for tracheal intubation in 19 patients in 65 ± 13 s (SD). The priming principle for the facilitation of rapid tracheal intubation was also found applicable to other non-depolarizing drugs. The recommended doses of these agents are given in tabl