Rocuronium--onset times and intubating conditions.

Many factors influence the minimum time required to achieve an easy and successful tracheal intubation after a non-depolarizing relaxant. The ideal study design has never been achieved in practice: an overall picture of the efficacy of rocuronium depends on careful interpretation of studies with different methodologies, which have usually compared the new drug with vecuronium or suxamethonium, currently the best alternatives. Despite lack of supporting animal data, the rapidity of onset of rocuronium in man appears to be due to an early presynaptic effect. Observations which are difficult to explain are that increasing the dose above about 2 x ED90 does not shorten the time to onset and 'priming' also has no beneficial effect. Although some studies have produced evidence that rocuronium can produce smooth easy intubation conditions in 60 s, 90 s would appear to be closer to the time when excellent conditions can be guaranteed. Whether this is an acceptable alternative to the 45 s or so needed after suxamethonium is a matter of clinical judgement which only testing in practice will answer.