How low can you go? Lowest effective dose of neuromuscular blocking agent for tracheal intubation

For most of the last half century, the holy grail of neuromuscular pharmacologists has been to develop a drug or a technique that can replace succinylcholine as the benchmark for rapid onset of neuromuscular block and that has, at the very least, the potential to promptly reverse its residual effects. With the neuromuscular blocking agent rapacuronium, it was established that ultra-fast onset and a nondepolarizing mechanism of action were not mutually incompatible. Unfortunately, rapacuronium was unacceptable because of serious side-effects. Rocuronium 1.2 mg kg, followed by sugammadex in appropriate dosage, can also be made to mimic the onset-offset profile of succinylcholine. Thus, the end of the ‘‘Era of Succinylcholine’’ is being announced at regular intervals, most recently by Lee, who this year opined, ‘‘...it finally appears that suxamethonium can be retired. Suxamethonium has done its job and has seen its day!’’ Perhaps; however, to paraphrase Mark Twain, ‘‘rumours of succinylcholine’s demise appear to be greatly exaggerated.’’ Nevertheless, in this issue of the Journal, Siddik-Sayyid et al. present an alternative to succinylcholine facilitated tracheal intubation, which some clinicians may find attractive and which, at its worst, provides the direction for additional clinical studies. Siddik-Sayyid et al. performed the following induction–intubation sequence. (1) After preoxygenation, the patients received lidocaine 1.5 mg kg as a bolus, immediately followed by rocuronium 0.30 mg kg. (2) During the next 30 sec, the patients received remifentanil 2 lg kg plus propofol 2.0 mg kg. (3) Laryngoscopy was initiated 60 sec after completion of the anesthetic induction (90 sec after the rocuronium). The intubation scores were compared with a group that received succinylcholine 1.5 mg kg immediately following an identical lidocaine-remifentanilpropofol sequence. Excellent intubating conditions were achieved in a similar proportion in both groups (90% vs 96%, respectively). Siddik-Sayyid et al. are not the first to suggest that administering a non-depolarizing neuromuscular blocker before induction of anesthesia shortens the ‘‘intubating interval’’. The method has been called the ‘‘timing principle’’. Nor are they the first to tout the virtues of low-dose rocuronium (short duration of action). The strength of the authors’ paper lies in its rigorous attention to detail. They used a randomized blinded prospective approach to their noteworthy study in comparing their proposed technique with the ‘‘gold standard’’ dose of succinylcholine (1.5 mg kg). In addition, the authors employed a well recognized method to evaluate conditions for intubation. Finally, when rocuronium was given as a single ED95 (effective dose for 95% block) bolus (0.30–0.35 mg kg), 90% of its peak effect at the adductor pollicis was reached in about 1.75 min. Rocuronium’s effect on those muscles that are more relevant to ease of intubation, such as the masseter and laryngeal adductors, likely occurred even sooner. Thus, the authors’ timing sequence (total induction time &100 sec) was probably close to ideal. The rationale for the authors’ technique is based on the rather unique pharmacodynamic properties of rocuronium. At a single ED95 bolus, rocuronium is probably best thought of as a drug with a short rather than an intermediate duration of effect. In fact, in a recent study by Pendeville et al., the authors compared the duration of effect of rocuronium 0.30 mg kg with that of mivacurium A. F. Kopman, MD (&) Department of Anesthesiology, Weill Cornell College of Medicine, 70 East 10th Street, Apt. 17F, New York, NY 10003, USA e-mail: akopman@nyc.rr.com; akopman@gmail.com