A Review of Current Literature of Interest to the Office-Based Anesthesiologist.

Abstract

When muscle relaxants are used to facilitate intubation, a significant amount of residual neuromuscular blockade remains when reversal drugs are not administered; however, routine reversal is not a universal practice. While most anesthesiologists routinely reverse neuromuscular blockade if muscular weakness is suspected at the time of extubation, others caution against the routine use of anticholinesterase reversal agents, which have been associated with impaired upper airway and breathing function with increased risk of adverse postoperative respiratory events. Neostigmine has neuromuscular blocking properties when given in the absence of neuromuscular blockade and can induce paradoxical reduction in the train-of-four ratio (TOF ratio). This study tested the hypothesis that TOF ratios in patients receiving neostigmine at the time of postanesthesia care unit admission would not be less than TOF ratios in patients randomly assigned to receive a saline placebo. The authors also tested the hypothesis that the incidence of postextubation adverse respiratory symptoms and muscle weakness would not be increased in the neostigmine group. One hundred twenty patients undergoing general anesthesia received a small dose of rocuronium to facilitate intubation. Ninety patients achieved a TOF ratio of 0.9 to 1.0 and received either neostigmine or saline. Patients were subsequently monitored for muscle strength and postextubation respiratory adverse events. No significant difference in these parameters was noted between the 2 groups, leading the authors to conclude that administration of neostigmine at neuromuscular recovery was not associated with clinical evidence of anticholinesterase-induced muscle weakness. Comment: This study is accompanied by an editorial (Brull SJ, Naguib M. How to catch unicorns (and other fairytales). Anesthesiology. 2018;128:1–3) that discusses long-standing beliefs and misconceptions about the relative risk and benefits of administering muscle relaxants. The editors praise the study by Murphy et al for debunking 4 common myths. First, the study shows no evidence that neostigmine, at a dose of 40 lg/ kg, induces signs or symptoms of neuromuscular weakness, contradicting previous reports. Second, it challenges the belief that clinical assessment alone (eg, 5second head lift) is sufficient to assess adequate muscle recovery and underscores the need for quantitative neuromuscular assessment (TOF ratio). The study also challenged the widely held belief that neuromuscular recovery can be subjectively assessed by watching or feeling the response to TOF stimulation. Finally, the ‘‘time elapsed’’ principle of reversal is debunked. This principle stated that reversal was not necessary if the duration since the last dose of neuromuscular blocking agent was greater than 1 or 2 elimination half-lives, noting that 21% of patients failed to recover to a TOF ratio of 0.9 in 163 minutes after a single dose of 0.3 mg/ kg rocuronium. The editorial provides an extensive discussion of the foundation of these myths and adequately shows how the strength of this well-designed, randomized controlled study adequately challenges reports based on weaker observational reports and studies. (M. A. Saxen)