Revisiting the Classification of Neuromuscular Blockade, Aligning Clinical Practice and Research

To the Editor Biro et al1 proposed changing the neuromuscular blockade (NMB) classification. We agree the original deep NMB definition (train-of-four count [TOF] = 0; post-tetanic count [PTC] ≥ 1) is too broad.2 However, a separate classification profound for PTC 1–3 and the “downgrading” of deep NMB to TOF = 0 and PTC ≥4 surprised us. Studies investigating deep NMB have explored the benefits of the deepest, but still quantifiable, block that can be achieved. The Table illustrates that most of these studies define deep NMB as PTC 1–2 and consider the terms “deep” and “profound” as synonymous. Recovery of the neuromuscular function of the diaphragm precedes recovery at the adductor pollicis muscle after NMB. Dhonneur et al3 illustrated this with electromyography (EMG) of the diaphragm: at PTC = 1, diaphragmatic activity is at 10% of control; at PTC ≤ 5, activity has already doubled to 21% of control. PTC = 0 is often undesirable as the exact level of NMB is unknown. There may be an excess of a neuromuscular blocking agent (NMBA) affecting reversal and recovery. We acknowledge that with the varied response to NMBAs, PTC 1–2 is a small range to maintain in clinical practice. However, when deep NMB is indicated during surgery, it should be maintained to reach deep relaxation of the relevant muscle groups. At PTC 1–2, this is the case in the majority of patients without an increased risk of residual effects.Table.: Levels of Neuromuscular BlockWe strongly agree with Naguib et al4 in the accompanying editorial to keep it simple; a straightforward classification should promote the use in clinical practice. A large survey among anesthesiologists revealed considerable inappropriate overconfidence regarding monitoring. This might cause residual NMB and related complications. There is unambiguous evidence that subjective or qualitative evaluation of TOF fade is not as reliable as quantitative assessments. We cannot safely antagonize from deep NMB without monitoring or rely on a time interval after which monitoring is not necessary.4 Postoperative residual NMB (TOF ratio [TOFR] <0.9) can effectively be prevented with routine quantitative monitoring. Finally, we advocate a previously proposed and clinically relevant new stage of full recovery of NMB at TOFR = 1.0. There is limited clinical data suggesting TOFR ≥0.9 may still be linked to nonoptimal strength recovery. However, acceleromyography is commonly used and possesses well-known overestimation problems. Moreover, TOFR represents the ratio of T1:T4 and does not imply recovery of the twitch height to the original level. With the use of sugammadex, recovery of T1 to original height occurs slower than recovery of the TOFR in contrast with spontaneous recovery or neostigmine reversal. This provides a false sense of security. Newer monitors can establish a pre-NMB reference value which solves this issue. Routine quantitative neuromuscular monitoring combined with full recovery at a TOFR = 1.0 could mitigate NMB-related complications in the postanesthesia care unit (PACU). Kim I. Albers, MDDepartments of Anaesthesiology and SurgeryRadboud University Medical CentreNijmegen, the Netherlands[email protected] Oscar Diaz-Cambronero, MD, PhDDepartment of AnaesthesiologyHospital Universitari i Politecnic la FeValencia, SpainPerioperative Medicine Research GroupInstituto de Investigación Sanitaria la FeValencia, Spain Christiaan Keijzer, MD, PhDDepartment of AnaesthesiologyRadboud University Medical CentreNijmegen, the Netherlands Marc M. J. Snoeck, MD, PhDDepartment of AnaesthesiologyCanisius Wilhelmina HospitalNijmegen, the Netherlands Michiel C. Warlé, MD, PhDDepartment of SurgeryRadboud University Medical CentreNijmegen, the Netherlands Thomas Fuchs-Buder, MD, PhDDépartement d’Anesthésie et de RéanimationCentre Hospitalier Universitaire Nancy/BraboisNancy, France