There is a growing body of literature documenting the use of deep neuromuscular block (NMB) during surgery. Traditional definitions of depth of NMB rely on train-of-four assessment, which can be less reliable in retrospective studies. The goal of our study was to investigate the real-world practice pattern of dosing of neuromuscular blocking agents (NMBA), utilizing the amount of NMBA used during the course of a case, adjusted for patient weight and case duration, as a surrogate measure of depth of NMB. We also aimed to identify case factors associated with larger NMBA doses. In this retrospective observational analysis of our anesthesia information management system, we analyzed all general endotracheal anesthesia cases from 2012 to 2015 in which an intermediate-acting NMBA was used. Cases using a long-acting NMBA or only succinylcholine were excluded. The expected duration of the case was calculated based on the cumulative dose of NMB used, normalized to the patient's ideal body weight and the ED95 of the drug. If the expected duration of the case was greater than the actual case duration documented in the case record, it was classified as higher dosing (HD). If the expected duration was equal to or less than the actual duration, it was considered predicted dosing (PD). Categorical comparisons between HD and PD groups were made for various patient, procedural, and provider factors. 72,684 cases were included in the final analysis, of which 46,358, or 64% of cases, used HD. Cases with patients who were morbidly obese, younger than 65 years, and who were lower ASA Physical Status classification (I or II) used more HD as opposed to PD. Cases that were non-open, used total intravenous anesthesia, emergent cases, or used non-rapid sequence anesthesia induction had higher rates of HD than their matched counterparts. All results were statistically significant. HD was more common in cases that documented train-of-four and used the reversal agent neostigmine. Approximately two-thirds of general endotracheal anesthesia cases using an intermediate-acting NMBA used HD. Cases with higher rates of HD may be those that are traditionally technically complex or emergent, would benefit from greater paralysis, or do not use adjunctive medications for muscle relaxation. Age greater than 65 years was shown to have lower rates of HD, likely due to provider awareness of age-related changes in pharmacokinetics and pharmacodynamics. Intraoperative monitoring and NMB antagonism with neostigmine were used more frequently with HD.
Keywords: Anesthesia; Depth; Monitoring; Neuromuscular blockade; Paralysis; Reversal; Surgery.