Objective: To determine the risk factors for residual neuromuscular blockade (rNMB).
Material and Method: This prospective observational study enrolled 209 patients with general anesthesia receiving neuromuscular blocking agents (NMBAs). Upon arrival at the post anesthesia care unit (PACU), the train-of-four (TOF) ratios were recorded using a TOF watch®. In addition, the respiratory peak flow rates were assessed, and the demographic and perioperative data were recorded. We defined rNMB as a TOF ratio less than 0.9.
Results: The incidence of rNMB was 53.1%. A univariate analysis identified the following as predictors of rNMB: increasing age, American Society of Anesthesiologist physical status classification II, low risk surgical procedures, high MAC of inhalation agent, an interval of <30 minutes between the last dose of NMBAs, and hypothermia on arrival at the PACU. Using a multivariate analysis: increasing age every 10 years (OR 1.31, 95% CI 1.04 to 1.65), inhalation agent more than 1 MAC (OR 1.95, 95% CI 1.02 to 3.71), an interval before relaxant reversal of <30 minutes (OR 2.27; 95% CI 1.17 to 4.40), and hypothermia at PACU (OR 3.31, 95% CI 1.35 to 8.09) remained significant risk factors.
Conclusion: Residual neuromuscular blockade after general anesthesia is common. Increasing age, MAC of inhalation agent >1, hypothermia at PACU and an interval between the last application of the NMBAs and reversal less than 30 minutes seem to be particular risk factors.

Keywords: Residual neuromuscular blockade, Train of four, Risk factors, Incidence, General anesthesia