Neuromuscular blocking (NMB) agents are used in the vast majority of surgical interventions. Although pharmacokinetic and pharmacodynamic data are available, there is a large interindividual variability in the time needed for recovery after neuromuscular blocking agents. In a previous study (NTC03550664) a mathematical model in order to estimate for each patient the time needed for full recovery based on the first measurable elements of train-of-four (TOF) recovery was established. After the first 14 TOF measurements, the estimated time to reach a recovery of 90%, expressed as % of recovery per 10 min, is calculated.

In this study, this algorithm will be evaluated on a new cohort of patients in order to measure its accuracy and precision. Patients scheduled for surgery with a single dose of 0.6 mg/kg of rocuronium will be included in this prospective observational study. Neuromuscular transmission will be measured at the adductor pollicis using the TOFScan (IdMed, Marseille, France), a CE approved, commercially available monitor for neuromuscular transmission. TOF ratios will be measured every 30 s and recorded on a PC connected to the TOFScan. According to our algorithm, patients will be classified as slow, intermediate or fast recovery; speed of recovery will be measured as % of recovery per 10 min. A McNemar test will be used to assess the correct classification of patients in each group. Accuracy of the estimated speed of recovery will be assessed by comparing to the 95% confidence interval of our model. If real speed of recovery falls within the 95% confidence interval of the model, the model will be classified as accurate. These measurements will be done at 2 time points: - first estimation available and - after TOF ratio has recovered to 40%.

Inclusion Criteria:

• Age ≥ 18 years
• Patients scheduled for surgery with a single bolus administration of 0.6 mg/kg of rocuronium

Exclusion Criteria:

• patient refusal to participate
• known or suspected allergy to rocuronium
• Body mass index < 20 kg/m2
• Body mass index > 30 kg/m2
• hepatic insufficiency, either clinical or hepatic test abnormalities
• renal insufficiency defined as a clearance < 40 mL/min (calculated by the Modification of diet in renal disease (MDRD) formula

All patients scheduled for surgery with a single bolus administartion of 0.6 mg/kg of rocuronium