Résumé : BACKGROUNDThere is a controversy in the literature whether deep compared with moderate neuromuscular block (NMB) improves surgical conditions for laparoscopic surgery.OBJECTIVESThe primary outcome measure was to examine whether switching from moderate to deep NMB improves surgical conditions for laparoscopic surgery in the obese; secondary outcome measures were changes in intra-abdominal pressure, time required to perform the gastrojejunal anastomosis and peri-operative surgical complications.DESIGNA single-centre, randomised controlled study. Each patient was taken as their own control and examined twice: at the first evaluation (E1), all patients had a moderate NMB, thereafter patients were randomised to deep or moderate block and a second evaluation (E2) was performed within 10 min. Patients with excellent rating at E1 were excluded from E2, as their surgical condition could not be further improved.SETTINGUniversity Hospital France.PATIENTSPatients undergoing laparoscopic gastric bypass surgery under general anaesthesia were included. Main exclusion criteria were hypersensitivity to the drugs used and absence of written informed consent.INTERVENTIONSAccording to the group assignment, patients received bolus doses of rocuronium or 0.9% saline.MAIN OUTCOME MEASURESSurgical conditions were assessed with a 4-point rating scale. Intra-operative adverse events were assessed with the Kaafarani-classification and postoperative complications with the Clavien-Dindo classification.RESULTSEighty-nine patients were initially included and data from 85 could be assessed at E1; surgical rating was excellent in 20, good in 35, acceptable in 18, poor in 12. After excluding those with an excellent rating, the remaining 65 patients were randomly assigned to deep or moderate block. At E2, an improvement of surgical conditions was observed in 29 out of 34 patients with deep block and in four out of 31 with moderate block; P < 0.0001. Poor surgical conditions were more frequently associated with surgical complications (61.5 versus 15.3%; P < 0.001).CONCLUSIONSwitching from moderate to deep block improves surgical conditions. Poor surgical conditions were associated with a higher incidence of surgical complications.TRIAL REGISTRATIONClinicalTrials.gov identifier: NCT02118844.