Magnesium sulphate enhances residual neuromuscular block induced by vecuronium

Magnesium sulphate (MgSO4) is currently used for haemodynamic controlduring anaesthesia and the early postoperative period. We have investigatedthe effect of this treatment on residual neuromuscular block afteradministration of vecuronium. Twenty adult patients were allocated randomlyto one of two groups to receive MgSO4 60 mg kg-1 either at recovery fromvecuronium block to a train-of-four (TOF) ratio of 0.7, or 1 h afterrecovery to a TOF ratio of 0.7. Neuromuscular transmission was monitoredusing electromyography and TOF stimulation. MgSO4 caused rapid and profoundrecurarization in all 20 patients. MgSO4 decreased the amount ofacetylcholine released at the motor nerve terminal and thus may lead torecurarization in patients previously exposed to neuromuscular blockingagents.