Factors that affect the onset of action of non-depolarizing neuromuscular blocking agents
Based on simple clinical and biochemical parameters of nutritional status, seventy adult patients scheduled for elective surgery under general anaesthesia were categorized as having normal nutrition, mild, moderate or severe malnutrition or obesity. Under anaesthesia, evoked responses on train-of-four nerve stimulation were recorded every 15 seconds on a mechanomyograph. Vecuronium 0.1 mg.kg-1 was used to achieve neuromuscular blockade. Compared with patients having normal nutrition, the time to onset of action was significantly prolonged in the moderate and severely malnourished groups; the time to no response on train-of-four stimulation was delayed only in severely malnourished groups (P < 0.001). The duration of action of the initial dose was shorter in the moderate and severely malnourished groups. The obese group had an earlier onset of action and a longer duration of action compared with patients of normal nutrition (P < 0.001). No significant difference in recovery time to a train-of-four ratio of 0.70 was observed between the malnourished and patients with normal nutrition. Malnutrition has a marked effect on vecuronium-induced neuromuscular blockade.