• K Kirov, C Motamed, and G Dhonneur.
• Department of Anesthesiology and Surgical Intensive Care Unit, Henri Mondor University Hospital, Paris XII School of Medicine, Créteil, France.
• Anesthesiology. 2001 Dec 1; 95 (6): 1323-8.

BackgroundRespiratory muscles are considered to be more resistant to muscle relaxants as compared with peripheral muscles. However, the relative sensitivity of respiratory muscles participating to the pump function has not been compared. We used electromyography to compare pharmacodynamic parameters of the diaphragm and abdominal muscles after mivacurium.MethodsForty adults undergoing elective surgery were randomly allocated in five dosing groups of mivacurium (50, 100, 150, 200, and 250 microg/kg). Patients anesthetized with propofol and fentanyl underwent intubation without relaxants. Anesthesia was maintained with nitrous oxide and propofol. The right phrenic nerve, the left 10th intercostal nerve, and the ulnar nerve were stimulated. Electromyography of the diaphragm and abdominal muscles was recorded from surface electrodes. Mechanomyography was used to measure adductor pollicis evoked contraction. After a 5-min stable recording period, patients received a single intravenous bolus (20 s) dose of mivacurium. By using log dose-probit effect regression analysis, dose-response curves were constructed. Effective doses and 95% confidence intervals were derived for the diaphragm and abdominal muscles and were compared.ResultsThe dose-response regression line of abdominal muscles differed from that of the diaphragm. Calculated ED50 and ED90 were higher for the diaphragm than for the abdominal muscles (104 [82-127] and 196 [177-213] microg/kg, and 67 [51-82] and 161 [143-181] microg/kg, respectively). The onset of block was faster and recovery of control responses were shorter at the diaphragm than at the abdominal muscles.ConclusionDiaphragm and abdominal muscles have differential sensitivity to mivacurium. The diaphragm is more resistant to mivacurium than abdominal muscles are.

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