Midazolam versus propofol for reducing contractility of fatigued canine diaphragm

The effects of midazolam and propofol on the contractility offatigued canine diaphragm were examined. Diaphragmatic fatiguewas induced by intermittent supramaximal bilateral electrophrenicstimulation at a frequency of 20 Hz applied for 30 min.After fatigue had been induced, group I (n=10) receivedno study drug, group II (n=10) was given a propofol infusion(0.1 mg kg^–1 loading dose plus 1.5 mg kg^–1 h^–1maintenance dose) and group III (n=10) was given a midazolaminfusion (0.1 mg kg^–1 loading dose plus 0.1 mg kg^–1 h^–1maintenance dose). Diaphragmatic contractility was assessedby measuring transdiaphragmatic pressure (P_di). After the fatigue-inducingperiod in each group, P_di at low-frequency (20 Hz) stimulationwas lower than the baseline values (P<0.05), whereas no changein P_di at high-frequency (100 Hz) stimulation was observed.In group II, P_di at 20 Hz stimulation was lower than fatiguedvalues (P<0.05); P_di at 100 Hz stimulation did not change.In group III, P_di at both stimulation frequencies was lowerthan fatigued values (P<0.05). Compared with group I, P_diat 20 Hz stimulation was lower than fatigued values (P<0.05)during administration of the study drug in groups II and III.The decrease in P_di was greater in group III than in group II(P<0.05). In conclusion, midazolam compared with propofolis associated with an inhibitory effect on contractility inthe fatigued canine diaphragm. Br J Anaesth 2001; 86: 879–81