Halothane does not depress contractile function of fresh or fatigued diaphragm in pentobarbitone-anaesthetized dogs

We have studied the effect of halothane on diaphragmatic contractile function by measuring transdiaphragmatic pressure (Pdi) and electromyogram of the diaphragm (Edi) during various stimulation frequencies in 15 pentobarbitone-anaesthetized dogs undergoing mechanical ventilation. We have examined also the effect of halothane on the fatigued diaphragm by repeating the measurements 5, 10, 15, 30, 60 and 90 min after 30 min of tetanic stimulation applied to the phrenic nerves. Administration of 1-2 MAC of halothane did not affect Pdi at any given stimulation frequency. Changes in the depth of halothane anaesthesia (0, 1 and 2 MAC) did not alter the force-frequency relationship of the diaphragm during recovery from fatigue. Edi was unaffected by halothane, except for a small decline during 100-Hz stimulation with 2 MAC. In contrast with the changes in Pdi, Edi during recovery from fatigue was the same as that determined before fatigue. It is concluded that halothane, in clinical concentrations, did not depress the contractile function of fresh or fatigued diaphragm in vivo.