Abstract
We compared the effects of intermittent mandatory ventilation (IMV) and pressure support ventilation (PSV) on the patient's spontaneous breathing and the work of breathing (WOB) of ventilated patients during the weaning from mechanical ventilation. A total of consecutive eighteen patients with radical esophagectomy was divided randomly into IMV group or PSV group by the method of weaning. The weaning from mechanical ventilation was performed by the gradual decreases of frequency of mandatory ventilation in IMV, or of support pressure level in PSV. The influence of IMV and PSV modes on patient was completely different, although the ventilator work decreased in the same fashion. The WOB in ventilated patients increased abruptly after the commencement of the weaning by IMV. On the other hand, the WOB during the weaning by PSV increased in a stepwise fashion. The WOB during the weaning by IMV was significantly higher than that during the weaning by PSV. High values of WOB in IMV were due to the fact that spontaneous breathing was completely established on the early stage of weaning and the mechanical assist of mandatory ventilation did not contribute to the reduction of WOB. The increases of imposed WOB and work for intrinsic PEEP were also involved in the higher WOB. PSV reduced WOB effectively and also loaded WOB in a stepwise fashion in the weaning from mechanical ventilation. We concluded that the weaning from mechanical ventilation by PSV has a definite usefulness compared with the weaning by IMV from the standpoint of WOB.
