SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION WITH AND WITHOUT PRESSURE SUPPORT VENTILATION IN WEANING PATIENTS WITH COPD FROM MECHANICALVENTILATION

This prospective study compared two weaning modalities in COPD patient s requiring mechanical ventilation (MV) for acute respiratory failure. Nineteen patients with COPD were studied when their precipitating ill ness was controlled. Although they satisfied the conventional bedside weaning criteria, they could not tolerate any reduction in the respira tor rate below 10 cycles/min. At this time, patients were randomized i nto two groups receiving either synchronized intermittent mandatory ve ntilation (SIMV) with pressure support ventilation (PSV) (group 1) or SIMV alone (group 2). The volumetric support of ventilation (SIMV rate ) was progressively decreased in both groups according to the patient' s tolerance with a concurrent decrease in the barometric support of ve ntilation (PSV levels from 15 cm H2O to 6 cm H2O). At each step of SIM V rate, we found no difference between group 1 and group 2 in arterial blood gases, blood pressure, heart rate, airway occlusion pressure, m aximal inspiratory pressure, and oxygen cost of breathing (OCB). At ea ch step, however, group 1 patients showed significantly higher spontan eous tidal volume and lower spontaneous breathing frequency than did g roup 2 patients, We found a slight but not significant tendency to a s horter weaning period with than without PSV, but no difference in the weaning success. We concluded that (1) conventional weaning criteria m ight be inaccurate in COPD patients, (2) SIMV appeared very useful in weaning COPD patients from MV, (3) PSV marginally reduced the weaning period when added to SIMV, and (4) the OCB was not significantly impro ved with PSV.