When pressure support ventilation (PSV) first became available, its use was limited to patients with a stable respiratory drive because no provision had been made for automatic ventilation if the patient became apneic. The combination of mandatory minute ventilation (MMV) and PSV has been introduced as a solution to this problem. MATERIALS AND METHODS: We compared the effects of PSV plus MMV and PSV alone as supplied by the Ohmeda CPU-1 to a canine model of respiratory depression. Sixteen mongrel dogs were randomly assigned to two equal groups, the one to receive PSV + MMV and the other PSV alone. Four levels of respiratory depression (baseline, mild, moderate, and severe) were achieved by the continuous infusion of sufentanil, with each level of respiratory depression after baseline maintained for 1 hour. Ventilation, oxygenation, and hemodynamic data were collected every 15 minutes, and were analyzed by multivariate analysis of variance for repeated measures. RESULTS: Ventilation was significantly better in the PSV + MMV group as shown by a lower P aCO2 (p < 0.0001) and higher pH (p < 0.0001). S aO2 (p = 0.031) was higher and venous admixture (p = 0.024) was lower in the PSV + MMV group. Hemodynamics were statistically no different between the two groups with the exception of cardiac output, which was lower in the PSV + MMV group probably due to the effects of positive pressure ventilation on venous return. CONCLUSION: The results of this study indicate that PSV + MMV will guarantee adequate ventilation even in cases of profound respiratory depression. PSV + MMV should make it possible to obtain the benefits of PSV in a much wider patient population.
East et al. (Fri,) studied this question.