Nasal Positive Pressure Ventilation in Patients with Acute Respiratory Failure (21)
Nevertheless, it remains quite possible that another technique, particularly PSV,* where the airway pressure mostly depends on the patients demand for air during the inspiratory time, would be better tolerated than AC-IPPV; in IPPV inspiration stops when a preset volume or pressure is reached; this feature can sometimes induce an active expiratory effort, which can be deleterious by causing dyspnea and incoordination of the respiratory muscles and can increase the work of breathing. Conversely, during PSV the positive pressure in the airways is cycled according to inspiratory flow and stops before the flow drops to zero. Therefore, no expiratory effort is generally observed in these patients.
Further research is clearly needed to precisely measure the amount of time and work spent by nurses when taking care of decompensated patients with COPD who are submitted to PSV, either with a facial or nasal mask; however, by having observed closely our three patients with obstructive disease, we were impressed by the poor tolerance of the nasal mask, which induced fear and anxiety during most of the positive-pressure ventilation time; we are not sure that a more tightly fitted mask, like a facial one, would be better tolerated.
In conclusion, our data show that in selected cases, acute NPPV can lower PaC02 and probably avoid intubation in some patients, particularly those with a restrictive respiratory disorder; however, this technique is not easy, is time-consuming for nurses, and, even if possible in a general nonspecialized ICU, requires some expertise and reasonable cooperation on the part of the patients.