To compare the physiologic effects of noninvasive pressure-support ventilation (NPSV) delivered by a facemask, a helmet with the same settings, and a helmet with specific settings. Inspiratory muscle effort, gas exchange, patient-ventilator synchrony, and comfort were evaluated.Design:
Prospective crossover study.Setting:
A 13-bed medical intensive care unit in a university hospital.Patients:
Eleven patients at risk for respiratory distress requiring early NPSV after extubation.Intervention:
One hour after extubation, three 20-minute NPSV periods were delivered in a random order by facemask, helmet, and helmet with 50% increases in both pressure support and positive end-expiratory pressure and with the highest pressurization rate (95% max).Measurements and Main Results:
Flow and airway, esophageal, and gastric pressure signals were measured under the three NPSV conditions and during spontaneous breathing. Compared with the facemask, the helmet with the same settings resulted in a greater inspiratory muscle effort, but this difference was abolished by the specific settings (pressure-time product in cm H2O·s·min−1, 63.8 [27.3–85.9], 81.8 [36.0–111.5], and 58.0 [25.4–79.5], respectively, p < 0.05, compared with 209.3 [29.8–239.6] during spontaneous breathing). Compared with the facemask, the helmet with the same settings worsened patient-ventilator synchrony, as indicated by longer triggering-on and cycling-off delays (0.14 [0.11–0.20] seconds vs. 0.32 [0.26–0.43] seconds, p < 0.05; and 0.20 [0.08–0.24] seconds vs. 0.27 [0.25–0.35] seconds, p < 0.01, respectively). The specific settings significantly improved the triggering-on delay compared with the helmet without specific settings (p < 0.01). Tolerance was the same with the three methods.Conclusions:
Our results suggest that increasing both the pressure-support level and positive end-expiratory pressure and using the highest pressurization rate may be advisable when providing NPSV via a helmet.