To determine whether NPPV had an independent effect on the improvement observed in gas exchange, arterial blood gas values at discharge and follow-up were compared in patients who complied with NPPV vs patients who were noncompliant with NPPV. As shown in Figure 4, Pao2/Fio2 tended to decrease (294 ± 12 to 259 ± 16; p = 0.10) and PaC02 tended to rise (54 ± 2 to 60 ± 4 mm Hg; p = 0.19) in the noncompliant group, but remained stable in patients who complied with NPPV.
As shown in Figure 3, functional scores in patients who complied with chronic NPPV therapy showed a further increase in score at 3 months in comparison with the score at discharge (5.53 ± 0.3 vs 4.8 ± 0.2 AUs; p = 0.02), with maintained improvements at the 6- and 12-month follow-ups. website
In contrast to the improvements in gas exchange and functional status, spirometry (FEV1 and FVC) and respiratory muscle strength (Plmax and PEmax) before and after approximately 6 months of NPPV therapy were not significantly different in patients with COPD or restrictive disorders (Fig 5, 6).
Side Effects of NPPV
Six months after discharge, 26 of the original 40 patients (65%) continued to be compliant with NPPV. Of the 20 original patients who had COPD, 10 completed the study (50%), while 16 of the 20 original patients with restrictive disorders (80%) remained on NPPV (Fig 1). Overall, outpatient use as actually measured on the meter log was 45% less than patients’ stated use (4.5 ± 0.58 vs 7.23 ± 0.24 h/night). Complications experienced with NPPV included significant mouth or mask leaks in 43%, skin irritation at the patient face mask interface in 23%, rhinitis or aerophagia in 13%, and discomfort from the mask or head gear in 8%. Thirty-six percent of patients required face mask or ventilator setting adjustments to maintain optimization of their gas exchange and compliance with therapy.
Figure 4. Gas exchange on discharge from the VRU and at the 6-month follow-up visit in patients who were compliant with NPPV (solid bars) and noncompliant with NPPV (open bars). Patients who were compliant with NPPV (n = 26) maintained improvements in gas exchange, in contrast to those who were noncompliant with NPPV treatment (n = 14).
Figure 5. FVC and FEV1 in all compliant patients with COPD (open bars) and restrictive ventilatory disorders (crosshatched bars) before and 6 months after implementation of NPPV. NPPV had no effect on FVC or FEV1 in either patient group.
Figure 6. Pimax (MIP) and PEmax (MEP) before (PRE) and after (POST) NPPV in compliant patients with obstructive disease and restrictive ventilatory disorders (restrictive disease), before and 6 months after NPPV. NPPV had no effect on maximum respiratory muscle pressures.
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