Nasal Positive Pressure Ventilation in Patients with Acute Respiratory Failure (14)

Results
Considered as a group, all six patients suffered from severe respiratory impairment (mean FEVX <1L) and acute-on-chronic respiratory acidosis (mean FaC02, 9.8 kPa [74 mm Hg]) with a marked gas exchange abnormality (mean P[A-a]02, 11 kPa [82 mm Hg]) (Table 2). In all patients, it was possible to lower the PaC02 to some extent by using NPPV and to reverse the trend of steadily increasing hypercapnia; PaC02 decreased by 33 ± 13 percent (Fig 2), and there was a significant difference between the PaC08 before (9.8 ±1.8 kFa [73 ±14 mm Hg]) and after (6.4 ±1.6 kPa [48 ± 12 mm Hg]; mean ± SD; p<0.005 by paired f-test) the NPPV trial.

The mean duration necessary to obtain such a result was 3.2±0.4 h. Nevertheless, when “success” or “failure” of NPPV was assessed by the need to require subsequent intubation, only patients 1 to 3 were eventually not intubated. These patients 1 to 3 were not different from those who were eventually intubated (ie, patients 4 to 6) when considering age, initial (pre-NPPV) severity of their respiratory failure assessed by arterial blood gas abnormalities, or FEVt values (Table 3). Only the FEVj/FVC ratio was different between the two groups: patients with “success” (patients 1 to 3) showed no airflow obstruction, whereas those with “failure” (patients 4 to 6) had a mean FEV/FVC ratio of 57 ± 14 percent (p = 0.048; unpaired Mest).

Table 2—Initial Conditions (before NPPV Trial)

Pulmonary Function Arterial Blood Gas Levels
Patient FVC, L FEVj, L/sec FEV/FVC,percent pH PaC02, kPa (mm Hg) PaOa, IcPk (mm Hg) P(A-a)Oa, kPa (mm Hg)
Patients1 0.65 0.48 73 7.25 9.2 (69) 6.5 (49) 11.8 (89)
2 2.10 1.50 71 7.29 11.5 (86) 12.0 (90) 19.6 (147)
3 1.06 0.76 72 7.27 10.5 (79) 6.3 (47) 5.1 (38)
4 2.52 1.21 54 7.32 10.0 (75) 5.6 (42) 3.8 (29)
5 1.91 0.93 49 7.30 6.4 (48) 7.2 (54) 15.7 (118)
6 1.69 0.47 44 7.24 10.9 (82) 6.4 (48) 9.7 (73)
Mean ± SD 1.66 ±0.68 0.89 ±0.41 61 ±13 7.28±0.03 9.8± 1.8 (73 ±14) 7.2 ±2.5 (55 ±18) 11.0±6.1 (82 ± 46)

Table 3—Companion of Initial Conditions (before NPPV) between Rstients wiih Restrictive vs Obstructive Pulmonary Function

Data Restrictive Obstructive p valuef
Age.yr 50 ±9 45± 17 0.223
Arterial blood gas levels
pH 7.27 ±0.02 7.28 ±0.04 0.548
PaCO„ kPla 10.4 ±1.2 9.1 ±2.4 0.468
PaOt>kPa 8.3 ±3.2 6.1 ±0.9 0.100
P(A-a)0„ kPa 12.2 ±7.3 9.7 ±5.9 0.672
Pulmonary function
FVC.L 1.27±0.75 2.04 ±0.43 0.252
FEV„ L/sec 0.91 ±0.48 0.87 ±0.37 0.359
FEVj/FVC, percent 76±1 57±14 0.048

Figure-2

Figure 2. Measurement of PaCO, immediately before NPPV and after NPPV use (ie, 3.2 ±0.4 hours after beginning of this procedure). All patients are shown (open circles) with means and SD (solid circles and bars).

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