[Non invasive ventilation in acute respiratory insufficiency: an alternative]

Effectiveness of non invasive positive pressure ventilation (NIPPV) was prospectively evaluated in 22 selected patients with acute respiratory failure, meeting criteria for orotracheal intubation and conventional mechanical ventilation. Patients were divided in two groups: group A (17 patients) with initial PaCO2 above 45 mm Hg and group B (5 patients) with initial PaCO2 below 45 mmHg. NIPPV was administered with 2 levels of pressure either by nasal or facial mask. Respiratory rate (RR), arterial blood pH, PaCO2 and PaO2/FiO2 were registered pretreatment, 1 hour and 24 hours after NIPPV. Statistical analysis was performed by ANOVA test, p < 0.05 was considered significant.

In group A there was a reduction in RR (X +/- DS) from 31.2 +/- 8.2 to 24.7 +/- 8.2 at one hour (h) (p = 0.02) and to 23.4 +/- 6.5 at 24 hs (p = 0.01), pH change from 7.33 +/- 0.07 to 7.37 +/- 0.07 at one hour (p = 0.13) and to 7.40 +/- 0.07 at 24 hs (p = 0.01), a PaCO2 change from 69.5 +/- 19.6 to 57.8 +/- 16.9 at one hour (p = 0.06) and to 54 +/- 13 at 24 hs (p = 0.02), and PaO2/FiO2 change from 187.3 +/- 60.2 to 223.9 +/- 6.5 at one hour (p = 0.12) and to 245.8 +/- 75 at 24 hs (p = 0.03). In group B there was a change in RR from 33 +/- 16.3 to 26.6 +/- 12.5 at one hour (p = 0.46) and to 21.3 +/- 4.2 at 24 hs (p = 0.27), PaO2/FiO2 change from 113.4 +/- 31 to 137.8 +/- 57.2 at one hour (p = 0.44) and to 208.7 +/- 51.2 at 24 hs (p = 0.03). Only two patients in group A and one in group B were converted to conventional ARM.

1) NIPPV is a therapeutic alternative for selective patients with acute respiratory insufficiency and may reduce known morbidity of conventional mechanical ventilation. 2) In the group with hypercapnic acute respiratory failure the improvement in respiratory function begins with an immediate reduction in RR. Significant improvement in arterial blood gases usually occurs within 24 hours of NIPPV.