Noninvasive ventilation for hypercapnic respiratory failure in COPD and initial post-support deterioration of pH and PaCO2 may not predict failure

Objectives: To correlate the degree of encephalopathy, baseline values of PaCO₂ and pH, and their early response to NIV with eventual in-hospital outcome in patients of severe acute-on-chronic hypercapnic respiratory failure in COPD.
Design: Retrospective review.
Setting: Intensive care unit.
Material and methods: 24 episodes of acute exacerbation of COPD in 17 patients (10 females, 7 males) with a mean age of 59.5 years (range 48 - 82) where NIV was initiated. Data collected: encephalopathy score at baseline and at 24 hours, respiratory rate, breathing pattern, serial arterial blood gases, duration of NIV support per day and hospital days.
Results: All patients had severe hypercapnia (mean peak PaCO₂ 89.0 mm Hg ± 21; range 66-143), respiratory acidosis (mean nadir pH 7.24 ± 0.058, range 7.14 - 7.33) and tachypnoea (mean respiratory rate 29.5 ± 4.69/mt; range 24 - 40). In 17 episodes, altered mental state was present (encephalopathy score 1.92 ± 1.32, median 2.5). Clinically stable condition occurred over several days (mean 13± 9.6 days; range 5 - 40). Intubation was avoided in 22 out of 24 episodes (91.6%) despite significant initial worsening of PaCO₂ and pH. Two patients died. The mean time on NIV was16.5 hours/day (range 4 - 22).
Conclusions: In selected patients of COPD with acute hypercapnic failure on NIV worsening PaCO₂ and pH in the initial hours may not predict failure provided the level of consciousness and respiratory distress improve.

Keywords
Positive pressure ventilation, Noninvasive ventilation, Chronic obstructive pulmonary disease, Respiratory failure, Hypercapnia, Mechanical ventilation