Non-invasive mechanical ventilation with average volume-assured pressure support. Results according to the aetiology of acute respiratory failure

Introduction
Until now, the ventilatory strategy with BiPAP S/T plus average volume-assured pressure support (AVAPS) has not been evaluated for its use in the different types of acute respiratory failure (ARF). Consequently we report the results of the use of this ventilatory strategy in these clinical scenarios.

Material and methods
This is a single-centre prospective study. The subjects were categorised according to the type of ARF: (1) hypercapnic ARF: chronic obstructive pulmonary disease and bronchial asthma; and (2) hypoxaemic ARF: pneumonia, acute respiratory distress syndrome, congestive heart failure, and interstitial lung disease. Multiple logistic regression was used to determine predictors of non-invasive mechanical ventilation (NIV) failure (intubation). Further, in a subgroup of patients with de novo hypoxaemic ARF, analysis of variances with repeated measures was used to determine factors associated with NIV outcome.

Results
Sixty-eight subjects were included in this study. The NIV success rate was 69.1% and the mortality rate was 20.6%. A multivariate analysis showed that the number of affected lung quadrants on chest X-ray (OR: 4.23, 95% CI: 4.17–4.31; P < 0.001) and ARF precipitating disease (OR: 4.46, 95% CI: 4.43–4.51; P < 0.001) were determinants of NIV failure. In the hypoxaemic ARF subgroup (n = 58), significant differences in several parameters were found between patients with positive and negative outcomes.

Conclusions
The use of BiPAP S/T – AVAPS in subjects with hypercapnic ARF is associated with a better outcome than in those with de novo hypoxaemic ARF.