Conventional versus noninvasive ventilation in acute respiratory failure

Introduction

Treatment of patients with acute respiratory failure (ARF) involves mechanical ventilation via endotracheal intubation (INV). Noninvasive positive pressure ventilation (NIV) using the Bi-level positive airway pressure (BiPAP) can be safe and effective in improving gas exchange. The aim of the study is to assess NIV (BiPAP) as an alternative method for ventilation in ARF and to determine factors that predict the successful use of BiPAP.

Methods

Thirty patients with ARF (type I and type II) were enrolled and divided into two groups. Group I included 10 patients subjected to INV ventilation. Group II included 20 patients subjected to NIV using BiPAP. Both groups were compared regarding arterial blood gases (ABG) on admission, 30 minutes after beginning of ventilation, at 1.5 hours and then once daily. Complications, namely ventilator-associated pneumonia (VAP), skin necrosis and carbon dioxide narcosis, static compliance and resistance, were measured at day 1 and day 2.

Results

Compared with group I, group II patients were associated with similar improvement in ABG at 30 minutes and at discontinuation of ventilation. Group II patients showed lower incidence of VAP (20% vs 80%), a shorter duration of ventilation (3 ± 3 vs 6 ± 5 days, P < 0.01), with shorter length of hospital stay (5.8 ± 3.6 vs 8.9 ± 2.7 days, P < 0.01) when compared with group I. Skin necrosis and carbon dioxide narcosis occurred in group II only. Group II patients showed a difference change in compliance and a change in resistance from day 1 to day 2 when compared with group I. On a univariate basis, parameters were analyzed to choose those associated with the outcome under concern (successful NIV). The following parameters were identified: level of consciousness, pH (7.3 ± 0.03 vs 7.26 ± 0.1, P = 0.009), PCO₂ (69.16 ± 13.14 vs 100.97 ± 12.04) on admission, 1.5 hours after NIV, pH (7.37 ± 0.03 vs 7.31 ± 0.17, P = 0.005), PCO₂ (53.98 ± 8.95 vs 77.47 ± 5.22, P = 0.0001) in whom NIV succeeded and failed, respectively. The variable identified was PCO₂ after 1.5 hours in the two models with 100% specificity.

Conclusion

In patients with ARF, NIV was as effective as conventional ventilation in improving gas exchange, associated with fewer serious complications and shorter stay in intensive care. A 1.5-hour trial with NIV can predict success with BiPAP, as shown by an improvement in pH and PCO₂ and the overall clinical picture. PCO₂ after 1.5 hours could be the sole predictor of successful NIV with 100% specificity.