Physiological variables predictive of survival in patients with acute type II respiratory failure on noninvasive ventilation

Introduction

There are very few data available from the Indian subcontinent regarding the use of noninvasive ventilation (NIV). We carried out this study to determine variables that could be used in the emergency room to predict survival in patients placed on NIV.

Methods

This was a prospective, observational cohort study carried out from 2001 to 2005 on all patients presenting with acute type II respiratory failure and meeting criteria for NIV use. NIV was started in the emergency room at settings that were titrated according to arterial blood gases. Univariate and multivariate regression analysis was used to determine the effect on survival. P < 0.05 was considered statistically significant. The software used was SPSS 11.

Results

The total number of patients enrolled was 119; 52.9% were males, 47.1% were females. The mean age was 63.3 years (± 11.9). The most common cause of respiratory failure was COPD in 91.6%. A total of 56.3% patients were stuporus at presentation, and 7.5% fulfilled criteria for severe sepsis. There was no statistically significant difference between the baseline characteristics of the groups that survived or died. The overall survival rate for patients placed on NIV was 76.5%, the intubation rate was 12.6% and the length of hospitalization was 11.4 days (± 10.9). Statistically significant improvements in pH and PaCO₂ occurred at 24 hours and 48 hours of NIV usage, compared with baseline (7.28 vs 7.37, P < 0.001; 74.2 vs 65.4, P = 0.003) (Figures 1 and 2). There was no significant change in PaO₂. The variables predicting survival were age (62.1 ± 12.5 years, 67.8 ± 8.7 years, P = 0.025), serum creatinine (1.1 ± 0.5 mg/dl, 1.7 ± 0.8 mg/dl, P = 0.002), pH at baseline (7.31 ± 0.09, 7.25 ± 0.9, P = 0.005), HCO₃ at baseline (36.1 ± 7.5 mEq/l, 32.4 ± 9.3 mEq/l, P = 0.032), pH at 48 hours (7.39 ± 0.07, 7.33 ± 0.06, P = 0.002), and need for endotracheal intubation (10%, 21%, P < 0.05).

Figure 1

Figure 2

Conclusion

NIV improves outcomes in our setting. Physiological variables and the need for intubation can predict an improved survival in these patients.