Outcome predictors of non-invasive positive pressure ventilation in acute respiratory failure in the emergency department and intensive care unit-a prospective observational comparative study

BACKGROUND Acute respiratory failure (ARF) is a common problem encountered by the emergency physicians. Patients may need ventilatory support when pharmacological measures fail to correct the pathophysiologic derangements. Noninvasive positive pressure ventilation (NIPPV) provides positive pressure airway support through a face or nasal mask without the use of an endotracheal tube or other airway device. OBJECTIVES: To identify the factors predicting the failure of NIPPV in acute respiratory failure (ARF) among patients presenting to the emergency department and ICU of MES Medical College METHODOLOGY: The study was a prospective observational comparative study.The study subjects were patients presenting with ARF in the emergency department and medical ICU of MES Medical college. The study period was one year. Sample size is 156 patients. All patients who fulfilled the inclusion criteria and  exclusion criteria were taken up for the study by convenient purposive sampling.The demographic data related to age, sex, etiology of ARF were recorded..Noninvasive ventilation was administered with the use of noninvasive ventilator VPAP II(RESMED).ABG values at one and four hours were monitored and periodically thereafter as clinically indicated. The duration of NIPPV and the time to stop the NIPPV was determined based on clinical judgment and arterial blood gas values. The data for heart rate, respiratory rate, arterial blood gas values (pH, PaO 2 ,PaCO 2 ) at baseline, one and four hours and anytime thereafter were recorded. RESULTS: The factors predicting the failure of NIPPV was assessed by logistic regression. In univariate analysis by logistic regression, the older the age of the patient, (70.4±16.5 vs 59±15.8) [failure of NIV (mean ± SD) vs non-failure group (mean ± SD)] higher  APACHE II score (32.3±5 vs 25.8±4.9), higher heart rate at admission (118.4±25.2 vs 104.5±15.4), higher respiratory rate at admission (37.4±4.3 vs 33.8±3.7), lower pH at admission/0 hours (7.1±0.2 vs 7.3±0.1), lower PaO2 at admission (53.5±14.5 vs 63.4±11.7), higher PaCO2 at admission (70.5±23.1 vs 57.6±17.7), baseline low serum sodium (118.4±12.3 vs 129.2±7.7) and potassium values (3.7±1.6 vs 4.5±0.9) predicted the failure of NIPPV in patients with acute respiratory failure. In the multivariate analysis, APACHE II scores (p=0.015, Odds ratio-1.23, 95% confidence interval 1.04-1.46),pH  at admission (p value-0.000),baseline serum sodium values(p=0.0.007,Odds ratio-0.92, 95% confidence interval 0.87-0.98) and baseline serum potassium values(p=0.009,Odds ratio-0.54, 95% confidence interval 0.34-0.86) are factors which predict the failure of NIPPV in acute respiratory failure. CONCLUSION: The age of the patient,APACHE II scores, heart rate and respiratory rate at admission(baseline), pH,PaO2 and pCO2 at admission, baseline serum sodium and potassium values were predictors of failure of NIPPV in Acute respiratory failure. By multivariate logistic regression, higher APACHE II score, lower baseline pH, lower baseline serum sodium and potassium values were significant predictors of NIPPV failure ARF patients. KEYWORDS: Non invasive ventilation(NIV),Acute Respiratory Failure(ARF)