Epidemiology and outcome in acute respiratory failure

Introduction

Acute respiratory failure (ARF) is the most common organ failure in the ICU, and mortality is high. The outcome worsens in association with any other organ failure. The objective of this study was to describe the aetiology, mortality rate and causes of ARF and to evaluate the outcome of ARF with/without concomitant organ failure.

Methods

A prospective cohort study that includes all patients admitted to the ICU of a tertiary hospital from January to July 2007. ARF was defined based on the SOFA score criteria, SOFA respiratory ≥ 3, PaO₂/FiO₂ <200 and mechanical ventilation.

Results

Two hundred and ninety-six patients were admitted, 48% with ARF (142 patients), 59.6% males. Primary diagnoses were 52.5% respiratory insufficiency, 27.7% neurological disease, 14.2% cardiologic/septic shock, and 5.7% cardiac arrest. Causes of ARF were 47.5% pneumonia, 11.5% pulmonary oedema, 11.5% chronic pulmonary disease, 10.8% nonpulmonary ARDS, 7.9% atelectasis, 3.5% bronchospasm, 3.5% pleural effusion, 2.1% pulmonary fibrosis. Severity was APACHE II score 23.17 ± 7.1, SAPS II score 50.5 ± 15.4, SAPS III score 66.5 ± 15.5, SOFA score at admission 8.6 ± 4.1, SOFA maximum score 10.23 ± 4.7, lactic acid 4.01 ± 3.3, and lung injury score (LIS) 1.7 ± 0.7 (0.66–3.5). Of patients, 21.6% received noninvasive ventilation and 78.4% invasive ventilation. The mean stay in the ICU was 9.6 ± 10.5 days, hospital stay was 19.8 ± 18.29 days. In the ICU, 73.8% developed multiorgan failure syndrome (MOFS). The mortality rate in the ICU was 39.7% and in the hospital was 50.4%. Mortality in patients without ARF was 15.6%, and in patients with ARF was 50.4% (RR = 5.53, 95% CI, 3.2–9.5). The mortality rate was lowest in the subgroup with ARF as a single organ failure (16.7%) and it increased with additional organs in failure (ARF + 1, 37.8%; ARF + 2, 69%; ARF + 3, 90%; ARF + 4 or 5, 91%; χ² test P = 0.000). The mortality rate of those with ARF at admission was 55.5%, versus 30% for those who developed ARF (RR = 2.95, 95% CI = 1.2–6.8). Patients with invasive ventilation had 2.45 times more risk to die than noninvasive ventilation (55% vs 33.3%). The mortality rate in acute respiratory distress syndrome (ARDS) was 77.8% vs 40.8% without ARDS (RR = 5.1, 95% CI = 2.1–12.2). The mortality rate in MOFS was 62.7% versus 16.2% only with ARF. Multivariant logistic regression showed there is no association with mortality rate and age, Barthel, PaO₂, HCO₃, and PaCO₂. The mortality rate associates with lactic acid, APACHE II and III scores, acute physiological score, SAPS II and III scores, MODS, SOFA score at admission, pH, LIS and PaO₂/FiO₂. Developing MOFS and the LIS score are independent predictors of mortality in ARF patients.

Conclusion

ARF has a high mortality rate especially if it is associated with severe failure of other organs. Developing MODS and the LIS score are good predictors of outcome in patients with ARF.