Acute hypoxemic respiratory failure in children: case mix and the utility of respiratory severity indices

Objective: Acute hypoxemic respiratory failure (AHRF) is a common reason for emergency pediatric intensive care. An objective assessment of disease severity from acute physiological parameters would be of value in clinical practice and in the design of clinical trials. We hypothesised that there was a difference in the best early respiratory indices in those who died compared with those who survived. Design: A prospective observational study of 118 consecutive AHRF admissions with data analysis incorporating all blood gases. Setting: A pediatric intensive care unit in a national children’s hospital. Interventions: None. Results: Mortality was 26/118,22% (95% confidence interval 18–26%). There were no significant differences in the best alveolar-arterial oxygen tension gradient (A-aDO(2), torr), oxygenation index (OI), ventilation index (VI), or PaO(2)/FIO(2) during the first 2 days of intensive care between the survivors and non-survivors. Only the mean airway pressure (MAP, cm H(2)O) used for supportive care was significantly different on days 0 and 1 (p≤0.05) with higher pressure being used in non-survivors. Multiple logistic regression analysis did not identify any gas exchange or ventilator parameter independently associated with mortality. Rather, all deaths were associated with coincident pathology or multi-organ system failure, or perceived treatment futility due to pre-existing diagnoses instead of unsupportable respiratory failure. When using previously published predictors of outcome (VI>40 and OI>40; A-aDO(2)>450 for 24 h; A-aDO(2)>470 or MAP>23; or A-aDO(2)>420) the risk of mortality was overestimated significantly in the current population. Conclusion: The original hypothesis was refuted. It appears that the outcome of AHRF in present day pediatric critical care is principally related to the severity of associated pathology and now no longer solely to the severity of respiratory failure. Further studies in larger series are needed to confirm these findings.