Identifying an Oxygenation Index Threshold for Increased Mortality in Acute Respiratory Failure

The objective of this work was to examine current oxygenation index (OI) data and outcomes using electronic medical record data to identify a specific OI value associated with mortality.

This study was a retrospective electronic medical record data review from the pediatric ICU of Phoenix Children's Hospital, with data mining for variables to calculate OIs on subjects age 1 month to 20 y mechanically ventilated > 24 h, excluding those with known intracardiac shunts or cyanotic heart disease. Age, length of hospital stay, duration of mechanical ventilation, and outcomes were also assessed. The Wilcoxon signed-rank test was used to compare continuous variables, receiver operating characteristic analysis was used in determining discriminant ability, and logistic regression was conducted to determine the odds ratio (OR) for risk of death with increasing OI.

OI was calculated on 65 subjects, of whom 6 died (9%). The median maximum OI was 10 for all subjects, 17 for non-survivors, and 8 for survivors (P = .14 via Wilcoxon rank-sum test). ORs indicated a 2.4-fold increase in the odds of death (P = .09, 95% CI 0.9-6.6) for each increasing point in maximum OI. Mean OI OR revealed a 1.9-fold increase in the odds of death (P = .25, 95% CI 0.6-5.9). Receiver operating characteristic analysis indicated a higher discriminate ability for maximum OI (area under the curve = 0.68) than mean OI (area under the curve = 0.58). OI cut-points for mortality were established. Mortality was unchanged until maximum OI > 17, for which mortality nearly tripled at a value of 18% versus 6-7% for range 0-17.

Limitations exist in obtaining serial OI values from current electronic medical records. Serial assessment of OI values may allow creation of alert values for increased mortality risk. Consideration of escalation of therapies for respiratory failure, such as high-frequency ventilation, inhaled nitric oxide, or extracorporeal membrane oxygenation may be warranted at lower OIs than historically reported.