Differences in mortality based on worsening ratio of partial pressure of oxygen to fraction of inspired oxygen corrected for immune system status and respiratory support.

OBJECTIVE

To define the relationship between worsening oxygenation status (worst PaO(2)/FiO(2) ratio in the first 24 hours after intensive care unit admission) and mortality in immunosuppressed and immunocompetent ICU patients in the presence and absence of mechanical ventilation.

DESIGN

Retrospective cohort study.

SETTING

Data were extracted from the Australian and New Zealand Intensive Care Society Adult Patient Database.

PARTICIPANTS

Adult patients admitted to 129 ICUs in Australasia, 2000-2010.

MAIN OUTCOME MEASURES

In hospital and ICU mortality; relationship between mortality and declining PaO(2)/FiO(2) ratio by ventilation status and immune status.

RESULTS

457 750 patient records were analysed. Worsening oxygenation status was associated with increasing mortality in all groups. Higher mortality was seen in immunosuppressed patients than immunocompetent patients. After multivariate analysis, in mechanically ventilated patients, declining PaO(2)/FiO(2) ratio in the first 24 hours of ICU admission was associated with a more rapidly rising mortality rate in immunosuppressed patients than non-immunosuppressed patients. Immunosuppression did not affect the relationship between oxygenation status and mortality in non-ventilated patients.

CONCLUSION

Immunosuppression increases the risk of mortality with progressively worsening oxygenation status, but only in the presence of mechanical ventilation. Further research into the impact of mechanical ventilation in immunosuppressed patients is required.