Monday, 13 April 2015

Hyperoxia and mortality in patients following cardiac surgery: is there an association?

Associate Professor Michael Bailey and Professor Rinaldo Bellomo have co-authored a paper with researchers from Austin Health and the Alfred Hospital, exploring the association between hyperoxia (PaO2) and the outcomes in patients in ICU after cardiac surgery.

Hyperoxia is defined as excess oxygen within lungs and body tissue. This results when organs or tissue are exposed to a higher than normal supply of oxygen or an excessive partial pressure of oxygen. Whilst hyperoxia does provide a safeguard for patients with high risk ventilation, it can also have be dangerous and cause injury within the lungs such as tracheobronchitis. It can also generate free radicals in some organs. There is however a paucity of research examining the impact of hyperoxia for patients who have had cardiac surgery.

There has been a vast amount of research exploring the association between hyperoxia and mortality of patients admitted to the ICU. The studies have had differing results and conclusions with a portion finding that hyperoxia can be associated with an increased in-hospital mortality rate in patients after a cardiac event than for patients with normoxia or hypoxia. However, another study indicated no possible association between the two outcomes. 

These inconsistencies have been present in similar cohorts of patients suffering from acute stroke. This relationship between hyperoxia and mortality remains inconclusive for patients in ICU’s. Therefore, the authors sought to assess this relationship further and determine whether an association is present.

The researchers adopted a retrospective cohort study design, utilising data from the Australian and New Zealand Intensive Care Society patient database. Participants included adults who had been admitted to the ICU after a cardiac surgery. Patients were residing in Australia and New Zealand from 2003 to 2012. These participants were then grouped into those with the poorest PaO2 level or alveolar-arterial O2 gradient in the first 24 hours following admission into the ICU. The main outcome was mortality during discharge from the hospital with the secondary outcomes being hospital length of stay and ICU mortality.

The results indicated that 14.7% of participants had hyperoxia, 65.5% patients had hypoxia and 19.8% had normoxia. The researchers stated that no relationship existed between hyperoxia and ICU or in-hospital mortality in comparison to normoxia. There was however an increased length of stay for patients with hyperoxia versus those with normoxia. They therefore conclude that there is no correlation between hyperoxia and ICU or in-hospital mortality for patients admitted to the ICU in the first 24 hours after cardiac surgery.

Read the paper here:

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