MORE OXYGEN TOXICITY

Oxygen toxicity has been getting a lot of attention the last couple of years. The evidence of how high FiO2 is harmful for patients who are critically ill is somewhat solid and has to some extent changed resus guidelines. An article I found in Anesthesia & Analgesia suggests high peroperative FiO2 increase mortality in a normal surgical population too. Significantly so in cancer patients.

Background
Improved surgical wound oxygenation, through increased oxygen content in the air patients inhale during surgery (FiO2), has been thought to protect against per- and postoperative wound infections. One proposed mechanism was improved oxidative killing by neutrophils.

Studies have showed mixed results. Some studies have showed decreased wound infection with higher FiO2s while others could demonstrate no difference.

One of the largest and most recent trials was the PROXI trial in which general surgical population was randomised into breathing either 80% or 30% O2 during surgery. The PROXI trial could demonstrate no reduction in surgical site infection. More troubling was the increased mortality in the high-O2 group. 30 day mortality in the 80% oxygen group was 4,4% versus 2,9% in the 30% oxygen group. Now, that’s worrying.

Study
From the PROXI-trial, it would seem high O2-concentrations are harmful not only in critical illness but is also harming a ´healthy´ population of elective and emergency laparotomies. So the researchers decided to do a follow up on the PROXI-trial. This time looking at the same patients´ long-term mortality and also to see if some patients were harmed more than others.

Results
A total of 1383 patients were randomised into breathing either 80% or 30% preoperatively and for two hours post-op.

After a median follow-up of 2,3 years
23,2% in the 80% O2 group had died.
18,3% in the 30% O2-group had died

Even more striking was mortality in the abdominal cancer patients, the patients who had abdominal cancer surgery.

33,5% of the cancer patients in the high O2 group were dead at follow-up, compared to 24,6% in the 30% O2group.

Take-home message
There is a possibility for higher inhaled O2-concentrations harming even reasonably healthy (from a critical care perspective) patients. Even if only exposed for a few hours. Cancer patients could be exceptionally susceptible to O2-toxicity.

More reasons to maintain anti-O2 vigilance in theatre, in the ED and in the ICU…

Study lives here
Increased long-term mortality after a high perioperative inspiratory oxygen fraction during abdominal surgery: follow-up of a randomized clinical trial. Meyhoff CS, Jorgensen LN, Wetterslev J, Christensen KB, Rasmussen LS; PROXI Trial Group. Anesth Analg. 2012 Oct;115(4):849-54. Epub 2012 Jul 13.

 

 

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