Follow up on Surigical Site infection and the anesthesiologist: tissue oxygen tension

Nearly 6 months ago an article was published in JAMA commonly known as the PROXI trial (1). In short, this was an RCT of 1400 patients undergoing acute or elective laparotomy. Patients received 80% or 30% oxygen in air both during and for 2 hours following surgery. The study looked at SSI within 14 days after surgery. They also considered atelectasis, pneumonia, respiratory failure, and mortality. They found an incidence of SSI of around 20% in both groups and concluded that high FiO2, was not beneficial in laparotomy. On the surface then, clinicians may be happy to use low FiO2 in patients undergoing laparotomy and believe that they are doing no harm. While this may be true, Dr. Hopf, author of the a notable study sited in my original post on SSI and the anesthesiologist, notes a few problems in the current study.
In the accompanying editorial she notes the following:
1) While wound oxygen levels can be raised by high FiO2, and this can reduce infection, it is only possible in the absence of vasoconstriction. This requires normothermia and meticulous fluid management as only slight hypovolemia may lead to vasoconstriction.
2) In the PROXI trial anesthesiologists were free to practice within the standard for their area. Unfortunately, fluid volumes administered were much lower than those administered in the trial by Greif et al. where SSI rates were lowered by high FiO2 (2).
3) In some cases mormothermia was not maintained with temperatures documented as low as 35C in a few patients.
4) Wound oxygen tension was not measured and therefore, it is unknown whether the high FiO2 group benefited from the intervention. The point is, it is well recognized that high FiO2 is not therapeutic, but as it often leads to high tissue O2 tension then thusly wound oxygen tension, it may be beneficial.
5) The PROXI trial found no evidence that high FiO2 increase the risk of pulmonary complications (atelectasis or pneumonia).

In summary, the PROXI trials does add information to the debate regarding FiO2 and SSI. But it underscores the subtleties that we deal with in anesthesia. Just because you are delivering an FiO2 of 100%, does not mean that the tissues are receiving this oxygen. Optimizing the vascular tension is also of prime importance.

1) Meyhoff CS, Wetterslev J, Jorgensen LN, et al; for the PROXI Trial Group. Effect of high perioperative oxygen fraction on surgical site infection and pulmonary complications after abdominal surgery. the PROXI randomized clinical trail. JAMA. 2009;302(14);1543.
2) Greif R, Akca O, Horn EP, Kurz A, Sessler DI; Outcomes Research Group. Supplemental peroperative oxygen to reduce the incidence of surgical-wound infection. N Engl J Med. 2000;342(3):161.