Supplemental oxygen and surgical site infection: getting to the truth

Surgical site infection (SSI) remains one of the most serious and expensive postoperative complications.¹ Infected patients are twice as likely to need admission to critical care and twice as likely to die.² The primary defence against SSI is oxidative killing by neutrophils, and molecular oxygen is the substrate.³ Resistance to infection is thus a strong function of tissue oxygen partial pressure over the clinical range. One might thus expect that supplemental perioperative oxygen (∼80%) would reduce infection risk when compared with more traditional inspired oxygen concentrations (∼30%) during anaesthesia and surgery. Despite some early evidence supporting the role of supplemental oxygen in reducing the risk of SSI,⁴ there have since been conflicting results from numerous randomized clinical trials. The most compelling data come from the PROXI trial,⁵ a large, multicentre, randomized trial enrolling 1400 patients undergoing abdominal surgery. This trial found no evidence of any beneficial effect of supplemental oxygen; SSI occurred in 131 of 685 patients (19%) receiving 80% oxygen and in 141 of 701 (20%) receiving 30% oxygen [odds ratio 0.94 (95% confidence interval 0.72–1.22), P=0.64]. Indeed, a long-term follow-up study (median 2.3 years after surgery) found poorer survival in the supplemental oxygen group.⁶

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