Inspiratory oxygen fraction and postoperative complications in obese patients: a subgroup analysis of the PROXI trial

Obese patients are at a high risk of postoperative complication, including surgical site infection (SSI). Our aim was to evaluate the effect of a high inspiratory oxygen fraction (80%) on SSI and pulmonary complications in obese patients undergoing laparotomy.

This study was a planned analysis of the obese patients (body mass index ≥ 30 kg/m²) recruited in the Danish multicenter, patient- and observer-blinded, PROXI Trial of 1,400 patients undergoing acute or elective laparotomy. Patients were randomized to receive either 80% or 30% oxygen during and for 2 h after surgery. The primary outcome was SSI within 14 days. Secondary outcomes were atelectasis, pneumonia, and respiratory failure.

Two hundred thirteen patients had a body mass index ≥ 30 kg/m². The median (5-95% range) body mass index was 34 kg/m² (30-44) and 33 kg/m² (30-41) in patients allocated to the 80% and 30% oxygen group. SSI occurred in 32 of 102 (31%) versus 29 of 111 (26%) patients given 80% and 30% oxygen, respectively (odds ratio, 1.29; 95% CI, 0.71-2.34; P = 0.40). In addition, the incidence of pulmonary complications was not significantly different, with atelectasis occurring in 9% versus 6%, pneumonia in 6% versus 5%, and respiratory failure in 8% versus 5% in patients given 80% and 30% oxygen, respectively.

Administration of 80% oxygen, compared with 30% oxygen, did not reduce the frequency of SSI in obese patients. Moreover, no significant association was found between oxygen fraction and the risk of pulmonary complications.