Influence of perioperative oxygen fraction on pulmonary function after abdominal surgery: a randomized controlled trial.

BACKGROUND: A high perioperative inspiratory oxygen fraction (FiO2) may reduce the frequency of surgical site infection. Perioperative atelectasis is caused by absorption, compression and reduced function of surfactant. It is well accepted, that ventilation with 100% oxygen for only a few minutes is associated with significant formation of atelectasis. However, it is still not clear if a longer period of 80% oxygen results in more atelectasis compared to a low FiO2.Our aim was to assess if a high FiO2 is associated with impaired oxygenation and decreased pulmonary functional residual capacity (FRC). METHODS: Thirty-five patients scheduled for laparotomy for ovarian cancer were randomized to receive either 30% oxygen (n = 15) or 80% oxygen (n = 20) during and for 2 h after surgery. The oxygenation index (PaO2/FiO2) was measured every 30 min during anesthesia and 90 min after extubation. FRC was measured the day before surgery and 2 h after extubation by a rebreathing method using the inert gas SF6. RESULTS: Five min after intubation, the median PaO2/FiO2 was 69 kPa [53-71] in the 30%-group vs. 60 kPa [47-69] in the 80%-group (P = 0.25). At the end of anesthesia, the PaO2/FiO2 was 58 kPa [40-70] vs. 57 kPa [46-67] in the 30%- and 80%-group, respectively (P = 0.10). The median FRC was 1993 mL [1610-2240] vs. 1875 mL [1545-2048] at baseline and 1615 mL [1375-2318] vs. 1633 mL [1343-1948] postoperatively in the 30%- and 80%-group, respectively (P = 0.70). CONCLUSION: We found no significant difference in oxygenation index or functional residual capacity between patients given 80% and 30% oxygen for a period of approximately 5 hours. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00637936.

Rational use of oxygen in medical disease and anesthesia.

PURPOSE OF REVIEW: Supplemental oxygen is often administered during anesthesia and in critical illness to treat hypoxia, but high oxygen concentrations are also given for a number of other reasons such as prevention of surgical site infection (SSI). The decision to use supplemental oxygen is, however, controversial, because of large heterogeneity in the reported results and emerging reports of side-effects. The aim of this article is to review the recent findings regarding benefits and harms of oxygen therapy in anesthesia and acute medical conditions. RECENT FINDINGS: Large randomized trials have not found significant reductions in SSI with 80% oxygen during and after abdominal surgery and cesarean section. There is no documented benefit of hyperbaric oxygen treatment for acute ischemic stroke, and there is emerging data to suggest increased mortality with normobaric supplemental oxygen for myocardial infarction without heart failure. Survival and neurologic outcome seem to be adversely affected by hyperoxia in patients with return of spontaneous circulation after cardiac arrest. SUMMARY: The benefits of supplemental oxygen are not yet confirmed, and new findings suggest that potential side-effects should be considered if the inspired oxygen concentration is increased above what is needed to maintain normal arterial oxygen saturation.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.