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Background: Animal studies have shown that peritoneal injury can be minimized by insufflating the abdominal cavity with warm humidified carbon dioxide gas.Methods: A single-blind RCT was performed at a tertiary colorectal unit. Inclusion criteria were patient aged 18 years and over undergoing open elective surgery. The intervention group received warmed (37 ∘ C), humidified (98 per cent relative humidity) carbon dioxide (WHCO 2 group). Multiple markers of peritoneal inflammation and oxidative damage were used to compare groups, including cytokines and chemokines, apoptosis, the 3-chlorotyrosine/native tyrosine ratio, and light microscopy on peritoneal biopsies at the start (T 0 ) and end (T end ) of the operation. Postoperative clinical outcomes were compared between the groups.Results: Of 40 patients enrolled, 20 in the WHCO 2 group and 19 in the control group were available for analysis. A significant log(T end /T 0 ) difference between control and WHCO 2 groups was documented for interleukin (IL) 2 (5⋅3 versus 2⋅8 respectively; P = 0⋅028) and IL-4 (3⋅5 versus 2⋅0; P = 0⋅041), whereas apoptosis assays documented no significant change in caspase activity, and similar apoptosis rates were documented along the peritoneal edge in both groups. The 3-chlorotyrosine/tyrosine ratio had increased at T end by 1⋅1-fold in the WHCO 2 group and by 3⋅1-fold in the control group. Under light microscopy, peritoneum was visible in 11 of 19 samples from the control group and in 19 of 20 samples from the WHCO 2 group (P = 0⋅006). The only difference in clinical outcomes between intervention and control groups was the number of days to passage of flatus (2⋅5 versus 5⋅0 days respectively; P = 0⋅008). Conclusion:The use of warmed, humidified carbon dioxide appears to reduce some markers related to peritoneal oxidative damage during laparotomy. No difference was observed in clinical outcomes, but the study was underpowered for analysis of surgical results. Registration number: NCT02975947 (www .ClinicalTrials.gov/). Effect of humidified carbon dioxide insufflation in open laparotomy for colorectal resectionAllocated to control group n = 20 Received allocated intervention n = 19 Did not receive allocated intervention n = 1 Withdrew due to pulmonary embolism n = 1Allocated to WHCO 2 group n = 20 Received allocated intervention n = 20 Did not receive allocated intervention n = 0 Peritoneal samples taken n = 20Lost to follow-up n = 0Analysed n = 20 Excluded from analysis n = 0 Analysed n = 19 Excluded from analysis n = 0Lost to follow-up n = 0 WHCO 2 , warmed, humidified carbon dioxide.

PurposeDuring a laparotomy, the peritoneum is exposed to the cold, dry ambient air of the operating room (20℃, 0%–5% relative humidity). The aim of this review is to determine whether the use of humidified and/or warmed CO2 in the intraperitoneal environment during open or laparoscopic operations influences postoperative outcomes.MethodsA review was performed in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The PubMed, OVID MEDLINE, Cochrane Central Register of Controlled Trials and Embase databases were searched for articles published between 1980 and 2016 (October). Comparative studies on humans or nonhuman animals that involved randomized controlled trials (RCTs) or prospective cohort studies were included. Both laparotomy and laparoscopic studies were included. The primary outcomes identified were peritoneal inflammation, core body temperature, and postoperative pain.ResultsThe literature search identified 37 articles for analysis, including 30 RCTs, 7 prospective cohort studies, 23 human studies, and 14 animal studies. Four studies found that compared with warmed/humidified CO2, cold, dry CO2 resulted in significant peritoneal injury, with greater lymphocytic infiltration, higher proinflammatory cytokine levels and peritoneal adhesion formation. Seven of 15 human RCTs reported a significantly higher core body temperature in the warmed, humidified CO2 group than in the cold, dry CO2 group. Seven human RCTs found lower postoperative pain with the use of humidified, warmed CO2.ConclusionWhile evidence supporting the benefits of using humidified and warmed CO2 can be found in the literature, a large human RCT is required to validate these findings.