Evaluation of carbon dioxide insufflation into the open surgical wound : influence on wound temperature, core temperature, and postoperative outcome

Sammanfattning: Introduction: When the internal organ tissues are abruptly exposed to the relative cold and dry ambient air during open surgery, body heat is lost through radiation, evaporation, and convection. Also general and neuraxial anesthesia contributes to a decrease in core temperature, mainly due to a shift of the threshold for thermoregulatory defense mechanism toward lower temperatures. It is well known that perioperative hypothermia is disadvantageous for the patient, since it increases the risk of surgical wound infections, blood loss, morbid cardiac events and postoperative shivering. Guidelines to keep the patient warm during surgery are today common practice, but despite routine preventive measures, mild intraoperative hypothermia is still common and contributes to postoperative morbidity and mortality. The aim of this thesis was to investigate if local insufflation of CO2 could increase both the open surgical wound temperature and core temperature, and affect postoperative outcome. Methods: I. In 10 patients undergoing cardiac surgery, the sternotomy wound was insufflated with dry, room-tempered CO2 via a gas diffuser for two minutes. A heat-sensitive camera measured the wound temperature before, during and after insufflation. II. 80 patients undergoing open colon surgery were randomized to either standard warming measures (n=39) or additional local wound insufflation (n=41) of warmed (30°C) humidified (93% rH) CO2 via a gas diffuser. A heat-sensitive camera measured the wound temperature and an ear thermometer measured the core temperature. III. 83 patients undergoing open colon surgery were randomized to either standard warming measures (n=39) or additional local wound insufflation (n=40) of warmed (37°C) humidified (100% rH) CO2 via a gas diffuser. A heat- sensitive camera measured the wound temperature and an ear thermometer measured the core temperature. IV. This is a post hoc retrospective study of study II and III, where patients were randomized to warmed humidified CO2 (n=80) or not (n=78). Results: I. Exposure to dry CO2 increased the median temperature of the whole wound by 0.5°C (p=0.01). The temperature of the area distant to the diffuser increased by 1.2°C (p<0.01) whereas in the area close to the diffuser it decreased by 1.8 °C (p<0.01). II. The median wound area and wound edge temperatures were 1.2oC (p<0.001) and 1.0oC (p=0.002) higher in the CO2 group, respectively, than in the control group. The mean core temperature after intubation was the same (35.9oC) in both groups, but at end of surgery the two groups differed with a mean of 36.2 ± 0.5 oC in the CO2 group and 35.8±0.5oC in the control group (p=0.003). III. The mean wound area temperature during surgery was 31.3oC in the CO2 group compared with 29.6oC in the control group (p<0.001). Also, the mean wound edge temperature during surgery was 30.3oC compared with 28.5oC in the control group (p<0.001). Mean core temperature before start of surgery was similar with 36.7 ± 0.5oC in the CO2 group versus 36.6 ± 0.5oC in the control group. At end of surgery the two groups differed significantly with 36.9 ± 0.5oC in the CO2 group versus 36.3 ± 0.5oC in the control group (p<0.001). IV. A multivariate analysis adjusted for age (p=0.001) and cancer (p=0.165) showed that the larger the temperature difference between final core temperature and wound edge temperature, the lower the overall survival rate (p=0.050). A lower end-of-operation wound edge temperature was negatively associated with mortality (OR=0.80, 95%CI=0.68- 0.95, P=0.011), whereas age (10-year increase, OR=1.78, 95% CI=1.37-2.33, P<0.001) and cancer (OR=8.1, 95% CI=1.95-33.7, P=0.004) were positively associated with mortality. Conclusions: The major finding of this thesis is that insufflation of dry room-tempered CO2 with a gas diffuser increases the average surface temperature in an open wound cavity. Insufflation of warmed humidified CO2 in an open surgical wound cavity results in significant increases of the surgical wound temperature as well as the core temperature. Insufflation of warmed fully humidified CO2 in an open surgical wound cavity increases surgical wound and core temperatures, and helps to maintain normothermia. A small end-of-operation temperature difference between final core and final wound edge temperature was positively associated with patient survival in open colon surgery, and a lower end-of-operation wound edge temperature was negatively associated with mortality.