Local insufflation of warm humidified CO2increases open wound and core temperature during open colon surgery: a randomized clinical trial.

BACKGROUND: The open surgical wound is exposed to cold and dry ambient air resulting in heat loss through radiation, evaporation, and convection. Also, general and neuraxial anesthesia decrease the patient's core temperature. Despite routine preventive measures mild intraoperative hypothermia is still common and contributes to postoperative morbidity and mortality. We hypothesized that local insufflation of warm fully humidified CO(2) would increase both the open surgical wound and core temperature. METHODS: Eighty-three patients undergoing open colon surgery were equally and parallelly randomized to either standard warming measures including forced-air warming, warm fluids, and insulation of limbs and head, or to additional local wound insufflation of warm (37°C) humidified (100% relative humidity) CO(2) at a laminar flow (10 L/min) via a gas diffuser. Wound surface and core temperatures were followed with a heat-sensitive infrared camera and a tympanic thermometer. RESULTS: The mean wound area temperature during surgery was 31.3°C in the warm humidified CO(2) group compared with 29.6°C in the control group (P < 0.001, 95% confidence interval [CI], 1.2°C to 2.3°C). Also, the mean wound edge temperature during surgery was 30.1°C compared with 28.5°C in the control group (P < 0.001, 95% CI, 0.2°C to 0.7°C). Mean core temperature before start of surgery was similar with 36.7°C ± 0.5°C in the warm humidified CO(2) group versus 36.6°C ± 0.5°C in the control group (95% CI, 0.4 to -0.1°C). At end of surgery, the 2 groups differed significantly with 36.9 ± 0.5°C in the warm humidified CO(2) group versus 36.3 ± 0.5°C in the control group (P < 0.001, 95% CI, 0.38°C to 0.82°C). Moreover, only 8 patients of 40 in the warm humidified CO(2) group had a core temperature <36.5°C (20%, 95% CI, 7 to 33%), whereas in the control group this was the case in 24 of 39 (62%, 95% CI, 46% to 78%, P = 0.001) patients (difference of the percentages between the groups 42%, 95% CI, 22% to 61%, P < 0.001). With a cutoff at <36.0°C none of the patients in the warm humidified CO(2) group compared with 7 patients (18%, 95% CI, 5% to 31%, P = 0.005) in the control group was hypothermic at end of surgery (difference of the percentages between the groups 18%, 95% CI, 6% to 30%, P = 0.005). The median (25th/75th percentile) operating time was 181.5 (147.5/288) minutes in the warm humidified CO(2) group versus 217 (149/288) minutes in the control group (P = 0.312). Clinical variables did not show any significant differences between the groups. CONCLUSIONS: Insufflation of warm fully humidified CO(2) in an open surgical wound cavity increases surgical wound and core temperatures and helps to maintain normothermia.

Intraoperative local insufflation of warmed humidified CO2 increases open wound and core temperatures: a randomized clinical trial.

BACKGROUND: The open surgical wound is exposed to cold dry ambient air, resulting in substantial heat loss through radiation, evaporation, and convection. At the same time, anesthesia decreases the patient's core temperature. Despite preventive measures, mild intraoperative hypothermia has been associated with postoperative morbidity. We hypothesized that local insufflation of warmed humidified carbon dioxide (CO(2)) would maintain wound and core temperature. METHODS: Eighty patients undergoing open colon surgery were randomized to standard warming measures, or to additional local wound insufflation of warmed (30 °C) humidified (93 % rH) CO(2) via a gas diffuser. Surface temperature of the open abdominal wound was measured with a heat-sensitive infrared camera, and core temperature was measured with an ear thermometer. RESULTS: Mean operative time was 219 ± 104 and 205 ± 85 min in the CO(2) group and the control group, respectively (p = 0.550). Clinical variables did not differ significantly between the groups. The median wound area and wound edge temperatures were 1.2 °C (p < 0.001) and 1.0 °C (p = 0.002) higher in the CO(2) group, respectively, than in the control group. The mean core temperature after intubation was the same (35.9 °C) in both groups, but at end of surgery core temperature in the two groups differed, with a mean of 36.2 ± 0.5 °C in the CO(2) group and a mean of 35.8 ± 0.5 °C in the control group (p = 0.003). CONCLUSIONS: Insufflation of warmed, humidified CO(2) in an open surgical wound cavity prevents intraoperative decrease in surgical wound temperature as well as core temperature.

Positive end-expiratory pressure redistributes regional blood flow and ventilation differently in supine and prone humans.

BACKGROUND: Animal studies have demonstrated an interaction between posture and the effect of positive end-expiratory pressure (PEEP) on regional ventilation and lung blood flow. The aim of this study was to explore this interaction in humans. METHODS: Regional lung blood flow and ventilation were compared between mechanical ventilation with and without PEEP in the supine and prone postures. Six normal subjects were studied in each posture. Regional lung blood flow was marked with In-labeled macroaggregates and ventilation with Technegas (Tc). Radiotracer distributions were mapped using quantitative single-photon emission computed tomography. RESULTS: In supine subjects, PEEP caused a similar redistribution of both ventilation and blood flow toward dependent (dorsal) lung regions, resulting in little change in the V/Q correlation. In contrast, in prone subjects, the redistribution toward dependent (ventral) regions was much greater for blood flow than for ventilation, causing increased V/Q mismatch. Without PEEP, the vertical ventilation-to-perfusion gradient was less in prone postures than in supine, but with PEEP, the gradient was similar. CONCLUSIONS: During mechanical ventilation of healthy volunteers, the addition of PEEP, 10 cm H2O, causes redistribution of both lung blood flow and ventilation, and the effect is different between the supine and prone postures. Our results suggest that the addition of PEEP in prone might be less beneficial than in supine and that optimal use of the prone posture requires reevaluation of the applied PEEP.

CO2 insufflation influences the temperature of the open surgical wound.

In open surgery, heat is lost due to radiation and evaporation through the wound. Hypothermia causes tissue hypoxia and impairs various cellular immune functions that increases the risk for postoperative wound infections and delayed wound healing. The patient's body is usually well protected with heating arrangements, but the open wound is left unprotected and until now no practical method has been available to protect it thermically. We therefore investigated if insufflation of an open surgical wound with carbon dioxide would affect wound temperature. In 10 patients undergoing cardiac surgery, the sternotomy wound was insufflated with dry, room temperature carbon dioxide via a gas diffuser for 2 minutes. A heat-sensitive camera measured the wound temperature before, during, and after insufflation. Exposure to carbon dioxide increased the median temperature of the whole wound by 0.5 degrees C (p=0.01). The temperature of the area distant to the diffuser increased by 1.2 degrees C (p<0.01) whereas in the area close to the diffuser it decreased by 1.8 degrees C (p<0.01). In conclusion, short-term insufflation of dry room temperature carbon dioxide in an open wound increases the surface temperature significantly. Although a small increase, it may reduce the incidence of postoperative wound infections in the future.

A novel molecule with peripheral opioid properties: the effects on hypercarbic and hypoxic ventilation at steady-state compared with morphine and placebo.

Frakefamide (FF), is a new peripherally acting mu-opioid receptor agonist. The aim of this double-blind, randomized, double-dummy, four-way, crossover study was to investigate FF effects on hypercarbic and hypoxic ventilation at steady-state after a 6-h infusion. We compared the effect with 2 clinical doses of morphine (M-small and M-large) and placebo in 12 healthy men. The subjects received 1.22 mg/kg of FF, 0.44 mg/kg of M-large, and 0.11 mg/kg of M-small. Sodium chloride 9 mg/mL was used as placebo. Ventilation was studied by pneumotachography and in-line capnography. There were no ventilatory effects caused by FF or placebo. As expected, large doses of morphine influenced both hypercarbic and hypoxic ventilatory responses. We conclude that there were no signs of central respiratory depression caused by FF after 6 h of constant infusion, which supports a peripheral action of the compound. However, morphine caused a dose-dependent central depression during the hypercarbic ventilatory response and a mild depression of hypoxic ventilatory response.

A novel molecule (frakefamide) with peripheral opioid properties: the effects on resting ventilation compared with morphine and placebo.

In animal models frakefamide (FF) is a potent analgesic that acts as a peripheral active mu-selective receptor agonist. In this double-blind, randomized, double dummy four-way crossover study in 12 healthy male subjects, we investigated the effects on resting ventilation of FF and 2 dose levels of morphine compared with placebo. Each drug was infused for 6 h. The subjects received 1.22 mg/kg FF, 0.43 mg/kg morphine (M-large), and 0.11 mg/kg morphine (M-small). Sodium chloride 9 mg/mL was used as placebo. Ventilation was measured by pneumotachography and inline capnography. Blood was collected and plasma concentrations of FF and morphine and its metabolites were analyzed. Within 15 min after administration of FF all subjects complained of a transient myalgia, which disappeared within 30 min. At target measurement (335 min), there were no differences in tidal volume among the groups. Respiratory rates were, however, slower in the two M-groups (P < 0.05 in M-small and P < 0.001 in M-large) compared with FF and placebo. Minute volume was significantly less in the M-large group compared with the FF (P < 0.01) and placebo (P < 0.01) groups. This difference was reflected by an elevated ETco(2) in the M-large group (P < 0.01). We conclude that, during resting ventilation, FF, unlike morphine, did not cause central respiratory depression. This suggests that FF has only peripheral mu-opioid agonist activity in humans.