Warm humidification for prevention of hypothermia during liver transplantation

The intervention for this study is the Humigard (Registered Trademark) system (Fisher and Paykel Healthcare, Auckland, New Zealand), which is a heat delivery system that allows insufflation of warm humidified CO2 into the open wound cavity. The device works by delivering dry medical CO2 is at a flow rate of 10 L/min and a pressure of 4.5 bar from a medical pressurized gas cylinder (AGA gas AB, Stockholm, Sweden) via a polyvinyl chloride tube into an open surgery humidification system. It consists of a bacterial filter, and a humidification chamber filled with sterile water, positioned on a humidifier controller that includes an integrated temperature and flow sensor. The outlet of the humidification chamber is connected to a thermally insulated heated insufflation tube that maintains temperature and humidity of the gas to its outlet. The humidified and warm CO2 enters a gas diffuser (VITA-diffuser (Registered Trademark), Cardia Innovation AB, Stockholm, Sweden) consisting of a polyvinyl chloride tube with polyurethane foam at its end. The cylindrical polyurethane foam tip diverts the gas jet into multiple directions via the many small paths inside the foam. The gas is thus uniformly distributed and the large diffuser surface area greatly reduces the velocity of the outflow. The humidified gas is delivered directly into the surgical wound. The final temperature of the humidified CO2 is 37 degrees Celcius, with a 100% relative humidity. Patients that will be receiving this intervention are adult patients undergoing liver transplantation in university teaching hospital. The sterile device is placed into the open abdominal cavity by the surgeon at commencement of the transplant. The device remains in situ until closure of the surgical wound at completion of surgery. The device settings do not change at any point and the humidification is delivered continuously. In addition to this device, all patients will also receive standard temperature homeostasis. This will include: 1. Pre-warming with a full body warming blanket (Bair Hugger 3M 'Trademark', Model 315) set at 43oC one hour prior to surgery. 2. Ambient operating room temperature set at 21oC 3. Underbody warming blanket (Bair Hugger 3M, Model 637) set at 43oC, placed over a standard operating table. These warming blanket devices will be continued during induction of anaesthesia and during insertion of all invasive monitoring lines, after which the full body warming blanket will be replaced with an intraoperative upper body warming device that covers both upper limbs and face (Bair Hugger 3M 'Trademark', Model 523XL) for the remainder of the case. 4. During the anhepatic phase, ambient operating temperature will be increased to 23oC, with no further adjustments for the remainder of the case. 5. Temperature of all fluids delivered will be via a Belmont (Registered Trademark) Rapid Infuser RI-2 system that will deliver preheated fluids at 42oC.