Surgical humidification is the conditioning of insufflation gas with water vapour (humidity) and heat during surgery. Surgical humidification is used to reduce the risk of tissue drying and evaporative cooling.
Laparoscopic surgery humidification
During laparoscopy (laparoscopic surgery or minimally invasive surgery), it is necessary to insufflate the abdominal cavity (i.e. inflate the abdomen like a balloon) with medical-grade carbon dioxide (CO2) to create a viewing and working space for the surgery. The CO2 may be unconditioned, or conditioned with heat, or with humidification and heat. During insufflation, the peritoneum (an extensive delicate membrane that lines the abdominal cavity and covers most of the abdominal organs) is exposed to the CO2.
Unconditioned medical-grade CO2 has virtually no moisture and enters the abdomen at room temperature (19 to 21 °C). The condition of the gas is dry and cold compared to that of the natural physiological state of the peritoneum which is immersed in fluid at body temperature (37 °C). Experimental and clinical investigations have demonstrated that insufflation with unconditioned CO2 causes evaporation of the fluid and drying of the peritoneum, resulting in inflammation and damage to its cells. Clinically, peritoneal injury caused by drying has been linked to post-operative pain, evaporative cooling resulting in a decrease in core temperature and increased risk of intra-operative hypothermia, as well as adhesion formation.
In addition, animal studies have revealed that surgical humidification reduces peritoneal tumor implantation and tumor load  suggesting a possible benefit in cancer patients undergoing abdominal surgery.
Conditioning the CO2 with only heat causes tissue drying. Warmer gas has a greater capacity for evaporation as the gas can hold more water vapor, therefore the tissues will dry faster than when unconditioned gas is used, potentially leading to increased adverse consequences. Conditioning the CO2 with humidity, in combination with heat, has been shown to decrease peritoneal damage by reducing the capacity of CO2 to carry moisture away from the tissue. Temperature loss during surgery, due to tissue drying, can be prevented by adequately humidifying and heating the CO2.
Open surgery humidification
During open surgery the surgeon exposes the peritoneal cavity to the ambient air. Exposure to ambient air results in evaporation and cooling. Current studies have shown that the use of surgical humidification during open abdominal surgery (laparotomy) have warmer core body temperatures and reduced risk of operative hypothermia. As with any operation, maintaining patient normothermia is a critical process to prevent surgical site infections, additional respiratory distress and surgical bleeding.
Methods of surgical humidification
CO2 for laparoscopic surgery is conditioned with humidity and heat via devices such as the HumiGard™ Surgical Humidification System (Fisher & Paykel Healthcare Ltd, Auckland, New Zealand) and the Insuflow® (LEXION Medical, St Paul, USA). Such devices are positioned between the gas source and the patient interface. CO2 for open surgery has been conditioned to date with the HumiGard™ Surgical Humidification System. These devices aim to condition the gas to body temperature and 100% Relative Humidity (although the exact temperature and humidity may vary slightly according to the manufacturer).
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