Same-Day Surgery Reports

Hypothermia during laparoscopy: Effects of warming and humidification of insufflation gas

Author: Girish P. Joshi, MD, MB, FFARCSI, Professor of Anesthesiology and Pain Management, Director of Perioperative Medicine and Ambulatory Anesthesia, University of Texas Southwestern Medical Center at Dallas.

Peer Reviewer: Larry Holtzin, MD, Attending Anesthesiologist, State University of New York, Brooklyn.


The development of "minimally invasive surgery" has revolutionized surgical procedures. The explosive growth of endoscopic procedures has resulted from increasing acceptance of their potential advantages. There is no doubt that such an approach reduces postoperative pain and immobility as a result of small incisions and limited surgical trauma.1 Recovery occurs sooner, hospital stays may be reduced, and there may be an earlier return to normal activities and work. Some procedures (but not all) have become possible on an outpatient basis, where previously a hospital stay of several days was mandatory.1

However, despite the potential advantages, there are also some disadvantages to laparoscopic surgery.1 Operative times may be longer (sometimes substantially so), especially during the learning phase. Endoscopic surgical procedures are associated with significant physiological changes and complications.1 One of the complications that can increase postoperative morbidity and delay recovery is the occurrence of intraoperative hypothermia.2, 3 With more extensive endoscopic procedures being performed on older and sicker patients, as well as on pregnant and pediatric patients, prevention of hypothermia has received significant attention. This article discusses the consequences and prevention of hypothermia during a laparoscopy with emphasis on warming and humidification of insufflation gas.

Perioperative hypothermia has been associated with several metabolic consequences.2, 3 Shivering increases oxygen demand and causes significant patient discomfort.2 In addition, hypothermia increases sympathoadrenal discharge, resulting in peripheral vasoconstriction, increased vascular resistance, and greater perioperative fluid requirements.4 In high-risk patients, a core temperature less than 35ºC is associated with a two- to threefold increase in the incidence of early postoperative ischemia.5 Hypothermia influences the coagulation system by affecting platelet function, the coagulation cascade, and fibrinolysis.6 Hypothermia impairs wound healing and increases the susceptibility to wound infection. Kurz and colleagues reported that perioperative hypothermia is an independent factor that increases the incidence of postoperative surgical infection and increases length of hospital stay. 7 Hypothermia delays drug metabolism and thus increases the duration of action of anesthetic drugs. This increase may delay emergence from general anesthesia, depress cognitive function, and prolong immediate recovery.8 Therefore, maintaining core normothermia can decrease the duration of postanesthesia care unit stay and reduce costs of health care.8 Inadvertent hypothermia, defined as core temperature less than 36ºC, occurs frequently in patients undergoing open abdominal surgery. During general anesthesia, patients become hypothermic because their ability to regulate core temperature by means of behavioral and shivering responses is abolished, and nonshivering thermogenesis is ineffective.3 Vasodilatation from anesthetic drugs results in heat loss to the cool, ambient environment of the operating room. In addition, there is heat loss from the exposed abdominal cavity and its contents. Redistribution of heat from the warm core thermal compartment to cooler peripheral tissues and inhibition of normal thermoregulatory heat production and retention mechanisms contribute to hypothermia.9, 10 Furthermore, the use of room temperature irrigation fluid further increases heat loss.11

Generally, it is expected that the degree of hypothermia during a closed procedure such as laparoscopy would be less than that occurring during an open procedure because the abdominal contents are not exposed to the atmosphere. However, hypothermia commonly occurs during a laparoscopic procedure.12-14 These observations are supported by studies investigating the heat loss caused by unheated insufflation gas15, 16 and irrigation fluid.11 Furthermore, the degree of hypothermia during a laparoscopic procedure is similar to that during an open procedure.16-20 Luck and colleagues compared the temperature change between patients undergoing open and laparoscopic colorectal surgery.19 The median operating times were 150 minutes (range 90-240 minutes) for open procedures and 180 minutes (range 60-285 minutes) for laparoscopic procedures. The investigators found that the incidence of hypothermia in the two groups was similar.19

It is postulated that heat loss during laparoscopy occurs mainly by convection (i.e., the loss of heat due to flows of a fluid [liquid or gas], when it circulates through a surface at a different temperature). The potential for heat loss during laparoscopic procedures is considerable with dry carbon dioxide (CO2), exiting the cylinder at 21ºC, being insufflated into a peritoneal cavity with a surface area similar to the external body surface of 1-2 m2. Ott estimated a 0.3ºC drop in core temperature resulted from every 50 liters of CO2 insufflated.21 With more prolonged laparoscopic procedures and larger volumes of gas exchanged through the patient, the potential for hypothermia increases.12, 22 Most advanced laparoscopic procedures (e.g., colorectal or esophageal procedures) need longer operating times and frequently require large gas flows because of significant leaks caused by the use of multiple large ports, frequent insertion and removal of laparoscopic instruments, and aspiration of gas during the suction of blood and electrocautery smoke, which increases the potential for heat loss. Thus, it is possible that warming and humidifying the gas prior to insufflation may prevent hypothermia.21

Stewart and colleagues18 compared the degree of hypothermia in patients undergoing open and laparoscopically assisted colorectal surgery with a standardized warming protocol but without any warming or humidification of the insufflation gas. The warming protocol included maintenance of operating room temperature at 22ºC, use of a standard circle system with a respiratory humidifier for anesthesia, warming of intravenous fluids to 37ºC, and use of an upper body forced air blanket at 40ºC placed over upper limbs, trunk, and face. Despite high insufflation volumes (mean 230 L, range 60-500 L) and prolonged operating times (median 180 minutes), there was no difference in the degree of hypothermia between the two groups.18 Only 10% of the patients had temperatures below 35ºC at the completion of the procedure, and the average drop in temperature was less than 0.5ºC across all cases. Although there was no difference in temperature drop between the open and laparoscopic approaches, a significant association was found between temperature loss and duration of surgery, which suggests that convective heat losses during laparoscopic procedures are similar to the evaporative and radiant losses during an open procedure.18 Furthermore, the authors emphasized that routine measures, including forced-air warming, should be used to prevent hypothermia during extensive laparoscopic procedures.

With initial reports suggesting that warming insufflation gas may decrease the incidence of hypothermia, commercial insufflators providing heated gas have become available. Cooling of the CO2 delivered to the patient can be prevented by application of heat at the gas regulator using a heating element. With the heater element activated, the temperature of the regulator could be set at 45ºC, and the temperature of the CO2 as it exits the insufflator at a flow rate of 10 L/min could reach approximately 30ºC. However, the clinical advantage of warming insufflation gas is being questioned.

Controlled animal studies have determined that the physiologic impact of warm gas insufflation is minimal.23 Using an animal model, Bessell and associates15 showed that insufflation of CO2 gas at high-flow rates over a prolonged period of time results in a significant fall in core temperature. CO2 is in the liquid form in the cylinders and is under pressure. When it is released to atmospheric pressure to be insufflated, it is converted to a gaseous form. This change from liquid to gas results in cooling of the gas. However, the insufflation of warm gas does not confer any protection against changes in core temperature. The lack of any advantage of heating the insufflation gas suggests that the heat required to warm the cold gas to body temperature is small and that the cause of intraoperative hypothermia may not be related to heat loss from gas flow. Other clinical studies have also shown the that the use of warmed CO2, particularly during laparoscopic procedures of short duration (median times 60 minutes), has no clinical benefit.24- 25 A study comparing the incidence of hypothermia in patients undergoing laparoscopic and open cholecystectomy found no difference in temperature loss between the two approaches.16 The mean operating time was 94 minutes (range 67-130 minutes) for the laparoscopy group and 74 minutes (range 46-120 minutes) for the open group. The gas flow was limited to less than 3.5 L/min. These investigators also observed a trend toward significant hypothermia with longer cases. They concluded that it was unnecessary to warm insufflated gas for laparoscopic procedures of short or medium duration.16

Interestingly, Nelskyla and colleagues found that the core temperature decrease was greater in the patients receiving heated gas than in those receiving cold gas.26 Similar observations have been reported by other investigators.18, 27 This paradox may be related to the fact that less energy is required for the saturation of water vapor at 24ºC than at 37ºC, because fewer molecules are vaporized. Therefore, most of the hypothermic effect may be because more latent heat is required to saturate the warm insufflated gas, which can be minimized by humidification of the gas.28 However, Biegner and colleagues found that insufflation of dry CO2 for extended periods does not result in significant fluid loss.29 It is now well accepted that warming (without humidification) of insufflation gas does not prevent a decrease in body temperature and is thus unnecessary during laparoscopy.

Insufflation of dry (nonhumidified) gas creates a potential for insensible water loss through transfer of water vapor to the gas in the peritoneal cavity. It is suggested that this evaporative heat loss is primarily responsible for hypothermia during laparoscopy. In addition, tissue surface super-cooling from the jet stream of insufflated gas can lead to tissue drying and damage. Therefore, heating and hydrating the gas to a physiologic condition may prevent hypothermia and tissue desiccation.30

In a pig model, changes in core temperature were evaluated over a three-hour operative period using high flow CO2 insufflation in three groups: controls (not gas-insufflated), insufflation with cool gas, and insufflation with warm, humidified gas.31 The investigators observed that insufflation with cool CO2 resulted in a drop in the core temperature by 1.8ºC as compared with only 0.6ºC decrease in the other two groups. They also determined that a 1.5ºC lower temperature would occur due to water evaporation alone in pigs insufflated with the cool dry CO2.31 These investigators concluded that the majority of heat lost during laparoscopy was due to water evaporation and that this effect could be prevented with heated humidified gas insufflation.31

In another study, patients undergoing laparoscopic cholecystectomy were randomized to receive either heated (34-37ºC) and humidified (88%) CO2 insufflation gas or cool (21-25ºC) CO2 insufflation with a humidity of 0-5%.32 The investigators reported that the drop in mean core temperature during the surgical procedure in the two groups was similar. They postulated that the lack of heat-preserving effect of humidified gas insufflation probably was due to the short (40-45 min) duration of the procedure.32 No adverse effects from the heated humidification of the CO2 gas were observed. Another study evaluated the effects of preconditioning of insufflation gas by filtering, heating, and hydrating on intraoperative hypothermia.

The authors found that preconditioning of insufflating gas reduced intraoperative hypothermia, length of stay in the postanesthesia care unit, and operative pain.33 Insufflated gas is humidified by incorporating a humidification chamber in the insufflator tubing line. It is suggested that any additional cost of humidifying the insufflation gas should be minimal, and if postoperative pain and time to return to normal activities is reduced, the small additional cost may be compensated.33 However, larger clinical trials comparing heated humidified CO2 and cool CO2 insufflation in longer laparoscopic procedures are necessary.

Pain after Laparoscopy

Although it is generally accepted that pain after laparoscopy is less than that after an open procedure, it is not completely abolished. Patients frequently complain of severe discomfort, which may delay discharge or increase the incidence of unanticipated hospital admission. One of the factors affecting postlaparoscopy pain is the humidity and temperature of the insufflated gas.34 It is suggested that insufflation with warmed gas can significantly reduce postlaparoscopy pain, particularly diaphragmatic and shoulder-tip pain.35-36 A randomized, controlled study observed significant pain reduction in patients receiving body-temperature insufflation gas compared with those receiving standard gas insufflation.37 Although the exact mechanism of reduced postoperative pain with the used of humidified and warmed gas is not known, it is possible that tissue injury from the cold and dry CO2 might be prevented. In contrast, Slim and colleagues found that warming the insufflation gas does not reduce — and actually can increase — shoulder-tip and subcostal pain after laparoscopic procedures.38 These authors also found that intraperitoneal temperatures did not increase with warming insufflation gas.38 Similarly, Saad and associates did not observe any reduction in pain after laparoscopic cholecystectomy in patients receiving warmed insufflation gas.25

A recent study by Mouton and colleagues reported that humidification and warming of insufflated gas reduced pain and showed a trend toward less need for analgesics after laparoscopic cholecystectomy, as well as an early return to normal activities and work; however, these differences did not reach statistical significance.32 Larger studies will be required to show any significant benefits of humidified insufflation gas.

The common techniques employed to reduce intraoperative hypothermia include raising ambient (operating room) temperature to 24-26ºC, humidification of inspired anesthetic gases with heat and moisture exchange filters, warming of intravenous fluids, use of warming blankets and mattresses, and use of forced-air warming devices.


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17. Makinen M-T. Comparison of body temperature changes during laparoscopic and open cholecystectomy. Acta Anaesthesiol Scand 1997; 41:736-740.

18. Stewart BT, Stitz RW, Tuch MM, et al. Hypothermia in open and laparoscopic colorectal surgery. Dis Colon Rectum 1999; 42:1,292-1,295.

19. Luck AJ, Moyes D, Maddern GJ, et al. Core temperature changes during open and laparoscopic colorectal surgery. Surg Endosc 1999; 13:480-483.

20. Holland AJA, Ford WDA. The influence of laparoscopic surgery on perioperative heat loss in infants. Pediatr Surg Int 1998; 13:350-351.

21. Ott DE. Correction of laparoscopic insufflation hypothermia. J Laparoendosc Surg 1991; 1:183-186.

22. Seitzinger MR, Dufgeon LS. Decreasing the degree of hypothermia during prolonged laparoscopic procedures. J Reprod Med 1993; 38:511-513.

23. Bessell JR, Maddern GJ. Influence of gas temperature during laparoscopic procedures. In: Rosenthal PJ, Fredman RC, Phillips EH (eds). The Pathophysiology of the Pneumoperitoneum. New York: Springer; 1997, 18-27.

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29. Biegner AR, Anderson D, Olson RL, et al. Quantification of insensible water loss associated with insufflation of nonhumidified CO2 in patients undergoing laparoscopic surgery. J Laparoendosc Adv Surg Tech 1999; 9:325-329.

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32. Mouton WG, Bessell JR, Millard SH, et al. A randomized controlled trial assessing the benefit of humidified insufflation gas during laparoscopic surgery. Surg Endosc 1999; 13:106-108.

33. Ott DE, Reich H, Love B, et al. Reduction of laparoscopic-induced hypothermia, postoperative pain and recovery room length of stay by pre-conditioning gas with the Insuflow device: A prospective randomized controlled multi-center study. J Soc Laparoendosc Surgeons 1998; 2:321-329.

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35. Semm K, Arp WD, Trappe M, et al. Pain reduction after pelvi/laparoscopic interventions by insufflation of CO2 gas at body temperature (Flow-Therme). Geburtshilfe Frauenheilkd 1994; 54:300-304.

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Physician CME questions

CME objective: After participating in this CME activity, the participant will be able to identify a true statement regarding hypothermia during a laparoscopic procedure.

1. Which of the following statements is true of hypothermia during a laparoscopic procedure?

A. It is more than that during a open abdominal procedure.

B. It is less than that during a open abdominal procedure.

C. It can always be reduced by warming the insufflated gas.

D. It can occur to the same degree as during an open abdominal procedure.

2. Controlled animal studies have determined that the physiologic impact of warm gas insufflation is:

A. nonexistent

B. minimal

C. significant

3. Nelskyla and colleagues found that the core temperature decrease in the patients receiving heated gas compared how with those receiving cold gas?

A. The core temperature decrease was greater in the patients receiving heated gas than in those receiving cold gas.

B. The core temperature decrease was the same in the patients receiving heated gas than in those receiving cold gas.

C. The core temperature decrease was less in the patients receiving heated gas than in those receiving cold gas.