Unintentional perioperative hypothermia as a risk factor for various complications - including infections

lek. Maciej Szmydt

mgr Karolina Motyssek

Skamex Sp. z o.o. Sp.k.



Unintentional perioperative hypothermia represents a significant clinical problem affecting over half of operated patients. Complications associated with it prolong hospital stay and increase treatment costs. International guidelines emphasize the importance of actively warming patients. The use of fluid warming systems in perioperative care significantly reduces the risk of perioperative hypothermia complications, including infections.


Summary in English:

Inadvertent perioperative hypothermia pose a serious clinical problem that apply to over half of all patients under surgical treatment. Any medical complications associated to this phenomenon extend the hospital length of stay and at the same time increase costs of treatment. International guidelines emphasise the significance of active patients’ warming. Usage of fluids warming systems, in case of perioperative care, substantially decreases the risk of perioperative hypothermia complications including infections.



hypothermia ➧ inadvertent perioperative hypothermia ➧ infections ➧ surgical site infection (SSI) ➧ fluid warming device ➧ guidelines hypothermia ➧ inadvertent perioperative hypothermia ➧ infections ➧ surgical site infection (SSI) ➧ fluid warming device, guidelines ➧ enFLow®


Inadvertent perioperative hypothermia

For several decades, discussions have been ongoing regarding perioperative hypothermia. These aim to define its main causes and to develop guidelines for hospital centers due to the potential complications and economic consequences associated with this phenomenon.

Perioperative hypothermia, defined as a central body temperature below 36°C, is a common complication associated with anesthesia and surgical procedures. It is estimated that 50-90% of operated patients experience inadvertent hypothermia [1, 2]. The significance of this issue is mainly determined by complications occurring both during and after surgery. These include respiratory, cardiovascular, coagulation, and electrolyte disturbances, increased susceptibility to infections, impaired wound healing, and altered drug metabolism [1, 3, 4]. The causes of such complications are diverse. The frequency and severity of perioperative hypothermia are influenced by conditions in the operating room (ambient temperature), maintenance of general and/or regional anesthesia, the patient's physiological status, heat loss from the surgical site, and the duration of the procedure [3]. Perioperative hypothermia is influenced by several factors. Currently, passive and active patient warming methods are used to maintain normothermia, including administering warmed intravenous fluids, using thermal mattresses or forced-air warming mattresses, and controlling room temperature [1].


Surgical Procedure and Anesthesia and the Risk of Perioperative Hypothermia 

As a result of the action of many anesthetic agents used in general anesthesia, there is impairment of the thermoregulatory mechanism responsible for maintaining normothermia by widening the threshold for vascular reactions. Dilation of precapillary vessels causes redistribution of heat from the central compartment to peripheral compartments of the body. Redistribution of heat between the central and peripheral compartments is responsible for 81% of heat loss. In intraoperative hypothermia, several phases can be distinguished. In the redistribution phase, there is a sudden and rapid decrease in deep body temperature. This transitions into a linear and uniform decline in the heat loss phase, leading to a stabilization phase where thermoregulatory mechanisms are activated.

According to data from the publication, the body temperature of a patient undergoing surgery under general anesthesia may deviate from the norm by up to 3°C. During procedures lasting approximately 60 minutes, the patient's body temperature may rapidly decrease by up to 1.5°C.


Hypothermia during prolonged procedures

During longer procedures under general anesthesia, there is a slowing of metabolism and a decrease in the activity of skeletal muscles, leading to heat loss through radiation and convection [5]. The percentage of heat loss for patients is estimated to be 60% through radiation and 10 to 15% through convection [8]. Perioperative hypothermia is associated with prolonged hospitalization and the implementation of additional pharmacological therapies, increasing the costs of treatment. Based on studies conducted in the USA, it has been estimated that a 1.5°C decrease in a patient's body temperature during perioperative care results in an additional financial burden ranging from $2500 to $7000 per patient [9].

The duration of the procedure and exposure of uncovered body surfaces and the surgical field increase the risk of inadvertent intraoperative hypothermia and may affect the postoperative period [3]. Studies by Harzowska have shown that the duration of the procedure affects the decrease in the patient's temperature in the postoperative period [1]. Moreover, the amount of fluid transfusions increases. During postoperative monitoring, it was found that the amount of non-warmed fluids administered to the patient significantly affected the decrease in their body temperature [1]. This confirms the results of studies conducted by Sessler in 1997. They showed that administering 1000 ml of fluids at 21°C (room temperature) can lower the body temperature by 0.25°C, while administering 2000 ml of fluids at 4°C lowers the body temperature by over 1°C [10]. It is therefore extremely important to pay attention to the fluid warming procedure because administering non-warmed fluids to the patient significantly contributes to temperature reduction.


Stages of Perioperative Hypothermia

Fazy hipotermii okołooperacyjnej podczas znieczulenia ogólnego na podstawie Sessler D., 2007 [6] (modyfikacja własna)

Ryc. 1. Stages of Perioperative Hypothermia during general anesthesia based on Sessler D., 2007 [6] (modified by the author).


Perioperative hypothermia and surgical site infections

Hypothermia affects the frequency of surgical site infections (SSI) and the rate of wound healing. Several publications have demonstrated the negative impact of decreased body temperature on the activity of the immune system. Reduction in core temperature disrupts leukopoiesis, negatively influences immunoglobulin production, and contributes to reduced blood clotting [4]. Hypothermia triples the risk of surgical site infections, leading to a 20% increase in hospitalization time [10]. Research by Flores-Maldonada in 2001 confirmed the findings of Kurz, showing increased susceptibility to surgical site infections in patients with perioperative hypothermia compared to those with normothermia. In normothermic patients, the incidence of wound infection decreased by 89% compared to patients with mild hypothermia (p = 0.01) [11].


Perioperative hypothermia and infections

Hipotermia okołooperacyjna jest czynnikiem zwiększającym ryzyko zakażeń u pacjentów [11, 12]. Przyczyny tych zakażeń mają różne podłoże. Z jednej strony ograniczony dostęp tlenu do miejsca operowanego (wazokonstrykcja) oraz z drugiej, reakcja układu odpornościowego pacjenta [3]. Ograniczenie dostępu tlenu do tkanek uniemożliwia proces syntezy wolnych rodników przez neutrofile. Dodatkowa inaktywacja komórek układu immunologicznego, spowodowana obniżoną temperaturą, prowadzi do zaburzeń fagocytozy, zredukowanej produkcji chemokin, zaburzając transfer neutrofilów do miejsca zakażenia [3]. Spadek temperatury głębokiej destabilizuje gospodarkę białek układu immunologicznego, m.in. białek układu zgodności tkankowej, czynnika martwicy nowotworów (TNF-α) i immunoglobulin, co powoduje zahamowanie kolejnego procesu obronnego organizmu operowanego pacjenta [3, 11, 12, 13].

Wong et al., in studies conducted in 2007 on patients undergoing elective colorectal surgery, demonstrated that in the group of patients warmed during the pre-, intra-, and postoperative periods, the incidence of surgical site infection decreased by 60% compared to patients warmed only during the intraoperative period [14].

In a study by Moslemi-Kebrii et al. in 2012, conducted on patients undergoing surgical cytoreduction for ovarian cancer, a 71% lower incidence of infections was found in the normothermic group compared to the hypothermic group [15].

The results obtained in the studies by Kurz, conducted on a group of patients undergoing colorectal surgery, confirmed the effectiveness and superiority of fluid warming over air warming. In patients warmed only with air, hypothermia occurred, while in the other group, normothermia was achieved by adding fluid warming to air warming. In the normothermic group, there was a 67% reduction in the incidence of infections and an 18% reduction in hospital stay compared to patients with hypothermia [12].


Intraoperative hypothermia - other complications

Hypothermia, especially in elderly patients, can triple the incidence of coronary events, leading to acute circulatory failure, numerous complications, or death [5, 10]. Maintaining normothermia in these patients reduces the risk of life-threatening cardiovascular events [10]. Research by Frank, conducted on a group of patients undergoing vascular, thoracic, and abdominal procedures, showed an 80% reduction in the frequency of cardiovascular incidents in the normothermic group compared to the group of patients with hypothermia [16].

Another complication of hypothermia is the disrupted blood coagulation cascade. It inhibits platelet activity, disturbs the function of clotting factors, including prothrombin, disrupts fibrinolysis, and disturbs the coagulation enzymatic balance [4, 5]. Even in patients with mild hypothermia, clotting mechanisms are disrupted [4]. These processes increase blood loss and the need for blood products. A meta-analysis conducted by Suman et al., published in 2008, included the results of 24 clinical studies. It showed that patients with normothermia had a 16% lower need for blood and a 23% lower risk of transfusion compared to patients with hypothermia [17]. Research by Schmied, conducted on patients undergoing hip arthroplasty, showed a 23% lower intraoperative blood loss in normothermic patients compared to patients with hypothermia [18].

Another consequence of intraoperative hypothermia is its impact on the patient's emergence time, related to the disturbance of drug metabolism [4]. This process prolongs the action of intravenous anesthetics and muscle relaxants. The duration of action of the intravenous anesthetic propofol is extended by 30%, and the muscle relaxant atracurium by 60% [19, 20]. The duration of action of another neuromuscular blocking agent, vecuronium, is twice as long in patients with mild hypothermia compared to the normothermic group [21].


Preventing inadvertent perioperative hypothermia – recommendations

The standard procedure from the preparation of the patient for surgery until their transfer to the postoperative care unit involves ensuring and monitoring the patient's physiological body temperature.

The modern comprehensive perioperative care protocol aimed at improving ERAS (Enhanced Recovery After Surgery) outcomes recommends warming intravenous fluids to maintain perioperative normothermia in patients [22].






60 min 60 min 30 min
Minor surgical procedures Moderate surgical procedures Minor surgical procedures


Fluid warming

+ Mattresses

Fluid warming

+ Mattresses

Fluid warming
LOW Fluid warming Fluid warming

+ Mattresses

Fluid warming


Table 1. Recommended methods of active patient warming based on the duration of anesthesia, type of surgery, and risk of cardiac complications (according to NICE, 2008)


Recomendations NICE (National Institute for Clinical Excellence)

According to the recommendations of the National Institute for Clinical Excellence (NICE), every patient is assessed for the risk of perioperative hypothermia. If the core temperature in the preoperative phase is below 36°C, immediate measures should be taken to restore the patient to normothermia before the start of the surgical procedure. Active intraoperative patient warming contributes to maintaining physiological body temperature and prevents many perioperative complications associated with its fluctuations. Guidelines regarding the warming of intravenous fluids and blood products are also highly significant. It is recommended that before administration, fluids and blood products should be warmed using dedicated devices when the volume exceeds 500 ml, for all patients undergoing surgical procedures lasting longer than 30 minutes [23].

According to the recommendations issued by NICE regarding the prevention of perioperative hypothermia, effective and readily available measures should be employed to prevent its occurrence, such as intravenous fluid warming devices and forced-air warming systems [23].

The analysis of the effectiveness of applied patient warming methods has shown that combining two warming methods, namely routine procedures along with intravenous fluid and blood warming, reduces the risk of perioperative hypothermia and related complications, including infections, by over 50%. Additionally, adding fluid warming to other active warming methods such as forced-air warming mattresses allows for a further 26% reduction in hypothermia risk and a 29% decrease in hypothermia-related complications, including infections [23].

Warming of administered fluids is always recommended as the optimal strategy for maintaining normothermia, regardless of the type of procedure, risk of cardiac complications, duration of anesthesia, or other patient warming methods [23].


Effective warming of blood and intravenous fluids

Devices used for warming fluids in perioperative care ensure patient safety in maintaining normothermia and facilitate the work of medical staff.


What features should an effective system for flow heating of blood and intravenous fluids have?

The main criterion set for manufacturers of systems for flow heating of fluids is their effectiveness. This encompasses several features that such a system should have. It should ensure maintaining the patient's proper temperature by providing a wide range of heating temperatures. The initiation of fluid heating should be as rapid as possible. The system should allow for high flow rates while maintaining the desired temperature. For blood transfusions, the system should have a safety certification issued by independent institutions. An essential element is simple, intuitive operation, and quick device preparation for work. The functionality of such a system also depends on the small volume of initial filling of the cartridge and the lack of frequent servicing requirements. An extremely important feature is the ability to use the device without age restrictions on the patient. An additional advantage of the heating system should be the ease of transporting the device together with the patient.


Is there a medical device available on the market for flow heating of blood and infusion fluids that exhibits the aforementioned features?

Among the medical devices currently available on the market for flow heating of infusion fluids and blood, the enFlow® system (manufactured by CareFusion) deserves attention as it meets all the aforementioned criteria. The device initiates heating of the flowing fluid just 18 seconds after connection to the patient. Automatic settings enable reaching a temperature of 40°C, aiding in maintaining normothermia in the patient. The system can maintain a temperature of 40°C even at high flow rates of up to 200 ml/min (12 liters of fluid/hour). The safety of maintaining the quality parameters of blood products has been confirmed by the Polish Institute of Hematology and Transfusion Medicine. The evaluation conducted by the Institute unequivocally determines that the enFlow® warmer is safe for transfused red blood cell concentrates. With a small initial filling volume of the cartridge (4 ml) and simple, intuitive operation, the system can be quickly prepared for use. The device can be used without age limits. The mobility of the enFlow system, achieved by using a small, portable cartridge, allows for the maintenance of normothermia in patients practically anywhere therapy and care are provided. The device is serviced every 5 years.



Numerous publications indicate that maintaining a patient in a state of normothermia throughout the perioperative period prevents complications. Therefore, if there are no clinical indications for inducing hypothermia in a patient, every effort should be made to maintain normothermia, adhering to existing recommendations. Inadvertent perioperative hypothermia occurs very frequently and is a cause of many complications, including infections. It can easily be avoided by using fluid warming. Fluid warming should be applied when infusing volumes ≥ 500 ml of fluids and during procedures lasting ≥ 30 minutes. Fluid warming should always be used, regardless of other methods of patient warming.



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Categories: Maski krtaniowe, nebulizatorypompy infuzyjne


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