Efficacy of an Infrared Radiator for Hypothermia Prevention in a Simulated Setup of Entrapped Vehicle Accident Victims

BackgroundProlonged extrication of entrapped patients after road traffic accidents increases the risk of sustained hypothermia. Accident-related hypothermia increases mortality in severely injured patients, and prehospital efforts to prevent hypothermia are essential. We evaluated various warming measures regarding their preclinical suitability and efficacy for patient warming, tested in realistically-simulated road traffic accident scenarios under cold ambient conditions in a climate chamber.MethodsThe effects of a chemical warming blanket (CWB), forced-air warming (FAW) device, or infrared radiator (IRR) on the core body and skin surface temperature of a subject previously exposed to a cold environment (5°C for 12 minutes) was recorded via temperature sensors and thermographically, respectively. Physiological parameters such as oxygen saturation, blood pressure, and heart rate were also monitored.ResultsUnder cold environmental conditions, all devices were able to compensate or overcompensate the cooling of body parts directly exposed to the heating measure. In the body areas that were not directly warmed (back, lower extremities), only the CWB limited further cooling. FAW and IR irradiation rapidly and effectively warmed the heat-exposed areas (head and arms). However, both methods – but especially the IRR – led to a noticeably accelerated cooling in body parts not directly exposed to heat (back, legs).ConclusionThe increased mortality associated with hypothermia in severely injured crash victims during prolonged vehicle extrication has intensified efforts to prevent sustained hypothermia. The use of a CWB, FAW or IRR are in principle all suitable for reducing or compensating for heat loss. The ongoing cooling of those body parts not directly exposed to the heat source was interpreted as a steal phenomenon in regional blood flow. However, the practicality and effectiveness of these measures, combined with their logistical requirements, must be evaluated in real extrication scenarios.     

Prevention and treatment of perioperative hypothermia

Less than 10% of metabolic heat is lost via respiration, even when patients are ventilated with dry, cool gas. Passive or active airway heating and humidification, therefore, contributes little to perioperative thermal management. Each litre of intravenous (i.v.) fluid infused into adult patients at ambient temperature, or each unit of blood infused at 4°C, decreases mean body temperature approximately 0.25°C. Administration of sufficient unwarmed fluid can thus markedly decrease body temperature. Heating fluids to near 37°C prevents this hypothermia, and is appropriate when large volumes are administered.Cutaneous heat loss predominates during surgery, although evaporation from large surgical incisions may also contribute significantly. Cutaneous heat loss can be passively decreased by covering skin with surgical drapes, blankets, plastic bags etc. A single layer of each insulator reduces heat loss by approximately 30%; unfortunately, adding additional layers does not proportionately increase the benefit. In most patients, some form of active warming is required to prevent intraoperative hypothermia. Among available active heaters, forced-air warming is generally most effective.Perioperative hypothermia is associated with numerous adverse outcomes. Consequently, body temperature should be measured in most surgical patients. Unless hypothermia is specifically indicated (e.g. for protection against ischaemia), intraoperative core temperature should be maintained above 36°C. Any method or combination of methods that maintains core temperature above 36°C is adequate.     

Update on trauma care in Canada. 5. Trauma and hypothermia

Trauma may be accompanied by hypothermia in all climates. Because of the associated increased death rate due to hypothermia (core body temperature less than 35 degrees C), traumatized patients must be protected from it. The body maintains heat balance by hypothalamic regulation of endogenous heat generation and heat loss. Decreased core temperature causes generalized physiologic deceleration and homeostatic disturbances in all organ systems. To prevent hypothermia in polytraumatized patients a number of methods may be used: warming crystalloid, increasing ambient temperature, the use of warming devices, irrigation of body cavities with warmed fluids, heating of inspired gases and, in severe cases when there is circulatory instability, the use of extracorporeal membrane oxygenation.     

Effects of anaesthesia on thermoregulation

Hypothermia is a common and serious complication during anaesthesia and surgery. It mainly results from anaesthetic-induced inhibition of thermoregulatory control and exposure to cold operating room environment. Perioperative hypothermia develops in three distinct phases: (1) anaesthetic-induced vasodilation during induction of anaesthesia results in core-to-peripheral redistribution of body heat and decreases core temperature 1–1.5°C during the first hour of general anaesthesia; (2) subsequently core temperature decreases linearly as heat loss to the environment exceeds metabolic heat production; (3) after 3–5 h of anaesthesia, core temperature often stops decreasing. This core temperature plateau results from reactivation of thermoregulatory vasoconstriction which decreases cutaneous heat loss and constrains metabolic heat to the core thermal compartment. Perioperative hypothermia is associated with numerous complications such as myocardial ischaemia, increased risk of wound infection and coagulopathy. On the other hand temperatures only 1–3°C below normal provide substantial protection against cerebral ischaemia and hypoxaemia in numerous animal species. Consequently, most anaesthesiologists believe mild hypothermia is indicated during operations likely to cause cerebral ischaemia such as carotid endarterectomy and neurosurgery or cardiac procedures. Thermal perturbations, therefore, deserve the same risk/benefit analysis as other medical interventions. Fortunately, effective methods of cooling and warming surgical patients are now available.     

Trauma and hypothermia

Hypothermia occurs commonly in patients sustaining injury and may result in morbidity and mortality due to impaired cardiorespiratory function, peripheral vasoconstriction, bleeding diathesis, metabolic acidosis, diminished hepatorenal function, and impaired immune response. Hypothermia decreases metabolic function of the body and is neuroprotective. However, injured patients in whom hypothermia develops have a higher mortality than do patients with a similar injury severity who remain normothermic. Also, post-injury life-threatening coagulopathy is predicted by persistent hypothermia in patients receiving massive transfusion. Treatment of hypothermia in the trauma patient should begin with the ABCs (airway with cervical spine protection, breathing, circulation and control of bleeding). Prevention of further heat loss is achieved by maintaining the patient in a thermoneutral environment at high ambient temperature and use of warmed intravenous (i.v.) fluids. The thermal stress from cold fluid resuscitation can substantially decrease core temperature mandating the use of effective fluid and blood warming devices in all severely injured patients. Several non-invasive and invasive rewarming methods are available. Of the various non-invasive treatment modalities, convective warming appears to be most effective for mild (32–35°C) and mild–moderate (30–32°C) hypothermia. Continuous arteriovenous rewarming may be used in the patient with moderate–severe (28–32°C) and severe (<30°C) hypothermia provided there is an adequate perfusing rhythm. Cardiopulmonary bypass or body cavity lavage may be indicated for severe hypothermia in the absence of a perfusing cardiac rhythm.     

Monitoring and thermal management

Anaesthesia alters normal thermoregulatory control of the body, usually leading to perioperative hypothermia. Hypothermia is associated with a large number of serious complications. To assess perianaesthetic hypothermia, core temperature should be monitored vigorously. Pulmonary artery, tympanic membrane, distal oesophageal or nasopharyngeal temperatures reflect core temperature reliably. Core temperatures can be often estimated with reasonable accuracy using oral, axillary and bladder temperatures, except during extreme thermal perturbations. The body site for measurements should be chosen according to the surgical procedure. Unless hypothermia is specifically indicated, efforts should be made to maintain intraoperative core temperatures above 36 °C. Forced air is the most effective, commonly available, non-invasive warming method. Resistive heating electrical blankets and circulating water garment systems are an equally effective alternative. Intravenous fluid warming is also helpful when large volumes are required.In some patients, induction of mild therapeutic hypothermia may become an issue for the future. Recent studies indicate that patients suffering from neurological disease may profit from rapid core cooling.     

Perioperative heat balance

Hypothermia during general anesthesia develops with a characteristic three-phase pattern. The initial rapid reduction in core temperature after induction of anesthesia results from an internal redistribution of body heat. Redistribution results because anesthetics inhibit the tonic vasoconstriction that normally maintains a large core-to-peripheral temperature gradient. Core temperature then decreases linearly at a rate determined by the difference between heat loss and production. However, when surgical patients become sufficiently hypothermic, they again trigger thermoregulatory vasoconstriction, which restricts core-to-peripheral flow of heat. Constraint of metabolic heat, in turn, maintains a core temperature plateau (despite continued systemic heat loss) and eventually reestablishes the normal core-to-peripheral temperature gradient. Together, these mechanisms indicate that alterations in the distribution of body heat contribute more to changes in core temperature than to systemic heat imbalance in most patients. Just as with general anesthesia, redistribution of body heat is the major initial cause of hypothermia in patients administered spinal or epidural anesthesia. However, redistribution during neuraxial anesthesia is typically restricted to the legs. Consequently, redistribution decreases core temperature about half as much during major conduction anesthesia. As during general anesthesia, core temperature subsequently decreases linearly at a rate determined by the inequality between heat loss and production. The major difference, however, is that the linear hypothermia phase is not discontinued by reemergence of thermoregulatory vasoconstriction because constriction in the legs is blocked peripherally. As a result, in patients undergoing large operations with neuraxial anesthesia, there is the potential of development of serious hypothermia. Hypothermic cardiopulmonary bypass is associated with enormous changes in body heat content. Furthermore, rapid cooling and rewarming produces large core-to-peripheral, longitudinal, and radial tissue temperature gradients. Inadequate rewarming of peripheral tissues typically produces a considerable core-to-peripheral gradient at the end of bypass. Subsequently, redistribution of heat from the core to the cooler arms and legs produces an afterdrop. Afterdrop magnitude can be reduced by prolonging rewarming, pharmacologic vasodilation, or peripheral warming. Postoperative return to normothermia occurs when brain anesthetic concentration decreases sufficiently to again trigger normal thermoregulatory defenses. However, residual anesthesia and opioids given for treatment of postoperative pain decreases the effectiveness of these responses. Consequently, return to normothermia often needs 2-5 h, depending on the degree of hypothermia and the age of the patient.     

Management of peri-operative hypothermia

Hypothermia (body temperature under 36°C) is the thermal disorder most frequently found in surgical patients, but should be avoided as a means of reducing morbidity and costs. Temperature should be considered as a vital sign and all staff involved in the care of surgical patients must be aware that it has to be maintained within normal limits. Maintaining body temperature is the result, as in any other system, of the balance between heat production and heat loss. Temperature regulation takes place through a system of positive and negative feedback in the central nervous system, being developed in three phases: thermal afferent, central regulation and efferent response. Prevention is the best way to ensure a normal temperature. The active warming of the patient during surgery is mandatory. Using warm air is the most effective, simple and cheap way to prevent and treat hypothermia.     

Optimal Duration and Temperature of Prewarming

Background: Core hypothermia developing immediately after induction of anesthesia results largely from an internal core-to-peripheral redistribution of body heat. Although difficult to treat, redistribution can be prevented by prewarming. The benefits of prewarming may be limited by sweating, thermal discomfort, and efficacy of the warming device. Accordingly, the optimal heater temperature and minimum warming duration likely to substantially reduce redistribution hypothermia were evaluated.

Methods: Sweating, thermal comfort, and extremity heat content were evaluated in seven volunteers. They participated on two study days, each consisting of a 2-h control period followed by 2 h of forced-air warming with the heater set on "medium" ([nearly equal] 40 degrees Celsius) or "high" ([nearly equal] 43 degrees Celsius). Arm and leg tissue heat contents were determined from 19 intramuscular needle thermocouples, ten skin temperatures, and "deep" foot temperature.

Results: Half the volunteers started sweating during the second hour of warming. None of the volunteers felt uncomfortably warm during the first hour of heating, but many subsequently did. With the heater set on "high," arm and leg heat content increased 69 kcal during the first 30 min of warming and 136 kcal during the first hour of warming, representing 38% and 75%, respectively, of the values observed after 2 h of warming. The increase was only slightly less when the heater was set to "medium."     

Non-therapeutic intraoperative hypothermia: prevention and treatment (part II)

General and regional anesthesia alter the physiological mechanisms of thermoregulation, and unintentional intraoperative hypothermia develops during most surgical procedures that last more than 1 hour. Monitoring of central temperatures among other vital signs is advisable in such interventions in order to detect temperature changes and check the efficacy of measures to prevent or treat hypothermia. Passive insulation reduces heat loss through the skin but most patients require active warming to maintain a normal temperature. Various skin surface warming systems prevent hypothermia from developing and provide effective warming. The most often used are forced-air or warm water circulation devices. When large volumes of fluids must be infused intravenously, they must be warmed to body temperature to avoid heat loss.     

Shiver suppression using focal hand warming in unanesthetized normal subjects.

BACKGROUND: A decrease of 1 or 2 degrees C in core temperature may provide protection against cerebral ischemia. However, during corporeal cooling of unanesthetized patients, the initiation of involuntary motor activity (shiver) prevents the reduction of core temperature. The authors' laboratory previously showed that focal facial warming suppressed whole-body shiver. The aim of the current study was to determine whether the use of hand warming alone could suppress shiver in unanesthetized subjects and hence potentiate core cooling. METHODS: Subjects (n = 8; healthy men) were positioned supine on a circulating water mattress (8-15 degrees C) with a convective-air coverlet (14 degrees C) extending from their necks to their feet. A dynamic protocol was used in which focal hand warming was used to suppress involuntary motor activity, enabling noninvasive cooling to decrease core temperatures. The following parameters were monitored: (1) heart rate; (2) blood pressure; (3) core temperature (rectal, tympanic); (4) cutaneous temperature and heat flux; (5) subjective shiver level (SSL scale 0-10) and thermal comfort index (scale 0-10); (6) metabolic data (n = 6); and (7) electromyograms. RESULTS: During cooling without hand warming, involuntary motor activity increased until it was widespread. After subjects reported whole-body shiver (SSL > or = 7), applied hand warming, in all cases, reduced shiver levels (SSL < o r= 3), decreased electromyographic root mean square amplitudes, and allowed core temperature to decrease from 37.0 +/- 0.2 to 35.9 +/- 0.5 degrees C (measured rectally). CONCLUSIONS: Focal hand warming seems to be valuable in minimizing or eliminating the need to suppress involuntary motor activity pharmacologically when it is desired to induce or maintain mild hypothermia; it may be used in conjunction with facial warming or in cases in which facial warming is contraindicated.     

Peri-operative hypothermia in the high-risk surgical patient

Peri-operative hypothermia is common in high-risk surgical patients. Anaesthesia impairs central thermoregulation, allowing redistribution of body heat. Cool ambient temperatures and high-volume fluid administration accelerate loss of heat to the environment. Randomized, controlled trials have proven that mild hypothermia increases the incidence of wound infection and prolongs hospitalization, increases the incidence of morbid cardiac events and ventricular tachycardia and impairs coagulation. Other complications include enhanced anaesthetic drug effects, prolonged recovery room stays, shivering and impaired immune function. There is compelling animal evidence for cerebral protection by mild hypothermia. However, evidence for protection in surgical patients is not yet available. The most effective means of preventing peri-operative hypothermia is active pre-warming. High ambient temperatures, warmed intravenous fluids and active cutaneous warming are useful intraoperatively, while active cutaneous warming and intravenous pethidine abolish post-operative shivering. Proper thermal management may reduce complications and improve the outcome in high-risk surgical patients.     

The effects of warming intravenous fluids on intraoperative hypothermia and postoperative shivering during prolonged abdominal surgery

Background: The infusion of several liters of crystalloid solution at room temperature may significantly contribute to intraoperative hypothermia because warming fluid to core temperature requires body heat. The aim of this study was to evaluate the effect of delivering warmed intravenous (IV) fluid to the patient on preventing intraoperative hypothermia.
Methods: Intraoperative core and mean skin temperatures were measured during prolonged abdominal surgery in 18 patients randomly divided into two groups according to intraoperative IV fluid management. In 9 patients (control group) all IV fluids infused were at room temperature. In the other 9 patients (group receiving warmed fluids) all IV fluids were warmed using an active IV fluid tube-warming system. In all 18 patients a warming blanket covered the skin surface available for cutaneous warming. Intraoperative changes in total body heat content (kJ) were calculated from core and mean skin temperatures.
Results: At the end of surgery, core temperature was 36.7±0.2°C in the group receiving warmed fluids and 35.8±0.2°C in the control group ( P <0.05). The estimated reduction in heat loss provided by warming IV fluid was 217 kJ, a value very close to the theoretical value expected from thermodynamic calculation. During recovery, one patient shivered in the group receiving warmed fluids and seven in the control group ( P <0.05).
Conclusion: In conclusion, infusion of warmed fluids, combined with skin-surface warming, helps to prevent hypothermia and reduces the incidence of postoperative shivering.     

The failure of negative pressure rewarming (Thermostat) to accelerate recovery from mild hypothermia in postoperative surgical patients

The Thermostat device (Aquarius Medical Corp., Phoenix, AZ) is used in a new technique to accelerate recovery from hypothermia by mechanically distending blood vessels in the hand, thereby increasing transfer of exogenous heat to the body core. We evaluated the use of the Thermostat device in patients with mild postoperative hypothermia (< 36 degrees C). We studied adult patients undergoing elective surgery, general anesthesia, and neuromuscular blockade. Patients with an initial postoperative tympanic membrane temperature < 36 degrees C were randomized into two groups: 1) Thermostat, which consisted of a hypothermia warming mitt/seal and thermal exchange chamber for 60 min, and 2) conventional treatment, which consisted of warm blankets and/or radiant heat. Of the 191 patients enrolled, 60 (31%) developed hypothermia and were randomized to receive the Thermostat (n = 30) or conventional methods (n = 30). Fourteen patients in the Thermostat group and 17 patients in the conventional group rewarmed to 36 degrees C before discharge from the recovery room (P is not significant). There were no differences in vital signs, rewarming time, time to discharge from the recovery room, or postoperative temperature between groups. We conclude that patients with mild postoperative hypothermia rewarmed in a similar fashion, regardless of whether the Thermostat or conventional methods were used. IMPLICATIONS: We found that a commercially available negative pressure rewarming device (Thermostat; Aquarius Medical Corp., Phoenix, AZ) was not effective in accelerating rewarming in postoperative hypothermic surgical patients after general anesthesia.     

Intraoperative Wärmekonservierung Viel Lärm um heiße Luft?

Thermoregulation and its impairment by anaesthesia and surgery has recently been brought back into focus by researchers and clinicians. All volatile and IV anaesthetics, opioids, as well as spinal and epidural anaesthesia increase the inter-threshold range of thermoregulation from 0.2°?C to 4°?C between vasodilation and vasoconstriction. Thermoregulatory vasoconstriction and shivering occurs in anaesthetized patients at lower core temperatures than in awake subjects. Following induction of general or spinal/epidural anaesthesia, core temperature decreases significantly due to internal redistribution of body heat from the core thermal compartment to peripheral tissues. About 1?h after induction of general anaesthesia and initial redistribution hypothermia, a real reduction in body heat occurs as heat loss exceeds metabolic heat production. Heat loss is further increased due to low operating room temperatures, evaporation from open body cavities, and cold IV fluids. Peripheral thermoregulatory vasoconstriction is triggered by core temperatures between 33°?C and 35°?C, and is able to slow heat loss. However, body heat content continues to decrease even though core temperatures remain nearly constant. During spinal or epidural anaesthesia thermoregulation remains intact in the unblocked body segments, leading to reduced real heat loss when compared to general anaesthesia. Inadvertent hypothermia markedly decreases drug metabolism. Coagulation is impaired by cold-induced defects of platelet function. Hypothermia reduces neutrophil phagocytosis and oxidative killing capacity, causing wound infections. Postoperative hypothermia represents an unnecessary stress for the circulatory system, elevating plasma catecholamines and leading to myocardial ischaemia and arrhythmias. These hypothermia-related morbidities therefore have consequences reaching fare into the postoperative period. Prevention of inadvertent hypothermia is always indicated. Forced-air warming is the most effective and safest method to prevent perioperative hypothermia.     

Predictors of Hypothermia during Spinal Anesthesia

Background: Body temperature often is ignored during regional anesthesia, despite evidence that hypothermia occurs commonly. Because hypothermia is associated with adverse clinical outcomes, it is important to recognize predictors of hypothermia and to monitor and control body temperature in patients at risk. The current study was designed to determine the predictors of core hypothermia in patients receiving spinal anesthesia for radical retropubic prostatectomy.

Methods: Forty-four patients undergoing radical retropubic prostatectomy were studied. A lumbar intrathecal injection of 18-22 mg bupivacaine, 0.75%, with 20 [mu]g fentanyl was given. No active warming measures were used other than intravenous fluid warming. The following clinical variables were assessed as potential predictors of core (tympanic) temperature at admission to the postanesthesia care unit: duration of surgery, average ambient operating room temperature, body habitus, age, and spinal blockade level.

Results: The mean core temperature at admission to the postanesthesia care unit was 35.1 +/- 0.6[degrees]C (range, 33.6-36.3[degrees]C). Duration of surgery, ambient operating room temperature, and body habitus were not predictors of hypothermia. A high level of spinal blockade and increasing age were predictors of hypothermia. For each incremental increase in block level, core temperature decreased by 0.15[degrees]C, and for each increase in age, core temperature decreased by 0.3[degrees]C.     

Myocardial cooling for reperfusion injury protection achieved by organ specific hypothermic autologous perfusion

OBJECTIVE: Whole body hypothermia has been suggested to reduce myocardial injury in patients with ST-segment elevation myocardial infarction. Because of the large human thermal mass, induction of generalized hypothermia is slow and the technique has encountered considerable side effects. The aim was to develop and validate a method for regional cooling during myocardial reperfusion using hypothermic autologous blood. DESIGN: In a myocardial ischemia-reperfusion pig model (n = 10), arterial blood was cooled in a closed circuit, and returned to the myocardium during reperfusion either through a perfusion catheter or through the guiding catheter. Myocardial temperatures were recorded using temperature electrodes. RESULTS: Stabile regional myocardial cooling was induced without complications within 4 min. Both flow rate and blood temperature had significant impact on temperature in the reperfused myocardium but did not influence systemic temperature. CONCLUSION: A method for organ specific hypothermic autologous arterial blood reperfusion has been developed and validated. The method is a simple and much faster alternative to systemic cooling and may have the potential to reduce myocardial injury in patients with acute myocardial infarction.     

Effect of heated and humidified carbon dioxide gas on core temperature and postoperative pain

Background: Intraoperative hypothermia is a common event during laparoscopic operations. An external warming blanket has been shown to be effective in preventing hypothermia. It has now been proposed that using heated and humidified insufflation gas can prevent hypothermia and decrease postoperative pain. Therefore, we examined the extent of intraoperative hypothermia in patients undergoing laparoscopic Nissen fundoplication using an upper body warming blanket. We also attempted to determine whether using heated and humidified insufflation gas in addition to an external warming blanket would help to maintain intraoperative core temperature or decrease postoperative pain. Methods: Twenty patients were randomized to receive either standard carbon dioxide (CO2) gas (control, n = 10) or heated and humidified gas (heated and humidified, n = 10). After the induction of anesthesia, an external warming blanket was placed on all patients in both groups. Intraoperative core temperature and intraabdominal temperature were measured at 15-min intervals. Postoperative pain intensity was assessed using a visual analogue pain scale, and the amount of analgesic consumption was recorded. Volume of gas delivered, number of lens-fogging episodes, intraoperative urine output, and hemodynamic data were also recorded. Results: There was no significant difference between the two groups in age, length of operation, or volume of CO2 gas delivered. Compared with baseline value, mean core temperature increased by 0.4°C in the heated and humidified group and by 0.3°C in the control group at 1.5 h after surgical incision. Intraabdominal temperature increased by 0.2°C in the heated and humidified group but decreased by 0.5°C in the control group at 1.5 h after abdominal insufflation. There was no significant difference between the two groups in visual analog pain scale (5.4 ± 1.6 control vs 4.5 ± 2.8 heated and humidified), morphine consumed (27 ± 26 mg control vs 32 ± 19 mg heated and humidified), urine output, lens-fogging episodes, or hemodynamic parameters. Conclusion: Heated and humidified gas, when used in addition to an external warming blanket, minimized the reduction of intraabdominal temperature but did not alter core temperature or reduce postoperative pain.     

Forced-air surface warming versus oesophageal heat exchanger in the prevention of peroperative hypothermia

Background: In a prospective, randomized, placebo-controlled study we investigated the efficacy of 2 different heating methods in 24 patients undergoing abdominal surgery of at least 2 h expected duration.
Methods: Group I: control, no active warming. Group II: forced-air surface warming on upper extremities and upper thorax. Group III: warming with oesophageal heat exchanger. All patients had a standardized, combined general and epidural anaesthesia. Core and skin temperatures were measured at induction of general anaesthesia, and subsequently every 30 min, and changes in total body temperature were calculated.
Results: There were no statistically significant differences between the 3 groups regarding demographic data. Patients in groups I and III developed hypothermia, while this was not the case with patients in group II. When using analysis of variance with repeated measurements, there was no significant difference in core temperature, comparing group I and group III ( P =0.299) or the interaction between time and treatment of these groups ( P =0.373). As a consequence, data from groups I and III were pooled and regarded as an internal group on the one hand, and group II as an external group on the other hand. Core temperature, the mean skin temperature and total body temperature were significantly different comparing the internal group and the external group. The interaction between time and treatment was likewise found to be significantly different.
Conclusions: We conclude that in major abdominal procedures lasting 2 h or more, serious hypothermia develops unless effective measures to prevent hypothermia are used. Forced-air warming of the upper part of the body is effective in maintaining normothermia in these patients, while central heating with an oesophageal heat exchanger, at least in its present form, does not suffice to prevent hypothermia.     

Perioperative hypothermia in the high-risk surgical patient

Perioperative hypothermia is common in high-risk surgical patients. Anaesthesia impairs central thermoregulation, allowing re-distribution of body heat. Cool ambient temperatures and high-volume fluid administration accelerate loss of heat to the environment. Randomized, controlled trials have proven that mild hypothermia increases the incidence of wound infection and prolongs hospitalization, increases the incidence of morbid cardiac events and ventricular tachycardia, and impairs coagulation. Other complications include enhanced anaesthetic drugs effects, prolonged recovery room stays, shivering, and impaired immune function. There is compelling animal evidence for cerebral protection by mild hypothermia. However, evidence for protection in surgical patients is not yet available. The most effective means of preventing perioperative hypothermia is active pre-warming. High ambient temperatures, warmed intravenous fluids and active cutaneous warming are useful intra-operatively, while active cutaneous warming and intravenous pethidine abolish post-operative shivering. Proper thermal management may reduce complications and improve the outcome in high-risk surgical patients.