03RC1- Greif. Temperature Monitoring. Robert Greif - 1 -

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1 03RC1- Greif Temperature Monitoring Robert Greif Department of Anaesthesiology and Pain Therapy, University Hospital Bern, Inselspital Bern, Switzerland Small decreases of core body temperature during anaesthesia ranging over only 1-2 C have a detrimental impact on the morbidity of our surgical patients. This effect been demonstrated in major outcome studies during the last decades [1]. Mild hypothermia decreases metabolism, resulting in prolonged drug action and delayed discharge from the post-anaesthesia recovery room [2]. Each decrease of 1 C in body temperature leads to increased blood losses of about 16%, with a relative risk of transfusion of 22% because of the associated decreases in coagulation cascade enzyme activity and platelet function [3]. Landmark studies assessing the effects of non-therapeutic unintentional mild intraoperative hypothermia showed an increase in cardiac morbidity [4] and a substantially higher incidence of surgical wound infection which nearly doubled hospitalization rates due to impaired wound healing [5]. The pathophysiology of thermoregulation and the impact of anaesthesia have also been studied in detail recently. We know quite a lot about how to control body temperature during anaesthesia and guidelines for the measurement of temperature during anaesthesia have been published [6-8]. The ESA Refresher Lecture and this summary will briefly summarize the background governing the measurement of temperature during anaesthesia. We humans have a core body temperature between 36.5 and 37.5 C. This is controlled by thermo-defence mechanisms within a range of 0.2 C. Temperature loss is initially reduced by vasoconstriction. Muscular shivering to generate heat also occurs later on. On the other hand, when we are too hot vasodilatation and sweating occurs (Figure 1). Behavioural changes such as the use of clothing for protection, rest, or movement are physiological and cultural reactions in response to external temperature changes. Figure 1: Thermoregulatory Response Thresholds The autonomic thermoregulatory response thresholds in normal conditions, during warming of the face/hands/feet, or under general anesthesia. (From: Induction of therapeutic Hypothermia requires Modulation of Thermoregulatory Defenses. Bandschapo et al. Therapeutic Hypothermia and Temperature Management 2011; 1: 77-85) - 1 -

2 During anaesthesia, many of these reactions change. Firstly, the patient can no longer initiate behavioural reactions to address a decrease or an increase of body temperature. Large body parts might be uncovered, open exposure of internal organs leads to heat loss and because of the reduction of metabolism that results from anaesthesia, heat production is reduced. But much more important is the fact that right after the induction of anaesthesia, a sudden decrease of core body temperature of about C occurs in the first 30 minutes. Anaesthetic drug-induced vasodilatation leads to a redistribution of heat from the warmer core to the colder periphery, resulting in a marked decline in core temperature (Figure 2) [1]. Figure 2: Redistribution of heat after induction of anaesthesia The next impact on heat loss stems from the fact that nearly all drugs used during anaesthesia (Figure 3, [9-12]) directly widen the threshold range between sweating or vasoconstriction and shivering by up to 2 C or more in a dose dependent manner. Consequently, more heat is lost during anaesthesia exceeding that able to be generated by metabolism. Figure 3: Drug action on thermoregulatory defence mechanisms (See: Talke, Anesthesiology 1997 [9], Kurz, Anesthesiology 1995[10], Annadata, Anesthesiology 1995 [11], Matsukawaet, Anesthesiology 1995 [12]) - 2 -

3 Taking all these facts together, patient-centred anaesthesia providers are increasingly paying greater attention to intraoperative heat loss by using intraoperative patient warming devices that are now widely available to maintain intraoperative core temperatures above 36 C. In order to guide therapeutic interventions to ensure maintenance of body temperature, and in order to detect cases in which the intraoperative temperature actually increases, we need to measure body temperature during anaesthesia, but when, how, and where should this be done? As a consequence of the pathophysiological changes during anaesthesia Dan Sessler, a pioneer in perioperative thermoregulatory disturbances, recommended monitoring body temperature in most patients undergoing general anaesthesia exceeding 30 minutes in duration. For research purposes, in the rare event of sudden changes, or for therapeutic indications demanding hypothermia, body temperature should be continuously monitored. In the majority of perioperative or diagnostic interventions under anaesthesia intervals of minutes might sufficiently reflect possible temperature changes in our patients. Because the whole purpose of temperature monitoring is the detection of thermal disturbances and the maintenance of a physiologically normal body temperature during anaesthesia, we also need temperature control during neuraxial anaesthesia [13]. Sympathetic blockade with profound vasodilatation and impaired temperature perception during spinal or epidural anaesthesia may lead to unrecognized hypothermia in elderly patients without temperature monitoring. Therefore, the American Society of Anesthesiologists recommend in their ASA Standards for Basic Anesthetic Monitoring for Body Temperature to aid in the maintenance of appropriate body temperature during all anesthetics and every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated or suspected. ( aspx - Standards for Basic Anesthetic Monitoring, Effective July 1, 2011). Now the question arises where exactly can we measure reliable core body temperature? or can we also rely on measurement of skin temperature in the surgical setting? The organs in the abdomen and the thorax, considered as the thermal core compartment (including spine and brain), are highly perfused tissues with almost the same high and constant temperature, unlike the peripheral compartment. For the purpose of temperature measurement this core is easily accessible using a pulmonary artery catheter, an oesophageal or naso-pharyngeal temperature probe, or a tympanic membrane sensor. These probes are able to measure core temperature reliably and to record even rapid thermal changes, for example during hypothermic cardiopulmonary bypass. On the other hand, core temperature correlates with the temperature measured in the bladder, the oral cavity, and the axilla with reasonable accuracy if the rate of temperature change is not extreme. For a large proportion of surgical cases this can be an inexpensive option to ensure safety standards for temperature measurement and monitoring to avoid the perioperative morbidity associated with accidental intraoperative hypothermia. Animal studies have demonstrated that rapid alterations in temperature, for example occurring during malignant hyperthermia, are not detected so well by rectal temperature measurement, although under normal conditions this form of measurement correlates quite well with core temperature [14]. This is also more or less true for skin-surface temperature monitoring, which is usually substantially lower than the core temperature. However for monitoring trends, especially if the difference in degrees Centigrade is considered, skin-surface temperature is able to reflect core temperature reasonably well [15]. Nevertheless, caution is needed when interpreting rectal and skinsurface temperature. Recently infrared aural thermometers have been introduced. These measure skin temperature at the tympanic membrane but have many pitfalls and are far less accurate in reflecting core temperature [16,17] compared with forehead skin-surface and deep-forehead temperature measurements [18,19]. New devices measuring temporal artery temperature as a substitute for core temperature may also be prone to error. A recent study found very poor correlation of the two temperatures in the perioperative setting [20]

4 European recommendations concerning temperature monitoring and management to ensure perioperative normothermia come from the Italian Society of Anaesthesiologists (Societa Italiana di Anestesia Analgesia Rianimazione e Terapia Intensiva S.I.A.A.R.T.I.), although only available in Italian [8] the recommendations are summarised in Table 1. Table 1 The Italian standards recommend: Keeping the body core temperature of surgical patients slightly above 36 C Using forced-air warming as an efficient active external warming system and hypothermia prevention method Monitoring temperature in patients at risk for malignant hyperthermia under general anaesthesia Always monitoring the body core temperature of children Measuring core temperature to prevent inadvertent hypothermia Keeping ambient temperature between 21 C and 24 C for adults; and between 21 C and 26 C for children, with a relative humidity level of 40-60% Always warming i.v. solutions to 38 C in children (this should be assessed on a case-by-case basis in adults) Always using active external warming systems in children, and in adults for cases lasting longer than 30 minutes or when the core body temperature falls below 36 C Not discharging patients from the recovery room until normothermia is restored Key learning points Monitor body temperature and use active external warming systems routinely in children, and for cases lasting longer than 30 minutes or when the core body temperature falls below 36 C in adults. Monitor temperature in patients at risk for malignant hyperthermia under general anaesthesia and to prevent inadvertent hypothermia. To detect rapid temperature changes use a pulmonary artery catheter, oesophageal, naso-pharyngeal or tympanic membrane temperature probe. Probes placed in the bladder, oral cavity, or the axilla are reliable if temperature changes are not extreme. Infrared aural and temporal artery thermometers do not reflect core temperature with sufficient precision. Keep the body core temperature of surgical patients above 36 C and ambient temperature between 21 C and 24 C for adults; and between 21 C and 26 C for children, with a relative humidity level of 40-60%. Always warm infusions to 38 C in children (for adults this aspect should be assessed on a case-by-case basis)

5 References 1. Sessler DI. Mild perioperative hypothermia. New England Journal of Medicine 1997; 336: Lenhardt R, et al. Mild intraoperative hypothermia prolongs postanesthetic recovery. Anesthesiology; 1997: 87; Rajagopalan S, et al. The effects of mild perioperative hypothermia on blood loss and transfusion requirement. Anesthesiology 2008; 108: Frank SM, et al. Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events. A randomized clinical trial. Journal of the American Medical Association 1997; 277: Kurz A, Sessler DI, Lenhardt R, Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. Study of Wound Infection and Temperature Group. New Engand Journal of Meicine 1996; 334: Sessler DI. A proposal for new temperature monitoring and thermal management guidelines. Anesthesiology 1998; 89: Hooper VD, et al. ASPAN s evidence-based clinical practice guideline for the promotion of perioperative normothermia. Journal of Perianesthetic Nursing 2009; 24: Montanini S, et al. Recommendations on perioperative normothermia. Working Group on Perioperative Hypothermia, Italian Society for Anesthesia, Analgesia, Resuscitation, and Intensive Care. Minerva Anestesiologica 2001; 67: Talke P, et al. Dexmedetomidine does not alter the sweating threshold, but comparably and linearly decreases the vasoconstriction and shivering thresholds. Anesthesiology 1997; 87: Kurz A, et al. Desflurane reduces the gain of thermoregulatory arteriovenous shunt vasoconstriction in humans. Anesthesiology 1995; 83: Annadata R, et al. Desflurane slightly increases the sweating threshold but produces marked, nonlinear decreases in the vasoconstriction and shivering thresholds. Anesthesiology 1995; 83: Matsukawa T, et al. Propofol linearly reduces the vasoconstriction and shivering thresholds. Anesthesiology 1995; 82: Frank SM, et al. Epidural versus general anesthesia, ambient operating room temperature, and patient age as predictors of inadvertent hypothermia. Anesthesiology 1992; 77: Iaizzo PA, et al. Thermal response in acute porcine malignant hyperthermia. Anesthesia and Analgesia 1996; 82: Ikeda T, et al. Influence of thermoregulatory vasomotion and ambient temperature variation on the accuracy of core-temperature estimates by cutaneous liquid-crystal thermometers. Anesthesiology 1997; 86: Duggan J, Sinha VK. What s hot and what s not: pitfalls in infrared tympanic thermometry. Anaesthesia 2010; 65: Imamura M, et al. The accuracy and precision of four infrared aural canal thermometers during cardiac surgery. Acta Anaesthesiologica Scandinavica 1998; 42: Langham GE, et al. Noninvasive temperature monitoring in postanesthesia care units. Anesthesiology 2009; 111: Harioka T, et al. Deep-forehead temperature correlates well with blood temperature. Canadian Journal of Anaesthesia 2000; 47: Kimberger O, et al. Temporal artery versus bladder thermometry during perioperative and intensive care unit monitoring. Anesthesia and Analgesia 2007; 105: