Temperature-Monitoring and Thermal Management Guidelines
- When tempertuare monitoring is required
- Where to monitor temperature
- Consequences of thermal disturbances
- Proposed guidelines
*Reprinted from Sessler DI: Anesthesiology 1998; 89:1298-300
The last decade has seen publication of hundreds of papers on perioperative thermoregulation, heat balance, and consequences of thermal disturbances. We thus now know far more about control of body temperature and the effects of thermal perturbations than when the original ASA Temperature Monitoring Standards were introduced. More importantly, four major outcome studies were published in recent years; these studies indicate that even small reductions in intraoperative body temperature produce substantial morbidity.
We must thus consider whether revision of the current Temperature Monitoring Standards might be appropriate. To that end, I would like to summarize major recent studies relevant to patient temperature monitoring and thermal management – and their clinical implications. I will then propose a revised set of guidelines based on our current understanding of perioperative temperature control.
Normal core temperature varies between 36.5 and 37.5°C. Core temperature usually decreases 0.5-1.5° C in the first 30 minutes following induction of general anesthesia. Hypothermia results from internal redistribution of heat and a variety of other factors whose importance in individual patients is hard to predict.1 As a result, core temperature perturbations during the first 30 minutes of anesthesia are difficult to interpret.
Significant subsequent decreases in core temperature are most likely in patients undergoing abdominal or thoracic surgery, but malignant hyperthermia — and hyperthermia from other causes — remains a risk in all patients. Consequently, body temperature should be monitored in most patients undergoing general anesthesia exceeding 30 minutes in duration. Body temperature might ideally be monitored continuously; however, 15-minute intervals are probably sufficient in most patients.
The drugs used during intravenous sedation or regional anesthesia do not trigger malignant hyperthermia. However, core hypothermia does occur during conduction anesthesia,2 especially when surgery involves major body cavities,3 and often is manifested as shivering. Core temperature should thus be measured during spinal or epidural anesthesia in patients whom clinicians believe likely to become hypothermic.
The core thermal compartment is composed of highly perfused tissues whose temperature is uniform and high compared with the rest of the body. Temperature in this compartment can be evaluated in the pulmonary artery, distal esophagus, tympanic membrane, or nasopharynx. Even during rapid thermal perturbations (e.g., cardiopulmonary bypass), these temperature monitoring sites remain reliable.4 Core temperature can be estimated with reasonable accuracy using oral, axillary, and bladder temperatures except during extreme thermal perturbations.5-7
Skin-surface temperatures are considerably lower than core temperature. Skin-surface temperatures – when adjusted with an appropriate offset – nonetheless reflect core temperature reasonably well.8 However, skin temperatures fail to reliably confirm the clinical signs of malignant hyperthermia (tachycardia and hypercarbia) in swine9 and have not been evaluated for this purpose in humans. Rectal temperature also normally correlates well with core temperature,5,6 but fails to increase rapidly during malignant hyperthermia crises9 and under other documented situations.10,11 Consequently, rectal and skin-surface temper-atures must be used with some caution.
Thermoregulatory responses are impaired by general anesthesia.12 Intraoperative core body temperature changes are thus largely determined by patients' environments. Because the typical operating room is cold and because factors associated with surgery increase heat loss,13 perioperative hypothermia is common. Mild hypothermia (33-35°C) provides substantial protection from tissue ischemia14,15 and hypoxemia.16 It also slows triggering of malignant hyperthermia and the syndrome is less severe once triggered in hypothermic swine.17,18
In contrast, mild hypothermia (about 2°C below normal) prolongs drug action19,20 by decreasing metabolism,21 causes protein wasting,22 impairs platelet23 and clotting-cascade enzyme function,24,25 and triggers postanesthetic shivering26,27 and thermal discom-fort.27,28 More importantly, core temperatures only 1-2°C below normal are associated with adverse patient outcomes. Two groups have demonstrated that mild hypothermia in selected patient populations prolongs post-anesthetic recovery,29 augments bleeding and transfusion requirement,30 increases morbid myocardial outcomes,31 and reduces resistance to surgical wound infections and prolonged hospitalization.32
The minor and major complications of hypothermia are thus well documented. In some patients, mild hypothermia is likely to be dangerous. In others, it will be uncomfortable and slow recovery. I thus propose that intraoperative core temperatures should usually be maintained >36°C unless hypothermia is specifically indicated.
To detect thermal disturbances and maintain appropriate body temperature during anesthesia.
1) Core body temperature should be measured or reliably estimated in most patients given general anesthesia for more than 30 minutes.
2) Temperature should also be measured or reliably estimated during regional anesthesia when changes in body temperature are intended, anticipated, or suspected.
3) Unless hypothermia is specifically indicated (e.g., for protection against ischemia), efforts should be made to maintain intra-operative core temperature >36°C.
2. Frank SM, Beattie C, Christopherson R, Norris EJ, Rock P, Parker S, Kimball AW: Epidural versus general anesthesia, ambient operating room temperature, and patient age as predictors of inadvertent hypothermia. Anesthesiology 1992; 77: 252-7
4. Stone JG, Yound WL, Smith CR, Solomon RA, Ostapkovich N, Reeg T, Wang A: Do temperature recorded at standard monitoring sites reflect actual brain temperature during deep hypothermia? Anesthesiology 1991; 75: A483
5. Bissonnette B, Sessler DI, LaFlamme P: Intraoperative temperature monitoring sites in infants and children and the effect of inspired gas warming on esophageal temperature. Anesth Analg 1989; 69: 192-6
6. Cork RC, Vaughan RW, Humphrey LS: Precision and accuracy of intraoperative temperature monitoring. Anesth Analg 1983; 62: 211-4
7. Glosten B, Sessler DI, Faure EAM, Støen R, Thisted RA, Karl L: Central temperature changes are not perceived during epidural anesthesia. Anesthesiology 1992; 77: 10-6
8. Ikeda T, Sessler DI, Marder D, Xiong J: The influence of thermoregulatory vasomotion and ambient temperature variation on the accuracy of core-temperature estimates by cutaneous liquid-crystal thermometers. Anesthesiology 1997; 86: 603-12
11. Buck SH, Zaritsky AL: Occult core hyperthermia complicating cardiogenic shock. Pediatrics 1989; 83: 782-4
14. Illievich UM, Zornow MH, Choi KT, Strnat MAP, Scheeller MS: Effects of hypothermia or anesthetics on hippocampal glutamate and glycine concentrations after repeated transient global cerebral ischemia. Anesthesiology 1994; 80: 177-86
15. Todd MM, Warner DS: A comfortable hypothesis reevaluated: Cerebral metabolic depression and brain protection during ischemia (editorial). Anesthesiology 1992; 76: 161-4
16. Keykhah MM, Hägerdal M, Welsh FA, Barrer MA, Sisco F, Harp JR: Effect of high vs. low arterial blood oxygen content on cerebral energy metabolite levels during hypoxia with normothermia and hypothermia in the rat. Anesthesiology 1980; 52: 492-5
18. Nelson TE: Porcine malignant hyperthermia: Critical temperatures for in vivo and in vitro responses. Anesthesiology 1990; 73: 449-54
19. Heier T, Caldwell JE, Sessler DI, Miller RD: Mild intraoperative hypothermia increases duration of action and spontaneous recovery of vecuronium blockade during nitrous oxide-isoflurane anesthesia in humans. Anesthesiology 1991; 74: 815-9
20. Leslie K, Sessler DI, Bjorksten AR, Moayeri A: Mild hypothermia alters propofol pharmacokinetics and increases the duration of action of atracurium. Anesth Analg 1995; 80: 1007-14
21. Heier T, Caldwell JE, Sharma ML, Gruenke LD, Miller RD: Mild intraoperative hypothermia does not change the pharmacodynamics (concentration-effect relationship) of vecuronium in humans. Anesth Analg 1994; 78: 973-7
23. Valeri CR, Khabbaz K, Khuri SF, Marquardt C, Ragno G, Feinhold H, Gray AD, Axford T: Effect of skin temperature on platelet function in patients undergoing extracorporeal bypass. J Thorac Cardiovasc Surg 1992; 104: 108-16
25. Staab DB, Sorensen VJ, Fath JJ, Raman SBK, Horst HM, Obeid, F N: Coagulation defects resulting from ambient temperature-induced hypothermia. J Trauma 1994; 36: 634-8
28. Sessler DI, Rubinstein EH, Moayeri A: Physiological responses to mild perianesthetic hypothermia in humans. Anesthesiology 1991; 75: 594-610
30. Schmied H, Kurz A, Sessler DI, Kozek S, Reiter A: Mild intraoperative hypothermia increases blood loss and allogeneic transfusion requirements during total hip arthroplasty. Lancet 1996; 347: 289-92
31. Frank SM, Fleisher LA, Breslow MJ, Higgins MS, Olson KF, Kelly S, Beattie C: Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events: A randomized clinical trial. JAMA 1997; 277: 1127-34
32. Kurz A, Sessler DI, Lenhardt RA, Study of wound infections and temperature group: Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. N Engl J Med 1996; 334: 1209-15
During all anesthetics, the patient's oxygenation, ventilation, circulation and temperature shall be continually evaluated.
To aid in the maintenance of appropriate body temperature during all anesthetics.
Every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated or suspected. For office-based sedation, regional anesthesia, or general anesthesia, the ASA also requires that "the body temperature of pediatric patient shall be measured contunuously."
Recognition of the inadequate management of the patient's perioperative thermoregulation prompted the American Society of PeriAnesthesia Nurses (ASPAN) to host a Consensus Conference on Perioperative Thermoregulation on February 7, 1998, in Bethesda, Maryland. A variety of health care disciplines and specialties endorsed and participated in the conference. One hundred ten perianesthesia nurses, operating room nurses, nurse anesthetists, anesthesiologists, surgeons, critical care nurses, medical surgical nurses, and industry representatives dialogued regarding temperature management and its impact on patient care.
The final outcome of the conference was the recommendation to establish a development panel to create a clinical guideline for the thermoregulatory management of perioperative patients. On August 29, 1998, a ten-member multidisciplinary and multispecialty Guideline Development Panel convened in New York, New York, to write the Clinical Guideline for the Prevention of Unplanned Perioperative Hypothermia.
The intent of the Guideline is to provide clinicians with a practical, bedside approach to the prevention, care, and management of the adult surgical patient with unplanned perioperative hypothermia. The Guideline is designed to explore the physiological basis for perioperative hypothermia and cite clinical studies linking perioperative hypothermia to adverse outcomes. The Guideline has five major goals:
1. Establish a definition for normothermia.
2. Establish a definition for hypothermia.
3. Alert health care providers in perioperative settings of the importance of maintaining perioperative normothermia.
4. Provide ways to address the management of unplanned perioperative hypothermia.
5. Improve patient outcomes by establishing strategies to maintain perioperative normothermia.
Italian Anesthesiologist Conference Recognizes Temperature Monitoring as A Standard of Care
Group Recommends Forced-Air Warming as Most Efficient Method for Warming Patients.
NAPLES, Italy, March 7 /PRNewswire/ -- The Italian society of anesthesiologists (Societa Italiana di Anestesia Analgesia Rianimazione e Terapia Intensiva S.I.A.A.R.T.I.). - S.I.A.A.R.T.I. recently recommended that the core body temperature of surgical patients should always be kept at, or slightly above, 36 degrees C to eliminate the onset of mild hypothermia (except in cases of intentionally-induced hypothermia). In addition, the group recognized forced-air warming as "the most efficient in warming the patient and preventing hypothermia." The Italian recommendations resulted from a Consensus Conference of Italian anesthesiologists, which was specifically held for the purpose of making recommendations for preventing and/or treating inadvertent perioperative hypothermia in adults and children. These are the first guidelines initiated by anesthesiologists. Although the American Society of Anesthesiologists' Standards for Basic Anesthetic Monitoring recommends body temperature monitoring in all patients, no guidelines have been issued by the US society. Mild hypothermia -- a core temperature between 36 degrees C and 33 degrees C -- is a common event during anesthesia, whether general, regional or combined. It has been shown that inadvertent hypothermia, even if mild, induces significant cardiovascular, endocrine, metabolic and blood composition changes, which may explain the higher mortality and morbidity rates observed in hypothermic patients when compared with patients in whom normothermia is maintained. For these reasons, S.I.A.A.R.T.I. concluded that inadvertent mild hypothermia must be prevented.
Forced-air warming declared the best The conferees also examined various forms of external warming systems, including circulating water mattresses, metallic blankets and forced-air warming. The conference paper stated that, "Forced-air warming systems are the most efficient in warming the patient and preventing perioperative hypothermia. If the patient is warmed for 30 minutes before induction of anesthesia, then the initial reduction of (core temperature) through redistribution can be limited. If preoperative warming is prolonged for another 30 minutes, it is possible to eliminate the decrease completely, since the thermal gradient between the core and periphery is obliterated."
Temperature monitoring as a standard of practice Until recently, body temperature monitoring was not a standard practice in anesthesia. In the mid-1960s the first cases of malignant hyperthermia were observed. At that time it was found that early diagnosis of temperature elevation enabled a decrease in the mortality associated with this syndrome (from 80 to 30 percent). In addition, it has been known for some time that the most common effect of anesthesia upon the human body is hypothermia. For example, in 1994, a study published in Anesthesiology (Frank, SM, et. al) found that among surgical patients, 50 percent showed core temperature values of less than 36 degrees C at the end of an intervention, while 33 percent of these patients experienced even higher levels of hypothermia, with a core temperature of less than 35 degrees C. The evidence has clearly been available.
Other recommendations from the conference included:
- In adult patients who are at risk for malignant hyperthermia or who are under general anesthesia for a period exceeding 30 minutes, temperature should be monitored.
- The core body temperature of children should always be monitored.
- Temperature monitoring should always be directed toward the core temperature. — Preventive measures should be instituted against inadvertent hypothermia.
- Ambient temperature should be kept between 21 degrees C and 24 degrees C for adults; and between 21 degrees C and 26 degrees C for children, with a relative humidity level of 40-60 percent.
- Warming of infusion fluids to 38 degrees C is always recommended in children. In adults, the use of this preventive measure should be assessed on a case-by-case basis.
- Active external warming systems are always recommended. — The forced-air warming system is always recommended for use in children by reason of its proven effectiveness, even under conditions of reduced usable surface.
- In adults, the use of a forced-air warming system should be considered when the intervention will last longer than 30 minutes or when the core body temperature falls below 36 degrees C.
- The patient should never be discharged from the recovery room until normothermia is restored, or if signs of hypothermia are present.