Temperature Monitoring and Regulation

Temperature Monitoring and Regulation ROBERT M. SMITH, M.D.*

Much emphasis is justly being placed upon the importance of body temperature during the operative period in pediatric surgery. 21 • 29 • 30• 41 • 44 The high incidence and severe consequences of both hypothermia6 • 12 • 15 • 36 and hyperthermia13• 14• 23 • 37• 47 have aroused widespread concern and have stimulated considerable enthusiasm for "monitoring" body temperature and attempting to regulate it. Because of numerous recent developments in both theoretical and technical. aspects of temperature control, there appears to be much confusion in the general application of available information. This confusion is seen in the choice of monitoring techniques, in the evaluation of data, and especially in the approach to temperature regulation. Failure to recognize obvious clinical syndromes on the one hand, and overzealous and poorly regulated use of temperature controlling devices on the other, have resulted in too many catastrophes. Outstanding examples of such incidents are those in which patients' temperatures have been allowed to reach 108° F. unnoticed, and others in which patients have been severely burned by faulty use of heating devices. 7 • 38 UNDERLYING PROBLEMS. Several underlying situations contribute to the increased incidence of temperature-related complications in pediatric surgery. It is common knowledge that children, and especially infants, are subject to greater variation in body temperature than are adults and that infants, due to greater body surface area and increased tissue conductivity, have a marked tendency to become hypothermic. 10• 31 • 41 The newborn infant begins to lose body heat the moment he is born and usually suffers a loss of 2 to 4° F. in the interval between delivery and arrival in the nursery. 30 Premature infants have greater difficulty maintaining temperature stability, and their problems may be compounded by interaction of hypoglycemia, metabolic acidosis, and respiratory distress syndrome. The effect of hypothermia upon the neonate was in question until recently, it having been held possible that intentional cooling of de*Clinical Associate Professor of Anesthesia, Harvard Medical School; Director of Anesthesia, Children's Hospital Medical Center, Boston, Massachusetts Pediatric Clinics of North America- Vol. 16., No. 3, August, 1969 643

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pressed neonates might reduce their oxygen requirement and improve over-all survival. Conclusive proof by Silverman40 that infants maintained at temperatures above 95° F. had better survival established the dictum that cooling was to be avoided in infants under all conditions. Subsequent investigation by numerous workers has disclosed the mechanism of nonshivering thermogenesis, 1• 4 • 9 • 24 • 45 which further explains the harmful effect of exposure of infants to cold. Other studies of the routes of heat loss by exposed naked infants have demonstrated that radiation accounts for approximately two thirds of the loss under normal conditions 10 and, consequently, have suggested proper avenues of correction. Many other factors contribute to the hazards of the neonate, most of them pointing in the direction of hypothermia. Older children undergoing operation have a greater tendency to develop hyperthermic complications. Rapid temperature elevation and convulsions were seen with ether and often terminated fatally. 32 • 33 At present, there is grave concern over a newly recognized syndrome of rapid "malignant" hyperthermia, 8 • 11 • 23 • 34 often seen in siblings and also associated with high mortality. Excessive cooling does occur with older children, though less frequently. It is seen in extensive operations, especially in procedures involving massive blood replacement. 42 In the postoperative recovery room, in intensive care units, and in nursing divisions, we are faced.with a variety of temperature regulating problems which actually may be more difficult to manage than those in the operating room. Their difficulty lies in the facts that, first, they are often of prolonged duration, and secondly, one has less choice in methods of treatment. For example, if a child had a fever of 103° F. in the operating room, he could be treated by application of ice or cold fluids to his body and his temperature would drop rapidly. Since this type of surface cooling makes conscious patients shiver actively, 5 • 22 • 43 it is ill-advised and other and less effective alternatives must be substituted. Unfortunately, these patients may be critically ill, whether with pneumonia, status asthmaticus, or some neurological lesion, and speed is important. This problem, which is one of our oldest, remains unsolved. The mechanisms of temperature control have been extensively described, as have various approaches to the situations mentioned above. These have been noted here merely to illustrate the present need for measuring and governing body temperature.

METHODS OF MONITORING TEMPERATURE The term "monitor," as currently used in the practice of medicine, is employed as a noun to describe any one of a variety of devices of increasing cost and complexity which measure and indicate or record some physiologic variable such as pulse or temperature, or else as a verb, here implying continuous watching or observation. In both cases it appears that the term has been altered somewhat from its original implication, that is, not only of measuring or observing, but of guarding. This is a significant point, because it brings out a real weakness encountered with

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increasing frequency, that of measuring or observing without meaningful application of the results. If our medical monitors were to live up to their names, they should either include a warning device or have a feedback system that would correct abnormal deviations automatically. To a certain extent, especially in temperature control, this has been initiated, but the term monitor usually does not imply this conclusion. The above digression actually has relevance here because, as has been shown by Adamsons and others, a single temperature reading or even a series of readings from any single area of the body may have little significance unless this information is related to measurement at other parts of the body or surrounding objects. Monitoring by Observation of Clinical Signs In order to monitor body temperature, we might expect to start with the use of the clinical thermometer. To begin with a device even as simple as this one, we should be disregarding a number of obvious leads which may be of great value. To one who has been sensitized to the dangers of body cooling, the mere sight of a newborn infant lying uncovered and exposed upon an operating table or treatment stand will set off a reaction which often includes a verbal alarm response. SIGNS OF HYPOTHERMIA. The clinical signs of hypothermia in infants are not so obvious as those of hyperthermia in older patients, but several situations may occur which, without recourse to a thermometer, should alert one to the possible existence of excessive cooling as in the exposure of infants at operation. Most pediatricians are aware of situations that involve increased danger of exposure and hence require more scrupulous observation and care. These include the immediate postnatal period and transportation, not only the infrequent moving between hospital and home, but much more common moves between various hospital facilities such as adinitting department, operating room, x-ray, and treatment room. The hazard of cooling during such trips is recognized, means to avoid them are available, and failure to regard them must be attributed to poor supervision or carelessness. One of the most obvious signs of changing body temperature is observed simply by feeling the patient's skin. Cold hands or feet should be noticed, but do not always denote severe change. However, when the body or head feels appreciably cooler than normal, this is a sign of serious nature. Direct observation of an infant who has become hypothermic gives relatively little proof of his plight, but there are several clues that should alert one to the danger. The child's skin may become more pallid, and his extremities often become cyanotic. The child's peripheral vasculature becomes constricted and with vasoconstriction, the blood pressure is reduced. The infant may increase his muscular activity at first, but with increasing cooling may become flaccid. This is seen especially in the anesthetized infant, where the usual degree of flaccidity may be increased by greater solubility of anesthetics in cool blood. With marked cooling, pupils will show greater dilation. Shivering is obviously a useful

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sign in older children, but rarely occurs in small infants. 2 • 39 Shivering is blocked in patients of all ages during general anesthesia. Several clinical situations should arouse immediate concern. During resuscitative procedures, when protective covers are usually thrown clear to allow accessibility of all areas of the body to the procedures of respiratory ventilation, cardiac massage, intravenous medication and samplings, and attachment of electrodes, after 5 minutes of such exposure the child may become so cold that his chances of revival are considerably diminished. In the operating suite, one occasionally finds that the room temperature has been so drastically reduced to comply with the wishes of the surgeon that circulating nurses have draped blankets over their shoulders for protection. One should immediately check to see that the anesthetized child has been equally protected. Occasions also have been noted in which operating rooms were so cold that vapor could be seen rising from the surface of the exposed bowel or lung. Here again, steps should be taken to correct the underlying cause and specific action initiated to meet the danger of severe hypothermia. SIGNS OF HYPERTHERMIA. The detection of hyperthermia is of extreme importance; however, one can find several accounts of anesthetized patients who were suddenly found to have temperatures of 106 to 108° F. These statements are made without explanation or apology, but would seem comparable to admission of having left the baby out all night. Signs of hyperthermia are gross and abundant. All body surfaces will become obviously overheated, especially those of the head, which is most frequently under the direct observation of the anesthesiologist. There also will be flushing of the skin, often accompanied by labored respiration, tachycardia, and increased blood pressure. Sweating is less marked in young children, but increased skin moisture is usually evident even in infancy. Undoubtedly, a most obvious and alarming sign of hyperpyreXia is a seizure of any form during anesthesia. In cardiac arrest of undetermined origin, hyperthermia must always be considered as a possible primary or secondary factor. Surgeons also may notice signs of hyperthermia. Although complaints about increased bleeding are heard too frequently to cause immediate alarm, they must always be investigated. At extremely high temperatures, the body tissues will feel so hot that the surgeon may remark upon it when he puts his hand in the chest or abdomen. This usually denotes a serious situation that demands immediate action. CLINICAL SIGNS IN THE REcovERY RooM. As patients awaken from anesthesia, the pattern of temperature control may be markedly altered and the signs correspondingly confusing. They frequently exhibit a variety of shaking motions that :r:esemble both convulsions and severe shivering. In the infant, these appear to be neither, but rather an irregular return of muscular control. 22 • 43 In slightly older children and adults, true shivering of an intense degree is frequently seen following anesthesia with thiopental or halothane. This shivering may occur with

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minimal loss of body heat and probably denotes an altered temperature threshold for shivering due in part to the depression of catechol release that is associated with these anesthetics.

Monitoring by Measurement of Temperature MEASUREMENT OF ENVIRONMENTAL CONDITIONS. Each nursing division or ward and every individual operating room should be fitted with a wall thermometer and hygrometer. Whether the thermostat should be exposed and at the mercy of everyone in the operating room seems doubtful, but a convenient control must be available. Air conditioning is usually provided in all operating rooms and undoubtedly will be in all modem nursing wards. Airflow meters should be available in the hospital to check the rate of air flow, which is measured in linear feet per minute (lf/m). 19 WHEN TO MEASURE BODY TEMPERATURE DURING PEDIATRIC SuRGERY. If possible, it is a commendable practice to measure the temperature of all children during all operative procedures. Whether or not this is performed routinely, there are certain operations that have carried a definitely higher incidence of serious temperature aberrations, and it seems extremely important to monitor children throughout these particular procedures. Obviously, one must follow very closely the temperatures of those who are to be warmed or cooled intentionally. Excessive cooling is a definite threat to all infants undergoing operation, and the threat is magnified in those with low blood pressure, severe body burns, or generalized muscle weakness, those undergoing prolonged neurosurgical operations, and children who require rapid infusion of large amounts of blood. While any patient may either gain or lose heat under anesthesia, there are several situations that suggest increased danger of hyperthermia. These include patients whose temperature is elevated before operation (most frequently those having appendicitis), as well as those with latent sources ·of infection, such as the patient having low-grade genitourinary infection. Other candidates are children who have been held without fluids for more than 4 hours, those receiving blood, and those operated upon in a warm room or under excessively warm operating lights. SITES OF MEASUREMENT OF BODY TEMPERATURE. The temperature of the body is measured at different locations, depending upon individual circumstances. No single site gives an accurate figure for the entire body. For nursing care during the course of most illnesses, the rectum serves as the most practical site in infants and small children, while sublingual temperature is sufficiently accurate for older patients. The axilla is used when access is denied to the infant's rectum. "Normal" temperatures at these sites have been established as 99.8, 98.8, and 96.8° F., respectively, with allowances of± 0. 7o F: for normal variation. 28 It is well known that there are many variables which may involve changes within and beyond these liinits without the presence of any disease process. Sleep, exercise, eating, excitement, and diurnal perio-

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dicity all affect body temperature to a modest extent, while bathing in cold water may reduce rectal temperature by 5 or 6° F. without untoward results. If one is measuring the rapid temperature changes that take place during intentionally induced hyperthermia or hypothermia, it is important to measure the core or central temperature. Although the liver is believed to be the warmest part of the body, it lends itself poorly to temperature measurement. Rectal temperature was originally believed to indicate core temperature satisfactorily, but has been found to show considerable time lag during rapid gain or loss of body heat, due probably to the presence of fecal material around the thermistor probe. The esophagus is a more reliable site to use during pronounced changes of temperature, and it is probable that the nasal turbinate is equally reliable and less subject to trauma than either esophagus or rectum. In clinical practice, it must be stated that each of these sites is used frequently. Furthermore, the temperature of all three sites should be the same. Investigation of energy requirements in infants has produced evidence that measurements of the gradient between surface or skin temperature and deeper core temperature are necessary to determine the stress imposed upon the infant. It is believed that measurement of skin temperature should replace that of the ambient air as routine practice.t. 41 Silverman bases his conviction on data showing oxygen consumption to be minimal when skin temperature is between 36 and 37o C. over the region of the liverY Further evidence has shown that the temperature of the walls surrounding the infant is of marked importance due to radiant heat loss of uncovered infants. 10 This is less critical during operations, because the child is mostly covered by drapes and surrounded by the operating team. Use of automatic temperature-sensing devices has already been incorporated into bassinets and involves less hazard than rectal thermistors. 3 • 16 • 27 • 35 It seems advisable to bring this method into operating rooms and constant care units. THERMOMETERS. Measurement of body temperature has been accomplished most widely by use of the so-called "clinical" thermometer, introduced in 1870 by Allbutt. At present, the standard device is the mercury-filled glass thermometer 4 inches in length with a 1/4-inch rounded bulb (Fig. 1). It is calibrated in degrees Fahrenheit, 94 to 106°, and is designed for rectal use in infants and children. A variation upon this is the thermometer designed for premature infants, which is similar in construction but calibrated from 84 to 108° F., in order to allow for the lower temperatures sometimes found in these weaker infants. A third type, designed for sublingual use, has an elongated (l-inch) mercury bulb to allow more surface contact with the tongue. Clinical thermometers are usually made as "nonretreating" thermometers, which means that near the base the mercury tube is angulated and constricted. 39 When warmed, the mercury expands and pushes past the constriction; but on cooling, the mercury above the constriction does not "retreat" past the constriction until forcibly shaken. Therefore, it continues to indicate the highest temperature measured. The clinical thermometer is so familiar that one often overlooks both its advantages and its faults. It is simple, widely available, and relatively

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cheap. In addition, it is remarkably accurate. In many states, each thermometer is inspected before sale and must be accurate to 0.2° F. The disadvantages of the clinical thermometer lie in the force required to "shake it down" after use, the ease with which it is broken, and more especially the dangers involved if it is broken during use. The development of an unbreakable thermometer for pediatric use seems long overdue. Actually a plastic disposable thermometer has been produced but has not reached a practical form. For continuous display or recording, electrically powered resistance thermometers constructed on the plan of a Wheatstone bridge are now generally employed for both clinical and investigational use. 26 Electric current may be supplied by battery or house current. Those running on batteries entail less hazard of explosion and are less expensive but less accurat~ than those working on house current. Although the batterydriven thermometer is more portable, it should be emphasized that the inaccuracy of these uni'ts is due in large measure to Inishandling. It is preferable to attach such devices to an anesthesia machine or similar stable object to keep them from being dropped or knocked about.

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Electric thermometers are available in numerous variations and may be constructed with jacks for 1 to 10 thermistor probes. The probes themselves are usually on 10-foot cords and may consist of (1) plastic tips· for nasal, oral, esophageal, or rectal use, (2) flat metal sensing tips for skin temperature, or (3) needle sensors to measure subcutaneous or intramuscular temperature. The accuracy of all electrical thermometers is still variable. Although they may "zero" or "balance" at time of use, either the central unit or the cord and sensing tip may be 2 to 3° F. in error. When one of these units is to be used, it is advisable to take the patient's temperature first with a glass thermometer, then insert the electrical probe thermometer, and correct subsequent readings of the electric device on the basis of the original reading of the glass thermometer. The battery-powered units usually read out on a scale, while most house current units are constructed with digital readout. The latter have more rapid response. Both types may be connected to recording devices.

EVALUATION OF DATA Problems in temperature regulation, like many others in medicine, may best be managed in a three-step process consisting of measurement, evaluation, and therapy. Methods of measurement and therapy, or control, of body temperature have at least been explored, but the rationale for suiting the type of treatment to the nature of the lesion remains vague. Although specific criteria are not available for all situations, some guidelines may be suggested. CHARTING TEMPERATURE. The best start in evaluating temperature change is to make a practice of charting it at frequent regular intervals during the operative period. It is advisable to have a regular column for this purpose in all charts used for pediatric anesthesia (Fig. 2). LIMITS OF VARIABILITY. Some variability of body temperature must be expected, but standards should be established determining the degree of acceptable variation. It has proved helpful to regard the range between 95 and 100° F. as the safe zone during anesthesia. When either limit is passed, suitable steps are taken. SIGNIFICANCE OF PROBLEM. Several factors must be considered in judging whether a situation is to be taken as a note of warning, or as a signal for immediate interruption of the operation and heroic therapy. Among these are the following: 1. Direction and degree of temperature change. Cooling of patients, though more common, is less to be feared than overheating. Cooling during anesthesia causes cardiorespiratory depression, reduces enzyme activity, prolongs recovery, and when carried to an extreme (below 85 to 88° F.) may induce ventricular fibrillation. However, irreversible changes do not occur until tissues are frozen. Hyperthermia, on the other hand, acts more rapidly and, in the vicinity of 108° F., causes irreversible brain damage. 2. Rate of temperature change. Obviously, a rapid fall or rise in temperature is more significant than one that occurs over several hours. When the change is abrupt, one should look for such specific. causes as use of cold blood or a faulty heating unit. It should be emphasized that cooling usually occurs as a passive phenomenon with decreasing speed, while the process of hyperthermia appears to feed upon itself and accelerates markedly as it advances.

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3. Physical characteristics of patient. The size, age, vigor, and underlying disease of the child have important bearing on the significance of temperature changes encountered. Similarly, the operation underway, its expected duration, and blood transfusion requirement are to be considered in planning treatment. If the temperature of a weak 4-year-old child undergoing removal of a large abdominal tumor falls to 94° F., one could expect that subsequent blood loss, manipulation, and transfusion might result in disaster. In a strong 12-year-old, however, undergoing a relatively atraumatic procedure, this degree of heat loss would be of little consequence.

METHODS OF CONTROLLING BODY TEMPERATURE When temperature changes are discovered or expected in pediatric surgery, there is a widespread tendency to place the child on a temper-

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ature-controlling water mattress and go ahead. Although this frequently does succeed, it must be emphasized that one should not depend primarily upon temperature-controlling devices that actively warm or cool patients. Whether acting by means of water blanket, air blower, or heating lamp, most of these devices entail definite hazards. It is preferable, whenever possible, to attempt by nonphysical means to correct existing hypothermic or hyperthermic abnormalities or to prevent their occurrence by other methods. Since there are numerous contributing factors, there are many methods available. If they are rationally employed, heating and cooling devices will serve more properly for supplemental use or often will be completely unnecessary.

Preventive Methods Among the many factors that contribute to undesirable temperature changes in operative patients, one must consider pre-existing hypothermia and hyperthermia of the child during surgical preparation, premedication, anesthetic agent and technique, temperature of irrigating fluids, temperature and amount of intravenous fluid and blood, type of wound, and duration of operation.

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D Figure 3. Methods for regulating temperature by water-filled devices. A, Hot water bottle (or ice bag). B, McQuiston mattress. C, Hot and cold water circulating mattress. D, Same with servo control unit.

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Details concerning only a few of these factors can be discussed here. Atropine, usually administered 40 to 60 minutes before operation, promotes heat retention. When a child already has a temperature elevation (as with acute appendicitis), it is preferable to delay administration of atropine until actual induction of anesthesia. As previously noted, environmental factors should be suited to individual needs. During transportation, warmth may be ensured by adequate covering, but operating rooms should be under accurate control. After investigation of proper room temperature for operations on neonates, Martin found 80° F. to be optimum for normal neonates and recommended 85° F. for premature infants (unpublished data). It would seem reasonable to use this temperature during preparation of the infant and then, for general comfort and efficiency, reduce it slightly after the infant has been draped. Relative humidity must be at least 50 per cent and if possible, the air conditioning should be run at reduced rate, preferably at an airflow rate of about 20 linear feet per minute. PROTECTIVE CovERING OF INFANTS. Undoubtedly, the period of greatest heat loss is when an infant lies exposed on the operating table during preparation for operation. To prevent cooling at this time and throughout the remainder of the procedure, every attempt should be made to retain the child's own body heat. An effective and safe method of protecting infants is to wrap their limbs in protective covering. 42 Sheet wadding, such as is used to line plaster casts, has proved excellent for this purpose as it serves several functions. It protects the tissues from mechanical or thermal trauma, assists in immobilizing the child, and reduces heat loss. Considerable heat loss can occur through the bare scalp of a small infant; consequently, the infant's head should be covered. Better methods of retaining heat by covering the body surface with plastic drapes, or by addition of plastic or silver foil outside protective sheet wadding, are under investigation. Fluids used during operation may precipitate rapid and even fatal complications. While irrigating solutions should play only contributing roles, rapid intravenous infusion of cold blood is known to have caused cardiac standstill. Use of warmed blood is believed mandatory when patients receive large amounts of blood rapidly. A guideline to follow is to warm blood if one third of the blood volume is or may be replaced. Anesthetic management may play a part in both cause and treatment of thermal complications. Halothane and relaxants act to increase heat loss, cyclopropane to reduce it. Open, semiopen, and nonrebreathing techniques promote heat loss, especially if gases are not humidified, while closed techniques act to retain body heat and moisture. Pulmonary ventilation is of extreme importance in the management of patients during hyperthermic crisis. These patients rapidly develop marked metabolic acidosis, and ventilation should be increased to approximately three times the usual volume. SUPPLEMENTAL WARMING AND COOLING DEVICES. Probably the first warming device brought into the operating room was the standard hot water bottle. If a temperature of 103° F. is pot exceeded, this can be effective; however, the speed with which this device loses heat and the

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Figure 4. A, Warmed plastic incubator with open ends for treatment (Sierracin). B and C, Open bassinets warmed by radiant heat and infrared lights (B, Air Shields infant warmer; C, Emerson Eastwood resuscitation crib).

high incidence of body burns due to use of excessive hot water makes this definitely unsatisfactory unless one is faced with an emergency. To provide greater safety, one may invert an instrument tray over two hot water bags. This makes a small platform on which a neonate may lie warmed by, but out of contact with, the source of heat. To provide continuous and controllable warmth (or cooling) during anesthesia, water circulating mattresses have been widely used. The first of these, designed by McQuiston, 29 was a mattress 20 X 30 inches with an inlet through which water at the desired temperature could be added from a suspended irrigation can and an outlet for drainage (Fig. 2). This was first used for cooling children during cardiac surgery, but is equally useful for warming infants and children. When in use, it should be covered by at least one thickness of a blanket or its equal. The danger of burning patients is greater, if anything, since the repeated addition of hot water increases the opportunity for error. Somewhat more versatile has been the unit which warms or cools fluid to a designated temperature and pumps it through coils of tubing that are incorporated into blankets of various sizes. 44 This combination has had wide commercial distribution. It is effective and, in some situations, essential and should be available in every hospital where pediatric surgery is performed. Because of the rapid development in this field, it would be unwise to recommend any specific make of heating-cooling device, but certain criteria are important in the choice. They include the following: 1. The machine should contain both heating and cooling units and pump. 2. One thermometer should read the temperature of the fluid in the central unit,. another, the temperature of the mattress where it contacts the patient.

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3. All construction must be sturdy and shockproof. 4. Mattresses should be varied in size and weight, and should be durable, resistant, and easily repaired if damaged. 5. The machine should be quiet when in action.

As an additional refinement in temperature controlling machines, a servomechanism may be attached to the unit just described. 48 This "brain" picks up the patient's temperature by a sensing probe to skin or rectum and then adjusts the heating and cooling mechanisms until the patient's temperature reaches the level for which the device has been programmed. Although this appears to represent an advanced step, performance has not been sufficiently reliable for enthusiastic acceptance. It appears less hazardous to operate a water circulating mattress by manual control, using an independent thermometer for temperature measurement and one's own judgment as the computer. Although pads and blankets warmed by means of electric coils have been popular in American homes, fear of faulty wiring has prevented their admission to our operating rooms. The British have used them and find them effective. 48 One obvious disadvantage is that even if they could be made to be entirely safe, they do not provide cooling as does a water mattress. At an early stage of open-heart surgery, Swan employed diathermy for rewarming children who had previously been cooled by immersion in a tub of ice water. 46 Both of these practices have largely been abandoned. Roe and Santulli36 have more recently investigated the use of an electrically controlled rectal probe for maintaining body heat. This proved effective in dogs, but it would seem inadvisable to attempt to introduce an appreciable amount of heat through such a limited area. If an infant must be exposed, it is natural to look for methods that do not require physical contact. Both air blowers and heating lamps have been advocated. An ordinary hair dryer, as used in many American homes, will deliver a jet of air at room temperature or heated to temperatures varying from 103 to 140° F. This instrument and variations upon its basic structure have been employed as supplemental devices for use during operative procedures. There are obvious dangers and disadvantages. Standard precautions must be observed with the heating coil, and the air temperature should never exceed 103° F. It is preferable not to direct the air stream toward a sterile surface or into the operating field. Actually, its best use might be for supplemental warmth delivered under draped-off areas. Neurosurgical procedures have provided opportunities for this approach, but the actual use has been limited. In England and Sweden, warm air has been employed, generated by heating units outside of the operating room and blown in via tubular conduits. Observations that the exposed infant's heat loss is largely due to radiation have resulted in attempts to meet this by use of radiant energy in the form of infrared lamps or similar sources. 16 • 27 • 35 Bassinets thus adapted are constructed with a plastic hood containing a heating element. A sensing device on the infant's abdomen activates the heating

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unit to vary its intensity as needed. Both ends of the bassinet are open to allow access for exchange transfusion or other prolonged therapeutic maneuvers that usually involve exposure of the infant. These bassinets are relatively safe and are recommended for use in nursing divisions and recovery room care, but do not allow sufficient access for use during major surgical procedures. Infrared lamps and radiant heat sources mounted above open-top bassinets for use in the delivery area and treatment room are now available. When they are used, one must observe strict precautions as to distance from patient and duration of exposure. At a distance of 27 inches, a single lamp generates 40° F., but at 18 inches, it generates 140° F! On clinical experience, Eastwood recommends exposure of not more than 15 minutes at a distance of 27 inches (unpublished data). It must be emphasized (1) that heating instruments are subject to faulty operation, (2) that tolerance of normal tissues to degrees of heat, distance from source, and time of exposure have not been determined, and (3) that any tissue that has less than normal circulation will tolerate less thermal trauma than tissues with normal circulation. Internal Methods of Temperature Control Lives have been lost by failure to realize that internal temperature control is far more effective than "surface" methods. For open-heart procedures, rapid cooling and warming has been effected by so-called "heat exchangers," which warm or cool blood during the extracorporeal phase of circulation. Most heat exchangers consist of water jackets of variable temperature, inside which blood is circulated. For simpler procedures, rapid reduction or elevation of body temperature can be brought about by irrigating any of the body cavities with iced or warmed saline. During thoracic or abdominal operations, one has an effective site immediately at hand. Every operating room should keep fluid refrigerated for this purpose, but if cooled fluid is not available, ample quantities of fluid at room temperature should be employed. Sterile saline or electrolyte mixtures should be used rather than water. The stomach and rectum usually offer easy avenues of approach for internal irrigation. It is our custom to irrigate the stomach of any patient whose temperature reaches 101° F. during operation. For this purpose, a liter of saline is poured into a pan of ice and irrigation is carried out with this fluid until the temperature falls. This maneuver can easily be performed by the anesthetist without interfering with the operation. Internal cooling methods are more rapid than surface methods and more accurate; furthermore, there is less. likelihood of having the temperature overshoot or "drift" beyond the desired level. ILLUSTRATIVE CAsEs. To emphasize suggested steps in temperature control, procedures are outlined in various types of situations. Case 1. Premature infant undergoing repair of intestinal obstruction. 1. Adjust operating room to temperature 85° F., relative humidity 50 per cent, and if possible, reduce airflow rate to 20 lf/m. 2. Transport infant to operating room in warm, covered bassinet. Keep in bassinet until surgeons are scrubbed and present inside operating room.

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3. Wrap infant's limbs in sheet wadding while still in bassinet. 4. Prepare water circulating mattress, covering mattress with two thicknesses of sheet. Warm mattress to 100° F. 5. Place covered infant on operating table for anesthetic induction. 6. Uncover only area required for operation. 7. Use nonvolatile liquids for skin preparation. 8. Fix one thermistor in rectum, another on skin near liver. 9. Chart both temperatures during operation. Case 2. Two-year-old facing removal of abdominal tumor and possible hemorrhage. 1. Warm the room to 75° F. 2. Use circulating water mattress (manual control) with esophageal or rectal thermistor. 3. Attach electrocardiogram to warn of cardiac depression. 4. Buffer blood and warm it by standing bags in 100° F. bath or by attaching additional length of tubing to infusion and submerging it in tub of water 90 to 100° F. Case 3. Six-month-old infant undergoing neurosurgical operation. Temperature falls to 94o F. 1. Warm room to 85° F. 2. Warm blood. 3. Cover patient with prewarmed blankets. 4. Blow warmed air under drapes (protect skin). 5. Humidify anesthetic gases. 6. Reduce gas flow to minimal acceptable flow. Case 4. Ten-year-old with ruptured appendix, temperature 104° F. before operation. 1. Pass nasogastric tube. 2. Start intravenous infusion (plasma or electrolyte mixture). 3. Start antibiotics. 4. Delay premedication and operation until hydration confirmed by passage of normal urine. 5. Reduce operating room temperature to 70° F. 6. At operation, place on cooling blanket, induce anesthesia with intravenous barbiturate and halothane. 7. Monitor rectal temperature. If 102° F. or above after induction, sponge with alcohol or ice water until temperature under 102° F. Continue to monitor during and after operation. 8. Watch for tremors, muscle rigidity, respiratory abnormality. Case 5. Hyperthermia during operation. If rectal temperature exceeds 99o F.: 1. Reduce room temperature. 2. Uncover patient where possible. 3. Employ semiopen or nonrebreathing anesthetic technique. 4. Increase ventilation to three times basal need. 5. Use cooling blanket, if in place. If 1. 2. 3.

temperature exceeds 102° F.: Notify surgeon and request all reasonable speed. Apply ice in plastic bags to limbs, head, neck, groin, as possible. Pass nasogastric tube. Irrigate with iced saline.

If temperature exceeds 104° F.: 1. Stop operation. 2. If thoracic or abdominal cavity is exposed,· irrigate with cooled, sterile solutions.

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3. If body cavities are not exposed, abdomen may be opened for this purpose if temperature is 108° F. or above; otherwise, remove drapes and apply ice all over body. Case 6. Neurosurgical patient 3 days post craniotomy. Temperature 105° F. 1. Aspirin. 2. Fluids. 3. Cooling mattress, temperature 95° F. 4. Thorazine. 5. Expose skin surface to air and electric fan. 6. Sponge with alcohol to shivering threshold. Case 7. Eight-year-old awakening from 3-hour orthopedic procedure under halothane anesthesia, shivering violently, temperature 97.3° F. 1. Continue intravenous infusion. 2. Administer morphine 4 mg. IV, stat, to control shivering. 3. Cover with blankets.

SUMMARY Although there is an increased incidence of complications related to body temperature in pediatric surgery, overenthusiasm in use of poorly controlled devices has resulted in many injuries. A practical guide to measurement and regulation of body temperature is presented with emphasis on the following points: (1) Monitoring of temperature is accomplished by use of many clinical signs, as well as by thermometer. (2) Preventive measures should be used to control heat loss, rather than relying upon heating devices. (3) Body tissues are damaged at much lower temperature when circulation is reduced by disease or position. (4) For rapid cooling during operating room emergencies, internal methods are more effective than surface methods. Sick children, particularly those under 3 years of age, often have as part of their illness many symptoms, including all kinds of rashes that resemble those seen in sensitivity reactions. But because they have been given various drugs (e.g., antibiotics, analgesics, sedatives, and tranquilizers) for their condition, these symptoms, especially the eruptions, are attributed to drug allergy rather than to the illness itself, with little or no definite evidence to support this therory. In the experience of the junior author, proven drug hypersensitivity actually is rare in infants and young children.

REFERENCES 1. Adamsons, K., Gandy, G. M., and James, L. S.: The influence of thermal factors upon oxygen consumption of the newborn human infant. J. Pediatrics, 66:495-508, 1965. 2. Adamsons, K., and Towell, M. E.: Thermal homeostasis in the fetus and newborn. Anesthesiology, 26:531-548, 1965. 3. Agate, F. J., Sr., and Silverman, W. A.: The control of body temperature in the small newborn infant by low-energy infrared radiation. Pediatrics, 31:725, 1963. 4. Aherne, W., and Hull, D.: Site of heat production in the newborn infant. Proc. Roy. Soc. Med., 57:1172,1964. 5. Birzis, L., and Hemingway, A.: Shivering as a result of brain stimulation. J. N europhysiol., 20:91-99, 1957. 6. Collins, H. A., Stahlman, M., and Scott, H. W.: Occurrence of subcutaneous fat necrosis in infant following induced hypothermia used as adjuvant in cardiac surgery. Ann. Surg., 138:880-885, 1953.

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7. Crino, M. H., and Nagel, E. L.: Thermal burns caused by warming blankets in the operating room. Anesthesiology, 29:149-150, 1968. 8. Cullen, W. G.: Malignant hyperpyrexia during general anaesthesia: A report of two cases. Canad. Anaesth. Soc. J., 13:437-444, 1966. 9. Dawkins, M. J. R., and Hull, D.: Brown adipose tissue and the response of new-born rabbits to cold. J. Physiol., 172:216, 1964. 10. Day, R.: Respiratory metabolism in infancy and childhood. XXVII. Regulation of body temperature of premature infants. Amer. J. Dis. Child., 65:376, 1943. 11. Denborough, M.A., Forster, J. E., Lovell, R. R. H., Mapleston, P. A., and Jilliers, J.D.: Anaesthetic deaths in a family. Brit. J. Anaesth., 34:395-399, 1962. 12. Farman, J. V.: Heat losses in infants undergoing surgery in air conditioned theatres. Brit. J. Anaesth., 34:543, 1962. 13. Feldberg, W., and Myers, R. D.: A new concept of temperature regulation by amines in the hypothalamus. Nature, 200:1325, 1963. 14. Feldberg, W., and Myers, R. D.: Changes in temperature produced by microinjections of amines into the anterior thalamus of cats. J. Physiol., 177:239-245, 1965. 15. France, G. C.: Hypothermia in newborn: Body temperatures following anesthesia. Brit. J. Anaes., 29:390, 1957. 16. Friedman, F., Adams, F. H., and Emmanouilides, G.: Regulation of body temperature of premature infants with low energy radiant heat. J. Pediatrics, 70:270-273, 1967. 17. Fuson, R. L., and Stephen, C. R.: Servo temperature control instrument for use in clinical medicine. Surg. Gynec. Obstet., 117:636-640, 1963. 18. Garrison, F. H.: An Introduction to the History of Medicine. 4th Ed. Philadelphia, W. B. Saunders Co., 1960. 19. Glasser, 0.: Medical Physics, 1944. Chicago, Year Book Medical Publishers, 1944. 20. Gollan, F.: Physiology of Cardiac Surgery. Springfield, Ill., Charles C Thomas, 1959. 21. Harrison, G. G., Bull, A. B., and Schmidt, H. J.: Temperature changes during general anesthesia. Brit. J. Anaesth., 32:60, 1960. 22. Hemingway, A.: Shivering. Physiol. Rev., 43:397, 1963. 23. Hogg, S., and Renwick, W.: Hyperpyrexia during anesthesia. Canad. Anaesth. Soc. J., 13:429-437, 1966. 24. Hull, D.: The structure and function of brown adipose tissue. Brit. Med. Bull., 22:92, 1966. 25. Joel, C. D.: The physiological role of brown adipose tissue. Handbook of Physiology V, Chapter 9, pp. 59-85. 26. Leonard; P. F.: Principles of electricity. I. The electric meter and thermistor. Anesth. Anal., 45:246-249, 1966. 27. Levision, H., Linsae, L., and Swyer, P. R.: A comparison of infra-red and convective heating for newborn infants. Lancet, 2:1346-1348, 1966. 28. MacBryde, C. M.: Signs and Symptoms. 3rd Ed. Philadelphia, J. B. Lippincott Co., 1957. 29. McQuiston, W. 0.: Anesthesia in cardiac surgery. Arch. Surg., 61:892-899, 1950. 30. North, W. C.: Control of the body temperature in the pediatric patient. North Carolina Med. J., 22:59-63, 1961. 31. Oliver, T. K., Jr.: Temperature regulation and heat production in the newborn. PEDIAT. CLIN. N. AMER., 12:765-779, 1965. 32. Owens, G., Dawson, R. E., and Scott, H. W.: Experimental production of "ether convulsions." Anesthesiology, 18:583-593, 1957. 33. Ray, B. S., and Marshall, V. F.: Convulsions during general anesthesia. Ann. Surg., 118: 130-148, 1943. 34. Relton, J. E. S., Creighton, R. E., Johnston, A .. E., Pelton, D. A., and Conn, A. W.: Hyperpyrexia in association with general anaesthesia in children. Canad. Anaesth. Soc. J., 13:419-425, 1966. 35. Rodaway, K. A., and Oliver, T. K.: Incubator accessory for exchange transfusion. Lancet, 1:1220, 1965. 36. Roe, C. F., Santulli, T.V., and Blair, C. S.: Heat loss in infants during general anesthesia and operations. J. Pediat. Surg., 1 :266-275, 1966. 37. Saidman, L. J., Havard, E. S., and Eger, I. E.: Hyperthermia during anesthesia. J.A.M.A., 190:1029-1032, 1964. 38. Scott, S.M.: Thermal blanket injury in the operating room. Arch. Surg., 94:181, 1967. 39. Silverman, W. A., and Sinclair, J. C.: Temperature regulation in the newborn infant. New Eng. J. Med., 274:92-94, 146-148, 1966. 40. Silverman, W. A., Fertig, J. W., and Berger, A. P.: The influence of the thermal environment upon the survival of newly born premature infants. Pediatrics, 22:876, 1958. 41. Silverman, W. A., Sinclair, S. C., and Scopes, J. W.: Regulation of body temperature in pediatric surgery. J. Pediat. Surg., 1:321-329, 1966. 42. Smith, R. M.: Anesthesia for Infants and Children. 3rd Ed. St. Louis, C. V. Mosby Co., 1968. 43. Smith, R. M., Bougas, T. P., and Bachman, L.: Shivering following thiopental sodium and other anesthetic agents. Anesthesiology, 16:655-664, 1955.

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44. Stephen, C. R., Dent, S. J., Hall, K. D., Knox, P.R., and North, W. C.: Body temperature regulation during anesthesia in infants and children. J.A.M.A., 174:15-79, 1960. 45. Stern, W., Lees, M. H., and Leduc, J.: Environmental temperature, oxygen consumption, and catecholamine excretion in newborn infants. Pediatrics, 36:367-373, 1965. 46. Swan, H., Zeavin, 1., Holmes, J. H., and Montgomery, V.: Cessation of circulation in general hypothermia. I. Physiological changes and their control. Ann. Sur g., 138:360376, 1953. 47. Warner, W. A., and Hamilton, W. K.: Inadvertant hypothermia with metabolic acidosis and circulatory depression. J.A.M.A., 199:411-412, 1967. 48. Wilton, T. N. P., and Wilson, F.: Neonatal Anesthesia. Philadelphia, F. A. Davis Co., 1965. 300 Longwood Avenue Boston, Massachusetts 02115