Hypothermia in trauma: The nurse's role in recognition, prevention, and management

Hypothermia in Trauma: The Nurse's Role in Recognition, Prevention, and Management S. Kay Sedlak, RN, MS, CEN Trauma patients are at risk for a number of complications that can jeopardize their ability to withstand the effects of injury. A serious and common problem is hypothermia, which can be caused or exacerbated by interventions used in resuscitation, surgery, and postoperative care. The trauma nurse has a primary responsibility in recognizing and beginning therapy to correct this potentially lethal condition. Many nursing measures can be modified to help the patient retain body heat or provide an exogenous source of warmth. (INT J TRAUMA NURS 1995;1:19-26)

REGULATION OF BODY ypothermia is a serious clinical problem of T EMPERATURE which all trauma nurses should be aware. It is a complication frequently associated A h u m a n being is capable of maintaining a with trauma and has potential lethal implications. Tc within a narrow range of 36.5 ~ to 37.5~ Multiple studies (97 ~ to 99~ by have d e m o n balancing heat proHypothermia...is a complication strated an induction (i.e., frequently associated with trauma and creased incidence thermogenesis) of morbidity and with heat loss. The has potential lethal implications. mortality w h e n Tc is regulated by a h y p o t h e r m i a is coordinated set of presentY Hypothermia is defined as a core body feedback systems located in the peripheral and temperature (Tc) below 35~ (95~ Significant central nervous system and controlled by the physiologic changes occur in hypothermia that comhypothalamic temperature-regulating center. promise a person's ability to maintain homeostasis Nerve receptors, located t h r o u g h o u t the body, or respond to therapy. sense temperature changes and transmit inAll patients with acute, and some with chronic, formation via peripheral sensory nerves to the trauma should be considered at risk of hypothspinal cord and eventually to the hypothalaermia. If hypothermia is found, measures should mus. It is a sensitive process that responds to be implemented to restore normothermia and changes in the blood temperature of as little to prevent additional loss of b o d y heat. as 0.5~ 8 With cooling, there is a series of coordinated responses that result in (1) peripheral vasoconstriction to decrease heat loss, S. Kay Sedlak is a clinical nurse specialist at St. Mary's Re(2) increased muscular tone and shivering to gional Medical Center in Reno, Nevada. generate heat, a n d (3) the p e r s o n s e e k i n g Reprints not available from author. warmth, appropriate clothing, and protective Copyright 9 1995 by the Emergency Nurses Association. posture. 9 1075-4210/95 $3,00 + 0 6511/61619

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T a b l e 1. Clinical c h a n g e s associated with h y p o t h e r m i a Central nervous system 9 Progressive decline in level of consciousness 28 9 Sluggish or absent pupillary response 2s 9 Slowed impulses in all nervous tissues, decreased reflexes 15 9 Linear decrease in cerebral metabolism of 6% to 7% per I~ 9 Loss of consciousness between 32 ~ and 30~ 9 Loss of activity on electroencephalogram at <20~ Cardiovascular system 9 Initial elevation of blood pressure, heart rate, cardiac output; decreases in these parameters with Tc <32~ 9 Atrial fibrillation (often resolves spontaneously with rewarming) 9 Osborn, or J, waves noted on electrocardiogram with Tc<24~ a 9 Ventricular fibrillation or asystole with temperatures <25~ 7 9 Dysrhythmias are refractory to defibrillation, medications, or artificial pacing at Tc <28~ is 9 Asystole universal at Tc <18~ 2r Respiratory system 9 Initial increase in rate and depth of respirations 9 Aspiration pneumonia (due to depressed cough reflex, bronchodilation, bronchorrhea) 8 9 Decreased ciliary motility, increased viscosity and amount of secretions, noncardiogenic pulmonary edema r 9 Respiratory arrest at Tc <24~ 21 Renal system 9 Cold diuresis of large quantities of dilute urine (due to peripheral vasoconstriction which produces relative central hypervolemia) 9 Acute tubular necrosis and renal failure due to renal hypoperfusion and myoglobinuria29 Hematologic system 9 Complete blood count Hemoconcentration (associated with diuresis, fluid shifts, decreased fluid intake) Leukopenia (due to bone marrow depression and pooling in liver and spleen) ~ Decreased chemotaxis and phagocytosis of neutrophils (predisposes to infection) 3~ 9 Increased blood viscosity al 9 Coagulation studies Prolonged prothrombin time and partial thromboplastin time 32 Impaired coagulation, possible disseminated intravascular coagulation (related to decreased enzyme activity, pooling of platelets in liver and spleen, and enhanced fibrinolytic activity) 33 9 Chemistry Hyperglycemia as insulin becomes inactive at 30~ 8 Hyperkalemia, hyponatremia 9 Arterial blood gases Metabolic acidosis (becomes more pronounced with rewarming and subsequent vasodilation and increased circulation)34 Digestive system 9 Slowed bowel peristalsis at Tc <34~ paralytic ileus at Tc <28~ ~3 9 Slowed hepatic function 9 Pancreatic necrosis at autopsy 3s

DEFINITION AND SIGNIFICANCE OF HYPOTHERMIA As Tc decreases, thermogenesis is triggered, along with a series of other physiologic responses. Table 1 provides a detailed list of signs and symptoms of hypothermia. Below 28~ (82 ~ F), all body functions are depressed and the patient appears lifeless. However, patients have

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recovered from Tc as low as 16~ (61~ 1~This is the basis for ruling out and correcting hypothermia before a person can be pronounced clinically dead. Overall, hypothermia complicates trauma care by interfering with ventilation and oxygenation; by causing vasoconstriction, which obscures arterial assessment and h a m p e r s VOLUME 1, NUMBER 1

Table 2. Persons at risk of hypothermia Conditions that predispose person to hypothermia 9 Young

9 Elderly 9 Alcohol 9 Impaired mobility

Have difficulty maintaining Tc due to increased heat losses with high ratio of body surface area to body mass, less subcutaneous tissue, and greater need for calories to keep warm Altered thermoregulatory system due to age-related changes Produces peripheral vasodilation, altered perception of thermal discomfort, and impaired shivering response 36 Patient unable to move to warmer environment or provide protective covering

Injuries prone to hypothermia 9 Large wounds, such as burns, significant abrasions, or open cavities 9 Central nervous system Brain stem, basilar skull fracture, intracerebral hemorrhage can damage thermoregulatory center in brain stem7 Cervical and high thoracic spinal cord injuries that disrupt sympathetic nervous system function and inhibit vasoconstriction, prevent shivering, and, chronically, cause muscle wasting and loss of natural insulation37

latrogenic causes of hypothermia 9 Medications 9 Use of unwarmed intravenous fluids 9 Use of unwarmed irrigation or lavage fluids 9 Failure to protect from other sourcesof heat loss

Narcotics, muscle relaxants, sedatives, hypnotics, and anesthetic agents inhibit normal thermogenesis or promote heat loss Rapid infusion of intravenous fluids cools the To; infusion of unwarmed, banked blood (4~ faster than 100 ml in 30 minutes is sufficient to lower Tc to 30~ a8

venous access; by producing coagulopathy and increased blood loss; and by slowing hepatic metabolism and elimination of drugs. RECOGNITION HYPOTHERMIA

AND TREATMENT

OF

Trauma patients can become hypothermic in several ways. Table 2 lists examples of patients who are at high risk of hypothermia. Nursing personnel should use this awareness, along with the physical assessment, to determine how severe the hypothermia and its associated syndrome are. Physical Assessment

Hypothermia produces a generalized depression in all body systems. Respirations are decreased as a result of depression of the medullary respiratory center. This results in changes in respiratory rate, decreased oxygenation, decreased oxygen consumption, and increased carbon dioxide retention. A low Tc increases the hemoglobin's affinity for an oxygen molecule and inhibits release of oxygen to tissue.

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In profound hypothermia, pulmonary edema complicates the ability to ventilate and exchange gases. Assessment of the oxygenation status via pulse oximetry is altered by the low perfusion state produced by hypothermia. 11 Cardiovascular changes associated with decreased Tc depend on the state of cooling. Fluctuations in heart rate and blood pressure will make the overall trauma assessment more difficult. Peripheral arteries become vasoconstricted and are difficult to assess. All patients with k n o w n or suspected hypothermia should have ongoing cardiac monitoring to determine heart rate (e.g., tachycardia is seen initially, followed by bradycardia) and cardiac rhythm (e.g., atrial fibrillation is seen in mild hypothermia; ventricular fibrillation and asystole occur with severe hypothermia). In some cases, an Osborn, or J, wave (Figure 1) can be identified. It has a characteristic extra deflection at the QRS-ST junction and may be present at Tc below 32~ (89.6~ 1~ Neurologic function is more difficult to assess in hypothermic patients. The level of con-

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Figure 1. Osborn waves are most frequently seen as positive deflections following the S wave. They are best seen in the inferior leads and Vs-V 6. They are more prominent in leads V 3 and V 4 with advanced hypothermia. (From Vincens J J, Mandak JS, McClellan JR. Ventricular fibrillation after massive blood transfusion. Choices Cardiol 1993;7;336-8. Used with permission.)

sciousness m a y be d e p r e s s e d b y hypothermia (i.e., cerebral b l o o d flow decreases as Tc drops), a preexisting condition (e.g., intoxication, metabolic derangement, medical problem), an injury, or a combination of all these. Pupillary and d e e p t e n d o n reflexes b e c o m e sluggish and eventually disappear. All forms of neurologic function are d e p r e s s e d b y hypothermia. As a c o n s e q u e n c e , m o r e aggressive diagnostic studies are n e e d e d to determine the cause of a decreased level of consciousness. Although the most valuable means of determining hypothermia is m e a s u r e m e n t of the Tc, it is often omitted. O n e study c o n d u c t e d in a level I trauma center f o u n d that the Tc was not likely to b e m e a s u r e d in the trauma resuscitation area, especially if the patient was in critical condition. 6 The Tc should be measured on admission and at 15-minute intervals to determine h o w effective interventions are. With rewarming, the Tc should increase at least 1~ per hour. A failure to raise the Tc as expected might be an indication of the n e e d for a more aggressive rewarming method? 2 22

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Conversely, once the patient's Tc has reached 32 ~ to 34~ rewarming should be discontinued to avoid causing pyrexia. 13 An oral or rectal temperature m a y b e practical for initial screening. However, the use of these m e t h o d s is limited for ongoing monitoring. Electronic thermometers generally register temperatures d o w n to 34.4~ Rectal temperatures can lag behind Tc changes and not reflect the actual Tc. A m o r e effective m e t h o d to measure Tc is with an esophageal temperature p r o b e or urinary catheter thermistor. Bladder temperature has b e e n s h o w n to correlate well with both p u l m o n a r y artery b l o o d temperature and esophageal temperature. TM Treatment

of H y p o t h e r m i a

Maintenance of an optimal Tc is important in trauma care. The goal is to prevent further heat loss and provide e x o g e n o u s heat. This is especially critical w h e n the person is unable to maintain adequate thermogenesis. The measures used to rewarm a person will d e p e n d on the patient's injuries and degree of hypothermia. VOLUME 1, NUMBER 1

Table 3. Treatment guidelines for trauma patients with mild hypothermia (35~ to 32~

Table 4. Treatment guidelines for trauma patients with profound hypothermia (<32~

Verify subnormal temperature with esophageal probe or urinary catheter thermistor. Notify physician. Place patient in warm environment. Use radiant lights. Avoid drafts. Remove wet clothing/linen/dressings. Dry patient thoroughly. Cover with warm blankets. Cover head with paper cap, unless injuries contraindicate. Monitor and record vital signs, including temperature every 15 minutes. Monitor urinary output via urinary catheter. Monitor for cardiac dysrhythmias. Avoid giving medications orally or intramuscularly, as intravenous route is preferred. Obtain culture specimens as indicated, administer antibiotics. Warm all intravenous and irrigation fluids. If giving blood products, or 1 L or more of intravenous fluids, use rapid solution administration sets with warmer. If oxygen is indicated, administer heated, humidified mist.

Initiate all therapies for mild hypothermia, as well as the following: Administer all intravenous fluids and blood products via rapid solution administration set. Administer heated, humidified oxygen to all patients. Monitor airway patency, suction as needed. Initiate active core rewarming with peritoneal lavage. Attempt one defibrillation if ventricular fibrillation is present. If unsuccessful, rewarm patient to 28 ~ to 30~ before further attempts. Avoid administering insulin until patient is rewarmed to 30~ Monitor for coagulopathies. Observe for development of aftershock and afterdrop. Discontinue active rewarming measures when core temperature reaches 32 ~ to 34~ to avoid pyrexia.

If temperature does not increase by 1~ per hour, if cardiovascular demise, or central nervous system injury is present, consider the need for additional active rewarming measures.

P r e v e n t i n g H e a t Loss. Normal heat loss occurs via convection (air blowing across exposed skin), conduction (direct contact between a body surface and a colder substance), infrared radiation (body radiates heat into cooler environment), and evaporation (water converted from liquid to gaseous state, normally responsible for 20% of body heat loss). The environment can accelerate heat loss. Under normal circumstances, only 2% of the body's heat is lost through conduction; yet if a person is wearing wet clothing, the losses can be increased by five times. If the body is submerged in cold water, the heat loss can be increased by 25 times. 8 R e w a r m i n g T h e r a p i e s . Rewarming should be instituted as soon as possible. Tables 3 and 4 provide guidelines for rewarming a patient according to the degree of hypothermia. The approach will vary because in mild cases the patient is still able to generate endogenous heat. In mild hypothermia, the trauma patient's injuJANUARY-MARCH 1995

Note: Because recovery is possible from profound hypothermia, resuscitation efforts should be continued until the patient has been adequately warmed.

Table 5. Complications associated with rewarming Aftershock With hypothermia, intravascular fluid is shifted to the core from the periphery. The kidneys respond by excreting excess fluid. When surface tissues are rewarmed, they vasodilate, creating a relative hypovolemia, which is manifested by hypotension. Afterdrop Afterdrop is defined as a decline in Tc during the first 30 minutes of rewarming. The drop may be 2 ~ to 3~ in adults, or 5~ in children. 13 With rewarming, the core continues to lose heat to the periphery29 Afterdrop has been associated with onset of ventricular fibrillationY Afterdrop is best avoided by rewarming core organs before the peripheryF ,39

ries are given priority of care, and measures taken to prevent further heat loss are secondary. 8 With severe hypothermia, failure to actively warm the Tc will render other interventions ineffective.15 The state of hypothermia is a life-threatening emergency and rewarming efforts receive the highest priority. 8 INTERNATIONAL JOURNAL OF TRAUMA NURSING

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Passive~external rewarming involves removing the person from the cold environment and providing insulation to maximize basal heat production. All sources of heat loss should be r e m o v e d (i.e., wet clothing, b e d linens), and the patient should be kept dry and covered with w a r m blankets. A forced-air skin-surface w a r m e r (Bair Hugger; Augustine Medical, Inc., Eden Prairie, Minn.) prevents heat loss 16 (Figure 2). The patient's h e a d should be covered because 25% to 60% of total b o d y heat m a y be lost from this area. 17 Ambient r o o m temperature should be increased with radiant heat lamps or a heating shield to at least 21 ~ C. TM Air drafts should be avoided by keeping the door or bedside curtains closed in the treatment area. The success of passive/spontaneous rewarming m e t h o d s is variable. In one retrospective review of 68 patients treated in this manner, Tc increases varied from 0.3 ~ to 2.0~ per hour. 19 The wide range of responses was attributed to differences in the physiologic status and age of the study subjects. The primary advantages of passive rewarming are ease of use and lack of expense. Because the reversal of peripheral vasoconstriction is gradual, fluid shifting from the central circulation to peripheral vessels occurs slowly. This reduces the potential for aftershock and afterdrop (see Table 5 for descriptions). Passive r e w a r m i n g has b e e n r e c o m m e n d e d for patients with a Tc of >32~ with a slow onset, and long duration. 2~ Passive rewarming will not be effective as the only m e t h o d of treatment for severe hypothermia (Tc below 30~ inasmuch as it requires the b o d y to be capable of thermogenesis.7 Below 30~ the b o d y loses its thermogenic ability and takes on the temperature of the envir o n m e n t (i.e., poikilothermy). Active external~surface rewarming involves direct transfer of e x o g e n o u s heat to external b o d y surfaces. A direct heat source (i.e., an electric blanket) is placed next to the person's skin. This approach to rewarming can raise the Tc 0.5 ~ to 3.0~ per hour. 13 Multiple studies have s h o w n increased mortality a m o n g hypothermic patients treated with active external/ surface rewarming. 19,21,= This is due to (1) the

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Figure 2. A forced-air skin-surface warmer (Bair Hugger) that works by blowing warm air through a disposable blanket and creating a shell of warm air around the patient. (Courtesy of Augustine Medical, Inc.) d e v e l o p m e n t of aftershock and afterdrop; (2) increased metabolic d e m a n d s from r e w a r m e d surface tissue that e x c e e d the heart's ability to m e e t those demands2~; and (3) the inhibition o f s h i v e r i n g b y w a r m i n g o f the skin a n d muscles. Active e x t e r n a l / s u r f a c e r e w a r m i n g s h o u l d not be u s e d as the o n l y r e w a r m i n g method, especially for the severely hypothermic patient.: Active internal~core rewarming uses methods to introduce heat to the body's internal surfaces, thereby rewarming core organs before peripheral tissues. Active internal/core rewarming takes advantage of the introduction of heat to large surface areas, such as the lungs, the intravascular system, and the intraperitoneal cavity. The lungs are a normal area of heat exchange. Providing heated, humidified gas (e.g., r o o m air or oxygen) can increase the Tc by 1~ to 2~ per hour, and this is a technically simple, inexpensive approach. 24 H o w rapidly the Tc

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Figure 3. Extracorporeal rewarming using an arteriovenous fistula as a means of active internal core rewarming. (Reprinted with permission from Gentilello LM, Cobean RA, Offner PJ, Soderberg BS, Jurkovich GJ. Continuous arteriovenous rewarming: rapid reversal of hypothermia in critically ill patients. J Trauma 1992;32:316-27.) rises d e p e n d s on the percent of humidification, flow rates, and route of administration (e.g., face mask or endotracheal tube). Humidifying the gas allows it to carry m o r e heat. Temperatures up to 44~ have b e e n u s e d without producing injury. Heated humidified gas decreases respiratory tract heat loss, stimulates cilia, liquidizes secretions, and increases oxygenation of the coronary arteries. 2~ All fluids to c o m e in contact with the patient should be w a r m e d to prevent conductive heat loss. Intravenous (IX() fluids can be stored in a temperature-controlled w a r m e r before administration but should still be given through a w a r m e r with as short a length of IV tubing as practical to decrease radiant heat loss from the tubing. Warmed IV fluids are safe and easy to provide; however, this m e t h o d will be of limited value if the patient's fluid intake is restricted. Use of extracorporeal circulation has b e e n reported to be associated with improved outc o m e s for h y p o t h e r m i c t r a u m a patients. 25, 26 P e r c u t a n e o u s l y p l a c e d femoral arterial a n d v e n o u s catheters c o n n e c t e d to a countercurrent fluid w a r m e r are used to create a fistula

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through a heating m e c h a n i s m (Figure 3). Patients treated in this m a n n e r have b e e n noted to have shorter rewarming time, improved survival after moderately severe injury, r e d u c e d blood and fluid requirements, less incidence of organ failure, and fewer intensive care days. 26 Peritoneal lavage with dialysate w a r m e d to 45~ can raise the Tc 1~ to 2~ per hour. 8 Advantages of this approach include helping to correct electrolyte abnormalities, detoxifying overdoses, reactivating hepatic functions, carwing minimal risk, and not interfering with other treatments, including cardiopulmonary resuscitation7 '~~ Peritoneal lavage is contraindicated if the patient has massive abdominal trauma. It is not r e c o m m e n d e d that b o d y cavities be irrigated. 27 The a m o u n t of b o d y surface area r e w a r m e d with stomach, colon, or bladder irrigation is small and has little apparent value in raising the Tc.

SUMMARY Nurses in all clinical areas have the ability to recognize hypothermia and begin interventions to prevent further heat loss. The Tc assessment

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must be done on admission and repeated periodically until the patient's condition has stabilized, interventions k n o w n to p r o d u c e decreased Tc are concluded, or other potential causes have been removed. Patients found to be hypothermic must be protected from lifethreatening complications and provided with appropriate rewarming methods. Tables 3 and 4 offer guidelines to be used in the treatment of hypothermic patients.

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16. Sessler DI, Stoen R, Glosten B. The Bait Hugger warmer significantly decreases heat loss to the environment. Anesthesiology 1987;71 : A 411. 17. Bidd le CJ. A plastic head cover to reduce surgical heat loss. Geriatr Nurs 1985:6;39-41. 18. Danzl DE Accidental hypothermia. In: Rosen P, et al., eds. Emergency medicine: concepts and clinical practice. 2rid ed. St. Louis: Mosby, 1988: 663-92, 19. Miler JW, Danzl DF, Thomas DM. Urban accidental hypothermia: 135 cases. Ann Emerg Med 1980;9:456-61. 20. Harnett RM, Pruitt JR, Sias FR. A review of the literature concerning resuscitation from hypothermia. Part II. Selected rewarming protocols. Aviat Space Environ Med 1983;54:487-95. 21. Best R, Syverud S, Nowak RM. Trauma and hypothermia. Am J Emerg Med 1985;3:48-55. 22. Danzl DF, Pozos RS. Multicenter hypothermia survey. Ann Emerg Med 1987;16:1042-55. 23. Brunett DD, Sterner S, Robinson EP, Ruiz E. Comparison of gastric lavage and thoracic cavity lavage in the treatment of severe hypothermia in dogs. Ann Emerg Med 1987;16:1222-7. 24. Slovis CM, Bachvarov HL. Heated inhalation treatment of hypothermia. Am J Emerg Med 1984;2:533-6. 25. Gentilello LM, Rifley WJ. Continuous arteriovenous rewarming: report of a new technique for treating hypothermia. J Trauma 1991; 31:1151-4. 26. Gentilello LM, Cobean RA, Offner PJ, Soderberg RW, Jurkovich GJ. Continuous arteriovenous rewarming: rapid reversal of hypothermia in critically ill patients. J Trauma 1992;32:316-27. 27. Kauffman FH. Profound accidental hypothermia. Trauma Q 1989; 6:7-15. 28. Meyer S, Gibb T, Jurkovich GJ. Evaluation and significance of the pupillary light reflex in trauma patients. Ann Emerg Med 1993; 22:1052-7. 29. Robinson M, Seward PN. Environmental hypothermia in children. Pediatr Emerg Care 1986;2:254-7. 30. Clardy CW, Edwards KM, Gay JC. Increased susceptibility to infection in hypothermic children: possible role of acquired neutrophil dysfunction. Pediatr Infect Dis 1985;4:379-82. 31. Roberts DE, Barr JC, Kerr D, Murray C, Harris R. Fluid replacement during hypothermia. Aviat Space Environ Med 1985; 56:333-7. 32. Rohrer MJ, Natale AM. Effect of hypothermia on the coagulation cascade. Crit Care Med 1992;20:1402-5. 33. Patt A, McCrowsky BL, Moore EE. Hypothermia-induced coagulopathies in trauma. Surg Clin North Am 1988;68:775-85. 34. Lawson LL. Hypothermia and trauma injury: temperature monitoring and rewarming strategies. Crit Care Nurse Q 1992; 15:21-32. 35. Reuler JB. Hypothermia: pathophysiology, clinical settings, and management. Ann Intern Med 1978;89:519-27. 36. Graham T, Baulk K. Effect of alcohol ingestion on man's thermoregulatory responses during cold water immersion. Aviat Space Environ Med 1980;51:155-9. 37. Carr ME, Wolfert AI. Rewarming by hemodialysis for hypothermia: failure of heparin to prevent DlC. J Emerg Med 1987;6:277-80. 38. Leaman PL, Martyak GG. Microwave warming of resuscitation fluids. Ann Emerg Med 1985;14:876-9. 39. Webb P. Afterdrop of body temperature during rewarming: an alternative explanation. J Appl Physiol 1986;60:385-90.

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