Contemporary Problems in Trauma Surgery
0039--6109/91 $0.00
+ .20
New Horizons in Management of Hypothermia and Frostbite Injury L. Delano Britt, MD, MPH, FACS, * William H. Dascombe, MD,t and Aurelio Rodriguez, MD, FACS:j: Warmth, warmth, more warmth! For we are dying of cold and not darkness. It is not the night that kills, but the frost. MIGUEL DE UNAMUNO
The Tragic Sense of Life
HYPOTHERMIA
Accidental hypothermia in humans is defined as the unintentional drop in body core temperature below 35°C (95°F). us Hypothermia is commonly classified as mild, moderate, or severe (Table 1). Accidental hypothermia develops in various settings. Common victims include winter-sports enthusiasts, victims of cold-water immersion, accident victims trapped in the cold, the elderly, the newborn, those under the influence of drugs or alcohol, and individuals who possess one or more of the medical risk factors predisposing them to thermal insult (Table 2).20, 57, us, 153 The term urban hypothermia has been coined to include those city dwellers who commonly present hypothermic, such as the alcoholic, the homeless, the elderly, or those with disabling medical problems. 6 The aged are at particularly high risk for the development of hypothermia because of an impairment in their ability to perceive cooler temperatures and thus an innocent neglect to seek warmer environments or to add clothing. A subset of the elderly has a decreased ability to generate heat (shivering) secondary to reduced muscle mass, are in a *Medical Director, Shock Trauma Center, Sentara Norfolk General Hospital; and Chief, Division of Trauma and Critical Care, and Associate Professor, Eastern Virginia Graduate School of Medicine, Norfolk, Virginia tChief Resident, Department of Surgery, Eastern Virginia Graduate School of Medicine, Norfolk, Virginia :j:Attending Traumatologist and Thoracic Surgeon, Maryland Institute for Emergency Medical Services System; and Assistant Professor of Surgery, University of Maryland, Baltimore, Maryland
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relatively poor premorbid state of health, and have a defect in autonomic function reflected by a decreased resting peripheral blood flow. 20, 75, 115 Neonatal infants, especially if they are premature, have a proclivity for hypothermia because of their large surface-to-body-mass ratio. 25, 98 Although hypothermia commonly occurs in cold environments, reports of hypothermic patients from Mrica and other temperate climates illustrate the fact that any ambient temperature below that of the body core can lead to thermal disarray. 45 Homoiothermy Man is a homoiothermic mammal suited best to survival in his evolutionary homeland, the tropics, at temperatures around 27°C (81°F). 6, 35, 115 Man is richly endowed with mechanisms with which to dissipate heat. However, he must rely largely on intelligent behavior to conserve heat. 58 In an effort to understand man's thermoregulatory mechanisms better, physiologists divide the body into a homoiothermic core, which includes the deep muscles and internal organs, and a poikilothermic shell, which includes the skin and its thermoreceptors, the subcutaneous tissue, and the superficial muscles. 5 The shell subserves the core in an attempt to maintain the central temperature. Heat loss occurs by four mechanisms, Radiation is the loss of heat to the environment via infrared radiation. Convection is the transfer of heat to the environment by air or water that is in contact with the body. Convection is dependent on air temperature and velOcity. Conduction is the transfer of heat to another object by direct contact, When this object is cold water, heat is transferred from the body at a rate 32 times that to air. 115 Finally, heat may be lost by evaporation, the conversion of water to its gaseous phase, at a cooling rate of 0.6 kcal/g. 93 Homoiothermic responses to cold are integrated by the hypothalamus. Changes in the ambient temperature are detected by thermal receptors in the skin. Afferent pathways in the spinal cord transmit these changes to the anterior hypothalamus. The posterior hypothalamus then initiates a series of changes designed to prevent further heat loss and to augment heat production. 35 Muscle tone is increased, which leads to shivering (physical thermogenesis), with an associated fivefold increase in heat production. 48, 53 However, shivering also increases the rate of heat loss, Metabolic thermogenesis entails increases in epinephrine, norepinephrine, and thyroxine release, with a subsequent rise in the basal metabolic rate. 35 One of the most important regulators of heat is blood flow to the skin, especially the extremities, which account for 50% of the total body surface area. 110 Integumentary blood flow during cold stress virtually ceases (0,5 ml/min per 100 ml of tissue in the digits) as vasoconstriction predominates, 16 When heat loss is desired, blood flow to the extremities at maximum vasodilatation is augmented to 30% of the cardiac output, 35 Finally, and perhaps most importantly, decreases in ambient temperature initiate conscious responses to seek shelter, increase physical activity, and apply protective clothing. Any interruption in either the perception of thermal adversity, the transmission of sensory signals to the central nervous system (CNS), the
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Table I. Classification of Hypothermia DEFINITION
TEMPERATURE
Mild
SIGNS AND SYMPTOMS
Shivering Complaint of cold Usually conscious Sometimes confused Normal blood pressure 80°-89°F 26. 7°-32. 2°C
Moderate
Severe
Semiconscious, combative Shivering ceases Muscle rigidity Dilated pupils Ventricular fibrillation with agitation Decreased breathing rate Blood pressure difficult to obtain Comatose No rigidity (flaccid) Apnea Spontaneous ventricular fibrillation
processing of neural input, or the efferent metabolic and behavioral changes directed by the CNS to diminish thermal stress predisposes one to hypothermia or hyperthermia (see Table 2). Furthermore, extremes of core temperature-greater than 41°C (106°F) or less than 34°C (94°F)-paralyze protective homoiothermic mechanisms, inviting further thermal insult. 35 Pathophysiology The pathophysiologic changes that accompany hypothermia are dependent on the severity of hypothermia, the causal factors, and the pre morbid characteristics of the patient. These will be described separately in relation to each of the organ systems. Table 2. Conditions Predisposing to Hypothermia Metabolic Factors Hypothyroidism Hypoglycemia Hypopituitarism Diabetic ketoacidosis Hypoadrenalism Renal failure Malnutrition Central Nervous System Conditions Head injury Spinal cord transection Cerebrovascular disease Hypothalamic lesions Alzheimer's disease Wernicke's encephalopathy Skin Disorders Burn injury Erythrodermas
Cold Exposure Cold water immersion Drugs Ethanol Phenothiazines General anesthetics Tricyclic antidepressants Barbiturates Benzodiazepines Opiates Reserpine Infections Peritonitis Meningitis Bacteremia
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Cardiovascular System. Cardiac output initially increases, then progressively decreases during worsening hypothermia, with a concomitant decrease in blood pressure. In severe hypothermia, there is lengthening of the QRS and ST segments as electrical conduction slows. 145 A characteristic J or Osborne wave is noted as a positive-negative deHection immediately after the QRS complex in as many as 30% of cases. 81, lOS, 142 As temperatures dip below 29°C, atrial fibrillation, bradycardia, and ventricular extrasystoles are common, Spontaneous ventricular fibrillation occurs at temperatures below 25°C, with cardiac standstill occuring at 21°C, U5 Pulmonary System. The respiratory rate usually increases after sudden immersion in cold water, However, the medullary respiratory center is increasingly depressed as hypothermia worsens, Reports of pulmonary edema after rewarming from severe hypothermia are common. 35, 45 Alteration in consciousness, depression of the cough reHex, and excessive production of tenacious bronchial secretions, "cold bronchorrhea," are thought to explain the atelectasis, bronchopneumonia, and aspiration present after rewarming. 139 Cold-induced slOwing of the tracheobronchial cilia may contribute to this respiratory insult,8 Renal Function. A "cold diuresis" accompanies hypothermia that is thought to be secondary to a cold-induced reduction in cellular enzyme activity with defects in distal tubular reabsorption of sodium and water. 99, 128 This occurs despite a decrease in the rates of glomerular filtration and renal blood How. l38 Other authors have suggested that this cold diuresis is the result of an altered sensitivity of the renal collecting tubules to antidiuretic hormone,l58 and still others have postulated that early peripheral vasoconstriction causes temporary central volume overload with a subsequent diuresis in an effort to reduce blood volume. 55 Central Nervous System. Hypothermia results in a progressive depression of neurologic activity. Clarity of consciousness gives way to confusion, lethargy, and, finally, unresponsiveness as hypothermia becomes more severe. Cerebral blood How decreases 6% to 7% for every 1°C decrease in body temperature. U5 Gastrointestinal Tract. Temperatures below 32°C result in mild ileus. 81 Hepatic function is depressed with a concomitant reduction in the detoxification of drugs. 81 Gastric stress ulcers and hemorrhagic pancreatitis have been noted at temperatures below 26.7°C (800F). 35 Oxygen Dynamics. Hypothermia shifts the oxyhemoglobin dissociation curve to the left, increasing the affinity of hemoglobin for oxygen, U5 This change is offset by an increase in the diffusion of oxygen and by a reduction in oxygen consumption by 50% at 30°C (860F). 35 Metabolism. The metabolic rate is reduced by 50% for every lOOC fall in temperature as stated by the rule of Van't Hoff Arrhenius, 88 The action of insulin to increase the cellular uptake of glucose is impaired when temperatures are below 30°C, contributing to the hyperglycemia often noted with hypothermia. 81 An alteration in the the sodium-potassium pump during hypothermia may result in elevated potassium levels. 109 Hypokalemia often develops after rewarming. Metabolic acidosis may be present in 30% of patients secondary to respiratory depression, lactic acid generation from shivering,
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the increase in CO 2 diffusibility, and the decreased hepatic metabolism of organic acids. 61 Blood. There is a 2% increase in blood viscosity for each 1°C drop in temperature. 51 An elevated hematocrit, as high as 60%, may be noted early in rewarming, thought to be secondary to the "cold diuresis" described earlier. 55 Impaired coagulation and disseminated intravascular coagulation, perhaps related to the release of tissue thromboplastin from ischemic tissue, may be present with severe hypothermia, only to resolve during rewarming. 18 Temporary thrombocytopenia has been reported with lower body temperatures, especially in neonates. 32. 143 In animal models, sequestration of platelets in the liver, spleen, and portal system during hypothermia has been demonstrated. 148 Pathologic Changes. There are no specific pathologic changes unique to hypothermic injury identified in patients who succumb. 79, 123, 133 Fatty infiltration and hemorrhagic and thrombotic lesions of the heart, liver, brain, and kidney have been reported, as well as changes consistent with pancreatic inHammation and necrosis. 31, 63, 123, 133 Whether these represent changes that accompany hypothermia or simply reHect the population of people susceptible to hypothermia is not clear, Treatment
Treatment in the Field. Victims should be removed from the cold environment, wet clothing should be removed, and a blanket, preferably heated, should be placed around them. Thereafter, the victim should be moved as little as possible to avoid triggering ventricular fibrillation. 6 Cardiopulmonary resuscitation (CPR) should be started on those with severe hypothermia who are in cardiac arrest from ventricular fibrillation or asystole. If personnel trained in CPR are not available or if an electrical rhythm is present without a palpable pulse or blood pressure (common in severe hypothermia), CPR is not recommended,39 because in such cases, chest compressions may result in ventricular fibrillation developing from a previously perfusing cardiac rhythm, Electrical defibrillation usually is unsuccessful at temperatures below 29°C. However, an attempt at defibrillation is suggested, to be repeated if necessary for every 2° to 4°C rise in the victim's temperature, Bretylium has been effective as an adjunct in managing hypothermia-induced ventricular fibrillation. Emergency Department Treatment. Making the diagnosis of hypothermia is the first challenge of resuscitation. 115 Diagnosis is complicated by the fact that most emergency department thermometers record temperatures only to 34.4°C, Adding "D" ("degree of temperature") to the ABCs of resuscitation is a simple way to avoid overlooking hypothermia. 132 A complete blood count; measurement of serum electrolytes, blood glucose, coagulation, arterial blood gases, and serum blood urea nitrogen and creatinine levels; and blood cultures are obtained. A Foley catheter is inserted. A chest radiograph to identify pulmonary pathology and an electrocardiogram to demonstrate dysrhythmias are ordered. Continuous monitoring of vital signs, central venous pressure if a central line has been placed, urine output, and serial electrolytes and arterial blood gases is conducted during rewarming.
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If alcohol abuse is suspected, thiamine should be given immediately. Hypoglycemia, often associated with hypothermia, should be ruled out. Gaining peripheral venous access may be difficult, necessitating placement of a central venous line. Pulmonary artery catheters, which may disturb the myocardium, should be avoided. Warm humidified oxygen should be administered to all patients. If apnea exists, humidified oxygen should be given first by face mask, then after preoxygenation, by insertion of an endotracheal tube. The literature warns about the risk of triggering ventricular fibrillation with oropharyngeal manipulation or intubation. 104, 126 However, Danzl and associates had no complications from nasotracheally intubating 117 patients who had temperatures less than 32.2°C.23 In addition, intubation proVides a means for inhalational core rewarming and ease of pulmonary toilet in this subset of patients who are likely to develop disabling bronchorrhea and pneumonia. 6 Rewarming Rewarming techniques are divided into passive (no added heat) and active (heat added). Active rewarming may be delivered by external means or by core rewarming. Table 3 lists different rewarming modalities. The advantages, disadvantages, and contraindications of each core rewarming technique will be discussed briefly. Warmed Intravenous Solutions. The administration of warmed intravenous fluids and blood is an effective way to initiate core rewarming. Fluids in plastic bags may be warmed to temperatures of 40°C by microwave. 43, 69 Peritoneal Lavage. Warmed peritoneal lavage can be performed with the insertion of two catheters so that fluid rates of up to 12 Uhour are possible. 60 The advantages of peritonal lavage include its simplicity and ready availability in most hospitals, its low risk to the patient, and the ability to provide large quantities of heat with concomitant removal of toxic Table 3. Rewarming Techniques for Treatment of Hypothermia Passive Warm environment Heat generation via shivering Blanket insulation Active External Heating pads Immersion in warm water Hot water bottles Environmental heaters Internal (core) Heated IV solutions Hemodialysis Gastric/colonic lavage Peritoneal lavage Mediastinal lavage Inhalation rewarming Diathermy Extracorporeal blood rewarming
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metabolic byproducts. 47, 49, 60, 68, 107, 116 Early revitalization of the liver, with the subsequent return of metabolite detoxification, is an added benefit, Contraindications to peritoneal lavage include abdominal trauma necessitating exploration, such as acute abdomen, hemoperitoneum, or free intra-abdominal air. In these cases, intraoperative warm peritoneal irrigation is possible, 49 Gastric-Colonic Lavage. Use of intragastric and intracolonic balloons in experimental animals, as well as of gastric and colonic lavage techniques in humans, has been described, The advantage of such techniques is that peritoneal penetration is avoided, The risks of gastric and colonic lavage include those associated with tube insertion and the potential for organ perforation. Contraindications include trauma circumstances in which a gastric or colonic injury is feared, Airway Rewarming. The inhalation of hot, moist gas either by facemask, if the patient is ventilating spontaneously, or by endotracheal intubation, if there is respiratory distress, has several advantages. First, continued respiratory heat loss is stopped, Second, the heart and lungs are the first organs to be warmed. Third, reversal of cold-induced ciliary dysfunction, thus improving bronchial evacuation of secretions, is possible,8 Finally, the equipment necessary for such core rewarming is readily available and easily applied, with few risks,49, 50, 129 Inspired air temperature should not exceed 40°C (104°F) in the awake patient and 50°C (122°F) in the unresponsive patient,73, 156 There are no significant contraindications to inhalation rewarming, When facial injuries preclude intubation, cricothyroidotomy or tracheostomy for inhalational rewarming is possible, Mediastinal Lavage. Median sternotomy with warm mediastinal lavage is another modality with reported success in the hemodynamically unstable, severely hypothermic patient. 3 The ability to perform open cardiac massage during rewarming is the unique advantage of this treatment modality. The principal disadvantage is the morbidity associated with a median sternotomy. Diathermy. Restoring lost body heat by ultrasonic waves, microwaves, or short waves is possible. 71 The advantage of diathermic rewarming is that the delivery of heat to the core tissues occurs without an invasive procedure. 49 Studies in dogs have shown that radiowave diathermy compares favorably with peritoneal lavage. 156 Clinical utilization of diathermy has not been widespread because of the difficulty associated with identifYing adequate dosages for patients. 49 Lehmann has summarized the many contraindications to diathermic rewarming. 71 Some of these are pacemakers, suspected hemorrhage, and areas of occlusive arterial disease. Extracorporeal Blood Rewarming. Successful resuscitation of patients having severe hypothermia with or without hemodynamic instability using extracorporeal rewarming has been reported frequently. 3, 13, 140, 158 This usually is performed by cannulation of one or both femoral veins and returning warmed blood via a femoral artery cannula. 21, 49 The primary advantage of extracorporeal rewarming is the ability to oxygenate the blood and rewarm patients rapidly while providing hemodynamic support to those
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who develop dysrhythmias or hypotension. Passive and active external rewarming techniques can be used as an adjunct with this method of core rewarming. The complications of extracorporeal rewarming are thrombophlebitis and the inherent risk associated with arterial venous access and heparinization. 49 The contraindications are those for heparin anticoagulation, such as gastrointestinal bleeding or general trauma. Rewarming Controversies The most controversial aspect of hypothermia is identifying the best way to rewarm the moderately to severely hypothermic patient (temperature
0039--6109/91 $0.00
+ .20
New Horizons in Management of Hypothermia and Frostbite Injury L. Delano Britt, MD, MPH, FACS, * William H. Dascombe, MD,t and Aurelio Rodriguez, MD, FACS:j: Warmth, warmth, more warmth! For we are dying of cold and not darkness. It is not the night that kills, but the frost. MIGUEL DE UNAMUNO
The Tragic Sense of Life
HYPOTHERMIA
Accidental hypothermia in humans is defined as the unintentional drop in body core temperature below 35°C (95°F). us Hypothermia is commonly classified as mild, moderate, or severe (Table 1). Accidental hypothermia develops in various settings. Common victims include winter-sports enthusiasts, victims of cold-water immersion, accident victims trapped in the cold, the elderly, the newborn, those under the influence of drugs or alcohol, and individuals who possess one or more of the medical risk factors predisposing them to thermal insult (Table 2).20, 57, us, 153 The term urban hypothermia has been coined to include those city dwellers who commonly present hypothermic, such as the alcoholic, the homeless, the elderly, or those with disabling medical problems. 6 The aged are at particularly high risk for the development of hypothermia because of an impairment in their ability to perceive cooler temperatures and thus an innocent neglect to seek warmer environments or to add clothing. A subset of the elderly has a decreased ability to generate heat (shivering) secondary to reduced muscle mass, are in a *Medical Director, Shock Trauma Center, Sentara Norfolk General Hospital; and Chief, Division of Trauma and Critical Care, and Associate Professor, Eastern Virginia Graduate School of Medicine, Norfolk, Virginia tChief Resident, Department of Surgery, Eastern Virginia Graduate School of Medicine, Norfolk, Virginia :j:Attending Traumatologist and Thoracic Surgeon, Maryland Institute for Emergency Medical Services System; and Assistant Professor of Surgery, University of Maryland, Baltimore, Maryland
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relatively poor premorbid state of health, and have a defect in autonomic function reflected by a decreased resting peripheral blood flow. 20, 75, 115 Neonatal infants, especially if they are premature, have a proclivity for hypothermia because of their large surface-to-body-mass ratio. 25, 98 Although hypothermia commonly occurs in cold environments, reports of hypothermic patients from Mrica and other temperate climates illustrate the fact that any ambient temperature below that of the body core can lead to thermal disarray. 45 Homoiothermy Man is a homoiothermic mammal suited best to survival in his evolutionary homeland, the tropics, at temperatures around 27°C (81°F). 6, 35, 115 Man is richly endowed with mechanisms with which to dissipate heat. However, he must rely largely on intelligent behavior to conserve heat. 58 In an effort to understand man's thermoregulatory mechanisms better, physiologists divide the body into a homoiothermic core, which includes the deep muscles and internal organs, and a poikilothermic shell, which includes the skin and its thermoreceptors, the subcutaneous tissue, and the superficial muscles. 5 The shell subserves the core in an attempt to maintain the central temperature. Heat loss occurs by four mechanisms, Radiation is the loss of heat to the environment via infrared radiation. Convection is the transfer of heat to the environment by air or water that is in contact with the body. Convection is dependent on air temperature and velOcity. Conduction is the transfer of heat to another object by direct contact, When this object is cold water, heat is transferred from the body at a rate 32 times that to air. 115 Finally, heat may be lost by evaporation, the conversion of water to its gaseous phase, at a cooling rate of 0.6 kcal/g. 93 Homoiothermic responses to cold are integrated by the hypothalamus. Changes in the ambient temperature are detected by thermal receptors in the skin. Afferent pathways in the spinal cord transmit these changes to the anterior hypothalamus. The posterior hypothalamus then initiates a series of changes designed to prevent further heat loss and to augment heat production. 35 Muscle tone is increased, which leads to shivering (physical thermogenesis), with an associated fivefold increase in heat production. 48, 53 However, shivering also increases the rate of heat loss, Metabolic thermogenesis entails increases in epinephrine, norepinephrine, and thyroxine release, with a subsequent rise in the basal metabolic rate. 35 One of the most important regulators of heat is blood flow to the skin, especially the extremities, which account for 50% of the total body surface area. 110 Integumentary blood flow during cold stress virtually ceases (0,5 ml/min per 100 ml of tissue in the digits) as vasoconstriction predominates, 16 When heat loss is desired, blood flow to the extremities at maximum vasodilatation is augmented to 30% of the cardiac output, 35 Finally, and perhaps most importantly, decreases in ambient temperature initiate conscious responses to seek shelter, increase physical activity, and apply protective clothing. Any interruption in either the perception of thermal adversity, the transmission of sensory signals to the central nervous system (CNS), the
f MANAGEMENT OF HYPOTHERMIA AND FROSTBITE INJURY
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Table I. Classification of Hypothermia DEFINITION
TEMPERATURE
Mild
SIGNS AND SYMPTOMS
Shivering Complaint of cold Usually conscious Sometimes confused Normal blood pressure 80°-89°F 26. 7°-32. 2°C
Moderate
Severe
Semiconscious, combative Shivering ceases Muscle rigidity Dilated pupils Ventricular fibrillation with agitation Decreased breathing rate Blood pressure difficult to obtain Comatose No rigidity (flaccid) Apnea Spontaneous ventricular fibrillation
processing of neural input, or the efferent metabolic and behavioral changes directed by the CNS to diminish thermal stress predisposes one to hypothermia or hyperthermia (see Table 2). Furthermore, extremes of core temperature-greater than 41°C (106°F) or less than 34°C (94°F)-paralyze protective homoiothermic mechanisms, inviting further thermal insult. 35 Pathophysiology The pathophysiologic changes that accompany hypothermia are dependent on the severity of hypothermia, the causal factors, and the pre morbid characteristics of the patient. These will be described separately in relation to each of the organ systems. Table 2. Conditions Predisposing to Hypothermia Metabolic Factors Hypothyroidism Hypoglycemia Hypopituitarism Diabetic ketoacidosis Hypoadrenalism Renal failure Malnutrition Central Nervous System Conditions Head injury Spinal cord transection Cerebrovascular disease Hypothalamic lesions Alzheimer's disease Wernicke's encephalopathy Skin Disorders Burn injury Erythrodermas
Cold Exposure Cold water immersion Drugs Ethanol Phenothiazines General anesthetics Tricyclic antidepressants Barbiturates Benzodiazepines Opiates Reserpine Infections Peritonitis Meningitis Bacteremia
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Cardiovascular System. Cardiac output initially increases, then progressively decreases during worsening hypothermia, with a concomitant decrease in blood pressure. In severe hypothermia, there is lengthening of the QRS and ST segments as electrical conduction slows. 145 A characteristic J or Osborne wave is noted as a positive-negative deHection immediately after the QRS complex in as many as 30% of cases. 81, lOS, 142 As temperatures dip below 29°C, atrial fibrillation, bradycardia, and ventricular extrasystoles are common, Spontaneous ventricular fibrillation occurs at temperatures below 25°C, with cardiac standstill occuring at 21°C, U5 Pulmonary System. The respiratory rate usually increases after sudden immersion in cold water, However, the medullary respiratory center is increasingly depressed as hypothermia worsens, Reports of pulmonary edema after rewarming from severe hypothermia are common. 35, 45 Alteration in consciousness, depression of the cough reHex, and excessive production of tenacious bronchial secretions, "cold bronchorrhea," are thought to explain the atelectasis, bronchopneumonia, and aspiration present after rewarming. 139 Cold-induced slOwing of the tracheobronchial cilia may contribute to this respiratory insult,8 Renal Function. A "cold diuresis" accompanies hypothermia that is thought to be secondary to a cold-induced reduction in cellular enzyme activity with defects in distal tubular reabsorption of sodium and water. 99, 128 This occurs despite a decrease in the rates of glomerular filtration and renal blood How. l38 Other authors have suggested that this cold diuresis is the result of an altered sensitivity of the renal collecting tubules to antidiuretic hormone,l58 and still others have postulated that early peripheral vasoconstriction causes temporary central volume overload with a subsequent diuresis in an effort to reduce blood volume. 55 Central Nervous System. Hypothermia results in a progressive depression of neurologic activity. Clarity of consciousness gives way to confusion, lethargy, and, finally, unresponsiveness as hypothermia becomes more severe. Cerebral blood How decreases 6% to 7% for every 1°C decrease in body temperature. U5 Gastrointestinal Tract. Temperatures below 32°C result in mild ileus. 81 Hepatic function is depressed with a concomitant reduction in the detoxification of drugs. 81 Gastric stress ulcers and hemorrhagic pancreatitis have been noted at temperatures below 26.7°C (800F). 35 Oxygen Dynamics. Hypothermia shifts the oxyhemoglobin dissociation curve to the left, increasing the affinity of hemoglobin for oxygen, U5 This change is offset by an increase in the diffusion of oxygen and by a reduction in oxygen consumption by 50% at 30°C (860F). 35 Metabolism. The metabolic rate is reduced by 50% for every lOOC fall in temperature as stated by the rule of Van't Hoff Arrhenius, 88 The action of insulin to increase the cellular uptake of glucose is impaired when temperatures are below 30°C, contributing to the hyperglycemia often noted with hypothermia. 81 An alteration in the the sodium-potassium pump during hypothermia may result in elevated potassium levels. 109 Hypokalemia often develops after rewarming. Metabolic acidosis may be present in 30% of patients secondary to respiratory depression, lactic acid generation from shivering,
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the increase in CO 2 diffusibility, and the decreased hepatic metabolism of organic acids. 61 Blood. There is a 2% increase in blood viscosity for each 1°C drop in temperature. 51 An elevated hematocrit, as high as 60%, may be noted early in rewarming, thought to be secondary to the "cold diuresis" described earlier. 55 Impaired coagulation and disseminated intravascular coagulation, perhaps related to the release of tissue thromboplastin from ischemic tissue, may be present with severe hypothermia, only to resolve during rewarming. 18 Temporary thrombocytopenia has been reported with lower body temperatures, especially in neonates. 32. 143 In animal models, sequestration of platelets in the liver, spleen, and portal system during hypothermia has been demonstrated. 148 Pathologic Changes. There are no specific pathologic changes unique to hypothermic injury identified in patients who succumb. 79, 123, 133 Fatty infiltration and hemorrhagic and thrombotic lesions of the heart, liver, brain, and kidney have been reported, as well as changes consistent with pancreatic inHammation and necrosis. 31, 63, 123, 133 Whether these represent changes that accompany hypothermia or simply reHect the population of people susceptible to hypothermia is not clear, Treatment
Treatment in the Field. Victims should be removed from the cold environment, wet clothing should be removed, and a blanket, preferably heated, should be placed around them. Thereafter, the victim should be moved as little as possible to avoid triggering ventricular fibrillation. 6 Cardiopulmonary resuscitation (CPR) should be started on those with severe hypothermia who are in cardiac arrest from ventricular fibrillation or asystole. If personnel trained in CPR are not available or if an electrical rhythm is present without a palpable pulse or blood pressure (common in severe hypothermia), CPR is not recommended,39 because in such cases, chest compressions may result in ventricular fibrillation developing from a previously perfusing cardiac rhythm, Electrical defibrillation usually is unsuccessful at temperatures below 29°C. However, an attempt at defibrillation is suggested, to be repeated if necessary for every 2° to 4°C rise in the victim's temperature, Bretylium has been effective as an adjunct in managing hypothermia-induced ventricular fibrillation. Emergency Department Treatment. Making the diagnosis of hypothermia is the first challenge of resuscitation. 115 Diagnosis is complicated by the fact that most emergency department thermometers record temperatures only to 34.4°C, Adding "D" ("degree of temperature") to the ABCs of resuscitation is a simple way to avoid overlooking hypothermia. 132 A complete blood count; measurement of serum electrolytes, blood glucose, coagulation, arterial blood gases, and serum blood urea nitrogen and creatinine levels; and blood cultures are obtained. A Foley catheter is inserted. A chest radiograph to identify pulmonary pathology and an electrocardiogram to demonstrate dysrhythmias are ordered. Continuous monitoring of vital signs, central venous pressure if a central line has been placed, urine output, and serial electrolytes and arterial blood gases is conducted during rewarming.
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If alcohol abuse is suspected, thiamine should be given immediately. Hypoglycemia, often associated with hypothermia, should be ruled out. Gaining peripheral venous access may be difficult, necessitating placement of a central venous line. Pulmonary artery catheters, which may disturb the myocardium, should be avoided. Warm humidified oxygen should be administered to all patients. If apnea exists, humidified oxygen should be given first by face mask, then after preoxygenation, by insertion of an endotracheal tube. The literature warns about the risk of triggering ventricular fibrillation with oropharyngeal manipulation or intubation. 104, 126 However, Danzl and associates had no complications from nasotracheally intubating 117 patients who had temperatures less than 32.2°C.23 In addition, intubation proVides a means for inhalational core rewarming and ease of pulmonary toilet in this subset of patients who are likely to develop disabling bronchorrhea and pneumonia. 6 Rewarming Rewarming techniques are divided into passive (no added heat) and active (heat added). Active rewarming may be delivered by external means or by core rewarming. Table 3 lists different rewarming modalities. The advantages, disadvantages, and contraindications of each core rewarming technique will be discussed briefly. Warmed Intravenous Solutions. The administration of warmed intravenous fluids and blood is an effective way to initiate core rewarming. Fluids in plastic bags may be warmed to temperatures of 40°C by microwave. 43, 69 Peritoneal Lavage. Warmed peritoneal lavage can be performed with the insertion of two catheters so that fluid rates of up to 12 Uhour are possible. 60 The advantages of peritonal lavage include its simplicity and ready availability in most hospitals, its low risk to the patient, and the ability to provide large quantities of heat with concomitant removal of toxic Table 3. Rewarming Techniques for Treatment of Hypothermia Passive Warm environment Heat generation via shivering Blanket insulation Active External Heating pads Immersion in warm water Hot water bottles Environmental heaters Internal (core) Heated IV solutions Hemodialysis Gastric/colonic lavage Peritoneal lavage Mediastinal lavage Inhalation rewarming Diathermy Extracorporeal blood rewarming
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metabolic byproducts. 47, 49, 60, 68, 107, 116 Early revitalization of the liver, with the subsequent return of metabolite detoxification, is an added benefit, Contraindications to peritoneal lavage include abdominal trauma necessitating exploration, such as acute abdomen, hemoperitoneum, or free intra-abdominal air. In these cases, intraoperative warm peritoneal irrigation is possible, 49 Gastric-Colonic Lavage. Use of intragastric and intracolonic balloons in experimental animals, as well as of gastric and colonic lavage techniques in humans, has been described, The advantage of such techniques is that peritoneal penetration is avoided, The risks of gastric and colonic lavage include those associated with tube insertion and the potential for organ perforation. Contraindications include trauma circumstances in which a gastric or colonic injury is feared, Airway Rewarming. The inhalation of hot, moist gas either by facemask, if the patient is ventilating spontaneously, or by endotracheal intubation, if there is respiratory distress, has several advantages. First, continued respiratory heat loss is stopped, Second, the heart and lungs are the first organs to be warmed. Third, reversal of cold-induced ciliary dysfunction, thus improving bronchial evacuation of secretions, is possible,8 Finally, the equipment necessary for such core rewarming is readily available and easily applied, with few risks,49, 50, 129 Inspired air temperature should not exceed 40°C (104°F) in the awake patient and 50°C (122°F) in the unresponsive patient,73, 156 There are no significant contraindications to inhalation rewarming, When facial injuries preclude intubation, cricothyroidotomy or tracheostomy for inhalational rewarming is possible, Mediastinal Lavage. Median sternotomy with warm mediastinal lavage is another modality with reported success in the hemodynamically unstable, severely hypothermic patient. 3 The ability to perform open cardiac massage during rewarming is the unique advantage of this treatment modality. The principal disadvantage is the morbidity associated with a median sternotomy. Diathermy. Restoring lost body heat by ultrasonic waves, microwaves, or short waves is possible. 71 The advantage of diathermic rewarming is that the delivery of heat to the core tissues occurs without an invasive procedure. 49 Studies in dogs have shown that radiowave diathermy compares favorably with peritoneal lavage. 156 Clinical utilization of diathermy has not been widespread because of the difficulty associated with identifYing adequate dosages for patients. 49 Lehmann has summarized the many contraindications to diathermic rewarming. 71 Some of these are pacemakers, suspected hemorrhage, and areas of occlusive arterial disease. Extracorporeal Blood Rewarming. Successful resuscitation of patients having severe hypothermia with or without hemodynamic instability using extracorporeal rewarming has been reported frequently. 3, 13, 140, 158 This usually is performed by cannulation of one or both femoral veins and returning warmed blood via a femoral artery cannula. 21, 49 The primary advantage of extracorporeal rewarming is the ability to oxygenate the blood and rewarm patients rapidly while providing hemodynamic support to those
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who develop dysrhythmias or hypotension. Passive and active external rewarming techniques can be used as an adjunct with this method of core rewarming. The complications of extracorporeal rewarming are thrombophlebitis and the inherent risk associated with arterial venous access and heparinization. 49 The contraindications are those for heparin anticoagulation, such as gastrointestinal bleeding or general trauma. Rewarming Controversies The most controversial aspect of hypothermia is identifying the best way to rewarm the moderately to severely hypothermic patient (temperature
