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Hypothermia
Chapter 10
Hypothermia
BRUCE C. PATON, MD
History includes circumstances of exposure (e.g., obvious accidental exposure, old age, or living conditions). It also notes associated diseases (i.e., neurologic, cardiovascular, or endocrine); drug or alcohol intoxication; and psychiatric disorders. B Hypothermia produces bradycardia, hypotension, and unconsciousness. Peripheral pulses are often impalpable. Inability to feel a pulse, measure blood pressure, or hear a heartbeat does not mean a cold patient is dead. Unconsciousness with a core temperature of greater than 32° C may be caused by associated drugs or head injury and not by hypothermia. Bradycardia and atrial fibrillation are common arrhythmias when temperature falls to less than 30° C. Ventricular fibrillation or asystole can occur with a temperature less than 25° C. C Any core temperature (e.g., esophageal, high rectal, bladder, or tympanic membrane) less than 35° C constitutes hypothermia. Accepted classifications include mild, 35 to 32° C; moderate, 32 to 28° C; deep, 28 to 25° C; and profound, less than 25° C. D Abnormalities of serum K+, Na+, and glucose are common. Blood urea nitrogen and creatinine are elevated if there is renal shutdown. Acidosis is common, especially during rewarming. Measurements of pH should not be corrected for temperature. A toxicant screen is essential to exclude drugs or alcohol as the cause of hypothermia. E Barring head injury or drug overdose, unconsciousness in a cold patient is considered to be caused by hypothermia (temperature usually less than 32° C). Those who arrive in the emergency room conscious should survive. F Unconscious cold patients must be admitted to the ICU or operating room (if extracorporeal circulation is to be used), and treatment of both
A
30
hypothermia and associated condition must be started. G Arrhythmias with ineffective cardiac output may occur during rewarming. Most arrhythmias disappear with normothermia. Active rewarming is commonly necessary before ventricular defibrillation is possible. Rewarming may cause relative hypovolemia, which should be treated with volume replacement as indicated by standard criteria. H Passive rewarming consists of removing wet clothing, covering the patient with warm blankets, monitoring the ECG and temperature, and allowing endogenous metabolism to rewarm the body. This can be done in the emergency room, the ICU, or a hospital room. I Determination of heartbeat can be difficult. Shivering interferes with ECG monitoring, and pulse blood pressure may not be palpable. Arterial cutdown may be necessary to measure blood pressure. J If the heart is beating, the patient should be treated with full intensive care monitoring. Treatment must be carefully controlled and cautious rather than overzealous. The patient is handled gently. Endotracheal intubation and the insertion of Swan-Ganz catheters must be done gently, but these measures should not be withheld for fear of inducing ventricular fibrillation. Acidosis and electrolyte abnormalities are corrected slowly as is the hypotension caused by vasodilation during rewarming. K Cardiopulmonary resuscitation is started as soon as the absence of a heartbeat is confirmed. Cardiopulmonary resuscitation started in the field must be continued until cardiac action can be definitively determined and treated. L Active rewarming may be external or internal. External methods are less traumatic than
internal ones and are more readily available but less efficient. The chosen method should be appropriate to the situation and, if possible, should allow resuscitation during rewarming. External rewarming may include hot water bottles, piped suits or blankets, radiant heat, warmed circulating air, or warm water tub (45° C). Immersion in warm water is the most efficient external method. Internal rewarming always begins with the administration of warm, humidified oxygen. This prevents further heat loss and provides additional heat. Body cavity lavage (peritoneum, pleura) is efficient and requires minimal equipment. Femorofemoral or total cardiopulmonary bypass with a heat exchanger is the most efficient method of rewarming but requires special equipment in a cardiac center. It is the optimal treatment for profound hypothermia with cardiac arrest. M Survival depends more on associated diseases and injuries than on the degree of hypothermia. Mild hypothermia should not cause death. Deep hypothermia with cardiac arrest treated by cardiopulmonary bypass has a 50% mortality. Elevated blood urea nitrogen or K+ and the need for resuscitation outside a hospital are associated with a poor prognosis. Serum K+ greater than 10 mEq/1 signifies inability to resuscitate. Hypothermia incidental to severe trauma adds significantly to mortality. REFERENCES Danzl DF: Accidental Hypothermia. In Auerbach PS (ed.): Wilderness Medicine, 4th ed. St. Louis: Mosby, 2001. Giesbrecht CG: Emergency treatment of hypothermia. Emerg Med 13:9–16, 2001. Walpoth BH, Walpoth-Aslan BN, Mattle HP, et al: Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. New Eng J Med 337:1500–1505, 1997. Wittmers LE, Jr.: Pathophysiology of cold exposure. Minn Med 84:30–36, 2001.
31
HYPOTHERMIA
History and physical examination Exposure A Associated disease Drugs Responsiveness B Pulse and heart rate Respiration
E Conscious ⬎32° C
C
O2 Warmed IV fluids
Passive H rewarming Warm water Warm air Radiant heat Blankets Hot water bottles
HYPOTHERMIA
F Unconscious ⬍30° C Labs Core temperature Electrolytes D ECG Urine Toxic screen
ECG monitor G O2 Endotracheal tube Arterial catheter I Central venous pressure Heart Arterial blood gases beating Foley catheter Chest x-ray Coagulation profile Heart not Standby defibrillation beating Swan-Ganz catheter Toxic drug screen Studies for associated injuries Warmed IV fluids
J Full intensive care
K Cardiopulmonary resuscitation
External
L
M
Active rewarming
Outcome
Internal
Body cavity lavage Femorofemoral or cardiopulmonary bypass
Hypothermia
BRUCE C. PATON, MD
History includes circumstances of exposure (e.g., obvious accidental exposure, old age, or living conditions). It also notes associated diseases (i.e., neurologic, cardiovascular, or endocrine); drug or alcohol intoxication; and psychiatric disorders. B Hypothermia produces bradycardia, hypotension, and unconsciousness. Peripheral pulses are often impalpable. Inability to feel a pulse, measure blood pressure, or hear a heartbeat does not mean a cold patient is dead. Unconsciousness with a core temperature of greater than 32° C may be caused by associated drugs or head injury and not by hypothermia. Bradycardia and atrial fibrillation are common arrhythmias when temperature falls to less than 30° C. Ventricular fibrillation or asystole can occur with a temperature less than 25° C. C Any core temperature (e.g., esophageal, high rectal, bladder, or tympanic membrane) less than 35° C constitutes hypothermia. Accepted classifications include mild, 35 to 32° C; moderate, 32 to 28° C; deep, 28 to 25° C; and profound, less than 25° C. D Abnormalities of serum K+, Na+, and glucose are common. Blood urea nitrogen and creatinine are elevated if there is renal shutdown. Acidosis is common, especially during rewarming. Measurements of pH should not be corrected for temperature. A toxicant screen is essential to exclude drugs or alcohol as the cause of hypothermia. E Barring head injury or drug overdose, unconsciousness in a cold patient is considered to be caused by hypothermia (temperature usually less than 32° C). Those who arrive in the emergency room conscious should survive. F Unconscious cold patients must be admitted to the ICU or operating room (if extracorporeal circulation is to be used), and treatment of both
A
30
hypothermia and associated condition must be started. G Arrhythmias with ineffective cardiac output may occur during rewarming. Most arrhythmias disappear with normothermia. Active rewarming is commonly necessary before ventricular defibrillation is possible. Rewarming may cause relative hypovolemia, which should be treated with volume replacement as indicated by standard criteria. H Passive rewarming consists of removing wet clothing, covering the patient with warm blankets, monitoring the ECG and temperature, and allowing endogenous metabolism to rewarm the body. This can be done in the emergency room, the ICU, or a hospital room. I Determination of heartbeat can be difficult. Shivering interferes with ECG monitoring, and pulse blood pressure may not be palpable. Arterial cutdown may be necessary to measure blood pressure. J If the heart is beating, the patient should be treated with full intensive care monitoring. Treatment must be carefully controlled and cautious rather than overzealous. The patient is handled gently. Endotracheal intubation and the insertion of Swan-Ganz catheters must be done gently, but these measures should not be withheld for fear of inducing ventricular fibrillation. Acidosis and electrolyte abnormalities are corrected slowly as is the hypotension caused by vasodilation during rewarming. K Cardiopulmonary resuscitation is started as soon as the absence of a heartbeat is confirmed. Cardiopulmonary resuscitation started in the field must be continued until cardiac action can be definitively determined and treated. L Active rewarming may be external or internal. External methods are less traumatic than
internal ones and are more readily available but less efficient. The chosen method should be appropriate to the situation and, if possible, should allow resuscitation during rewarming. External rewarming may include hot water bottles, piped suits or blankets, radiant heat, warmed circulating air, or warm water tub (45° C). Immersion in warm water is the most efficient external method. Internal rewarming always begins with the administration of warm, humidified oxygen. This prevents further heat loss and provides additional heat. Body cavity lavage (peritoneum, pleura) is efficient and requires minimal equipment. Femorofemoral or total cardiopulmonary bypass with a heat exchanger is the most efficient method of rewarming but requires special equipment in a cardiac center. It is the optimal treatment for profound hypothermia with cardiac arrest. M Survival depends more on associated diseases and injuries than on the degree of hypothermia. Mild hypothermia should not cause death. Deep hypothermia with cardiac arrest treated by cardiopulmonary bypass has a 50% mortality. Elevated blood urea nitrogen or K+ and the need for resuscitation outside a hospital are associated with a poor prognosis. Serum K+ greater than 10 mEq/1 signifies inability to resuscitate. Hypothermia incidental to severe trauma adds significantly to mortality. REFERENCES Danzl DF: Accidental Hypothermia. In Auerbach PS (ed.): Wilderness Medicine, 4th ed. St. Louis: Mosby, 2001. Giesbrecht CG: Emergency treatment of hypothermia. Emerg Med 13:9–16, 2001. Walpoth BH, Walpoth-Aslan BN, Mattle HP, et al: Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. New Eng J Med 337:1500–1505, 1997. Wittmers LE, Jr.: Pathophysiology of cold exposure. Minn Med 84:30–36, 2001.
31
HYPOTHERMIA
History and physical examination Exposure A Associated disease Drugs Responsiveness B Pulse and heart rate Respiration
E Conscious ⬎32° C
C
O2 Warmed IV fluids
Passive H rewarming Warm water Warm air Radiant heat Blankets Hot water bottles
HYPOTHERMIA
F Unconscious ⬍30° C Labs Core temperature Electrolytes D ECG Urine Toxic screen
ECG monitor G O2 Endotracheal tube Arterial catheter I Central venous pressure Heart Arterial blood gases beating Foley catheter Chest x-ray Coagulation profile Heart not Standby defibrillation beating Swan-Ganz catheter Toxic drug screen Studies for associated injuries Warmed IV fluids
J Full intensive care
K Cardiopulmonary resuscitation
External
L
M
Active rewarming
Outcome
Internal
Body cavity lavage Femorofemoral or cardiopulmonary bypass