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Hyperthermia and Hypothermia

Hyperthermia and Hypothermia. Back to Basics April 2011 Dr. J. Clow, ER. Case 1:. 22 y.o. female Out with friends celebrating her birthday (February 19 th ) Dropped off at her front door by friends Found by her parents in the morning, passed out just inside the screen door

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Hyperthermia and Hypothermia

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  1. Hyperthermia and Hypothermia Back to Basics April 2011 Dr. J. Clow, ER

  2. Case 1: • 22 y.o. female • Out with friends celebrating her birthday (February 19th) • Dropped off at her front door by friends • Found by her parents in the morning, passed out just inside the screen door • Unable to wake her… call 911

  3. Case 2: • 85 y.o. male • Mid-August, during heat wave • Son goes to apartment and finds patient confused and lethargic • Patient unable to give history

  4. Heat Regulation • Four mechanisms of heat loss/dissipation: • Radiation • Convection • Conduction • Evaporation

  5. Radiation • Physical transfer of heat between the body and the environment by electromagnetic waves • 65% of heat transfer under normal circumstances • Modified by insulation (clothing, fat layer), cutaneous blood flow

  6. Convection • Energy transfer between the body and a gas or liquid • Affected by temperature gradient, motion at the interface, and liquid • Not usually a major source for heat loss or dissipation, but this increases with wind and body motion

  7. Conduction • Direct transfer of heat energy between two surfaces • Responsible for only a small proportion of heat loss under normal circumstances • Increases significantly with immersion in cold water • Major cause of accidental hypothermia

  8. Evaporation • Most important source of cooling under extreme heat stress; important for hypothermia when in wet environment • 25% of heat loss in temperate/cool conditions… may be increased significantly by sweating, increased respiratory rate • Affected by relative humidity and clothing

  9. Hypothermia…

  10. Definition • Core body temperature less than 35oC • Mild: 32.2 - 35oC • Moderate: 28 - 32.2oC • Severe: < 28oC

  11. Causes… • Decreased heat production • Endocrine, insufficient fuel, neuromuscular inactivity • Increased heat loss • Accidental/immersion hypothermia, vasodilatation, skin disorders, iatrogenic • Impaired thermoregulation • Central (metabolic, drugs, CNS) • Peripheral (spinal cord injury, neuropathy, diabetes, neuromuscular disorders)

  12. Predisposing Factors

  13. Signs and Symptoms

  14. Signs and Symptoms, cont’d

  15. History • Often from bystanders/medics • Circumstances surrounding exposure • Where, submersion, ambient temperature? • Length of exposure • Mental status changes • Any predisposing illness – acute/chronic? • Alcohol/drugs?

  16. Physical Exam • Vitals… • Temperature – want a core temperature • Where do we take it? • Signs of other injuries? • Can you find the cause of hypothermia? • Any focal findings? • Esp. neurologic, cardiovascular, respiratory

  17. Diagnositics • ECG (always), CXR (most patients) • Other tests depend on the clinical scenario • Any signs of trauma? May need imaging… • Are you able to take a history? • Past medical history? • Labs for all: • CBC, electrolytes, glucose, renal function, toxicology, coags, ABGs, LFTs, lipase/amylase, cultures

  18. ECG Changes • May see J waves • late, terminal upright deflection of QRS complex; best seen in leads V3-V6 • Multiple arrhythmias • Heart block • Atrial fibrillation • Ventricular fibrillation

  19. ECG Changes, cont’d

  20. Management…

  21. Interventions • Airway: need for intubation? • Breathing: spontaneous respiration? • Warmed humidified oxygen – either through an ETT, or via mask • Circulation: pulse? BP? • Large IVs – warmed IV fluids • Arrhythmias – when do we treat? • CPR?

  22. Interventions, cont’d • Disability • GCS • Glucoscan, narcan, thiamine • C-spine immobilization prn • Exposure • Undress, assess for trauma • Re-cover quickly

  23. Rewarming

  24. Active Rewarming • When? • Cardiovascular instability • Temp less than 32oC • Concominant illnesses • Extremes of age • Failure of passive rewarming • Active external or internal?

  25. Rewarming - Extracorporeal

  26. Hyperthermia…

  27. Definition • Core body temperature > 38oC • Caused by a failure of thermoregulation • Contrast with fever – cause is cytokine activ’n • Spectrum of heat-related illnesses • Heat cramps • Heat exhaustion • Heat stroke

  28. Spectrum • Heat cramps • Cramps in big muscles – spasms • Normal temperature, mentation • Caused by dilutionalhyponatremia (hypotonic fluid replacement)

  29. Spectrum, cont’d • Heat exhaustion • Weakness, dizziness, headache, syncope • Nausea, vomiting • Temperature 39-41.1oC • Normal mentation • Profuse sweating

  30. Spectrum, cont’d • Heat Stroke • Temperature >41.1oC • Coma, seizures, confusion • No sweating • Classic triad: hyperpyrexia, CNS dysfunction, anhidrosis • Mortality of 10-20% with treatment • Classic vs. Exertional

  31. Spectrum, cont’d • Heat Stroke: • Classic (non-exertional): • Persistent environmental exposure • Impaired thermoregulation • Exertional: • Heavy exercise in setting of high temperature and humidity

  32. Causes of Hyperthermia • Increased heat load • Heat absorption from environment • Heat stroke (exertional, classic) • Metabolic heat • Diminished heat dissipation • Obesity, anhidrosis, drugs • Sepsis

  33. Predisposing Factors…

  34. Causes of Hyperthermia…

  35. Differential Diagnosis

  36. History • Circumstances (as per hypothermia) • Exertion? • Fluids? • Past medical history – any acute or chronic illnesses that may worsen situation • Medications/Drugs • Trauma?

  37. Physical Examination • Temperature • Where do we take it? And how? • Vitals! • Look for complications or other causes of the patients symptoms • Respiratory, cardiac, neurologic examination • Signs of bleeding

  38. Diagnostics • ECG (all), CXR (most) • Imaging guided by history • CBC, electrolytes, renal function, LFTs, Ca, Mg, PO4, coags, CK • Urine – myoglobin • Pan-cultures

  39. Poor prognostic factors • Temperature > 41.1oC • AST > 1000 • Coma • Rhabdomyolysis • Renal Failure • Hypotension

  40. Treatment • ABC’s!!! • Remove to cool environment! • Active cooling • Correct fluid and electrolyte imbalances • Supportive care

  41. Treatment

  42. Complications of Heat Stroke

  43. Back to the cases…

  44. Case 1: Hypothermia • What do you want to know? • Physical Exam? • Labs? • Any imaging? • How are you going to treat her?

  45. Case 2: Hyperthermia • What do you want to know? • Physical Exam? • Labs? • Any imaging? • How are you going to treat him?

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