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Hyperthermia and hypothermia

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Hyperthermia and hypothermia

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Hyperthermia and hypothermia

  1. 1. HOT & COLD
  2. 2. HYPERTHERMIA & HEAT RELATED DR PETER R WATSON
  3. 3. HYPERTHERMIA HEAT RELATED ILLNESSES ▸Broad range of ætiology and manifestations ▸Primary disorder due to failure of thermal homeostasis ▸But hyperthermia may be a secondary disorder ▸Major causes of hyperthermia are: ▸Exercise-associated collapse (EAC) ▸Heatstroke ▸Drug related heat illness
  4. 4. HYPERTHERMIA PATHOPHYSIOLOGY OF HYPERTHERMIA ▸Core body temperature >41.5°C ▸Progressive denaturing of vital cellular proteins ▸Failure of vital energy-producing processes ▸Loss of cellular membrane function ▸Organ dysfunction: ▸rhabdomyolysis, APO, DIC, cardiovascular dysfunction, electrolyte disturbance, renal failure, liver failure, permanent neurological damage.
  5. 5. HYPERTHERMIA EXERCISE-ASSOCIATED COLLAPSE ▸Most common heat-related illness at sporting events ▸Manifests at end of a race ▸Muscle pump enhanced venous return ceases and cardiac output drops. ▸Leads to collapse, often with brief LOC ▸Due primarily to failure of prompt baroreceptor responses and not haemodynamically significant dehydration (rare).
  6. 6. HYPERTHERMIA HEATSTROKE ▸Hallmark is failure of the hypothalamic thermostat ▸Leading to hyperthermia and organ dysfunction ▸Exertional heatstroke due to exercise in a thermally stressful environment ▸Classic heatstroke occurs in patients with impaired thermostatic regulation
  7. 7. HYPERTHERMIA TOXIDROMES ▸Serotonin syndrome ▸Neuroleptic malignant syndrome ▸Malignant hyperthermia
  8. 8. HYPERTHERMIA SEROTONIN SYNDROME ▸Serotonin toxicity: the effects are a consequence of a relative excess of central nervous system serotonin. ▸Dose related, selective serotonin re-uptake inhibitors (SSRIs), lithium, pethidine, monoamine oxidase inhibitors (MAOIs) and amphetamines. ▸Clinical diagnosis characterised by CNS, autonomic & motor dysfunction ▸Develops after a latent period, usually of a few hours, but may be several days ▸Most patients are only mildly affected and may escape clinical detection. ▸Severe cases with hyperthermia with muscular rigidity with complications of rhabdomyolysis, DIC, and renal failure. ▸Most cases resolve within 24–48hr once the precipitant is withdrawn. ▸Even in severe cases, the underlying biochemical abnormality rapidly improves, usually with the institution of muscular paralysis. ▸Mortality & morbidity is due to the complications of the syndrome
  9. 9. HYPERTHERMIA NEUROLEPTIC MALIGNANT SYNDROME ▸Neuroleptic malignant syndrome: dopamine depletion or dopamine receptor blockade is responsible ▸Rare idiosyncratic reaction to neuroleptic agents with an incidence of between 0.02% and 3.0% Manifests in patients who recently started or increased neuroleptic treatment ▸Associated with almost all antipsychotics (both first and second generation) ▸Reported in patients in whom a dopaminergic agent has been rapidly withdrawn (e.g. in Parkinsonism). ▸Latent period of onset of several hours to days. ▸Four classic signs: fever, rigidity, altered mental state and autonomic instability. ▸Only the more severe cases develop hyperthermia and its complications.
  10. 10. HYPERTHERMIA MALIGNANT HYPERTHERMIA ▸Due to exposure to volatile anaesthetic agents or suxamethonium ▸Malignant hyperthermia is a genetically inherited disorder in which triggering agents cause a release of sarcoplasmic Ca2+ stores. ▸Elevated levels of myoplasmic Ca2+ stimulates many intercellular processes, including glycolysis, muscle contraction and an uncoupling of oxidative phosphorylation. Leading to hyperthermia that is purely peripheral in origin.
  11. 11. HYPERTHERMIA RISK FACTORS FOR HEATSTROKE ▸ Behavioural ▸ Army Recruits ▸ Athletes ▸ Exertion ▸ Inappropriate exposure to high heat &/or humidity ▸ Babies left in cars ▸ Manual workers ▸ Pilgrims
  12. 12. HYPERTHERMIA RISK FACTORS FOR HEATSTROKE ▸ Illness ▸ Delirium tremens ▸ Dystonias ▸ Infections ▸ Seizures
  13. 13. HYPERTHERMIA RISK FACTORS FOR HEATSTROKE ▸ Drugs ▸ Anticholinergics ▸ Diuretics ▸ Phenothiazines ▸ Salicylates ▸ Stimulants/hallucinogens
  14. 14. HYPERTHERMIA DRUGS CAUSING SEVERE SEROTONIN TOXICITY ▸Antidepressants ▸Monoamine oxidase inhibitors (MAOIs) ▸Selective serotonin reuptake inhibitors (SSRIs) ▸Selective serotonin and noradrenaline reuptake inhibitors (SSNRIs) ▸St John’s wort ▸Tricyclics ▸Analgesics ▸Pethidine ▸Tramadol ▸Recreational drugs ▸Amphetamines ▸Methylenedioxymethamphetamine (MDMA, ‘ecstasy’)
  15. 15. HYPERTHERMIA RISK FACTORS FOR NEUROLEPTIC MALIGNANT SYNDROME ▸Patient factors ▸Agitation ▸Dehydration ▸Male sex (M:F = 2:1) ▸Organic brain disease ▸Drug dosing factors ▸Depot neuroleptics ▸High initial neuroleptic dose ▸High-potency neuroleptic (e.g. haloperidol) ▸Rapid dosage increase
  16. 16. HYPERTHERMIA PREVENTION OF HEATSTROKE ▸Education of at risk groups ▸Exertional heatstoke is most often in short, high intensity exercise where marked dehydration is unlikely. ▸Dehydration is not as important as previously thought ▸Exercise in high heat and humidity environments should be limited.
  17. 17. HYPERTHERMIA CLINICAL FEATURES OF EXERCISE- ASSOCIATED COLLAPSE (EAC) ▸Nausea, vomiting, malaise, dizziness ▸History of collapse ▸Tachycardia (likely) and orthostatic hypotension ▸Core temperature <40°C ▸Neurological function rapidly returns to normal
  18. 18. HYPERTHERMIA CLINICAL FEATURES OF HEAT STROKE ▸Neurological dysfunction ▸Loss of consciousness is a constant feature ▸Core temperature >41.5°C ▸Hot dry skin ▸Profuse sweating is a more common feature than previously believed ▸Other features include, tachycardia, hyperventilation, seizures, vomiting and hypotension
  19. 19. HYPERTHERMIA INVESTIGATIONS ▸Exclude other possible cause, ie infection, metabolic, or to evaluate the effect of hyperthermia ▸UEC (hyponatraemia) ▸CK (rhabdomyolysis) ▸BSL ▸ECG
  20. 20. HYPERTHERMIA TREATMENT FOR EXERCISE- ASSOCIATED COLLAPSE (EAC) ▸Rapidly responds to supine posture (lying down), rest, and oral fluids ▸IV rehydration rarely required ▸May worsen hyponatraemia due to fluid overload ▸It increases ADH levels
  21. 21. HYPERTHERMIA TREATMENT FOR HEATSTROKE ▸Medical emergency!!! Early recognition and early treatment decrease morbidity and mortality. ▸Need aggressive cooling of 0.1°C/min ▸Remove clothing, fine mist spray, ice packs neck, axilla & groin ▸Iced water immersion, ice slush, cool water immersion, iced peritoneal lavage and drugs (paralysis with ventilatory support) ▸IV fluids should be used judiciously ▸Monitor UEC & clotting closely
  22. 22. HYPERTHERMIA TREATMENT FOR DRUG RELATED HYPERTHERMIA ▸Serotonin syndrome ▸Cool them +/- paralysis ▸Chlorpromazine (12.5–50 mg IM/IV) ▸Cyproheptadine (4–8 mg orally 8-hourly). ▸NMS ▸Bromocriptine 2.5–10 mg tds. (May reduce the duration) ▸Malignant hyperthermia ▸Dantrolene 15-30mg/kg IV ▸Cease precipitating agent ▸Full support
  23. 23. HYPERTHERMIA PROGNOSIS ▸Maximum core temperature and duration of temperature elevation are predictors of outcome. ▸Prolonged coma and oliguric renal failure are poor prognostic signs. ▸Mortality is still about 10%, but survivors will not suffer long- term sequelae. ▸Heat stroke should be referred to ICU ▸EAC should recover in SSU of ED or onsite
  24. 24. HYPOTHER PETER R WATSON
  25. 25. HYPOTHERMIA DEFINITION ▸Hypothermia: Core temperature < 35°C ▸Mild (32–35°C) ▸Thermogenesis is still possible ▸Moderate (29–32°C) ▸Progressive failure of thermogenesis ▸Severe (<29°C) ▸Poikilothermic and increasing risk of malignant cardia arrhythmias
  26. 26. HYPOTHERMIA ÆTIOLOGY ▸Elderly are at greater risk of hypothermia because of reduced metabolic heat production and impaired responses to a cold environment. ▸Alcohol is a common ætiological factor and acts via: ▸Cutaneous vasodilatation ▸Altered behavioural responses ▸Impaired shivering ▸Hypothalamic dysfunction. ▸Hypothermia in the ED setting is often associated with underlying infection
  27. 27. HYPOTHERMIA ÆTIOLOGY: “IN ANY SEASON OR SETTING” ▸Environmental ▸Cold, wet, windy ambient conditions ▸Cold water immersion ▸Exhaustion ▸Trauma ▸Multitrauma (entrapment, resuscitation, head injury) ▸Minor trauma and immobility (e.g. #NOF, #NOH) ▸Major burns ▸Drugs ▸Ethanol ▸Sedatives (e.g. benzodiazepines) in overdose ▸Phenothiazines (impaired shivering) ▸Neurological ▸CVA ▸Paraplegia ▸Parkinson’s disease ▸Endocrine ▸Hypoglycaemia ▸Hypothyroidism ▸Hypoadrenalism ▸Systemic illness ▸Sepsis ▸Malnutrition
  28. 28. HYPOTHERMIA MILD HYPOTHERMIA (32–35°C) ▸ Clinical features: ▸ shivering ▸ apathy ▸ ataxia ▸ dysarthria ▸ tachycardia.
  29. 29. HYPOTHERMIA MODERATE HYPOTHERMIA (29– 32°C)▸ Clinical features: ▸ loss of shivering ▸ altered mental state ▸ muscular rigidity ▸ bradycardia ▸ hypotension
  30. 30. HYPOTHERMIA SEVERE HYPOTHERMIA (<29°C)▸ Clinical features: ▸ Almost undetectable signs of life ▸ coma ▸ fixed & dilated pupils ▸ areflexia ▸ profound bradycardia & hypotension.
  31. 31. HYPOTHERMIA CARDIAC RHYTHM IN HYPOTHERMIA
  32. 32. HYPOTHERMIA CARDIAC RHYTHM IN HYPOTHERMIA - 29.5°C
  33. 33. HYPOTHERMIA CARDIAC RHYTHM IN HYPOTHERMIA ▸Shivering artefact on ECG ▸In severe hypothermia typically this is slow atrial fibrillation ▸Extra positive deflection in the QRS (the J or Osborn wave) in leads II, V3–V6 with worsening hypothermia. ▸With handling or may spontaneously degenerate into VF or asystole
  34. 34. HYPOTHERMIA COMPLICATIONS ▸Cardiac arrhythmias ▸Thromboembolism ▸Rhabdomyolysis ▸Renal failure ▸DIC ▸Pancreatitis
  35. 35. HYPOTHERMIA INVESTIGATIONS ▸UEC (Na2+, K+, Glucose, Cr, Urea) ▸ Ca2+, PO4 -, Mg2+ ▸Amylase ▸CK ▸Ethanol ▸FBE ▸Coag ▸ABG/VBG - accept at face value; don’t correct values ▸CXR - impair ciliary function/aspiration ▸Other imaging as indicated ie trauma
  36. 36. HYPOTHERMIA MANAGEMENT - FLUIDS ▸Preferential substrate to generate heat by shivering is muscle glycogen ▸Oral glucose may be appropriate in mild hypothermia ▸In severe hypothermia, gastric stasis and ileus are common ▸Glucose IV: 5% dextrose IVI 200 ml/hr ▸Gentle warm IV fluid resuscitation due to relative dehydration as vascular beds dilate with rewarming ▸Severe hypotension at 37°C is a normal physiological state at 27°C.
  37. 37. HYPOTHERMIA MANAGEMENT - INTERVENTIONS ▸Intubation where needed allows protection of the airway and an avenue of rewarming via the ventilator ▸AF - should correct with warming alone ▸no need for chemical correction ▸Pulse VT/VF; manage along conventional pathways ▸If DC shocks do not work; repeat every 1°C warmer ▸Mg2+ may be the anti arrhythmic of choice ▸Pacing ▸Transcutaneous pacing may be indicated in a bradycardic patient whose blood pressure is too low to allow arteriovenous rewarming ▸Due to cardiac irritability, transvenous pacing is contraindicated in hypothermia
  38. 38. HYPOTHERMIA MANAGEMENT - DRUGS ▸Pharmacokinetics/Pharmacodynamics change with temperature. ie insulin is inactive <30°C, thus hyperglycaemia is common in hypothermia ▸Drug metabolism of drugs is decreased and protein binding may be increased in hypothermia.1 ▸With rewarming drugs may become bioavailable at toxic levels. ▸It may be prudent not to give vasoactive drugs to a patient with core temperature less than 30C
  39. 39. HYPOTHERMIA MANAGEMENT - WARMING ▸Stop them becoming cold/colder ▸Remove wet clothing ▸Avoid drafts, and multiple exposures of the patient once warming has begun ▸Endogenous rewarming ▸Warm, dry, wind-free environment ▸Warmed intravenous fluids (to prevent cooling) ▸External exogenous rewarming ▸Hot bath immersion ▸Forced-air blankets ▸Heat packs ▸Body-to-body contact ▸Core exogenous rewarming ▸Warmed, humidified inhalation ▸Left pleural cavity lavage ▸Extracorporeal circulation
  40. 40. HYPOTHERMIA OUT OF HOSPITAL HYPOTHERMIA
  41. 41. HYPOTHERMIA SUGGESTED HYPOTHERMIA WARMING ALGORITHM ▸ Mild hypothermia ▸ Manage at home ▸ Moderate hypothermia ▸ Manage in SSU/Ward ▸ Severe Hypothermia ▸ ICU treatment as risk of MOF ▸ Severe Hypothermia + lethal injuries ▸ Palliation
  42. 42. HYPOTHERMIA PROGNOSIS ▸0-85% mortality ▸Coldest survivor: core temp of 13.5°C ▸Very dependent on cause for hypothermia
  43. 43. HYPOTHERMIA SUMMARY ▸Minimise further heat loss ▸Begin rewarming of hypothermic patients early ▸Some patients are cold and dead but other cold patients who appear dead can be resuscitated with full neurologic recovery ▸Endogenous rewarming should occur in moderate-severe hypothermia ▸Rewarming with forced-air rewarming blankets in most cases of moderate-to- severe hypothermia can be done without the need to resort to more aggressive techniques. ▸Rewarming should be with cardiopulmonary bypass or warm left pleural lavage in the arrested hypothermic patient.
  44. 44. HYPERTHERMIA/HYPOTHERMIA REFERENCES ▸Rogers, Ian. Heat-related illness, draft chapter TEXTBOOK OF ADULT EMERGENCY MEDICINE ▸Heat-Related Illness Emergency Medicine Clinics of North America. Atha, Walter F., MD.. Published November 1, 2013. Volume 31, Issue 4. Pages 1097-1108. ▸Drug-Induced Hyperthermic Syndromes. Bryan D. Hayes PharmD, Joseph P. Martinez MD and Fermin Barrueto MDEmergency Medicine Clinics of North America, 2013-11-01, Volume 31, Issue 4, Pages 1019- 1033, ▸Hyperthermia Caused by Drug Interactions and Adverse Reactions. Mary S. Paden MD, Lucy Franjic MD and S. Eliza Halcomb MD. Emergency Medicine Clinics of North America, 2013-11-01, Volume 31, Issue 4, Pages 1035-1044 ▸TEXTBOOK OF ADULT EMERGENCY MEDICINE. 4th Ed. Churchill Livingstone 2015 Elsevier Ltd ▸Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia. Ken Zafren. Emergency Medicine Clinics of North America, 2017-05-01, Volume 35, Issue 2, Pages 261-279, ▸https://www.pharmacytimes.com/contributor/patrick-wieruszewski-bs-pharmd-candidate- 2016/2016/03/pharmacokinetic-and-pharmacodynamic-considerations-for-patients-undergoing-therapeutic- hypothermia

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