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  1. 1. Hypothermia Noora Al-Sukaiti R2
  2. 2. Outline: <ul><li>Definition </li></ul><ul><li>Pathophysiology </li></ul><ul><li>Predisposing factors </li></ul><ul><li>Clinical features </li></ul><ul><li>Diagnostic strategies </li></ul><ul><li>Management </li></ul><ul><li>Disposition </li></ul>
  3. 3. What is hypothermia? <ul><li>Core temp <35 C </li></ul><ul><ul><ul><li>Mild 32-35 </li></ul></ul></ul><ul><ul><ul><li>Mod 32-27 </li></ul></ul></ul><ul><ul><ul><li>Severe <27 </li></ul></ul></ul>
  4. 4. <ul><li>Basal heat production (40-60kcal/m2 of BSA) </li></ul><ul><li>inc. with food, mus. activity, fever and acute cold exposure </li></ul><ul><li>Max production lasts for a few hrs (b/c of fatigue and glycogen depletion) </li></ul>
  5. 6. Mechanisms of normal heat loss: <ul><li>Radiation (65%) most important </li></ul><ul><ul><ul><li>by electromagnetic waves </li></ul></ul></ul><ul><li>Evaporation (25%): liquid to a gas </li></ul><ul><li>0.56 kcal/ml of evaporated H2O </li></ul><ul><li>Convection (10-15%) heat loss to air and vapor circulating arnd the body </li></ul><ul><li>wind temp and velocity </li></ul><ul><li>Conduction (2+ %): direct contact </li></ul><ul><li>important with immersion </li></ul>
  6. 7. <ul><li>37-32 C : vasoconstriction, shivering and non-shivering endocrine thermogenesis </li></ul><ul><li>32-24 C : prog. reduction in basal met rate (NO shivering) </li></ul><ul><li><24 C : autonomic and endocrine mech. inactive </li></ul>
  7. 8. Which of the following cardiac findings is expected in hypothermia: <ul><li>QT interval prolongation </li></ul><ul><li>Sinus bradycardia </li></ul><ul><li>Atrial fibrilation </li></ul><ul><li>J waves </li></ul><ul><li>All of the above </li></ul>
  8. 9. Identify Hypothermic J waves
  9. 10. J waves on ECG (false): <ul><li>Potentially diagnostic of hypothermia </li></ul><ul><li>size decreases with temperature depression </li></ul><ul><li>appear at <32 C at junction of QRS and ST segment </li></ul><ul><li>DDx local cardiac ischemia, sepsis or CNS lesions </li></ul><ul><li>Can occur in young normothermic pts </li></ul>
  10. 12. CVS and hypothermia (false): <ul><li>A Fib occurs at <32C and usually converts spontaneously during rewarming </li></ul><ul><li>Asystole and VF occur at <25 C </li></ul><ul><li>Myocardium is more sensitive to cold than conduction system </li></ul><ul><li>Core T afterdrop is a decline in core T after removal from cold environment </li></ul><ul><li>Bradycardia is refractory to atropine </li></ul>
  11. 13. Other changes: <ul><li>CNS: </li></ul><ul><li>Progressive dep. >>> silent EEG at 20 C </li></ul><ul><li>Loss of autoregulation <25 C </li></ul><ul><li>Renal: </li></ul><ul><ul><ul><li>Hypothermia: ↓ renal bld flow  secrete lg amounts of dilute urine (cold diuresis) </li></ul></ul></ul><ul><ul><ul><li>Periph vasocons  relative central hypervolemia  cold diuresis </li></ul></ul></ul><ul><ul><ul><li>EtOH doubles ↑ in urine volume </li></ul></ul></ul>
  12. 14. <ul><li>RS : </li></ul><ul><ul><ul><li>Initial ↑in RR then ↓ RR proportional to ↓ metabolism </li></ul></ul></ul><ul><ul><ul><li>CO2 retention & RS acidosis in sev. hypothermia. </li></ul></ul></ul><ul><ul><ul><li>Bronchorrhea, ↓ciliary motility and noncardiogenic pulm edema </li></ul></ul></ul>
  13. 15. Factors predisposing to hypothermia (mention 3 main) <ul><li>Dec heat production </li></ul><ul><ul><ul><li>Endocrine </li></ul></ul></ul><ul><ul><ul><li>Insufficient fuel </li></ul></ul></ul><ul><ul><ul><li>Neuromuscular </li></ul></ul></ul><ul><ul><ul><li>Ineffeciency </li></ul></ul></ul><ul><li>Inc heat loss </li></ul><ul><ul><ul><li>Environment </li></ul></ul></ul><ul><ul><ul><li>Vasodilation </li></ul></ul></ul><ul><ul><ul><li>erythrodermas </li></ul></ul></ul><ul><li>Impaired thermoregulation </li></ul><ul><ul><ul><li>Periph. </li></ul></ul></ul><ul><ul><ul><li>central </li></ul></ul></ul><ul><li>Others </li></ul><ul><ul><ul><li>Sepsis </li></ul></ul></ul><ul><ul><ul><li>Trauma </li></ul></ul></ul><ul><ul><ul><li>Carcinomas </li></ul></ul></ul><ul><ul><ul><li>Etc… </li></ul></ul></ul>
  14. 16. Why old people are more at risk for hypothermia? <ul><li>Dec ability to sense cold </li></ul><ul><li>Poor adaptive and behavioral responses </li></ul><ul><li>Dec glycogen stores for shivering </li></ul><ul><li>Dec muscle mass for shivering </li></ul><ul><li>Poor glucose use </li></ul><ul><li>Autonomic dysfunction- poor vasoconstrictive ability </li></ul><ul><li>Co morbid illness </li></ul><ul><ul><ul><li>Peripheral vascular disease </li></ul></ul></ul><ul><ul><ul><li>CNS dysfunction </li></ul></ul></ul><ul><ul><ul><li>Cardiac disease </li></ul></ul></ul>
  15. 17. Ethanol with hypothermia (false): <ul><li>Interacts with every neurotransmitter in brain </li></ul><ul><li>Metabolized faster in hypothermic patients </li></ul><ul><li>Possible direct damage to hypothalamus </li></ul><ul><li>Peripheral vasodilation </li></ul><ul><li>Impaired cognition and immobility </li></ul><ul><li>Hypoglycemia and/or malnutrition </li></ul>
  16. 18. Clinical Features <ul><li>Mild hypothermia : vague sxs (e.g. hunger, nausea, confusion, dizziness, chills, pruritis and SOB) </li></ul><ul><li>Paradoxical undressing </li></ul><ul><li>Progressive ↓ in LOC </li></ul><ul><li><22 : unreactive pupils (↓ perfusion) </li></ul><ul><li>Hyperreflexia till 32 C >>> hypo >>> absent at 26C </li></ul><ul><li>Q : … is last reflex to disappear and first to reappear? </li></ul><ul><li>Knee jerk </li></ul>
  17. 19. Name T: <ul><li>Maximum shivering </li></ul><ul><li>Extinguish shivering </li></ul><ul><li>A fib </li></ul><ul><li>V fib </li></ul><ul><li>Dilated pupils </li></ul><ul><li>No reflex/response </li></ul><ul><li>Ataxia </li></ul><ul><li>35 C </li></ul><ul><li>31 C </li></ul><ul><li>30 C </li></ul><ul><li>26 C </li></ul><ul><li>29 C </li></ul><ul><li>26 C </li></ul><ul><li>33 C </li></ul>
  18. 20. 56 yrs old man is brought in by the police after he was found under a bridge in a winter night. His core T is 30. which of the following findings is likely to be seen : <ul><li>Anemia </li></ul><ul><li>Pinpoint pupils </li></ul><ul><li>Shivering </li></ul><ul><li>Tachypnea </li></ul><ul><li>Urinary diuresis </li></ul>
  19. 21. Which of the following physiologic changes is expected in hypothermic pt: <ul><li>Hemoconcentration </li></ul><ul><li>Hypoglycemia </li></ul><ul><li>Metabolic alkalosis </li></ul><ul><li>Oliguria </li></ul><ul><li>Seizures </li></ul>
  20. 22. Lab facts; <ul><li>Normally; PCO2 inc 10 mmHg, pH dec 0.08 units </li></ul><ul><li>pH reduction DOUBLES at 28 C </li></ul><ul><li>Hematocrit inc 2% for every 1C fall </li></ul><ul><li>Persistent hyperglycemia with rewarming,, DKA or hrgic pancreatitis </li></ul><ul><li>Rewarming is the only effective treatment for coagulopathy </li></ul>
  21. 23. Hypothermia management (false) <ul><li>Goals of pre-hospital care are to rescue, examine, insulate and rapidly transport </li></ul><ul><li>Rectal T is the most practical for core T evaluation and should be inserted to 15 cm </li></ul><ul><li>ET intubation is necessary unless pt is alert with intact protective reflexes </li></ul><ul><li>NGT is indicated in mod-sev hypothermia after intubation </li></ul><ul><li>Cardiac monitoring is better by central venous pressure catheter </li></ul>
  22. 24. Volume resuscitation in hypothermia (false): <ul><li>Rapid volume expansion is critical </li></ul><ul><li>Adults should receive 250-500ml fluid challenge of heated 5% dex in NS </li></ul><ul><li>IV fluids should be heated to 40-42 C </li></ul><ul><li>Microwaving is an option for heating IVF </li></ul><ul><li>IVF should not be shaken before administration </li></ul>
  23. 25. Withhold CPR in hypothermia (false): <ul><li>Pt with tissue decomposition, rigor mortis, dependent lividity and fixed dilated pupils </li></ul><ul><li>Obvious lethal injuries </li></ul><ul><li>Impossible chest wall depression </li></ul><ul><li>Signs of life are present </li></ul><ul><li>Rescuers are in danger </li></ul>
  24. 26. Pharmacology and hypothermia (false): <ul><li>Intramuscular and oral medications should be avoided </li></ul><ul><li>Epineph., dopamine and other vasocnstricors should be avoided </li></ul><ul><li>Most hypothermia-induced dysrhythmias convert spontaneously during rewarming </li></ul><ul><li>Defibrillation attempts are usually unsuccessful until the core T is above 28-30 C </li></ul><ul><li>At any T, 3 defibrillation attempts should be initiated </li></ul>
  25. 27. Rewarming <ul><li>Passive external rewarming </li></ul><ul><ul><ul><li>patient rewarms on their own, using endogenous heat production mechanisms </li></ul></ul></ul><ul><li>Active rewarming: </li></ul><ul><ul><ul><li>Active external rewarming: application of exogenous heat to the body externally </li></ul></ul></ul><ul><ul><ul><li>Active core rewarming </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Airway rewarming </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Peritoneal dialysis </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Heated irrigation </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Diathermy </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Extracorporeal blood rewarming </li></ul></ul></ul></ul></ul>
  26. 28. Active ext. rewarming (false) <ul><li>Indications are controversial due to the risks of shock and afterdrop </li></ul><ul><li>Optimal candidates are young previously healthy people in whom there are minimal circulatory changes </li></ul><ul><li>Heat packs, water bottles and immersion baths of 40 C are options </li></ul><ul><li>Forced-air warming system is currently most practical in ED </li></ul><ul><li>Heat sources should be applied to thorax and extremities </li></ul>
  27. 30. Active core rewarming (true) <ul><li>Airway rewarming is not indicated in all mod or severe hypothermia </li></ul><ul><li>Peritoneal dialysis delivers heated dialysate at <40 C to the peritoneal cavity </li></ul><ul><li>Peritoneal dialysis can exacerbate preexisting hyperkalemia </li></ul><ul><li>Mediastinal irrigation and direct myocardial lavage should only be considered in pts without spontaneous perfusion </li></ul><ul><li>Extracorporial blood rewarming should not be attempted in hypothermic cardiac arrest </li></ul>
  28. 31. Active internal rewarming <ul><li>Airway rewarming </li></ul><ul><ul><li>Indicated in all moderate to sever hypotherm,, non invasive </li></ul></ul><ul><ul><li>Gas should be 40-42 C and humidified </li></ul></ul><ul><ul><li>Reduces bronchorrhea </li></ul></ul><ul><ul><li>Rewarming rate of 1 to 2.5 C/hr </li></ul></ul>
  29. 32. Air inhalation rewarming
  30. 33. <ul><li>Extracorporeal rewarming </li></ul><ul><ul><li>Only in extreme situations </li></ul></ul><ul><ul><li>Indications: Arrest, No response to other methods, frozen extremities, sever electrolyte abnormalities and rhabdomyolysis </li></ul></ul><ul><ul><li>Rewarming rate of 1-2 C every five minutes! </li></ul></ul><ul><li>Diathermy </li></ul><ul><ul><li>Transmission of heat by conversion of energy </li></ul></ul><ul><ul><li>Use low frequency microwave radiation </li></ul></ul><ul><ul><li>Contraindication- frostbite, burns, metallic implants, edema </li></ul></ul>
  31. 34. Indications for Active Rewarming (list 4) <ul><li>Cardiovascular instability </li></ul><ul><li>Moderate or severe hypothermia (<32.2° C) </li></ul><ul><li>Inadequate rate or failure to rewarm </li></ul><ul><li>Endocrinologic insufficiency, ↓ glycogen stores </li></ul><ul><li>Traumatic or toxicologic periph vasodilatat’n </li></ul><ul><li>Sec hypothermia impairing thermoregulation </li></ul>
  32. 36. Disposition: <ul><li>May D/C pts with mild accidental primary hypothermia (>32 C) </li></ul><ul><li>admit anyone else </li></ul><ul><li>Always r/o underlying medical diseases as causes of hypothermia </li></ul>
  33. 37. Outcomes <ul><li>Predictors of outcome </li></ul><ul><ul><ul><li>prehospital arrest </li></ul></ul></ul><ul><ul><ul><li>low/absent BP </li></ul></ul></ul><ul><ul><ul><li>elevated BUN </li></ul></ul></ul><ul><ul><ul><li>need for intubation/NGT in ED. </li></ul></ul></ul><ul><li>Bad prognostic indicator </li></ul><ul><ul><ul><li>intravascular thrombosis (fibrinogen <50) </li></ul></ul></ul><ul><ul><ul><li>cell lysis (K>10) </li></ul></ul></ul><ul><ul><ul><li>ammonia (>250) </li></ul></ul></ul><ul><ul><ul><li>(not prospectively validated!) </li></ul></ul></ul>
  34. 38. Thank you!