1. Hypothermia By Paul Rega MD, FACEP

2. Key Celsius/Fahrenheit Conversions 19°C = 66°F 19°C = 66°F 20°C = 68°F 20°C = 68°F 25°C = 77°F 25°C = 77°F 28°C = 82°F 28°C = 82°F 30°C = 86°F 30°C = 86°F 32°C = 90°F 32°C = 90°F 33°C = 91°F 33°C = 91°F 34°C = 93°F 34°C = 93°F 35°C = 95°F 35°C = 95°F 43°C = 109°F 43°C = 109°F

3. Diagnosis of Hypothermia Requires Requires 1) High index of suspicion1) High index of suspicion 2) Low-reading thermometer (down to 25°C)2) Low-reading thermometer (down to 25°C) At least 10cm into rectum At least 10cm into rectum Check for fecal cache Check for fecal cache Impaction will give a falsely elevated readingImpaction will give a falsely elevated reading

4. Definition Core temperature <35º C (95º F) Core temperature <35º C (95º F) Mild: 32.1º C-35º C Mild: 32.1º C-35º C Moderate: 28º C-32º C Moderate: 28º C-32º C Severe: <28º C Severe: <28º C

5. Classification Accidental Accidental Primary: Patients with normal intact thermoregulatory systemPrimary: Patients with normal intact thermoregulatory system Usually exposed to extreme cold Usually exposed to extreme cold Secondary: Patients with impaired thermoregulatory systemSecondary: Patients with impaired thermoregulatory system Intentional Intentional

6. Frequency 700 die annually from accidental primary hypothermia 700 die annually from accidental primary hypothermia Majority Majority Urban setting due to environmental exposureUrban setting due to environmental exposure Aggravated by homelessness, illicit drug use, alcoholism, mental illnessAggravated by homelessness, illicit drug use, alcoholism, mental illness Minority Minority Outdoor setting: hunters, swimmers, hikers, etc.Outdoor setting: hunters, swimmers, hikers, etc.

7. Mortality Mild (32-35° C): No significant morbidity/mortality Mild (32-35° C): No significant morbidity/mortality Moderate (29° C-32° C): 21% mortality Moderate (29° C-32° C): 21% mortality Severe (<28° C): Even higher mortality rate Severe (<28° C): Even higher mortality rate

8. Hypothermia and Trauma 38,520 trauma patients (2000-2002) 38,520 trauma patients (2000-2002) 16 yo and greater16 yo and greater 1,921 (5%) hypothermic on admission 1,921 (5%) hypothermic on admission Hypothermia independently tripled chances of death Hypothermia independently tripled chances of death Isolated head injury: hypothermia associated with >twice risk of death Isolated head injury: hypothermia associated with >twice risk of death CCM 33:1296-1301 CCM 33:1296-1301

9. At risk populations Very young/elderly Very young/elderly May present with symptoms not clinically obvious (e.g. altered mental status)May present with symptoms not clinically obvious (e.g. altered mental status) Those with decreased muscle mass Those with decreased muscle mass Trauma, burns, and other stressors worsen body’s response to cold. Trauma, burns, and other stressors worsen body’s response to cold.

10. Normal Physiology Body regulates core temp through mechanisms of heat loss and heat gain Body regulates core temp through mechanisms of heat loss and heat gain Hypothalamus controls thermoregulation Hypothalamus controls thermoregulation Rest: 40-60kcal heat/m² produced Rest: 40-60kcal heat/m² produced Shivering: Heat production increases 2-5 times Shivering: Heat production increases 2-5 times Hindered by endocrine derangements Hindered by endocrine derangements

11. Heat Loss Conduction (Transfer of heat from body to environment) Conduction (Transfer of heat from body to environment) Water has 25-35 times heat conduction ability of airWater has 25-35 times heat conduction ability of air Convection Convection Heat transfer from movement of liquid or gases over a victimHeat transfer from movement of liquid or gases over a victim e.g. Wind chille.g. Wind chill Conduction + convection: 15% heat loss Conduction + convection: 15% heat loss Cold water immersion increases conductive heat loss up to 25 timesCold water immersion increases conductive heat loss up to 25 times Radiation (Heat transfer by electromagnetic waves through space) Radiation (Heat transfer by electromagnetic waves through space) 55-65% of heat loss55-65% of heat loss Evaporation (sweat, exhaled breath) Evaporation (sweat, exhaled breath) Heat loss from conversion of water to a gasHeat loss from conversion of water to a gas Respiration + evaporation: Remainder of heat lossRespiration + evaporation: Remainder of heat loss

12. Heat Gain Peripheral vasoconstriction Peripheral vasoconstriction Increased metabolic rate Increased metabolic rate Shivering Shivering Behavior Behavior Warm clothesWarm clothes Removal from cold environmentRemoval from cold environment

13. Hypothermic Predisposing Factors Impede circulation Impede circulation Dehydration, DM, Peripheral vascular disease, tight clothes, tobaccoDehydration, DM, Peripheral vascular disease, tight clothes, tobacco Increase heat loss Increase heat loss Burns, skin diseases, environment, alcohol/drugs, infancy,Burns, skin diseases, environment, alcohol/drugs, infancy, Decrease heat production Decrease heat production Endocrine failure, hypoadrenalism, hypoglycemia, hypopituitarism, hypothyroidism, infancy, old age, malnutritionEndocrine failure, hypoadrenalism, hypoglycemia, hypopituitarism, hypothyroidism, infancy, old age, malnutrition Impair thermoregulation Impair thermoregulation DM, Parkinson’s, spinal cord injuries, strokeDM, Parkinson’s, spinal cord injuries, stroke

15. Answer

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19. CNS in Hypothermia All organ systems affected All organ systems affected <33°C: Abnormal brain activity <33°C: Abnormal brain activity 19°-20°C: EEG consistent with brain death 19°-20°C: EEG consistent with brain death

20. Cardiovascular Response in Hypothermia Osborne J waves Osborne J waves T-wave inversion T-wave inversion Prolonged PR, QRS, and QT intervals Prolonged PR, QRS, and QT intervals Bradycardia, slow a fib, v fib, asystole Bradycardia, slow a fib, v fib, asystole Bradycardia: Decreased depolarization of pacemaker cellsBradycardia: Decreased depolarization of pacemaker cells Refractory to atropine since not vagally mediated Refractory to atropine since not vagally mediated Atrial/ventricular arrhythmiasAtrial/ventricular arrhythmias 25°C: Asystole/ventricular fibrillation25°C: Asystole/ventricular fibrillation Increased risk of thrombosis and embolism Increased risk of thrombosis and embolism Due to decreased intravascular volume and increased blood viscosityDue to decreased intravascular volume and increased blood viscosity

21. Osborne or J wave was first described in 1938. It is best seen in leads aVL, aVF, and the lateral chest leads. Its presence is suggestive of, but no pathognomonic for, hypothermia. May appear at temperatures below 32°C.

22. Bradycardia appears in 50% of patients with temperatures below 28°C.

23. The presence of acute atrial fibrillation often precedes ventricular fibrillation.

24. These rhythms may be refractory to electricity and drugs in severe hypothermia

25. Pulmonary Response in Hypothermia Rate initially increases then decreases below 32ºC. Rate initially increases then decreases below 32ºC. Tidal volume decreases Tidal volume decreases Cough/gag reflexes fail Cough/gag reflexes fail Risk of aspiration grows Risk of aspiration grows Decreased O2 delivery to tissues Decreased O2 delivery to tissues Higher O2 and CO2 levels and a lower pH than a patient’s actual values because analyzers warm blood to 37 °C Higher O2 and CO2 levels and a lower pH than a patient’s actual values because analyzers warm blood to 37 °C Interpret uncorrected ABGs (i.e. at the patient’s core temp) Interpret uncorrected ABGs (i.e. at the patient’s core temp) Aspiration pneumonia and pulmonary edema: common Aspiration pneumonia and pulmonary edema: common

26. Renal Response Loss of ability to concentrate urine Loss of ability to concentrate urine Cold diuresis initially result of increased blood flow to kidneys with peripheral vasoconstriction Cold diuresis initially result of increased blood flow to kidneys with peripheral vasoconstriction Volume depletion can result in decreased renal blood flow. Volume depletion can result in decreased renal blood flow. Decreased renal blood flow (depressed by 50% at 27°-30°C) and increased tissue breakdown products Decreased renal blood flow (depressed by 50% at 27°-30°C) and increased tissue breakdown products Acute tubular necrosisAcute tubular necrosis Renal failureRenal failure

28. Mild Hypothermia (32°-35° C) Lethargy Lethargy Increased metabolic activity Increased metabolic activity Superficial vessels constrict Superficial vessels constrict Confusion Confusion Altered judgment, amnesia, dysarthria: <34 °CAltered judgment, amnesia, dysarthria: <34 °C Shivering Shivering Greatest between 34 °-35 °CGreatest between 34 °-35 °C Loss of fine motor coordination Loss of fine motor coordination Ataxia & apathy at 33 °C Ataxia & apathy at 33 °C Respiratory rate may be higher Respiratory rate may be higher Pulse/blood pressure intact Pulse/blood pressure intact May be increase in CO, Heart rate, and B/PMay be increase in CO, Heart rate, and B/P

29. Moderate Hypothermia (28°-32° C) Delirium Delirium Stupor Stupor Shivering dissipates Shivering dissipates Metabolic activity slows Metabolic activity slows Drop in O2 and CO2 production Drop in O2 and CO2 production Slowed reflexes Slowed reflexes Drop in CO, heart rate, B/P Drop in CO, heart rate, B/P Arrhythmias may begin at 30 °C Arrhythmias may begin at 30 °C Atrial fibrillationAtrial fibrillation Ventricular hyperactivityVentricular hyperactivity Pupils dilate and minimally react to light (may mimic death) Pupils dilate and minimally react to light (may mimic death)

30. Severe Hypothermia (<28° C) Very cold skin Very cold skin Unresponsive Unresponsive Coma Coma Difficulty breathing to apnea Difficulty breathing to apnea Shock Shock Arrhythmias Arrhythmias Markedly susceptible to v. fib.Markedly susceptible to v. fib. Rigidity Rigidity Pupils fixed Pupils fixed

32. General Care Remove wet clothes Remove wet clothes Insulate victim from environment Insulate victim from environment Don’t delay urgent procedures (e.g. intubation, IVs) Don’t delay urgent procedures (e.g. intubation, IVs) Remember: Because of rigidity of jaw and chest wall, it may be next to impossible to intubate orotracheally as well as to ventilate a patient. Remember: Because of rigidity of jaw and chest wall, it may be next to impossible to intubate orotracheally as well as to ventilate a patient.

33. Caution Perform procedures gently Perform procedures gently Monitor cardiac rhythm Monitor cardiac rhythm May go into V. fib.May go into V. fib.

34. Rewarming Techniques Passive external Passive external Active external Active external Active internal (core) Active internal (core)

35. Passive External Rewarming Usually adequate for mild hypothermia Usually adequate for mild hypothermia Place in warm environment Place in warm environment Remove wet clothing Remove wet clothing Cover with blankets Cover with blankets Rewarming rate: 0.5°C-1°C/hour Rewarming rate: 0.5°C-1°C/hour

36. Active External Rewarming Added for moderate-severe hypothermia Added for moderate-severe hypothermia Hot water bottles to groin/axillae (43°C) Hot water bottles to groin/axillae (43°C) Radiant heaters Radiant heaters Heating pads, circulating hot water mattresses Heating pads, circulating hot water mattresses Forced air rewarming Forced air rewarming Rewarming rate: 2.4°C/hourRewarming rate: 2.4°C/hour Warm IV solutions Warm IV solutions Rate: 1°C-2.5°C/hour Rate: 1°C-2.5°C/hour

37. Complications of External Rewarming Core Temp afterdrop: Cold blood returning from periphery further cools body core Core Temp afterdrop: Cold blood returning from periphery further cools body core Rewarming acidosis: Cold blood returning from periphery brings lactic acid with it. Rewarming acidosis: Cold blood returning from periphery brings lactic acid with it. Rewarming shock: Relative hypovolemia occurs secondary to peripheral vasodilatation Rewarming shock: Relative hypovolemia occurs secondary to peripheral vasodilatation Note: Complications minimized using combo of external rewarming with active core rewarming. Note: Complications minimized using combo of external rewarming with active core rewarming.

38. Active Core Rewarming Core temp <30°C Core temp <30°C Best especially if core temp is <30ºC or cardiac instability is present Best especially if core temp is <30ºC or cardiac instability is present Techniques Techniques Warmed (42°C-45°C) humidified O2Warmed (42°C-45°C) humidified O2 Warmed (42°C-44°C) IV fluids (D5NS preferred): 150-200cc/hrWarmed (42°C-44°C) IV fluids (D5NS preferred): 150-200cc/hr Gastric, colonic, bladder, peritoneal lavage (40°C-45°C) with warm saline potassium-free solutionsGastric, colonic, bladder, peritoneal lavage (40°C-45°C) with warm saline potassium-free solutions Rewarming rate: 1°C-3°C/hour Rewarming rate: 1°C-3°C/hour

39. Active Core Rewarming Closed thoracic cavity lavage Closed thoracic cavity lavage Chest tube anteriorly, chest tube posteriorlyChest tube anteriorly, chest tube posteriorly 14 cases (8-72 yrs of age): Thoracic cavity lavage14 cases (8-72 yrs of age): Thoracic cavity lavage Mean core temp: 24.5°C Mean core temp: 24.5°C most without B/P or pulse most without B/P or pulse Predominant rhythm: V. fib. Predominant rhythm: V. fib. 7: Thoracotomy; 7: thoracostomy 7: Thoracotomy; 7: thoracostomy Median rewarming rate: 2.95°C/hour Median rewarming rate: 2.95°C/hour Median time to sinus rhythm: 120 min. Median time to sinus rhythm: 120 min. Median length of hospital stay: 2 weeks Median length of hospital stay: 2 weeks 4 died 4 died Survivors: 8 neurologically intact; 2 with residual impairments Survivors: 8 neurologically intact; 2 with residual impairments

40. Active Core Rewarming (Extracorporeal) Hemodialysis, AV rewarming, VV rewarming Hemodialysis, AV rewarming, VV rewarming Cardiopulmonary bypass (CPB) Cardiopulmonary bypass (CPB) Provides central rewarming and circulatory supportProvides central rewarming and circulatory support 32 patients (mean age: 25.2 years)32 patients (mean age: 25.2 years) Mean time from discovery to CPB: 141 min.Mean time from discovery to CPB: 141 min. 15 long-term survivors15 long-term survivors All in cardiopulmonary arrest at hospital All in cardiopulmonary arrest at hospital All intubated and receiving CPR prior to hospital All intubated and receiving CPR prior to hospital Mean core temp rose from21.8°C to 35.6°C within 97.9 min after rewarming (other CPB reports: 8°C-10°C/hour) Mean core temp rose from21.8°C to 35.6°C within 97.9 min after rewarming (other CPB reports: 8°C-10°C/hour) Follow-up: no or minimal cerebral impairment Follow-up: no or minimal cerebral impairment Keys to success:Keys to success: Hypothermia: deep Hypothermia: deep No prior hypoxic brain damage prior to hypothermia No prior hypoxic brain damage prior to hypothermia Young Young Great medical infrastructure in Switzerland Great medical infrastructure in Switzerland Hypothermia maintained prior to CPB Hypothermia maintained prior to CPB

41. Key Points Method of rewarming dependent on core temp and patient stability Method of rewarming dependent on core temp and patient stability Active rewarming recommended with life-threatening dysrhythmias Active rewarming recommended with life-threatening dysrhythmias All hypothermic patients must be examined for any trauma or underlying medical condition All hypothermic patients must be examined for any trauma or underlying medical condition

42. Pre-hospital Care Avoid needless sudden movements Avoid needless sudden movements Especially with cold-water immersionEspecially with cold-water immersion Supine to avoid postural hypotension Supine to avoid postural hypotension O2 O2 Monitors Monitors CPR and intubation should not be withheld if needed CPR and intubation should not be withheld if needed Trauma immobilization as needed Trauma immobilization as needed Intense vasoconstriction at <30 °C may make IV meds ineffective Intense vasoconstriction at <30 °C may make IV meds ineffective Lidocaine/atropine: ineffective Lidocaine/atropine: ineffective Prophylactic (<30 °C) and therapeutic bretylium Prophylactic (<30 °C) and therapeutic bretylium Treat life-threatening arrhythmias only; the remainder will self-correct with re-warmingTreat life-threatening arrhythmias only; the remainder will self-correct with re-warming Attempt defibrillation up to 3 times and no re-attempts until core temp reaches 30ºCAttempt defibrillation up to 3 times and no re-attempts until core temp reaches 30ºC Magnesium sulfate: Helpful in spontaneous resolution of v fibMagnesium sulfate: Helpful in spontaneous resolution of v fib Reduce further heat loss Reduce further heat loss Begin re-warming Begin re-warming Heat packs in axillae, groin, bellyHeat packs in axillae, groin, belly Intubate as needed; pre-oxygenate first Intubate as needed; pre-oxygenate first Resuscitate cold and dead to warm and dead (at least by 30- 33ºC) Resuscitate cold and dead to warm and dead (at least by 30- 33ºC)

43. ER Care Baseline studies Baseline studies CBC, lytes, BUN. Cr, BS, ABGs, PT/PTTCBC, lytes, BUN. Cr, BS, ABGs, PT/PTT Tox screen where appropriateTox screen where appropriate EKGEKG CXRCXR

44. Labs in Hypothermia Coagulation mechanism can fail Coagulation mechanism can fail Failure of enzymatic reactions of the clotting cascadeFailure of enzymatic reactions of the clotting cascade Coag studies typically performed at 37 °C and so results may be deceptively normal Coag studies typically performed at 37 °C and so results may be deceptively normal DIC may develop DIC may develop Hyperglycemia in acute hypothermia Hyperglycemia in acute hypothermia Hypoglycemia in chronic or secondary hypothermia Hypoglycemia in chronic or secondary hypothermia K+: Levels of 10mmol/L associated with low likelihood of recovery K+: Levels of 10mmol/L associated with low likelihood of recovery Classic EKG changes of hyperkalemia may be absent or diminished Classic EKG changes of hyperkalemia may be absent or diminished Hct may be deceptively high Hct may be deceptively high Hypothermic patients are volume contracted because of cold diuresisHypothermic patients are volume contracted because of cold diuresis Increase 2% for each 1 °C drop in core tempIncrease 2% for each 1 °C drop in core temp

45. Differential Diagnosis Alcohol/other intoxicants Alcohol/other intoxicants Endocrine problems Endocrine problems Hyper/hypoglycemia Hyper/hypoglycemia Hypoxemia Hypoxemia Narcotics Narcotics Uremia Uremia Trauma Trauma Infection Infection Psychiatric Psychiatric CNS: SAH, space-occupying lesions CNS: SAH, space-occupying lesions

46. Positive Benefit of Hypothermia May exert a protective effect on brain and organs in cardiac arrest. May exert a protective effect on brain and organs in cardiac arrest.

47. Hypothermia with Perfusing Rhythm Mild (> 34°C or 93.2°F): Passive rewarming Mild (> 34°C or 93.2°F): Passive rewarming Warmed blanketsWarmed blankets Warm environmentWarm environment

48. Hypothermia with Perfusing Rhythm Moderate (30° C-34° C or 86° F – Moderate (30° C-34° C or 86° F – 93.2° F): Active external rewarming Heating blanketsHeating blankets Forced hot airForced hot air Warmed infusionsWarmed infusions Warmed water packsWarmed water packs Carefully monitor for hemodynamic changes Carefully monitor for hemodynamic changes

49. Hypothermia with Perfusing Rhythm Severe (<30°C or 86 °F): Active internal rewarming Severe (<30°C or 86 °F): Active internal rewarming Peritoneal lavagePeritoneal lavage Esophageal rewarming tubesEsophageal rewarming tubes CP bypassCP bypass Extracorporeal circulationExtracorporeal circulation

50. Cardiac Arrest at 30 °-34 °C (Moderate Hypothermia) Overview CPR CPR Defib once Defib once IV IV Intubate Intubate IV medications IV medications Active Internal Rewarming Active Internal Rewarming

51. Cardiac Arrest at < 30 ° (Severe Hypothermia) Overview CPR CPR Defib once Defib once IV IV Intubate Intubate IV medications when at core temp >34 °C IV medications when at core temp >34 °C Active Internal Rewarming Active Internal Rewarming

52. BLS Modifications Check breathing and pulse for 30-45 sec. to confirm arrest state. Check breathing and pulse for 30-45 sec. to confirm arrest state. If doubt, commence CPR anywayIf doubt, commence CPR anyway Warmed humidified O2 if possible (42°-46° C) Warmed humidified O2 if possible (42°-46° C) 1 defib attempt and defer further attempts until patient warmed to 30°- 32° C 1 defib attempt and defer further attempts until patient warmed to 30°- 32° C

53. ALS Modifications Intubation Intubation Delivers warmed O2 betterDelivers warmed O2 better Prevents aspirationPrevents aspiration Focus on active core rewarming: warmed humidified O2 (42-46 °C), warmed IV fluids (43 °C, warm peritoneal lavage fluids, pleural lavage extracorporeal blood warming) Focus on active core rewarming: warmed humidified O2 (42-46 °C), warmed IV fluids (43 °C, warm peritoneal lavage fluids, pleural lavage extracorporeal blood warming) Hypothermic heart unresponsive to drugs, pacemakers, and defib Hypothermic heart unresponsive to drugs, pacemakers, and defib Drug metabolism reduced Drug metabolism reduced Cardioactive drugs can accumulate to toxic levels in peripheral circulation Cardioactive drugs can accumulate to toxic levels in peripheral circulation IV drugs often withheld at temps <30 ° C IV drugs often withheld at temps <30 ° C IV meds given at >30 °C but at increased intervals IV meds given at >30 °C but at increased intervals May not need to pace bradycardic rhythm since it may be physiologic due to hypothermia May not need to pace bradycardic rhythm since it may be physiologic due to hypothermia If after rewarming and return of pulse, the B/P is low push fluids to compensate for vasodilation If after rewarming and return of pulse, the B/P is low push fluids to compensate for vasodilation

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55. References Plaisier BR. Thoracic Lavage in Accidental Hypothermia with Cardiac Arrest – Report of a Case and Review of the Literature. Resuscitation 2005; 66:99-104. Plaisier BR. Thoracic Lavage in Accidental Hypothermia with Cardiac Arrest – Report of a Case and Review of the Literature. Resuscitation 2005; 66:99-104. Walpoth BH, Walpoth-Aslan BN, et al. Outcome of Survivors of Accidental Hypothermia with Circulatory Arrest Treated with Extracorporeal Blood Warming. NEJM 1997; 337:1500-1505. Walpoth BH, Walpoth-Aslan BN, et al. Outcome of Survivors of Accidental Hypothermia with Circulatory Arrest Treated with Extracorporeal Blood Warming. NEJM 1997; 337:1500-1505. Rice R. Hypothermia – Potentially Deadly All Year Around. JAAPA 2005; 18:47-52. Rice R. Hypothermia – Potentially Deadly All Year Around. JAAPA 2005; 18:47-52. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, Part 2: Hypothermia. Circulation 2005; 112(suppl IV):IV-136-139. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, Part 2: Hypothermia. Circulation 2005; 112(suppl IV):IV-136-139.