Hypothermia

1. Hypothermia By Paul Rega MD, FACEP

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

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

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

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

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

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

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

9. At risk populations • Very young/elderly • May present with symptoms not clinically obvious (e.g. altered mental status) • Those with decreased muscle mass • 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 • Hypothalamus controls thermoregulation • Rest: 40-60kcal heat/m² produced • Shivering: Heat production increases 2-5 times • Hindered by endocrine derangements

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

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

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

14. What is the lowest recorded temperature for a survivor of accidental hypothermia?

15. Answer 15.2°C (59.2°F) 23-day-old infant

16. The lowest temperature recorded in an adult survivor?

17. Answer 16°C (60.8°F)

18. System Response to Hypothermia

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

20. Cardiovascular Response in Hypothermia • Osborne J waves • T-wave inversion • Prolonged PR, QRS, and QT intervals • Bradycardia, slow a fib, v fib, asystole • Bradycardia: Decreased depolarization of pacemaker cells • Refractory to atropine since not vagally mediated • Atrial/ventricular arrhythmias • 25°C: Asystole/ventricular fibrillation • Increased risk of thrombosis and embolism • Due 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. • Tidal volume decreases • Cough/gag reflexes fail • Risk of aspiration grows • 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 • Interpret uncorrected ABGs (i.e. at the patient’s core temp) • Aspiration pneumonia and pulmonary edema: common

26. Renal Response • Loss of ability to concentrate urine • Cold diuresis initially result of increased blood flow to kidneys with peripheral vasoconstriction • 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 • Acute tubular necrosis • Renal failure

27. Clinical Manifestations According to Temperature Change

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

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

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

31. Patient Management

32. General Care • Remove wet clothes • Insulate victim from environment • 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.

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

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

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

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

37. Complications of External Rewarming • 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 shock: Relative hypovolemia occurs secondary to peripheral vasodilatation • Note: Complications minimized using combo of external rewarming with active core rewarming.

38. Active Core Rewarming • Core temp <30°C • Best especially if core temp is <30ºC or cardiac instability is present • Techniques • Warmed (42°C-45°C) humidified O2 • Warmed (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 solutions • Rewarming rate: 1°C-3°C/hour

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

40. Active Core Rewarming (Extracorporeal) • Hemodialysis, AV rewarming, VV rewarming • Cardiopulmonary bypass (CPB) • Provides central rewarming and circulatory support • 32 patients (mean age: 25.2 years) • Mean time from discovery to CPB: 141 min. • 15 long-term survivors • All in cardiopulmonary arrest at 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) • Follow-up: no or minimal cerebral impairment • Keys to success: • Hypothermia: deep • No prior hypoxic brain damage prior to hypothermia • Young • Great medical infrastructure in Switzerland • Hypothermia maintained prior to CPB

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

42. Pre-hospital Care • Avoid needless sudden movements • Especially with cold-water immersion • Supine to avoid postural hypotension • O2 • Monitors • CPR and intubation should not be withheld if needed • Trauma immobilization as needed • Intense vasoconstriction at <30 °C may make IV meds ineffective • Lidocaine/atropine: ineffective • Prophylactic (<30 °C) and therapeutic bretylium • Treat 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 30ºC • Magnesium sulfate: Helpful in spontaneous resolution of v fib • Reduce further heat loss • Begin re-warming • Heat packs in axillae, groin, belly • Intubate as needed; pre-oxygenate first • Resuscitate cold and dead to warm and dead (at least by 30-33ºC)

43. ER Care • Baseline studies • CBC, lytes, BUN. Cr, BS, ABGs, PT/PTT • Tox screen where appropriate • EKG • CXR

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

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

46. Positive Benefit of Hypothermia • 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 • Warmed blankets • Warm environment

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

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

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