Therapeutic Hypothermia

Indications

Cardiac Arrest (see Cardiac Arrest, [[Cardiac Arrest]])

  • Clinical Efficacy
    • TTM Trial: Therapeutic Hypothermia (33°C versus 36°C) After Cardiac Arrest (NEJM, 2013) [MEDLINE]: hypothermia to 33°C did not confer a benefit as compared with hypothermia to 36°C
    • Pre-Hospital Mild Hypothermia After Cardiac Arrest (JAMA, 2014) [MEDLINE]: pre-hospital cooling reduced core temperature by hospital arrival and reduced the time to reach a temperature of 34°C, but it did not improve survival or neurological outcome
    • Pre-Hospital Mild Hypothermia After Cardiac Arrest (J Am Heart Assoc, 2015) [MEDLINE]: pre-hospital hypothermia did not improve neurological outcome or 1‐year mortality rate
  • Recommendations (2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care) [MEDLINE]
    • Therapeutic Hypothermia is Recommended (Between 32-36 Degrees) for At Least 24 hrs for Comatose Adult Patients with Return of Spontaneous Circulation After Cardiac Arrest (Including In-Hospital Cardiac Arrest)
      • The temperature sensitivity of the brain after cardiac arrest may persist as long as the brain dysfunction (coma) is present: consequently, the upper limit time duration for temperature management is unknown
      • Similar recommendation was provided from the 2015 Recommendations from the International Liaison Committee on Resuscitation (ILCOR)
    • Pre-Hospital Hypothermia with Rapid Infusion of Cold Intravenous Fluids is Not Recommended: no evidence that this intervention has clinical benefit

XXX

  • xxx

Physiology

Physiologic Effects of Therapeutic Hypothermia

Cardiovascular

  • Decreaased Heart Rate
  • Decreased Infarct Size with Cardiac Arrest or Acute Myocardial Infarction
  • Increased Myocardial Salvage: with use of therapeutic hypothermia before revascularization in STEMI
  • Increased Systemic Vascular Resistance (SVR)

Neurologic

  • Decreased Cerebral Oxygen Demand
  • Decreased Formation of Reactive Oxygen Species in Brain
  • Direct Cellular Effects on Brain

Technique

Devices

  • Arctic Sun Device
  • Surface Cooling with Cooling Blankets/Ice Packs
  • Endovascular Cooling Catheters: more accurate and reliable at maintaining target temperature than other methods
  • Gaymar Medi-Therm II
  • Transnasal Evaporation: novel method which may be used during cardiac arrest

Sedation and Analgesia

  • Required

Mechanical Ventilation

  • Required

Rewarming

  • Rewarming Rate: 0.25–0.51 degrees C/hr until the patient reaches normothermia
    • Avoid Rapid Rapid Rewarming: since it increases the risk of hypotension from substantial vasodilation, hypoglycemia, hyperkalemia
  • Once Normothermia is Achieved, Avoid the Development of Fever: surface cooling method may be left in place to prevent hyperthermia

Adverse Effects

Cardiovascular Adverse Effects

Arrhythmias

  • xxx

Sinus Bradycardia (see Sinus Bradycardia, [[Sinus Bradycardia]])

  • Epidemiology: common
  • Treatment: only requires treatment if associated with hemodynamic instablity

Hypotension (see Hypotension, [[Hypotension]])

  • Physiology: although therapeutic hypothermia increases SVR
    • xxx
  • Treatment: standard therapies

Intravascular Volume Changes

  • xxx

Endocrinologic Adverse Effects

Hyperglycemia (see Hyperglycemia, [[Hyperglycemia]])

  • Physiology: due to decreased insulin secretion and sensitivity at colder temperatures

Hematologic Adverse Effects

  • Coagulopathy (see xxxx, [[xxxx]])
  • Immunologic Impairment

Infectious Adverse Effects

Increased Risk of Infection

  • Epidemiology: common
  • Physiology
    • Catheter-Related Infections
    • Immune Suppression
    • Mechanical Ventilation
    • Possible Aspiration During Prior Cardiac Arrest (Particularly with Emergent Intubation): in relavent cases

Neurologic Adverse Effects

Shivering

  • Epidemiology: common
  • Physiology: occurs when body temperature reaches 35-37 degrees C
  • Treatment: shivering requires treatment, as it increases metabolic activity and impairs the ability to cool the patient
    • Blankets/Hot Air Warmer: to keep the skin warm
    • Intravenous Magnesium (see Magnesium Sulfate, [[Magnesium Sulfate]]): may minimize shivering
    • Increase in Sedation/Analgesia
    • Neuromuscular Blockade: may be required -> highly effective

Renal Adverse Effects

Hypokalemia (see Hypokalemia, [[Hypokalemia]])

  • Epidemiology: common during hypothermia
  • Physiology: due to inward cellular flux of potassium and mild diuresis (which occurs as a result of hypothermia)
  • Treatment: treat with standard therapies
    • Potassium repletion should be stopped starting 4 hrs before rewarming due to the significant flux of potassium out of cells which occurs during rewarming

Hyperkalmeia (see xxxx, [[xxxx]])

  • Epidemiology: may occur during rewarming
  • Physiology: xxx

Other Adverse Effects

  • xx

References

  • Lack of effect of induction of hypothermia after acute brain injury. N Engl J Med 2001;344:556 [MEDLINE]
  • Therapeutic hypothermia after cardiac arrest. N Engl J Med 2002;346:612 [MEDLINE]
  • From evidence to clinical practice: Effective implementation of therapeutic hypothermia to improve patient outcome after cardiac arrest. Crit Care Med 2006;34:1865 [MEDLINE]
  • Induced hypothermia and fever control for prevention and treatment of neurological injuries. Lancet 2008;371:1955 [MEDLINE]
  • Early goal-directed hemodynamic optimization combined with therapeutic hypothermia in comatose survivors of out-of-hospital cardiac arrest. Resuscitation. 2009;80:418-424 [MEDLINE]
  • Targeted temperature management at 33°C versus 36°C after cardiac arrest. N Engl J Med. 2013 Dec 5;369(23):2197-206. doi: 10.1056/NEJMoa1310519. Epub 2013 Nov 17 [MEDLINE]
  • Effect of prehospital induction of mild hypothermia on survival and neurological status among adults with cardiac arrest: a randomized clinical trial. JAMA. 2014 Jan 1;311(1):45-52. doi: 10.1001/jama.2013.282173 [MEDLINE]
  • Effect of prehospital induction of mild hypothermia on 3-month neurological status and 1-year survival among adults with cardiac arrest: long-term follow-up of a randomized, clinical trial. J Am Heart Assoc. 2015 Mar 11;4(3):e001693. doi: 10.1161/JAHA.114.001693 [MEDLINE]
  • Cardiac arrest and therapeutic hypothermia. Trends Cardiovasc Med. 2015 Oct 22. pii: S1050-1738(15)00240-6. doi: 10.1016/j.tcm.2015.10.002 [MEDLINE]