Therapeutic hypothermia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Priyamvada Singh, M.B.B.S. [3]

Overview

Brain temperature during the first 24 hours after resuscitation from cardiac arrest has a significant effect on survival and neurological recovery. Fever (Tmax) during the first 48 hours is associated with a decreased chance of good neurological recovery (OR 2.26 [1.24, 4.12] for each 1°C over 37°C)[1]. Cooling to 32-34°C for 24 hours decreases chance of death (OR 0.74 [0.58, 0.95]) and increases chance of good neurological recovery (OR 1.40 [1.08,1.81])[2]. Cooling to 32-34°C for 12 hours increases chance of good neurological recovery (OR 2.65 [1.02, 6.88])[3].

Mechanism of Effects

Eligibility Criteria for Post-Cardiac Arrest Therapeutic Hypothermia

  • Meets eligibility criteria for Post-Cardiac Arrest Care Pathway
  • Comatose at enrollment with a Glasgow Coma Motor Score <6 pre-sedation (i.e., patient doesn’t follow commands)
  • No other obvious reasons for coma
  • No uncontrolled bleeding
  • Hemodynamically stable with no evidence of:
  • Uncontrollable dysrhythmias
  • Severe cardiogenic shock
  • Refractory hypotension (MAP <60 mm Hg) despite preload optimization and use of vasoactive medications
  • No existing, multi-organ dysfunction syndrome, severe sepsis, or comorbidities with minimal chance of meaningful survival independent of neurological status

Other indications

Therapeutic hypothermia is an active area of research. Many trials are underway to see its possible benefits in conditions other than post-cardiac arrests like:

  • Traumatic brain injury - Benefits are seen in patients with elevated intra cranial pressure [6], [7] and those treated with long-term hypothermia. However, studies on pediatrics population found an increase in rates of pulmonary hypertension and seizures in pediatric patients treated with therapeutic hypothermia
  • Traumatic spinal cord injury

Therapeutic goals

Therapeutic hypothermia is practiced in many tertiary hospitals. The treatment goals followed in most of them are:

  • Goal temperature- 32-34 degree celsius
  • Active cooling for 24 hours.
  • Rapid achievement of cooling temperature (within 3-4 hours)
  • Rewarming
    • Slow rewarming (may take 8-10 hours) is preferred over rapid rewarming as the latter may cause dilatation of the vessel and result in hypotension
    • It can be achieved by discontinuation of methods used for cooling like cooling blankets, ice and drugs
    • Continuous blood pressure monitoring should be done to avoid development of hypotension
    • It should be started 24 hours after the time of initiation of cooling
    • Slow rewarming @ 0.3-0.5ºC/hr
    • Target rewarming temperature 36°C

Contraindications

  • Prolonged arrest time (> 60 minutes)
  • Thrombocytopenia or other coagulopathies (hypothermia may impair the clotting factors)
  • Pregnancy (Therapeutic hypothermia can potentially be performed on pregnant female in consultation with OB/Gyn)
  • Major surgery within 14 days (it may increase risk of infections and bleeding in this group of patients)
  • Sepsis and other systemic infections (decreased immune function due to hypothermia)
  • Coma from other causes like drug intoxication
  • Patients who have signed a 'Do not resuscitate'(DNR)

Cooling techniques

Surface cooling with ice packs

  • Head, neck, axilla, and groin are preferred sites (these areas have good heat exchange)
  • Advantage - Inexpensive
  • Disadvantages
    • Difficulties in achieving and maintaining rapid rates of cooling
    • Variable and unpredictable rates of cooling

Blankets or surface heat-exchange device and ice

  • During cooling phases blankets, the cooling device's (heat-exchange pads) and ice packs are applied. Ice packs are removed once target temperature is achieved. The temperature is maintained with blanket or heat exchange pads.
  • Disadvantages
    • Difficulties in achieving and maintaining rapid rates of cooling
    • Variable and unpredictable rates of cooling

Surface cooling helmet

  • The helmet has a solution of aqueous glycerol that helps in achieving hypothermia.
  • Disadvantage - Slow, unpredictable attainment of target temperature

Catheter based internal cooling methods / Endovascular heat-exchange catheters

  • Devices available: Celsius Control System and Cool Line System
  • Placed in femoral vein
  • Advantages
    • Both endovascular cooling and rewarming are faster
    • Good at maintaining target temperature
    • Low rates of complications
    • Minimization of shivering
    • Decreased need for chemical paralysis

Infusion of cold fluids

  • Achieved by infusion of normal saline or lactated Ringer solution
  • Advantage - Rapid cooling
  • Disadvantage - rate of cooling is unpredictable
  • No increased risks of pulmonary edema, cardiac arrhythmias or other major complications was found [10], [11].

Complications

References

  1. Zeiner A, Holzer M, Sterz F, et al. Hyperthermia after cardiac arrest is associated with an unfavorable neurologic outcome. Arch Intern Med. Sep 10 2001;161(16):2007-2012.
  2. Hypothermia after Cardiac Arrest Study G. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest.[see comment][erratum appears in N Engl J Med 2002 May 30;346(22):1756]. New England Journal of Medicine. Feb 21 2002;346(8): 549-556.
  3. Bernard SA, Gray TW, Buist MD, et al. Treatment of comatose survivors of out-ofhospital cardiac arrest with induced hypothermia.[see comment]. New England Journal of Medicine. Feb 21 2002;346(8):557-563.
  4. Sunde K, Pytte M, Jacobsen D, Mangschau A, Jensen LP, Smedsrud C, et al. Implementation of a standardised treatment protocol for post resuscitation care after out-of-hospital cardiac arrest. Resuscitation 2007;73:29-39
  5. Kim F, Olsufka M, Longstreth WT Jr, Maynard C, Carlbom D, Deem S, et al. Pilot randomized clinical trial of prehospital induction of mild hypothermia in out-of-hospital cardiac arrest patients with a rapid infusion of 4 degrees C normal saline. Circulation 2007;115:3064-70
  6. Booth CM, Boone RH, Tomlinson G, Detsky AS (2004). "Is this patient dead, vegetative, or severely neurologically impaired? Assessing outcome for comatose survivors of cardiac arrest". JAMA. 291 (7): 870–9. doi:10.1001/jama.291.7.870. PMID 14970067. Review in: ACP J Club. 2004 Sep-Oct;141(2):49
  7. Jiang JY, Xu W, Li WP, Gao GY, Bao YH, Liang YM; et al. (2006). "Effect of long-term mild hypothermia or short-term mild hypothermia on outcome of patients with severe traumatic brain injury". J Cereb Blood Flow Metab. 26 (6): 771–6. doi:10.1038/sj.jcbfm.9600253. PMID 16306933.
  8. Kammersgaard LP, Rasmussen BH, Jørgensen HS, Reith J, Weber U, Olsen TS (2000). "Feasibility and safety of inducing modest hypothermia in awake patients with acute stroke through surface cooling: A case-control study: the Copenhagen Stroke Study". Stroke. 31 (9): 2251–6. PMID 10978060.
  9. 9.0 9.1 Nolan JP, Deakin CD, Soar J, Böttiger BW, Smith G, European Resuscitation Council (2005). "European Resuscitation Council guidelines for resuscitation 2005. Section 4. Adult advanced life support". Resuscitation. 67 Suppl 1: S39–86. doi:10.1016/j.resuscitation.2005.10.009. PMID 16321716.
  10. Kim F, Olsufka M, Longstreth WT, Maynard C, Carlbom D, Deem S; et al. (2007). "Pilot randomized clinical trial of prehospital induction of mild hypothermia in out-of-hospital cardiac arrest patients with a rapid infusion of 4 degrees C normal saline". Circulation. 115 (24): 3064–70. doi:10.1161/CIRCULATIONAHA.106.655480. PMID 17548731.
  11. Bernard S, Buist M, Monteiro O, Smith K (2003). "Induced hypothermia using large volume, ice-cold intravenous fluid in comatose survivors of out-of-hospital cardiac arrest: a preliminary report". Resuscitation. 56 (1): 9–13. PMID 12505732.


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