Therapeutic hypothermia
| Therapeutic hypothermia |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Associate Editor: Cafer Zorkun, M.D., Ph.D. [2]
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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
- Hypothermia activates the sympathetic nervous system causing vasoconstriction and shivering. Shivering increases O2 consumption by 40-100%. Sedatives, opiates, and neuromuscular blockers can counteract these responses and enhance the effectiveness of active cooling. However, initiating paralysis in a patient that is already hypothermic should be avoided because it can result in a precipitous drop in core body temperature. Elderly patients will cool more quickly than younger or obese patients. [4]
- Hypothermia shifts the oxyhemoglobin curve to the left may result in decreased O2 delivery. However, the metabolic rate is also lowered, decreasing O2 consumption / CO2 production, cardiac output and cerebral blood flow. Ventilator settings may need to be adjusted due to decreased CO2 production, using temperature corrected blood gases. [5]
- Hypothermia initially causes sinus tachycardia, then bradycardia. With temp <30º C there is an increased risk for arrhythmias. With temp <28º C there is an increased risk for ventricular fibrillation. The severely hypothermic myocardium (<30°C) is less responsive to defibrillation and medications. Therefore it is extremely important to keep temp >30ºC.
- Hypothermia can induce coagulopathy which is treatable with platelets and FFP.
- Hypothermia-induced diuresis is to be expected and should be treated aggressively with fluid and electrolyte repletion. Magnesium, phosphorus and potassium should be monitored closely and maintained in the normal (because it will rebound to very high) range.
- Decreased insulin secretion and sensitivity leads to hyperglycemia, which should be treated aggressively.
- Re-warming too rapidly can cause vasodilation, hypotension, and rapid electrolyte shifts.
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 should be started 24 hours after the time of initiation of cooling
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
Relative Contraindications for Therapeutic Hypothermia:
- 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)
References
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ 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
- ↑ 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