Hypothermia after Cardiac Arrest - Guideline of Care

Two randomized, controlled trials have shown that the application of therapeutic hypothermia may improve neurological recovery for comatose survivors of out-of-hospital cardiac arrest.

For patients who are unconscious after successful resuscitation from cardiac arrest caused by ventricular fibrillation or pulseless ventricular tachycardia, good evidence exists that induced hypothermia with a target temperature of 32°C to 34°C (89.6°F to 93.2°F) for 12 to 24 hours improves neurologic outcome. Patients receiving hypothermia are significantly more likely to have a favorable neurologic outcome and lower mortality

Thrombolytics, antiplatelet agents, or anticoagulants necessary for the primary cardiac condition are permitted.

Cooling after PEA, asystole, or in-hospital arrest has not been similarly studied but is allowed per MD discretion.

• 1. Patient Selection: Patients who may benefit from therapeutic hypothermia include:

     • Downtime = 30 minutes.

       • Downtime is defined as the time of onset of cardiac arrest to the initiation of ACLS; bystander CPR does not count.

     • Comatose patients (GCS =8) within 8 hours of return of spontaneous circulation

     • Demonstrated benefit for pulseless VT and VF

     • SBP =90, MAP =90 mmHg

       • Vasoactive or inotropic agents are permissible

     • Operational definition of coma

       • No purposeful localization to external noxious stimuli

         • Pathological or hypertonic posturing are permissible

       • Intact brain stem reflexes

       • No spontaneous eye opening

       • Patients who do not respond appropriately to verbal commands. Agitated/combative patients are comatose by this definition and should be cooled.

       • No speech production nor ability to understand verbal or non-verbal language

  2. No age limit: Pre-arrest quality of life is the important factor.

  3. Neurocritical Care Consultation: For evaluation of coma and documentation-initiation of hypothermia

  4. Relative Exclusion and/or Discontinuation Criteria: Patients for whom therapeutic hypothermia may increase risk:

     • Clinically important traumatic brain injury

       • If suspected, obtain a non-contrast CT of head to examine for ICH prior to cooling.

     • Patients in coma from non-cardiac causes

       • Drug intoxication or coma pre-dating cardiac arrest

       • Consider CT/MRI/EEG if clinically indicated

     • Major surgery within 14 days

       • Hypothermia may increase infection and/or bleeding risk.

     • Patients with a known bleeding diathesis, or with active ongoing bleeding

       • Hypothermia may impair coagulation

       • Check PT/PTT/INR, fibrinogen, D-dimer before cooling.

     • Refractory cardiogenic or septic shock in spite of IV fluids and vasopressors

       • Cardiac instability

       • New or worsening ischemia

       • Recurrent VF or refractory VT in spite of appropriate therapy

     • Evidence of brain herniation

     • Isolated respiratory arrest without cardiac involvement

     • Pregnancy test must be obtained in all child-bearing aged females

     • CPR for more than 45 minutes

     • Unwitnessed PEA or unwitnessed asystolic arrest with CPR and/or ACLS for 10 minutes or more.

Recommendation

1. Goal body temperature = 33° C within 1 hour.

2. Blood Pressure:

   1. For adequate cerebral perfusion, recommend goal of MAP between 90-100 mm Hg.

   2. Peripheral vasoconstriction during hypothermia may elevate BP. Hypertension potentially adds to the neuroprotection of hypothermia. The primary team should determine the MAP goal, balancing cardiac safety with the potential advantage of higher cerebral perfusion pressures.

3. Fluid Management

• 1. Use normal saline to a goal of euvolemia.

  2. All IV solutions should be DEXTROSE FREE during the cooling and rewarming phase

4. Cardiac Monitoring

• 1. Bradycardia is the most common dysrhythmia associated with hypothermia.

  2. EKG changes may include:

i. Left precordial leads with Osborne or J-wave (at QRS junction to ST segment). This wave disappears with warming.

ii. Prolongation of PR, QRS, and/or QT intervals

iii. T wave inversion, PVCs or junctional rhythm

iv. Atrial fibrillation with a slow ventricular response

v. Fatal sustained ventricular arrhythmias.

• 1. Caution: AVOID moving the patient or insertion of a PA catheter if T < 32oC (risk for arrhythmias).

  2. If antiarrhythmics therapy is required, amiodarone is recommended (may be mixed in D5W).

1. Vital Signs Documentation:

   1. Every 30 minutes: Pulse, BP, and temperature during hypothermia initiation and active cooling, rewarming, and 24 hours after rewarming

   2. Pulse, BP and temperature every 2 hours otherwise while in the ICU, after rewarming completed

   3. Patient’s total body weight should be recorded daily in kg.

2. Neurological exam must be documented every hour during the active cooling phase.

3. Routine Blood Labs:

• 1. Electrolyte panel, glucose and CBC prior to cooling and at 12 and 24 hours after initiation of hypothermia

i. Potassium

1. Hypokalemia is a common disturbance in hypothermia and may be exacerbated by insulin use

2. Conversely, re-warming leads to potassium efflux and potentially, hyperkalemia. Caution for increased serum potassium during rewarming. Check at least every six hours.

ii. Serum amylase & lipase have been observed to increase during therapeutic hypothermia. Check prior to cooling and at 12 and 24 hours after initiation of hypothermia and, during rewarming, check every six hours.

1. No heated humidification on the ventilator

   1. ABG measurements must be analyzed at the patient’s actual body temperature.

   2. CO2 should be maintained in the normal range (35-45 mm Hg).

   3. PO2 90-100 mmHg and pH normal range

2. Blood cultures: Obtain at 12 hours after initiation of cooling as infection may be masked during cooling.

3. Skin Assessment for Cold-Induced Burns

• 1. Every 12 hours, if NOT being given vasoconstrictive agent(s).

  2. Every 6 hours if BEING GIVEN vasoconstrictive agent(s).

4. Gastrointestinal and Deep Venous Thrombosis Prophylaxis:

• 1. Use H2-blockers unless there is thrombocytopenia (then use lansoprazole NG)

  2. Use sequential compression devices and SQ heparin 5000 units q8h (if no HIT suspected).

5. Maintain HOB at 30o elevation

6. Begin enteric feeding as soon as practical

• 1. Obtain REE/RQ

7. Maintain normoglycemia (80-140 mg/dL)

8. Shivering Prophylaxis and Treatment Strategies

• 1. Apply stocking-glove warming. Begin by wrapping the patient’s hands and feet in dry towels to decrease the shivering stimulus.

  2. Acetaminophen 650mg every 4 hours per nasogastric tube or rectum

  3. Buspirone 30 mg q 8 hrs per nasogastric tube

  4. Apply face warming.

  5. Use heated gel pack for hands and feet warming and heated oxygen mask or face tent for face.

  6. May give Meperidine 0.5 - 1.0 mg/kg every 30 minutes to effect or sedation

i. Maximum dose is 600 mg/day; use 12.5 mg increments IV

ii. Adjust for renal insufficiency, as needed

• 1. For intubated patients, initiate propofol 5 micrograms/kg/minute IV. Increase to effect OR until maximum dose 55 micrograms/kg/min or maximum 2 grams per day

  2. OR Midazolam, 0.2 mg/kg loading dose IV, followed by 0.2 mg/kg/hr IV

  3. OR Neuromuscular blocking agents (NMBA) may be necessary. Pancuronium is preferred. Use vecuronium for clinically important tachycardia. Cisatracurium may be used in setting of concomitant steroid use or CrCl < 50 mL/min. Continuous infusion, per hospital guidelines is preferred over intermittent dosing.

i. IV bolus load 0.3 mg/kg IVP

ii. IV maintenance infusion 4-12 mcg/kg/min

iii. Infusion concentration 1 mg/mL in 100 mL NS

• 1. Obtain baseline "Train of Four" (T.O.F.) using peripheral nerve stimulator prior to initiation of NMBA. Baseline goal is four twitches out of four stimulations (4/4)

  2. Maintain T.O.F. 1-2/4 to prevent shivering

  3. Administer analgesic/sedative prior to initiation of NMBA to ensure patient is not awake during paralysis and cooling. RASS score minus 4.

  4. If propofol used, instead of meperidine, morphine may be substituted:

i. IV bolus load 0.05-0.01 mg/kg IVP

ii. IV maintenance infusion: 1-10 mg/hour, titrated

iii. Infusion in NS

iv. Equianalgesic doses of fentanyl of hydromorphone are acceptable substitutes

1. Rewarming:

   1. The re-warming phase is critical, as peripheral beds, which were once constricted, will undergo dilation. This shift in vascular tone may elicit clinically significant hypotension. The literature supports re-warming rates 0.25o C per hour with full re-warming at about eight hours. Sedation is maintained until core temperature is 36 o C AND train-of-four is present.

   2. 24 hours from start of active cooling:

i. Program the Arctic Sun for controlled re-warming over 8 hours, to goal temp of 37o C

ii. Dial in the desired warming rate on the machine (0.25o C per hour)

• 1. Discontinue paralytics

  2. Maintain sedation until body temp is 36 o C AND train-of-four is present

  3. When temperature = 37°C. Program the Artic Sun to maintain 37o C for the subsequent 48 hours

  4. Address any hypotension related to the re-warming vasodilatation phenomenon.

  5. Address hypokalemia that may occur during re-warming (goal ≥ 3.5 mEq/L)

  6. The goal after re-warming is normothermia (i.e., 37o C, avoidance of hyperthermia)

  7. If clinically important dysrhythmias, hemodynamic instability or bleeding develop, or if neurological status improves to the point, that patient is able to follow commands, discontinue cooling and initiate re-warming.

The Neurocritical Care service will follow and reassess the neurological status after discontinuation of hypothermia.

http://emedicine.medscape.com/article/812407-overview

Anterior nucleus (preoptic) of hypothalamus regulated body temperature.

Prostaglandin E2 is the common mediator affecting the temperature set point.

Neuroprotective effects of induced mild hypothermia

• • Early 0-30 min:

    • Lowers metabolic demand

    • Slows O2 consumption, ATP stores preserved

    • Every 1°C reduction in body temp reduces cerebral metabolic rate of O2 (CMRO2) by 6-7%

  • Intermediate hours:

    • Inhibition of glutamate release, less excitotoxicity

    • Suppression of O2 free radicals

  • Late: upto 24 hours:

    • Decreased BBB breakdown

    • Less edema and H'gic transformation of ischemic stroke

Complication of Hypothermia:

• • Metabolic:

    • Decreased BMR

    • Plasma conc increased for morphine, fentanyl, propofol

    • Duration of action increased for vecuronium, atracurium

  • Electrolytes:

    • During cooling: hypokalemia, hypomagenesemia, hypophosphatemia, hyperglycemia (insulin resistance)

    • During rewarming: rebound hyperkalemia.

  • Neurologic:

    • Slurred speech, confusion, stupor, coma with progressing hypothermia, elevated ICP and cerebral edema upon rewarming.

  • Cardiac:

    • AF <32°C; ventricular arrhythmia at <30°C

    • Arrhythmia is often refractory to conventional medical therapy. Must rewarm to treat; ECG repolarization abnormalities, Osborne waves.

  • Hemodynamic:

    • Cold diuresis; ▲ SVR, ▼ BP; ▼ HR, ▼ CO

  • Hematologic:

    • Coagulopathy: platelet dysfunction, prolonged bleeding time, DIC, enhanced fibrinolysis, leukopenia, thrombocytopenia,

    • Must rewarm to life-threatening bleeding

  • Renal:

    • RTA (ATN)

  • Pulmonary:

    • Increased pulmonary edema

  • Infection:

    • Increased sepsis/bacteremia, pneumonia, wound infection

  • GI:

    • Ileus, stress ulcer, elevated lipase/amylase