What are you cooling for… Therapeutic Cooling Post Cardiac Arrest
Objectives: • Discuss the nature and scope of therapeutic hypothermia and clinical potential. • Review why it works. • Survey essential clinical literature. • Define the challenges of each phase of therapeutic hypothermia.
Definitions • Therapeutic hypothermia - controlled reduction of core temperature to provide neuroprotection. • Mild hypothermia - 33°- 36°C (91-97°F) • Return of Spontaneous Circulation (ROSC) - Patient has a sustainable rhythm, pulse, and BP. • Good Outcome - Home and independent with basic ADLs by 3-6 months
What’s the problem? • Post cardio-pulmonary arrest - Global ischemia of the brain - Successful resuscitation with residual coma indicates a severe brain injury. • Good recovery - “Standard of care” 0 to 15% - Normothermia 20-25% - Hypothermia 50-60%
Neuroprotection of Hypothermia • ↓cerebral metabolism by 5% for every 1°C - more important with focal ischemia than global. - not the most important mechanism • ↓ release of excitatory neurotransmission (e.g. glutamine and glycine) and free radical production during early reperfusion (up to 1 hour after reperfusion).
Neuroprotection of Hypothermia • Prevent Na+ and H2O entry into the cell. • ↓ destructive enzymes production (protease, lipase, phospholipase, etc.) • Suppresses the inflammation cascade (cytokine, interleukines, caspase C, etc.) • Stabilizes the blood-brain barrier.
THERAPEUTIC HYPOTHERMIA STUDIES
Post Cardiac Arrest • Out of hospital arrest • N= 77 randomized • Surface cooling X 12 hours • Good neurological outcome - hypothermia 49% - normothermia 26% • No significant difference in complications
Post Cardiac Arrest • Out of hospital arrest • N= 275 randomized • Surface cooling X 24 hours • No significant difference in complications.
AHA (ACLS Guidelines 2005) • Unconscious adult patients with spontaneous circulation after ROSC after out of hospital cardiac arrest should be cooled to 32°C to 34°C for 12 to 24 hours when initial rhythm was ventricular fib (VF) level of evidence IIa. • Such cooling may also be beneficial for other rhythms or in-hospital cardiac arrest. Level of evidence IIb. • Recommend not actively. • Rewarming post-hypothermia
How is it done?
Surface Ice packs Ice H2O and/or alcohol baths Cooling blanket with H2O or air Cooling pads and wraps OGH will be performing IV infusion of iced fluids Internal - IV infusions of iced fluids Gastric and/or rectal infusions of iced fluids Intravascular heart exchange Gaymar cooling blankets Common methods for induction of Hypothermia
Cooling Phases • Induction - Bring temperature down to target - 1-4 hours • Maintenance - Stay at target 33°C for 24 hours • Rewarming - return to normal - 24 hour time frame • Post warming - monitor for rebound hyperthermia 1-2 days
Induction • Intubation/Sedation • Initiation of monitoring - temperature (core) esophageal/bladder - cardiac - hemodynamic (A-line) - volume (CVP monitoring) - labs (especially K+, mag, coags)
Induction Initiate cooling - Gaymar cooling vest and leg pads - intravascular (2 Liters 4°C NS bolus) max of 3L Supportive Care - Hygiene - Nutrition and hydration - VAP, DVT, GI prophylaxis
Shiver Prophylaxis • Tylenol • Demerol • Zemuron
Induction • Risks - cooling too slowly * reduces potential effectiveness • Overshoot - cooling too low (esp. < 30°C) - ↑ risk of significant arrhythmias * VF/VT/Asystole
Maintenance • Monitoring Temperature Cardiac Hemodynamics Volume Labs (K+)
Maintenance • Cooling - maintain target temp +/- 0.5°C • Supportive Care - skin *meticulous routine care • VAP prophylaxis - mouth care - HOB > 30° - Subglotic suction - DVT Prophylaxis
Maintenance • Nutrition - ↓ or absent bowel sounds common - Ileus is possible - feeding via NG at a low rate is SAFE • Fluids - Initial ↑ CVP due to vasoconstriction - Dehydration due to * Increased GFR * Cold diuresis * Underlying pathology (head injury, etc).
Rewarming • Controlled - warming too quickly can induce injury • Active vs. Passive - active (over 24 hours): cooling/warming machine - passive: remove machine and allow patient to rewarm on own.
Rewarming and Post Rewarming • Rebound hyperthermia - development of fever > 38.5°C (101.3°F) within 24 hours of rewarming *Very Common *Associated with worsening neurologic damage. • Shiver Prophylaxis - Maintain until after core temp > 36°C (96.8°F) • Prevention - Maintain normothermia for 24-48 hours after rewarming
CONCLUSIONS Mild Therapeutic Hypothermia SAFE EFFECTIVE IMPROVES OUTCOMES DECREASES ICP IMPROVES CEREBRAL PERFUSION SUPPRESSES SEIZURES
Reference 2008, Gaymar Industries, Inc. DVD “What are you cooling for…Therapeutic Hypothermia Post Cardiac Arrest”.