Newsweek July 2007
New York Times Dec 2008
Historical Perspective of HypothermiaHypothermia for
clinical purposes has ancient roots, used by Egyptians, Greeks, and Romans
Hippocrates advocated packing wounded patients in snow and ice to reduce hemorrhage
1950’s Hypothermia was utilized for intracranial aneurysm clipping and for cardiac surgery during circulatory arrest
1960’s Clinical trials with hypothermia (30 degrees Celsius or lower) were discontinued because of the side effects, uncertain benefits, and management problems
1980’s Animal studies showed benefits of mild (32-35 degrees Celsius) hypothermia rather than moderate or deep hypothermia (less severe side effects)
2002 ILCOR (International Liaison Committee on Resuscitation)
2005 AHA guidelines for Post Resuscitation Induced Hypothermia
Epidemiology of Cardiac ArrestApproximately
450,000 people experience Sudden Cardiac Arrest (SCD) every year
95% of patients that have experienced SCD died before they reach the hospital
The StudiesThe Studies-1. Bernard SA, Gray TW Treatment of comatose survivors of
out-of-hospital cardiacarrest with induced hypothermia NEJM 2002;346:557-563,
AustraliaResults: 49% vs 26%, hypo vs normo, had a “good outcome” - as defined by discharge to home or rehab2. Hypothermia After Cardiac Arrest Study Group. Mild
therapeutic hypothermia to improve the neurologic outcome after cardiac arrest NEJM
2002;346:549-556AustriaResults: 55% vs 39%, hypo vs normo, had a CPC-cerebral
performance category score of “good recovery” or “moderate disability”
Effect of Hyperthermia on Prognosis After Acute Ischemic Stroke
Methods—Data of 5305 patients in acute stroke trials from the Virtual International Stroke Trials Archive (VISTA) data Hyperthermia was defined as temperature 37.2°C
Conclusions—Hyperthermia, in acute ischemic stroke, is associated with a poor clinical outcome. The later the hyperthermia occurs within the first week, the worse the prognosis. Severity of stroke and inflammation are important determinants of hyperthermia after ischemic stroke. In patients with acute ischemic stroke, aggressive measures to prevent and treat hyperthermia could improve the clinical outcomes. (Stroke. 2009;40:3051-3059.)
PathophysiologyBrain loses oxygen stores within 20 secondsDamage starts 4-6 minutes after the heart
stopsGlucose and adenosine triphosphate stores
deplete (brain energy)Membrane depolarizationCalcium influxesGlutamine is releasedAcidosis and edema develop
Ischemia may persist for several hours after resuscitation (re-perfusion injury)
CardiovascularBradycardiaSlight increase in
blood Pressure (10mmHG)
Mild arrhythmias Increased PR intervalIncreased QT intervalWidened QRS
Increased Systemic Vascular Resistance
Increased Central Venous Pressure
Decreased Cardiac Output
Hematologic
ThrombocytopeniaImpaired platelet
functionLeukopeniaImpaired Leukocyte
functionIncreased PT/PTT
Gastrointestinal
Impaired Bowel Function
Decreased GI motility/ Ileus
Mild Pancreatitis (increased amylase)
Increased liver enzymes
Pharmacokinetics
Altered clearance of medicationsClearance is slowed
having a prolonged effect
Keep this in mind when re-warming.
GeneralBody attempts to
maintain homeostasisShiveringPeripheral
vasoconstrictionDecreased
circulation to skin
MetabolismIncreased fat
metabolism with increased production of glycerol, free fatty acids, ketonic acids, lactate
Metabolic acidosisDecreased oxygen
consumptionDecrease CO2
production
NeurologicDecreased metabolic rate 5-7 % for each 1
degree CDecreased Cerebral Blood Flow
(vasoconstriction)Decreased Magnesium- associated with
worse outcomes. Maycause Cerebral and Coronary
Vasoconstriction
Endocrine
Increased epinephrine, Nor epinephrine, and Cortisol levels
Hyperglycemia due to decreased insulin sensitivity and decreased insulin levels
Renal
DiuresisRenal Tubular
DysfunctionElectrolyte loss (K,
MG, Ca, Phos)
Mechanics of CoolingPassive Cooling
Ineffective have to wait on temperature to decrease to 33◦ Celsius
Active CoolingConvection
Air Cooling Blanket Therma cool Bair Hugger
Conduction Ice packs Cold Blankets
Infusion Cold NS infusion (2L
over 4 hours)
Exclusion Criteria• CPR for more than 45 minutes• Comatose or vegetative state prior to cardiac arrest• Evidence of hypotension (MAP < 60) for more than 30minutes after ROSC and prior to initiation of hypothermia• Terminal illness that preceded the arrest (life
expectancy < 1year)• Trauma• Temperature <34°C• Inability to intubate patient• Appearance of the gravid abdomen• Active bleeding/known pre existing coagulopathy (Note:Thrombolytic therapy does not preclude the use ofhypothermia)
Inclusion Criteria• Non-Traumatic cardiac arrest with return of spontaneouscirculation (ROSC) but remains unconscious• Patient > 16 years of age• Initial temperature > 34° C (93.2 °F)• Patient remains comatose (no purposeful response to pain)• Patient must be intubated to initiate protocol.• If patient meets other criteria for induced hypothermia and isnot intubated, then intubate according to protocol beforeinduced cooling.• If unable to intubate DO NOT initiate induced hypothermia.• Initiated within 3 hours of cardiac arrest• If there is loss of spontaneous circulation after cooling isinitiated, discontinue cooling and initiate appropriate protocol.
MonitoringABG’s every 8 hours.
(temperature adjusted)
Art line monitor B/P closely
SedationMAP greater than 80
mmHgCardiac Rhythm
Assess frequency of arrhythmias
Prolonged QT interval
Monitor Lytes every 8 hours
12 Lead ECG every 8 hours
Complications of HypothermiaPneumonia RiskVentilator DependencyDecreased WBC / BM
SuppressionDecreased Inflammatory
cytokinesElevated Glucose
Miscellaneous ComplicationsDoes NOT significantly increase metabolic
acidosisor Lactate levelsWill often cause mild HYPOTENSION, use
Pressorsto maintain MAP > 80 for cerebral perfusion
(90 – 100)Drug Metabolism slowed significantly(Propofol / Fentanyl / Verapamil / Propanolol)
ShiveringIncreases O2 Consumption between 40 – 100%Shivering responses occur primarily between 30 – 35
CSedation and anesthesia to halt shivering also
increasePeripheral Blood FlowIf you paralyze, you can’t screen for seizuresBuspirone (Buspar) 20mg PO q 8hrs / hold for SCr >
1.7Meperidine (Demerol) 25 – 50mg IV q 4 hrs prnUse Paralytics as second line
The Future is in Our Hands