HypothermiaHypothermia HypothermiaHypothermia

Noora Al-Sukaiti

R2

Noora Al-Sukaiti

R2

Outline:Outline:Outline:Outline:

• DefinitionDefinition

• PathophysiologyPathophysiology

• Predisposing factorsPredisposing factors

• Clinical featuresClinical features

• Diagnostic strategiesDiagnostic strategies

• ManagementManagement

• Disposition Disposition

What is hypothermia?What is hypothermia?What is hypothermia?What is hypothermia?

• Core temp <35 CCore temp <35 C

• Mild 32-35Mild 32-35

• Mod 32-27Mod 32-27

• Severe <27 Severe <27

• Basal heat production (40-60kcal/m2 of BSA) Basal heat production (40-60kcal/m2 of BSA)

• inc. with food, mus. activity, fever and acute cold inc. with food, mus. activity, fever and acute cold exposure exposure

• Max production lasts for a few hrs (b/c of fatigue Max production lasts for a few hrs (b/c of fatigue and glycogen depletion)and glycogen depletion)

Mechanisms of normal heat loss:Mechanisms of normal heat loss:Mechanisms of normal heat loss:Mechanisms of normal heat loss:

• RadiationRadiation (65%) most important (65%) most important

by electromagnetic wavesby electromagnetic waves

• EvaporationEvaporation (25%): liquid to a gas (25%): liquid to a gas

0.56 kcal/ml of evaporated H2O0.56 kcal/ml of evaporated H2O

• ConvectionConvection (10-15%) heat loss to air and vapor (10-15%) heat loss to air and vapor circulating arnd the bodycirculating arnd the body

wind temp and velocitywind temp and velocity

• ConductionConduction (2+ %): direct contact (2+ %): direct contact

important with immersion important with immersion

• 37-32 C : 37-32 C : vasoconstriction, shivering and non- vasoconstriction, shivering and non-shivering endocrine thermogenesisshivering endocrine thermogenesis

• 32-24 C : 32-24 C : prog. reduction in basal met rate (NO prog. reduction in basal met rate (NO shivering)shivering)

• <24 C : <24 C : autonomic and endocrine mech. inactive autonomic and endocrine mech. inactive

Which of the following cardiac findings Which of the following cardiac findings is expected in hypothermia:is expected in hypothermia:

1. QT interval prolongation

2. Sinus bradycardia

3. Atrial fibrilation

4. J waves

5. All of the above

IdentifyIdentify

Hypothermic J wavesHypothermic J waves

J waves on ECG (false):J waves on ECG (false):

1.1. Potentially diagnostic of hypothermiaPotentially diagnostic of hypothermia

2.2. size decreases with temperature size decreases with temperature depressiondepression

3.3. appear at <32 C at junction of QRS and ST appear at <32 C at junction of QRS and ST segmentsegment

4.4. DDx local cardiac ischemia, sepsis or CNS DDx local cardiac ischemia, sepsis or CNS lesionslesions

5.5. Can occur in young normothermic pts Can occur in young normothermic pts

CVS and hypothermia (false):CVS and hypothermia (false):

1.1. A Fib occurs at <32C and usually converts A Fib occurs at <32C and usually converts spontaneously during rewarmingspontaneously during rewarming

2.2. Asystole and VF occur at <25 C Asystole and VF occur at <25 C

3.3. Myocardium is more sensitive to cold than Myocardium is more sensitive to cold than conduction systemconduction system

4.4. Core T afterdrop is a decline in core T after Core T afterdrop is a decline in core T after removal from cold environmentremoval from cold environment

5.5. Bradycardia is refractory to atropine Bradycardia is refractory to atropine

Other changes:Other changes:

• CNS:CNS:

Progressive dep. >>> silent EEG at 20 CProgressive dep. >>> silent EEG at 20 C

Loss of autoregulation <25 CLoss of autoregulation <25 C

• Renal:Renal:• Hypothermia: ↓ renal bld flow Hypothermia: ↓ renal bld flow secrete lg secrete lg

amounts of dilute urine (cold diuresis)amounts of dilute urine (cold diuresis)• Periph vasocons Periph vasocons relative central relative central

hypervolemia hypervolemia cold diuresis cold diuresis• EtOH doubles ↑ in urine volumeEtOH doubles ↑ in urine volume

• RS : RS : • Initial ↑in RR then ↓ RR proportional to ↓ Initial ↑in RR then ↓ RR proportional to ↓

metabolism metabolism • CO2 retention & RS acidosis in sev. CO2 retention & RS acidosis in sev.

hypothermia.hypothermia.• Bronchorrhea, ↓ciliary motility and Bronchorrhea, ↓ciliary motility and

noncardiogenic pulm edemanoncardiogenic pulm edema

Factors predisposing to hypothermiaFactors predisposing to hypothermia(mention 3 main)(mention 3 main)

• Dec heat Dec heat productionproduction

• EndocrineEndocrine• Insufficient fuelInsufficient fuel• NeuromuscularNeuromuscular• IneffeciencyIneffeciency

• Inc heat lossInc heat loss• EnvironmentEnvironment• VasodilationVasodilation• erythrodermaserythrodermas

• Impaired Impaired thermoregulationthermoregulation

• Periph.Periph.• centralcentral

• OthersOthers• SepsisSepsis• TraumaTrauma• CarcinomasCarcinomas• Etc…Etc…

Why old people are more at risk for Why old people are more at risk for hypothermia?hypothermia?

• Dec ability to sense coldDec ability to sense cold• Poor adaptive and behavioral responsesPoor adaptive and behavioral responses• Dec glycogen stores for shiveringDec glycogen stores for shivering• Dec muscle mass for shiveringDec muscle mass for shivering• Poor glucose usePoor glucose use• Autonomic dysfunction- poor vasoconstrictive Autonomic dysfunction- poor vasoconstrictive

abilityability• Co morbid illnessCo morbid illness

• Peripheral vascular diseasePeripheral vascular disease• CNS dysfunctionCNS dysfunction• Cardiac disease Cardiac disease

Ethanol with hypothermia (false):Ethanol with hypothermia (false):

1.1. Interacts with every neurotransmitter in Interacts with every neurotransmitter in brainbrain

2.2. Metabolized faster in hypothermic patientsMetabolized faster in hypothermic patients

3.3. Possible direct damage to hypothalamusPossible direct damage to hypothalamus

4.4. Peripheral vasodilationPeripheral vasodilation

5.5. Impaired cognition and immobilityImpaired cognition and immobility

6.6. Hypoglycemia and/or malnutritionHypoglycemia and/or malnutrition

Clinical FeaturesClinical FeaturesClinical FeaturesClinical Features

• Mild hypothermiaMild hypothermia: vague sxs (e.g. hunger, : vague sxs (e.g. hunger, nausea, confusion, dizziness, chills, pruritis and nausea, confusion, dizziness, chills, pruritis and SOB)SOB)

• Paradoxical undressingParadoxical undressing

• Progressive Progressive ↓ in LOC↓ in LOC• <22 : unreactive pupils (↓ perfusion)<22 : unreactive pupils (↓ perfusion)• Hyperreflexia till 32 C >>> hypo >>> absent at Hyperreflexia till 32 C >>> hypo >>> absent at

26C26C• Q : … is last reflex to disappear and first to Q : … is last reflex to disappear and first to

reappear?reappear?

Knee jerkKnee jerk

Name T:Name T:Name T:Name T:

• Maximum shiveringMaximum shivering• Extinguish shiveringExtinguish shivering• A fibA fib• V fibV fib• Dilated pupilsDilated pupils• No reflex/responseNo reflex/response• AtaxiaAtaxia

35 C35 C

31 C31 C

30 C30 C

26 C26 C

29 C29 C

26 C26 C

33 C33 C

56 yrs old man is brought in by the police after he 56 yrs old man is brought in by the police after he was found under a bridge in a winter night. His was found under a bridge in a winter night. His core T is 30.core T is 30.which of the following findings is likely to be seenwhich of the following findings is likely to be seen::

1.1. AnemiaAnemia

2.2. Pinpoint pupilsPinpoint pupils

3.3. ShiveringShivering

4.4. TachypneaTachypnea

5.5. Urinary diuresisUrinary diuresis

Which of the following physiologic changes is Which of the following physiologic changes is expected in hypothermic pt:expected in hypothermic pt:

1.1. HemoconcentrationHemoconcentration

2.2. HypoglycemiaHypoglycemia

3.3. Metabolic alkalosisMetabolic alkalosis

4.4. OliguriaOliguria

5.5. SeizuresSeizures

Lab facts;Lab facts;

• Normally; PCO2 inc 10 mmHg, pH dec 0.08 unitsNormally; PCO2 inc 10 mmHg, pH dec 0.08 units

• pH reduction DOUBLES at 28 CpH reduction DOUBLES at 28 C

• Hematocrit inc 2% for every 1C fallHematocrit inc 2% for every 1C fall

• Persistent hyperglycemia with rewarming,, DKA Persistent hyperglycemia with rewarming,, DKA or hrgic pancreatitisor hrgic pancreatitis

• Rewarming is the only effective treatment for Rewarming is the only effective treatment for coagulopathycoagulopathy

Hypothermia management (false)Hypothermia management (false)

1.1. Goals of pre-hospital care are to rescue, examine, Goals of pre-hospital care are to rescue, examine, insulate and rapidly transportinsulate and rapidly transport

2.2. Rectal T is the most practical for core T evaluation Rectal T is the most practical for core T evaluation and should be inserted to 15 cmand should be inserted to 15 cm

3.3. ET intubation is necessary unless pt is alert with ET intubation is necessary unless pt is alert with intact protective reflexesintact protective reflexes

4.4. NGT is indicated in mod-sev hypothermia after NGT is indicated in mod-sev hypothermia after intubationintubation

5.5. Cardiac monitoring is better by central venous Cardiac monitoring is better by central venous pressure catheterpressure catheter

Volume resuscitation in hypothermiaVolume resuscitation in hypothermia(false):(false):

1.1. Rapid volume expansion is criticalRapid volume expansion is critical

2.2. Adults should receive 250-500ml fluid Adults should receive 250-500ml fluid challenge of heated 5% dex in NSchallenge of heated 5% dex in NS

3.3. IV fluids should be heated to 40-42 CIV fluids should be heated to 40-42 C

4.4. Microwaving is an option for heating IVFMicrowaving is an option for heating IVF

5.5. IVF should not be shaken before IVF should not be shaken before administration administration

Withhold CPR in hypothermia Withhold CPR in hypothermia (false):(false):

1.1. Pt with tissue decomposition, rigor mortis, Pt with tissue decomposition, rigor mortis, dependent lividity and fixed dilated pupilsdependent lividity and fixed dilated pupils

2.2. Obvious lethal injuriesObvious lethal injuries

3.3. Impossible chest wall depressionImpossible chest wall depression

4.4. Signs of life are presentSigns of life are present

5.5. Rescuers are in dangerRescuers are in danger

Pharmacology and hypothermia Pharmacology and hypothermia (false):(false):

1.1. Intramuscular and oral medications should be Intramuscular and oral medications should be avoidedavoided

2.2. Epineph., dopamine and other vasocnstricors Epineph., dopamine and other vasocnstricors should be avoidedshould be avoided

3.3. Most hypothermia-induced dysrhythmias Most hypothermia-induced dysrhythmias convert spontaneously during rewarmingconvert spontaneously during rewarming

4.4. Defibrillation attempts are usually Defibrillation attempts are usually unsuccessful until the core T is above 28-30 Cunsuccessful until the core T is above 28-30 C

5.5. At any T, 3 defibrillation attempts should be At any T, 3 defibrillation attempts should be initiatedinitiated

RewarmingRewarming

• PassivePassive external rewarming external rewarming patient rewarms on their own, using endogenous heat patient rewarms on their own, using endogenous heat

production mechanismsproduction mechanisms

• ActiveActive rewarming: rewarming:• Active Active externalexternal rewarming: application of rewarming: application of

exogenous heat to the body externallyexogenous heat to the body externally• Active Active corecore rewarming rewarming

» Airway rewarmingAirway rewarming» Peritoneal dialysisPeritoneal dialysis» Heated irrigationHeated irrigation» DiathermyDiathermy» Extracorporeal blood rewarmingExtracorporeal blood rewarming

Active ext. rewarming (false)Active ext. rewarming (false)

1.1. Indications are controversial due to the risks of Indications are controversial due to the risks of shock and afterdropshock and afterdrop

2.2. Optimal candidates are young previously healthy Optimal candidates are young previously healthy people in whom there are minimal circulatory people in whom there are minimal circulatory changeschanges

3.3. Heat packs, water bottles and immersion baths of Heat packs, water bottles and immersion baths of 40 C are options40 C are options

4.4. Forced-air warming system is currently most Forced-air warming system is currently most practical in EDpractical in ED

5.5. Heat sources should be applied to thorax and Heat sources should be applied to thorax and extremitiesextremities

Active core rewarming (true)Active core rewarming (true)

1.1. Airway rewarming is not indicated in all mod or Airway rewarming is not indicated in all mod or severe hypothermiasevere hypothermia

2.2. Peritoneal dialysis delivers heated dialysate at Peritoneal dialysis delivers heated dialysate at <40 C to the peritoneal cavity<40 C to the peritoneal cavity

3.3. Peritoneal dialysis can exacerbate preexisting Peritoneal dialysis can exacerbate preexisting hyperkalemiahyperkalemia

4.4. Mediastinal irrigation and direct myocardial Mediastinal irrigation and direct myocardial lavage should only be considered in pts lavage should only be considered in pts without spontaneous perfusionwithout spontaneous perfusion

5.5. Extracorporial blood rewarming should not be Extracorporial blood rewarming should not be attempted in hypothermic cardiac arrestattempted in hypothermic cardiac arrest

Active internal rewarmingActive internal rewarming

• Airway rewarmingAirway rewarming– Indicated in all moderate to sever Indicated in all moderate to sever

hypotherm,, non invasivehypotherm,, non invasive– Gas should be 40-42 C and humidifiedGas should be 40-42 C and humidified– Reduces bronchorrheaReduces bronchorrhea– Rewarming rate of 1 to 2.5 C/hrRewarming rate of 1 to 2.5 C/hr

Air inhalation rewarmingAir inhalation rewarming

• Extracorporeal rewarmingExtracorporeal rewarming– Only in extreme situationsOnly in extreme situations– Indications: Arrest, No response to other Indications: Arrest, No response to other

methods, frozen extremities, sever electrolyte methods, frozen extremities, sever electrolyte abnormalities and rhabdomyolysisabnormalities and rhabdomyolysis

– Rewarming rate of 1-2 C every five minutes!Rewarming rate of 1-2 C every five minutes!

• DiathermyDiathermy– Transmission of heat by conversion of energyTransmission of heat by conversion of energy– Use low frequency microwave radiationUse low frequency microwave radiation– Contraindication- frostbite, burns, metallic Contraindication- frostbite, burns, metallic

implants, edemaimplants, edema

Indications for Active RewarmingIndications for Active Rewarming(list 4)(list 4)

1.1. Cardiovascular instability Cardiovascular instability

2.2. Moderate or severe hypothermia (<32.2° C) Moderate or severe hypothermia (<32.2° C)

3.3. Inadequate rate or failure to rewarmInadequate rate or failure to rewarm

4.4. Endocrinologic insufficiency, Endocrinologic insufficiency, ↓ glycogen ↓ glycogen stores stores

5.5. Traumatic or toxicologic periph vasodilatat’n Traumatic or toxicologic periph vasodilatat’n

6.6. Sec hypothermia impairing thermoregulationSec hypothermia impairing thermoregulation

Disposition:Disposition:Disposition:Disposition:

• May D/C pts with mild accidental primary May D/C pts with mild accidental primary hypothermia (>32 C)hypothermia (>32 C)

• admit anyone elseadmit anyone else

• Always r/o underlying medical diseases as Always r/o underlying medical diseases as

causes of hypothermiacauses of hypothermia

OutcomesOutcomes

• Predictors of outcomePredictors of outcome• prehospital arrestprehospital arrest• low/absent BPlow/absent BP• elevated BUNelevated BUN• need for intubation/NGT in ED.need for intubation/NGT in ED.

• Bad prognostic indicatorBad prognostic indicator1.1. intravascular thrombosis (fibrinogen <50)intravascular thrombosis (fibrinogen <50)2.2. cell lysis (K>10)cell lysis (K>10)3.3. ammonia (>250) ammonia (>250)

(not prospectively validated!)(not prospectively validated!)

Thank you!Thank you! Thank you!Thank you!