Hyperthermia and Hypothermia
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Hyperthermia and HypothermiaBack to BasicsApril 2011Dr. J. Clow, ER
Case 1:22 y.o. femaleOut with friends celebrating her birthday (February 19th)Dropped off at her front door by friendsFound by her parents in the morning, passed out just inside the screen doorUnable to wake her call 911
Case 2:85 y.o. maleMid-August, during heat waveSon goes to apartment and finds patient confused and lethargicPatient unable to give history
Heat RegulationFour mechanisms of heat loss/dissipation:RadiationConvectionConductionEvaporation
RadiationPhysical transfer of heat between the body and the environment by electromagnetic waves65% of heat transfer under normal circumstancesModified by insulation (clothing, fat layer), cutaneous blood flow
ConvectionEnergy transfer between the body and a gas or liquidAffected by temperature gradient, motion at the interface, and liquidNot usually a major source for heat loss or dissipation, but this increases with wind and body motion
ConductionDirect transfer of heat energy between two surfacesResponsible for only a small proportion of heat loss under normal circumstancesIncreases significantly with immersion in cold waterMajor cause of accidental hypothermia
EvaporationMost important source of cooling under extreme heat stress; important for hypothermia when in wet environment25% of heat loss in temperate/cool conditions may be increased significantly by sweating, increased respiratory rateAffected by relative humidity and clothing
DefinitionCore body temperature less than 35oCMild: 32.2 - 35oCModerate: 28 - 32.2oCSevere: < 28oC
CausesDecreased heat productionEndocrine, insufficient fuel, neuromuscular inactivityIncreased heat lossAccidental/immersion hypothermia, vasodilatation, skin disorders, iatrogenicImpaired thermoregulationCentral (metabolic, drugs, CNS)Peripheral (spinal cord injury, neuropathy, diabetes, neuromuscular disorders)
Risk Factors for Hypothermia Age extremes Elderly Neonates Outdoor exposure Occupational Sports-related Inadequate clothing Drugs and intoxicants Ethanol Phenothiazines Barbiturates Anesthetics Neuromuscular blockers Others Endocrine-related Hypoglycemia Hypothyroidism Adrenal insufficiency Hypopituitarism Neurologic-related Stroke Hypothalamic disorders Parkinson's disease Spinal cord injury Multisystem Malnutrition Sepsis Shock Hepatic or renal failure Burns and exfoliative dermatologic disorders Immobility or debilitation
Signs and Symptoms
Clinical Manifestations of HypothermiaSystemMild HypothermiaModerate HypothermiaSevere HypothermiaCNSConfusion, slurred speech, impaired judgment, amnesiaLethargy, hallucinations, loss of pupillary reflex, EEG abnormalitiesLoss of cerebrovascular regulation, decline in EEG activity, coma, loss of ocular reflexCVSTachycardia, increased cardiac output and systemic vascular resistanceProgressive bradycardia (unresponsive to atropine), decreased cardiac output and BP, atrial and ventricular arrhythmias, J (Osborn) wave on ECGDecline in BP and cardiac output, ventricular fibrillation (< 28C) & asystole (< 20C)RespiratoryTachypnea, bronchorrheaHypoventilation (decreased rate and tidal volume), decreased oxygen consumption and CO2 production, loss of cough reflexPulmonary edema, apnea
Signs and Symptoms, contd
TABLE 110-2. Clinical Manifestations of Hypothermia, contdSystemMild HypothermiaModerate hypothermiaSevere HypothermiaRenalCold diuresisCold diuresisDecreased renal perfusion and GFR, oliguriaHematologicIncreased hematocrit, decreased platelet & white blood cell counts, coagulopathy, DICGIIleus, pancreatitis, gastric stress ulcers, hepatic dysfunctionMetabolicIncreased metabolic rate, hyperglycemiaDecreased metabolic rate, hyper- or hypoglycemiaMusculoskeletalIncreased shiveringDecreased shivering (< 32C, 90F), muscle rigidityPatient appears dead, "pseudo-rigor mortis"
HistoryOften from bystanders/medicsCircumstances surrounding exposureWhere, submersion, ambient temperature?Length of exposureMental status changesAny predisposing illness acute/chronic?Alcohol/drugs?
Physical ExamVitalsTemperature want a core temperatureWhere do we take it?Signs of other injuries?Can you find the cause of hypothermia?Any focal findings?Esp. neurologic, cardiovascular, respiratory
DiagnositicsECG (always), CXR (most patients)Other tests depend on the clinical scenarioAny signs of trauma? May need imagingAre you able to take a history?Past medical history?Labs for all:CBC, electrolytes, glucose, renal function, toxicology, coags, ABGs, LFTs, lipase/amylase, cultures
ECG ChangesMay see J waveslate, terminal upright deflection of QRS complex; best seen in leads V3-V6Multiple arrhythmiasHeart blockAtrial fibrillationVentricular fibrillation
ECG Changes, contd
InterventionsAirway: need for intubation?Breathing: spontaneous respiration?Warmed humidified oxygen either through an ETT, or via maskCirculation: pulse? BP?Large IVs warmed IV fluidsArrhythmias when do we treat?CPR?
Interventions, contdDisabilityGCSGlucoscan, narcan, thiamineC-spine immobilization prnExposureUndress, assess for traumaRe-cover quickly
Rewarming Techniques Passive rewarming: Removal from cold environment Insulation, Warm blankets (e.g. Bair hugger) Active external rewarming: Warm water immersion Heating blankets set at 40C Radiant heat Forced air Active core rewarming at 40C: Inhalation rewarming Heated IV fluids GI tract lavage Bladder lavage Peritoneal lavage Pleural lavage Extracorporeal rewarming
Active RewarmingWhen?Cardiovascular instabilityTemp less than 32oCConcominant illnessesExtremes of ageFailure of passive rewarmingActive external or internal?
Rewarming - Extracorporeal
Options for Extracorporeal RewarmingExtracorporeal Rewarming (ECR) Technique ConsiderationsVenovenous (VV)Circuit CV catheter to CV or peripheral catheter No oxygenator/circulatory support Flow rates 150-400 mL/min ROR 2-3C/hHemodialysis (HD)Circuit single-or dual-vessel cannulation Stabilizes electrolyte or toxicologic abnormalities Exchange cycle volumes 200-500 mL/min ROR 2-3C/hContinuous arteriovenous rewarming (CAVR)Circuit percutaneous 8.5 Fr femoral catheters Requires BP 60 mmHg systolic No perfusionist/pump/anticoagulation Flow rates 225-375 mL/min ROR 3-4C/hCardiopulmonary bypass (CPB)Circuit full circulatory support with pump and oxygenator Perfusate-temperature gradient (5-10C) Flow rates 2-7 L/min (ave. 3-4) ROR up to 9.5C/hNote: BP, blood pressure; CV, central venous; ROR, rate of rewarming.
DefinitionCore body temperature > 38oCCaused by a failure of thermoregulationContrast with fever cause is cytokine activnSpectrum of heat-related illnessesHeat crampsHeat exhaustionHeat stroke
SpectrumHeat crampsCramps in big muscles spasmsNormal temperature, mentationCaused by dilutional hyponatremia (hypotonic fluid replacement)
Spectrum, contdHeat exhaustionWeakness, dizziness, headache, syncopeNausea, vomitingTemperature 39-41.1oCNormal mentationProfuse sweating
Spectrum, contdHeat StrokeTemperature >41.1oCComa, seizures, confusionNo sweatingClassic triad: hyperpyrexia, CNS dysfunction, anhidrosisMortality of 10-20% with treatmentClassic vs. Exertional
Spectrum, contdHeat Stroke:Classic (non-exertional):Persistent environmental exposureImpaired thermoregulationExertional:Heavy exercise in setting of high temperature and humidity
Causes of HyperthermiaIncreased heat loadHeat absorption from environmentHeat stroke (exertional, classic)Metabolic heatDiminished heat dissipationObesity, anhidrosis, drugsSepsis
Predisposing Factors for Heat StrokeIncreased Heat ProductionDecreased Heat LossEnvironmental heat stressEnvironmental heat stressExertionCardiac diseaseFeverPeripheral vascular diseaseHypothalamic dysfunctionDehydrationDrugs (sympathomimetics)Anticholinergic drugsHyperthyroidismObesitySkin diseaseEthanol Blockers
Causes of Hyperthermia
Causes of Hyperthermia SyndromesHEAT STROKEExertional: Exercise in higher-than-normal heat and/or humidityNonexertional: Anticholinergics, including antihistamines; antiparkinsonian drugs; diuretics; phenothiazinesDRUG-INDUCED HYPERTHERMIAAmphetamines, cocaine, phencyclidine (PCP), methylenedioxymethamphetamine (MDMA; "ecstasy"), lysergic acid diethylamide (LSD), salicylates, lithium, anticholinergics, sympathomimeticsNEUROLEPTIC MALIGNANT SYNDROMEPhenothiazines; butyrophenones, including haloperidol and bromperidol; fluoxetine; loxapine; tricyclic dibenzodiazepines; metoclopramide; domperidone; thiothixene; molindone; withdrawal of dopaminergic agentsSEROTONIN SYNDROMESelective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), tricyclic antidepressantsMALIGNANT HYPERTHERMIAInhalational anesthetics, succinylcholineENDOCRINOPATHYThyrotoxicosis, pheochromocytomaCENTRAL NERVOUS SYSTEM DAMAGECerebral hemorrhage, status epilepticus, hypothalamic injury
Differential Diagnosis of Heatstroke Drug toxicity: anticholinergic toxicity, stimulant toxicity (phencyclidine, cocaine, amphetamines, ephedrine), salicylate toxicity Drug withdrawal syndrome: ethanol withdrawal Serotonin syndrome Neuroleptic malignant syndrome Generalized infections: bacterial sepsis, malaria