Hyperthermia and Hypothermia Back to Basics April 2008 Dr. Jennifer Clow, ER

Case 1: 22 y.o. female Out with friends celebrating her birthday (February 19 th ) Dropped off at her front door by friends Found by her parents in the morning, passed out just inside the screen door Unable to wake her… call 911

Case 2: 85 y.o. male Mid-august, during heat wave Son goes to apartment and finds patient confused and lethargic Patient unable to give history

Heat Regulation Four mechanisms of heat loss/dissipation: –Radiation –Convection –Conduction –Evaporation

Radiation Physical transfer of heat between the body and the environment by electromagnetic waves 65% of heat transfer Modified by insulation (clothing, fat layer), cutaneous blood flow

Convection Energy transfer between the body and a gas or liquid Affected by temperature gradient, motion at the interface, and liquid Not usually a major source for heat loss or dissipation, but this increases with wind chill and body motion

Conduction Direct transfer of heat energy between two surfaces Responsible for only a small proportion of heat loss under normal circumstances Increases significantly with immersion in cold water

Evaporation Most important source of cooling under extreme heat stress 25% of heat loss in temperate/cool conditions… may be increased significantly by sweating, increased respiratory rate Affected by relative humidity and clothing

Hypothermia…

Definition Core body temperature less than 35 o C –Mild: o C –Moderate: o C –Severe: < 30 o C

Causes… Decreased heat production –Endocrine, insufficient fuel, neuromuscular inactivity Increased heat loss –Accidental/immersion hypothermia, vasodilatation, skin disorders, iatrogenic Impaired thermoregulation –Central (metabolic, drugs, CNS) –Peripheral (spinal cord injury, neuropathy, diabetes, neuromuscular disorders)

Predisposing Factors TABLE 19-1 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 TABLE Clinical Manifestations of Hypothermia SystemMild HypothermiaModerate HypothermiaSevere Hypothermia CNSConfusion, slurred speech, impaired judgment, amnesia Lethargy, hallucinations, loss of pupillary reflex, EEG abnormalities Loss of cerebrovascular regulation, decline in EEG activity, coma, loss of ocular reflex CVSTachycardia, increased cardiac output and systemic vascular resistance Progressive bradycardia (unresponsive to atropine), decreased cardiac output and BP, atrial and ventricular arrhythmias, J (Osborn) wave on ECG Decline in BP and cardiac output, ventricular fibrillation (< 28°C) and asystole (< 20°C) RespiratoryTachypnea, bronchorrheaHypoventilation (decreased rate and tidal volume), decreased oxygen consumption and CO 2 production, loss of cough reflex Pulmonary edema, apnea

Signs and Symptoms, cont’d TABLE Clinical Manifestations of Hypothermia, cont’d SystemMild HypothermiaModerate hypothermiaSevere Hypothermia RenalCold diuresis Decreased renal perfusion and GFR, oliguria HematologicIncreased hematocrit and decreased platelet, white blood cell count, coagulopathy, and DIC GIIleus, pancreatitis, gastric stress ulcers, hepatic dysfunction Metabolic endocrine Increased metabolic rate, hyperglycemia Decreased metabolic rate, hyper- or hypoglycemia MusculoskeletalIncreased shiveringDecreased shivering (< 32°C, 90°F), muscle rigidity Patient appears dead, "pseudo-rigor mortis"

History Often from bystanders/medics Circumstances surrounding exposure –Where, submersion, ambient temperature? –Length of exposure Mental status changes Any predisposing illness – acute/chronic? Alcohol/drugs?

Physical Exam Vitals… Temperature – want a core temperature –Where do we take it? Signs of other injuries? Can you find the cause of hypothermia? Any focal findings?

Diagnositics ECG!!! Will depend on the clinical scenario –Any signs of trauma? May need imaging… –Are you able to take a history? –Past medical history? Labs for all: –CBC, electrolytes, glucose, renal function, toxicology, coags, ABGs, cultures

Management…

Interventions Airway: need for intubation? Breathing: spontaneous respiration? –Warmed humidified oxygen – either through an ETT, or via mask Circulation: pulse? BP? –Large IVs – warmed IV fluids –Arrhythmias – when do we treat? –CPR?

Interventions, cont’d Disability –GCS –Glucoscan, narcan, thiamine –C-spine immobilization prn Exposure –Undress, assess for trauma –Recover quickly

Rewarming TABLE Rewarming Techniques Passive rewarming: Removal from cold environment Insulation, Warm blankets Active external rewarming: Warm water immersion Heating blankets set at 40°C Radiant heat Forced air Active core rewarming at 40°C: Inhalation rewarming Heated IV fluids GI tract lavage Bladder lavage Peritoneal lavage Pleural lavage Extracorporeal rewarming

Active Rewarming When? –Cardiovascular instability –Temp less than 32C –Concominant illnesses –Extremes of age –Failure of passive rewarming Active external or Internal?

Rewarming - Extracorporeal TABLE 19-3 Options for Extracorporeal Rewarming Extracorporeal Rewarming (ECR) TechniqueConsiderations Venovenous (VV)Circuit — CV catheter to CV or peripheral catheter No oxygenator/circulatory support Flow rates mL/min ROR 2°-3°C/h Hemodialysis (HD)Circuit — single-or dual-vessel cannulation Stabilizes electrolyte or toxicologic abnormalities Exchange cycle volumes mL/min ROR 2°-3°C/h Continuous arteriovenous rewarming (CAVR) Circuit — percutaneous 8.5 Fr femoral catheters Requires BP 60 mmHg systolic No perfusionist/pump/anticoagulation Flow rates mL/min ROR 3°-4°C/h Cardiopulmonary bypass (CPB)Circuit — full circulatory support with pump and oxygenator Perfusate-temperature gradient (5°-10°C) Flow rates 2-7 L/min (ave. 3-4) ROR up to 9.5°C/h Note: BP, blood pressure; CV, central venous; ROR, rate of rewarming.

Hyperthermia…

Definition Core body temperature > 38 o C Spectrum of heat-related illnesses –Heat cramps –Heat exhaustion –Heat stroke

Causes Increased heat load –Heat absorption from environment Heat stroke (exertional, classic) –Metabolic heat Diminished heat dissipation –Obesity, anhidrosis, drugs Sepsis

Predisposing Factors… TABLE Predisposing Factors for Heat Stroke Increased Heat ProductionDecreased Heat Loss Environmental heat stress ExertionCardiac disease FeverPeripheral vascular disease Hypothalamic dysfunctionDehydration Drugs (sympathomimetics)Anticholinergic drugs HyperthyroidismObesity Skin disease Ethanol β Blockers

Causes of Hyperthermia… TABLE 16-1 Causes of Hyperthermia Syndromes HEAT STROKE Exertional: Exercise in higher-than-normal heat and/or humidity Nonexertional: Anticholinergics, including antihistamines; antiparkinsonian drugs; diuretics; phenothiazines DRUG-INDUCED HYPERTHERMIA Amphetamines, cocaine, phencyclidine (PCP), methylenedioxymethamphetamine (MDMA; "ecstasy"), lysergic acid diethylamide (LSD), salicylates, lithium, anticholinergics, sympathomimetics NEUROLEPTIC MALIGNANT SYNDROME Phenothiazines; butyrophenones, including haloperidol and bromperidol; fluoxetine; loxapine; tricyclic dibenzodiazepines; metoclopramide; domperidone; thiothixene; molindone; withdrawal of dopaminergic agents SEROTONIN SYNDROME Selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants MALIGNANT HYPERTHERMIA Inhalational anesthetics, succinylcholine ENDOCRINOPATHY Thyrotoxicosis, pheochromocytoma CENTRAL NERVOUS SYSTEM DAMAGE Cerebral hemorrhage, status epilepticus, hypothalamic injury

Differential Diagnosis TABLE 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, typhoid fever, tetanus Central nervous system infections: meningitis, encephalitis, brain abscess Endocrine derangements: diabetic ketoacidosis, thyroid storm Neurologic: status epilepticus, cerebral hemorrhage

Signs and Symptoms Heat cramps –Cramps in big muscles – spasms –Normal temperature, mentation –Caused by dilutional hyponatremia (hypotonic fluid replacement)

Signs and Symptoms, cont’d Heat exhaustion –Weakness, dizziness, headache, syncope –Nausea, vomiting –Temperature o C –Normal mentation –Profuse sweating

Signs and Symptoms, cont’d Heat Stroke –Mortality of 10-20% with current treatment –Coma, seizures, confusion –No sweating –Temperature >41.1 o C –Classic triad: hyperpyrexia, CNS dysfunction, anhidrosis –Classic vs. Exertional

History Circumstances (as per hypothermia) Exertion? Fluids? Past medical history – any acute or chronic illnesses that may worsen situation Trauma?

Physical Examination Temperature –Where do we take it? And how? Vitals! Look for complications or other causes of the patients symptoms

Diagnostics ECG Imaging guided by history CBC, electrolytes, renal function, LFTs, Ca, Mg, PO4, coags Urine – myoglobin Pan-cultures

Poor prognostic factors Temperature > 41.1 o C AST > 1000 Coma Rhabdomyolysis Renal Failure Hypotension

Treatment ABC’s!!! Cooling Remove to cool environment! Correct fluid and electrolyte imbalances

Treatment TABLE Comparison of Cooling Techniques TechniqueAdvantagesDisadvantages Evaporative Simple, Readily available Noninvasive Easy patient access Relatively effective Shivering Difficult to maintain monitoring electrodes in position ImmersionNoninvasive Relatively effective Shivering, Cumbersome Poorly tolerated Logistically difficult to access Difficult to maintain monitoring Ice packing Noninvasive Readily available Shivering Poorly tolerated Strategic ice packs Noninvasive Readily available Combined with other techniques Shivering Poorly tolerated Medium efficiency Cold gastric lavage Generally available Invasive Labor intensive Potential for water intoxication May require airway protection Limited human experience Cold peritoneal lavage Theoretically beneficialInvasive Limited human experience

Complications of Heat Stroke TABLE Complications of Heatstroke InitialDelayed Vital signs Hypotension Hypothermia overshoot Hyperthermic rebound Muscular Shivering Rhabdomyolysis Neurologic Delirium Seizures Coma Cerebral edema CardiacHeart failure PulmonaryPulmonary edemaAcute respiratory distress syndrome RenalOliguriaRenal failure Gastrointestinal Diarrhea Hepatic necrosis Mucosal gastrointestinal hemorrhage Metabolic Hypokalemia Hypernatremia Hyperkalemia Hypocalcemia Hyperuricemia Hematologic Thrombocytopenia Disseminated intravascular coagulation

Back to the cases…

Case 1: Hypothermia What do you want to know? Physical Exam? Labs? Any imaging? How are you going to treat her?

Case 2: Hyperthermia What do you want to know? Physical Exam? Labs? Any imaging? How are you going to treat him?