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 19th)

• 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 35oC– Mild: 34-36oC– Moderate: 30-34oC– Severe: < 30oC

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 NeonatesOutdoor exposure Occupational Sports-related Inadequate clothingDrugs and intoxicants Ethanol Phenothiazines Barbiturates Anesthetics Neuromuscular blockersOthers

Endocrine-related Hypoglycemia Hypothyroidism Adrenal insufficiency HypopituitarismNeurologic-related Stroke Hypothalamic disorders Parkinson's disease Spinal cord injuryMultisystem Malnutrition Sepsis Shock Hepatic or renal failureBurns and exfoliative dermatologic disordersImmobility or debilitation

Signs and Symptoms

TABLE 110-2. Clinical Manifestations of Hypothermia

System Mild Hypothermia Moderate Hypothermia Severe Hypothermia

CNS Confusion, 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

CVS Tachycardia, 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)

Respiratory Tachypnea, bronchorrhea Hypoventilation (decreased rate and tidal volume), decreased oxygen consumption and CO2

production, loss of cough reflex

Pulmonary edema, apnea

Signs and Symptoms, cont’d

TABLE 110-2. Clinical Manifestations of Hypothermia, cont’d

System Mild Hypothermia Moderate hypothermia Severe Hypothermia

Renal Cold diuresis Cold diuresis Decreased renal perfusion and GFR, oliguria

Hematologic Increased hematocrit and decreased platelet, white blood cell count, coagulopathy, and DIC

   

GI Ileus, pancreatitis, gastric stress ulcers, hepatic dysfunction

   

Metabolic endocrine

Increased metabolic rate, hyperglycemia

Decreased metabolic rate, hyper- or hypoglycemia

 

Musculoskeletal Increased shivering Decreased 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 192-3 Rewarming Techniques

Passive rewarming: Removal from cold environment Insulation, Warm blanketsActive external rewarming: Warm water immersion Heating blankets set at 40°C Radiant heat Forced airActive core rewarming at 40°C: Inhalation rewarming Heated IV fluids GI tract lavage Bladder lavage Peritoneal lavage Pleural lavageExtracorporeal 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) Technique Considerations

Venovenous (VV) Circuit — CV catheter to CV or peripheral catheterNo oxygenator/circulatory supportFlow rates 150-400 mL/minROR 2°-3°C/h

Hemodialysis (HD) Circuit — single-or dual-vessel cannulationStabilizes electrolyte or toxicologic abnormalitiesExchange cycle volumes 200-500 mL/minROR 2°-3°C/h

Continuous arteriovenous rewarming (CAVR)

Circuit — percutaneous 8.5 Fr femoral cathetersRequires BP 60 mmHg systolicNo perfusionist/pump/anticoagulationFlow rates 225-375 mL/minROR 3°-4°C/h

Cardiopulmonary bypass (CPB) Circuit — full circulatory support with pump and oxygenatorPerfusate-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 > 38oC

• 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 111-1. Predisposing Factors for Heat Stroke

Increased Heat Production Decreased Heat Loss

Environmental heat stress Environmental heat stress

Exertion Cardiac disease

Fever Peripheral vascular disease

Hypothalamic dysfunction Dehydration

Drugs (sympathomimetics) Anticholinergic drugs

Hyperthyroidism Obesity

  Skin disease

  Ethanol

  β Blockers

Causes of Hyperthermia…TABLE 16-1 Causes of Hyperthermia Syndromes

HEAT STROKEExertional: Exercise in higher-than-normal heat and/or humidityNonexertional: Anticholinergics, including antihistamines; antiparkinsonian drugs; diuretics; phenothiazines

DRUG-INDUCED HYPERTHERMIAAmphetamines, cocaine, phencyclidine (PCP), methylenedioxymethamphetamine (MDMA; "ecstasy"), lysergic

acid diethylamide (LSD), salicylates, lithium, anticholinergics, sympathomimetics

NEUROLEPTIC MALIGNANT SYNDROMEPhenothiazines; butyrophenones, including haloperidol and bromperidol; fluoxetine; loxapine; tricyclic

dibenzodiazepines; metoclopramide; domperidone; thiothixene; molindone; withdrawal of dopaminergic agents

SEROTONIN SYNDROMESelective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), tricyclic

antidepressants

MALIGNANT HYPERTHERMIAInhalational anesthetics, succinylcholine

ENDOCRINOPATHYThyrotoxicosis, pheochromocytoma

CENTRAL NERVOUS SYSTEM DAMAGECerebral hemorrhage, status epilepticus, hypothalamic injury

Differential Diagnosis

TABLE 193-1 Differential Diagnosis of Heatstroke

Drug toxicity: anticholinergic toxicity, stimulant toxicity (phencyclidine, cocaine, amphetamines, ephedrine), salicylate toxicity

Drug withdrawal syndrome: ethanol withdrawalSerotonin syndromeNeuroleptic malignant syndromeGeneralized infections: bacterial sepsis, malaria, typhoid fever, tetanusCentral nervous system infections: meningitis, encephalitis, brain abscessEndocrine derangements: diabetic ketoacidosis, thyroid stormNeurologic: 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 39-41.1oC– Normal mentation– Profuse sweating

Signs and Symptoms, cont’d

• Heat Stroke– Mortality of 10-20% with current treatment– Coma, seizures, confusion– No sweating– Temperature >41.1oC– 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 > 41.1oC

• AST > 1000

• Coma

• Rhabdomyolysis

• Renal Failure

• Hypotension

Treatment

• ABC’s!!!

• Cooling

• Remove to cool environment!

• Correct fluid and electrolyte imbalances

TreatmentTABLE 193-2 Comparison of Cooling Techniques

Technique Advantages Disadvantages

Evaporative 

Simple, Readily availableNoninvasiveEasy patient accessRelatively effective

ShiveringDifficult to maintain monitoring electrodes in position

Immersion NoninvasiveRelatively effective 

Shivering, CumbersomePoorly toleratedLogistically difficult to accessDifficult to maintain monitoring

Ice packing 

NoninvasiveReadily available

ShiveringPoorly tolerated

Strategic ice packs 

NoninvasiveReadily availableCombined with other techniques

ShiveringPoorly toleratedMedium efficiency

Cold gastric lavage   

Generally available    

InvasiveLabor intensivePotential for water intoxicationMay require airway protectionLimited human experience

Cold peritoneal lavage 

Theoretically beneficial InvasiveLimited human experience

Complications of Heat StrokeTABLE 193-3 Complications of Heatstroke

  Initial Delayed

Vital signs  

HypotensionHypothermia overshootHyperthermic rebound

   

Muscular 

ShiveringRhabdomyolysis

  

Neurologic  

DeliriumSeizuresComa

Cerebral edema  

Cardiac Heart failure  

Pulmonary Pulmonary edema Acute respiratory distress syndrome

Renal Oliguria Renal failure

Gastrointestinal 

Diarrhea 

Hepatic necrosisMucosal gastrointestinal hemorrhage

Metabolic  

HypokalemiaHypernatremia 

HyperkalemiaHypocalcemiaHyperuricemia

Hematologic 

  

ThrombocytopeniaDisseminated 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?