year 4 - emergency medicine - tutorial - hypothermia

8/2/2019 Year 4 - Emergency Medicine - Tutorial - Hypothermia

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HYPOTHERMIA

Mohd Hafis Zul Arif Bin Awang01201005 0476


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Contents Introduction & Definition

Pathophysiology

History

Physical Examination

Causes Differential Diagnoses


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Introduction

Hypothermia describes a state in which thebody's mechanism for temperatureregulation is overwhelmed in the face of a

cold stressor.

Hypothermia is classified aso accidental or intentional,

o primary or secondary, and

o degree of hypothermia (mild, moderate &severe).


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ACCIDENTAL HYPOTHERMIA generallyresults from unanticipated exposure in an

inadequately prepared person;o examples include inadequate shelter for a

homeless person, someone caught in a winterstorm or motor vehicle accident, or an outdoor

sport enthusiast caught off guard by the elements. INTENTIONAL HYPOTHERMIA is an induced

stategenerally directed at neuroprotection afteran at-risk situation (therapeutic hypothermiaafter cardiac arrest,).


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PRIMARY HYPOTHERMIA is due toenvironmental exposure, withno underlying

medical conditioncausing disruption oftemperature regulation.

SECONDARY HYPOTHERMIA is low bodytemperature resultingfrom a medical illnesslowering the temperature set-point.

Many patients have recovered from severehypothermia, so early recognition and prompt

initiation of optimal treatment is paramount.

Systemic hypothermia may also beaccompanied by localized cold injury (frostbite).


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Pathophysiology The body's core temperature is tightly regulated in

the thermo neutral zone between 36.5C and37.5C, outside of which thermoregulatoryresponses are usually activated.

The body maintains a stable core temperaturethrough balancing heat production and heat loss.

At rest, humans produce 40-60 kilocalories (kcal) ofheat per square meter of body surface area through

generation by cellular metabolism, most prominentlyin the liver and the heart.

Heat production increases with striated musclecontraction; shivering increases the rate of heat

production 2-5 times.


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Mechanisms of Heat Losso Radiation 55 65% - under dry

conditions

the most significant.

o Convection & Conduction 15% are the most common causes of accidental

hypothermia

conduction is a particularly significant

mechanism of heat loss indrowning/immersion accidents as thermalconductivity of water is up to 30 times that ofair.

o Respiration & Evaporation 20%


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The hypothalamus controls thermoregulation viaincreased heat conservation (peripheralvasoconstriction and behavior responses) and heatproduction (shivering and increasing levels of thyroxineand epinephrine).

o Alterations of the CNS may impair these mechanisms.

The threshold for shivering is 1 degree lowerthan that of vasoconstriction and is considered alast resort mechanism by the body to maintaintemperature.

The mechanisms for heat preservation may beoverwhelmed in the face of cold stress and coretemperature can drop secondary to fatigue or

glycogen depletion.


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Effect of Hypothermia

Hypothermia affects virtually all organ systems.Perhaps the most significant effects are seen inthe cardiovascular system and the CNS.

o Hypothermia results in decreased

depolarization of cardiac pacemaker cells,causing bradycardia.

o Mean arterial pressure and cardiac outputdecrease

o Electrocardiogram (ECG) may showcharacteristic J or Osborne wave.

While generally associated with hypothermia, the J

wave may be a normal variant and is seenoccasionally in sepsis and myocardial ischemia.


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Osborne (J) waves (V3) in a patient with a rectal core temperature of

26.7C (80.1F).


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o Atrial and ventricular arrhythmias can resultfrom hypothermia; asystole and ventricularfibrillation have been noted to beginspontaneously at core temperatures below 25-28C.

Hypothermia progressively depresses the CNS,

decreasing CNS metabolism in a linear fashionas the core temperature drops.

At core temperatures less than 33C, brainelectrical activity becomes abnormal;

Between 19C and 20C, anelectroencephalogram (EEG) may appearconsistent with brain death.

Tissues have decreased oxygen consumption


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History

Hypothermia is usually readily apparent in thesetting of severe environmental exposure.

In elderly patients or indoor patients, or for apatientparticularly a wet patient, with exposure

to less extreme cold, the history may be subtleand less obvious.

These patients may have a higher mortality ratesecondary to a longer time to diagnosis and

increased age and fragility.

Mild or moderate hypothermia can present withmisleading symptoms, such as confusion,

dizziness, chills, or dyspnea.


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A patient's companions often note initialsymptoms in the field.

Symptoms can include mood change, irritability,poor judgment, and lassitude.

Companions may note the patient todemonstrate paradoxical undressing (a severelyhypothermic person removes clothing inresponse to prolonged cold stress) or rhythmicor repeated motions such as rocking.

Slurred speech and ataxia may mimic a stroke,alcohol intoxication, or high-altitude cerebraledema.

Similarly, profound hypothermia may present ascoma or cardiac arrest.


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In an urban environment, the use of alcohol orillicit drugs, overdose, psychiatric emergency,

and major trauma all are associated with anincreased risk of hypothermia.


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Physical Examination

The key to establishing a diagnosis ofhypothermia is rapid determination of true coretemperature.

In the emergency department, core temperature

is best measured using a low-readingtemperature probe in the bladder or rectum oran esophageal probe.

Obtaining a core temperature may help preventerroneous diagnosis for patients with an alteredmental status due to stroke, drug overdose,alcohol intoxication, or mental illness.


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Standard temperature measuring devicescommonly used for triage may lack the capability

to report unusually low temperature; obtain acore temperature reading for any patientsuspected of being significantly hypothermic.

At a given temperature, specific physicalexamination findings vary among patients.

However, an examination does provide a frameof reference for dividing presenting symptoms

into mild, moderate, and severe hypothermicsigns.


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Mild Hypothermia (32-35C)

Between 34C and 35C, most people shivervigorously, usually in all extremities.

As the temperature drops below 34C, a patientmay develop altered judgment, amnesia, and

dysarthria. Respiratory rate may increase. At approximately 33C, ataxia and apathy may

be seen. Patients generally are stablehemodynamically and able to compensate for

the symptoms.

In this temperature range, the following may alsobe observed: hyperventilation, tachypnea,

tachycardia, and cold diuresis as renalconcentratin abilit is com romised.

M d t H th i (28


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Moderate Hypothermia (28-32C)

Oxygen consumption decreases, and the CNSdepresses further; hypoventilation, hyporeflexia,decreased renal flow, and paradoxicalundressing may be noted.

Most patients with temperatures of 32C orlower present in stupor. As the core reaches temperatures of 31C or

below, the body loses its ability to generate heat

by shivering.


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At 30C, patients develop a higher risk forarrhythmias.

o Atrial fibrillation and other atrial and ventricular

rhythms become more likely.o The pulse continues to slow progressively, and

cardiac output is reduced.

o J wave may be seen on ECG in moderate

hypothermia. Between 28C and 30C, pupils may become

markedly dilated and minimally responsive tolight, a condition that can mimic brain death.


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Causes

A. Decreased Heat Production

o Endocrine derangements - hypopituitarism,hypoadrenalism, and hypothyroidism.

o Consider all these conditions in patients

presenting with unexplained hypothermia whofail to rewarm with standard therapy.

o Other causes include severe malnutrition orhypoglycemia and neuromuscularinefficiencies seen in the extremes of age.


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B. Increased Heat Loss

o Accidental hypothermia due to both immersion

etiologies and non-immersion etiologies and isthe most common form of hypothermiaencountered in the emergency department.

o Patients may present with inducedvasodilatation from pharmacologic ortoxicologic agents.

o Erythrodermas, such as burns or psoriasis,

that decrease the body's ability to preserveheat, or

o Iatrogenic etiologies, such as cold infusions,overenthusiastic treatment of heatstroke, or

emergency deliveries, may cause hypothermia


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C. Impaired Thermoregulation

o A variety of causes may be associated with

impaired thermoregulation, but, generally, it isassociated with failure of the hypothalamus toregulate core body temperature.

o This may occur with CNS trauma, strokes,toxicologic and metabolic derangements,intracranial bleeding, Parkinson disease, CNStumors, Wernicke disease, and multiple

sclerosis.


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D. Other Causes

o Miscellaneous causes include sepsis,

multiple trauma, pancreatitis, prolongedcardiac arrest, and uremia.

o Hypothermia may be related to drug

administration; such medications includebeta-blockers, clonidine, meperidine,neuroleptics, and general anesthetic

agents.o Ethanol, phenothiazines, and sedative-

hypnotics also reduce the bodys ability

to respond to low ambient temperatures.


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Differentials

Hemorrhagic Stroke Ischemic Stroke Therapeutic

Hypothermia

Alcohols Toxicity Barbiturate Toxicity

BenzodiazepineToxicity

Carbon Monoxide

Toxicity Narcotics Toxicity Ventricular Fibrillation

VentricularTachycardia


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To Be Continued

Thank You

year 4 - emergency medicine - tutorial - hypothermia

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