Back to Basics Thermias Dr Chow 2011.ppt

8/14/2019 Back to Basics Thermias Dr Chow 2011.ppt

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Hyperthermiaand

Hypothermia

Back to BasicsApril 2011

Dr. J. Clow, ER


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Case 2:

85 y.o. male

Mid-August, during heat wave

Son goes to apartment and finds patientconfused and lethargic

Patient unable to give history


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Heat Regulation

Four mechanisms of heat loss/dissipation:

Radiation

Convection

Conduction

Evaporation


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Radiation

Physical transfer of heat between thebody and the environment by

electromagnetic waves 65% of heat transfer under normal

circumstances

Modified by insulation (clothing, fat layer),cutaneous blood flow


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Convection

Energy transfer between the body and agas or liquid

Affected by temperature gradient, motionat the interface, and liquid

Not usually a major source for heat loss or

dissipation, but this increases with windand body motion


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Evaporation

Most important source of cooling underextreme heat stress; important for

hypothermia when in wet environment 25% of heat loss in temperate/cool

conditions may be increased significantly

by sweating, increased respiratory rateAffected by relative humidity and clothing


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Hypothermia


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Definition

Core body temperature less than 35oC

Mild: 32.2 - 35oC

Moderate: 28 - 32.2oC

Severe: < 28oC


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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)


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Predisposing Factors

Risk Factors for HypothermiaAge extremes

Elderly

Neonates

Outdoor exposure

Occupational

Sports-related

Inadequate clothing

Drugs and intoxicants

Ethanol

Phenothiazines

Barbiturates

AnestheticsNeuromuscular blockers

Others

Endocrine-related

Hypoglycemia

Hypothyroidism

Adrenal insufficiency

Hypopituitarism

Neurologic-related

Stroke

Hypothalamic disorders

Parkinson's disease

Spinal cord injury

Multisystem

MalnutritionSepsis

Shock

Hepatic or renal failure

Burnsand exfoliative dermatologic disorders

Immobilityor debilitation


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Signs and SymptomsClinical Manifestations of HypothermiaSystem Mild Hypothermia Moderate Hypothermia Severe HypothermiaCNS Confusion, slurred speech,

impaired judgment,

amnesiaLethargy, hallucinations, loss of

pupillary reflex, EEG

abnormalitiesLoss of cerebrovascular

regulation, decline in

EEG activity, coma,

loss of ocular reflexCVS 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 (< 28C)

& asystole (< 20C)

Respiratory Tachypnea, bronchorrhea Hypoventilation (decreased rateand tidal volume),

decreased oxygen

consumption and CO2

production, loss of cough

reflex

Pulmonary edema, apnea


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Signs and Symptoms, contdTABLE 110-2. Clinical Manifestations of Hypothermia, contdSystem Mild Hypothermia Moderate hypothermia Severe HypothermiaRenal Cold diuresis Cold diuresis Decreased renal perfusion

and GFR, oliguriaHematologic Increased hematocrit,

decreased platelet &

white blood cell

counts, coagulopathy,

DICGI Ileus, pancreatitis, gastric

stress ulcers, hepatic

dysfunctionMetabolic Increased metabolic rate,

hyperglycemia Decreased metabolic rate,hyper- or hypoglycemiaMusculoskeletal Increased shivering Decreased shivering (< 32C,

90F), muscle rigidity Patient appears dead,"pseudo-rigormortis"


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History

Often from bystanders/medics

Circumstances surrounding exposure

Where, submersion, ambient temperature?

Length of exposure

Mental status changes

Any predisposing illnessacute/chronic?

Alcohol/drugs?


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Physical Exam

Vitals

Temperaturewant a core temperature

Where do we take it?

Signs of other injuries?

Can you find the cause of hypothermia?

Any focal findings?

Esp. neurologic, cardiovascular, respiratory


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Diagnositics

ECG (always), CXR (most patients)

Other tests 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, LFTs, lipase/amylase, cultures


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ECG Changes

May see J waves

late, terminal upright deflection of QRS

complex; best seen in leads V3-V6

Multiple arrhythmias

Heart block

Atrial fibrillationVentricular fibrillation


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ECG Changes, contd


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Management


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Interventions

Airway: need for intubation?

Breathing: spontaneous respiration? Warmed humidified oxygeneither through

an ETT, or via mask

Circulation: pulse? BP?

Large IVswarmed IV fluidsArrhythmiaswhen do we treat?

CPR?


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Interventions, contd

Disability

GCS

Glucoscan, narcan, thiamine

C-spine immobilization prn

Exposure

Undress, assess for trauma

Re-cover quickly


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Rewarming

Rewarming TechniquesPassive rewarming:

Removal from cold environment

Insulation, Warm blankets (e.g. Bair hugger)

Active external rewarming:

Warm water immersionHeating 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


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Rewarming - ExtracorporealOptions for Extracorporeal RewarmingExtracorporeal Rewarming

(ECR) Technique ConsiderationsVenovenous (VV) CircuitCV catheter to CV or peripheral catheter

No oxygenator/circulatory support

Flow rates 150-400 mL/min

ROR 2-3C/hHemodialysis (HD) Circuitsingle-or dual-vessel cannulation

Stabilizes electrolyte or toxicologic abnormalities

Exchange cycle volumes 200-500 mL/min

ROR 2-3C/hContinuous arteriovenous rewarming

(CAVR) Circuitpercutaneous 8.5 Fr femoral cathetersRequires BP 60 mmHg systolicNo perfusionist/pump/anticoagulation

Flow rates 225-375 mL/min

ROR 3-4C/hCardiopulmonary bypass (CPB) Circuitfull 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.


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Hyperthermia


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Spectrum

Heat cramps

Cramps in big musclesspasms

Normal temperature, mentation

Caused by dilutional hyponatremia (hypotonicfluid replacement)


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Spectrum, contd

Heat exhaustion

Weakness, dizziness, headache, syncope

Nausea, vomiting

Temperature 39-41.1oC

Normal mentation

Profuse sweating


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Spectrum, contd

Heat Stroke

Temperature >41.1oC

Coma, seizures, confusion

No sweating

Classic triad: hyperpyrexia, CNS dysfunction,

anhidrosis Mortality of 10-20% withtreatment

Classic vs. Exertional


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Spectrum, contd

Heat Stroke:

Classic (non-exertional):

Persistent environmental exposure Impaired thermoregulation

Exertional:

Heavy exercise in setting of high temperature andhumidity


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Causes of Hyperthermia

Increased heat load

Heat absorption from environment

Heat stroke (exertional, classic)

Metabolic heat

Diminished heat dissipation

Obesity, anhidrosis, drugs Sepsis


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Predisposing Factors

Predisposing Factors for Heat StrokeIncreased Heat Production Decreased Heat LossEnvironmental heat stress Environmental heat stressExertion

Cardiac disease

Fever Peripheral vascular diseaseHypothalamic dysfunction DehydrationDrugs (sympathomimetics) Anticholinergic drugsHyperthyroidism Obesity

Skin diseaseEthanol Blockers


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Causes of HyperthermiaCauses 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


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Differential Diagnosis

Differential Diagnosis of HeatstrokeDrug toxicity: anticholinergic toxicity, stimulant toxicity (phencyclidine, cocaine,

amphetamines, ephedrine), salicylate toxicity

Drug withdrawal syndrome: ethanol withdrawal

Serotonin syndromeNeuroleptic 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


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Diagnostics

ECG (all), CXR (most)

Imaging guided by history

CBC, electrolytes, renal function, LFTs, Ca,Mg, PO4, coags, CK

Urinemyoglobin

Pan-cultures


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Poor prognostic factors

Temperature > 41.1oC

AST > 1000

Coma

Rhabdomyolysis

Renal Failure

Hypotension


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Treatment

ABCs!!!

Remove to cool environment!

Active cooling

Correct fluid and electrolyte imbalances

Supportive care


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TreatmentComparison of Cooling TechniquesTechnique Advantages DisadvantagesEvaporative

(i.e. wet the patients gown,

sheets then use fan)

Simple, Readily available

Noninvasive

Easy patient access

Relatively effective

Shivering

Difficult to maintain monitoring electrodes in position

Immersion

(in cold/ice water)

Noninvasive

Relatively effective

Shivering, Cumbersome

Poorly toleratedLogistically difficult to access

Difficult to maintain monitoringIce packing (cover w/ ice) Noninvasive

Readily available ShiveringPoorly toleratedStrategic ice packs Noninvasive

Readily available

Combined with other techniquesShivering

Poorly tolerated

Medium efficiencyCold gastric lavage Generally available Invasive

Labor intensive

Potential for water intoxication

May require airway protection

Limited human experienceCold peritoneal lavage Theoretically beneficial Invasive

Limited human experience


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Complications of Heat StrokeComplications of Heatstroke

Immediate DelayedVital signs Hypotension

HypothermiaovershootHyperthermic rebound

Muscular ShiveringRhabdomyolysis

Neurologic DeliriumSeizuresComa

Cerebral edema

Cardiac Heart failurePulmonary Pulmonary edema Acute respiratory distress syndromeRenal Oliguria Renal failureGastrointestinal Diarrhea Hepatic necrosis

Mucosal gastrointestinal hemorrhageMetabolic Hypokalemia

Hypernatremia HyperkalemiaHypocalcemiaHyperuricemia

Hematologic ThrombocytopeniaDisseminated intravascular coagulation


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Back to the cases


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Case 1: Hypothermia

What do you want to know?

Physical Exam?

Labs?

Any imaging?

How are you going to treat her?


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Case 2: Hyperthermia

What do you want to know?

Physical Exam?

Labs?

Any imaging?

How are you going to treat him?

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Back to Basics Thermias Dr Chow 2011.ppt