Hyperthermia and Hypothermia
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Transcript of Hyperthermia and Hypothermia
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?