Heat Stroke

• Spectrum: Heat exhaustion → Heat injury → Heat stroke
• Heat stroke: Severe elevation in body temperature (>40°C) with CNS dysfunction (ataxia, delirium, seizures)
• Risk factors: Environmental variables, medications, drug use, medical comorbidities

Etiology

• Differentiate patient’s position on heat illness continuum:
  • Heat exhaustion: Cramping, fatigue, dizziness, nausea, vomiting, headache
  • Heat injury: Progression with end-organ damage
  • Heat stroke: Neurologic alteration
• Types of heat stroke:
  • Classic heat stroke: Affects elderly with chronic conditions
  • Exertional heat stroke: Affects healthy individuals during strenuous exercise in hot/humid conditions

Epidemiology

• Difficult to estimate due to lack of mandatory reporting
• U.S. (2006-2010): At least 3332 deaths from heat stroke
• Mortality correlates: Degree of temperature elevation, time to cooling, number of affected organ systems

Pathophysiology

• Efficient thermoregulation: 1°C change in core temperature for every 25°C to 30°C change in ambient temperature
• Heat-shock proteins repair hyperthermia damage
• Effective heat dissipation mechanisms:
  • Cardiac output increase
  • Splanchnic circulation vasoconstriction
  • Sweating
• High humidity (>75%): Ineffective evaporative cooling
• Inadequate water repletion → Electrolyte abnormalities (normonatremia/hypernatremia dehydration)
• Severe dehydration: Hemorrhage, brain edema, permanent brain damage
• Hyponatremia: Overcompensation with hypotonic fluids (seen in marathon runners)
• Hyperkalemia: Muscle breakdown, acidosis
• Consequences:
  • Rhabdomyolysis: Hypocalcemia, acute renal failure
  • Cardiac conduction abnormalities: QT prolongation, ST-segment changes, arrhythmias
  • Coagulopathies: Platelet aggregation, microvascular thrombosis, disseminated intravascular coagulation

History and Physical

• Common findings: Elevated core body temperature, sinus tachycardia, tachypnea, widened pulse pressure, hypotension
• Associated symptoms: Weakness, lethargy, nausea, vomiting, dizziness, flushing, lung crackles, oliguria, excessive bleeding, neurologic dysfunction
• Classic heat stroke: Hot, dry skin (anhidrosis)
• Exertional heat stroke: Prolonged sweating after exercise

Evaluation

• Frequent monitoring of vital signs
• Rectal temperature measurement
• Laboratory studies:
  • CBC, CMP, PT/PTT, blood gases, serum CPK, urine myoglobin
  • Possible toxicology screening, chest radiograph, EKG
• EKG changes: ST depression, QT prolongation, T-wave changes
• Respiratory patterns:
  • Classic heat stroke: Respiratory alkalosis
  • Exertional heat stroke: Respiratory alkalosis + lactic acidosis
• Electrolyte derangements:
  • Exertional heat stroke: Hypocalcemia, hyperphosphatemia, hyperkalemia
• Rhabdomyolysis: More common in exertional heat stroke
• Liver abnormalities: AST and ALT elevations
• Associated end-organ damage: Kidney injury, liver manifestations

Treatment / Management

General Management

• Ensure adequate airway protection, breathing, and circulation (ABCs)
• Rapid cooling is the mainstay of treatment
• Manage end-organ damage
• Intubation rarely needed as rapid cooling improves Glasgow coma scale
• Adequate rehydration essential without over-correcting sodium derangements
• Measure core temperature continuously with rectal or esophageal probe
• Stop cooling at 38-39°C
• No definitive studies support one cooling method over another

Cooling Methods

General Management

• Ensure ABCs: Airway, Breathing, Circulation
• Rapid cooling is the mainstay of treatment
• Manage end-organ damage
• Continuous core temperature monitoring with rectal or esophageal probe
• Stop cooling at 38-39°C

Cooling Methods

• Conduction and Evaporation:
  • Ice-water immersion: Most effective but may have barriers in emergency departments
  • Evaporation (mist and fan): Second most rapid cooling method
  • Ice packs: Groin, axilla, neck, and near great vessels; less effective
  • Cooled IV fluids: Studied but controversial due to potential induced shivering
• Commercially Available Products:
  • Invasive cooling catheters
  • Non-invasive adhesive pads with chilled water
  • Designed for targeted hypothermia post-cardiac arrest but usable for heat-related illnesses

Indications

• Signs of heat-related illness with elevated body temperature
• Cooling indicated even with slight temperature elevation in symptomatic patients
• Rapid decrease below 40°C, target normal range (36-38°C)

Contraindications

• Absolute contraindication: Normal or low body temperature
• Consider other etiologies (sepsis, toxic ingestion, withdrawal) for hyperthermia

Equipment

• Cooling blanket
• Cold saline
• Ice packs
• Cool water bath
• Foley catheter
• Sheets/towels
• Spray bottle and fan

Personnel

• Single provider can perform cooling techniques
• Additional personnel for faster cooling with parallel interventions

Preparation

• Expose patient completely
• Establish intravenous access
• Cardiac monitor if available
• Intra-cavitary thermometer for core temperature monitoring (esophageal, rectal, bladder probes)

Technique or Treatment

• Evaporative Cooling:
  • Cold water application via sponging or spray bottle
  • Fan to increase evaporation rate
  • Cold water-soaked sheet wrapping
• Ice Pack Application:
  • Groin, axillae, neck, torso
  • Frequent ice pack changes
• Cold Saline:
  • Infusion with monitoring for shivering
  • Bladder irrigation via Foley catheter
• Water Bath:
  • Optimal temperature: 26.7°C (90°F)
  • Colder temperatures may induce shivering

Complications

• Monitor vital signs closely
• Watch for shivering, which hinders cooling
• Risk of hypothermia (body temperature <36°C)
  • Hypothermia complications: Arrhythmias, coagulopathy
• Skin damage from prolonged ice exposure
  • Mitigation: Cover ice packs with towel/sheet, adjust application site regularly

Pharmacologic Adjuncts

• Dantrolene: No effect on patient outcomes in heat stroke
• High-dose benzodiazepines: May blunt shivering reflex, decrease oxygen consumption; not universally recommended but may benefit agitated, shivering patients
• Antipyretics: No role, potentially toxic to liver

Differential Diagnosis

• Polypharmacy
• Toxic ingestions
• Meningitis
• Sepsis
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Malaria
• Detailed medication review to exclude other diseases
• Muscle rigidity/clonus distinguishes neuroleptic malignancy and serotonin syndrome

Prognosis

• Mortality varies by etiology:
  • Exertional heat stroke: 3-5% mortality
  • Classic heat stroke: 10-65% mortality
• Higher mortality in classic heat stroke due to comorbidities and older age
• Immediate rapid cooling can result in zero-fatality rate for young exertional heat-stroke patients

Complications

• Persistent CNS dysfunction
• Injury to gut, kidney, skeletal muscle, other organs
• Complications:
  • Acute respiratory distress syndrome
  • Disseminated intravascular coagulation
  • Acute kidney injury
  • Hepatic injury
  • Hypoglycemia
  • Rhabdomyolysis
  • Seizures
• Recovery may take longer than 7 weeks even for reversible complications

Deterrence and Patient Education

• Prevention is key:
  • Check on elderly frequently
  • Ensure access to air-conditioning
  • Wear appropriate clothing
  • Avoid leaving children unattended in cars
  • Reschedule strenuous activities in hot/humid weather
  • Seek shade if experiencing signs of heat stroke
• Rapid cooling and careful monitoring once diagnosed
• Abstain from exercise for at least 7 days after exertional heat stroke
• Follow-up a week after presentation to screen for end-organ damage

Enhancing Healthcare Team Outcomes

• Early recognition and rapid cooling essential
• Prepare designated areas with cooling equipment in anticipation of heatwaves
• Use available resources effectively for cooling (evaporative, ice-bath, etc.)
• Coordinate closely with nursing staff for continuous monitoring and stopping cooling at 38-39°C
• Cardiac monitoring and consultation with intensivists if end-organ damage present
• Avoid empiric use of dantrolene and benzodiazepines until further studies
• Expedite rapid cooling as the most effective treatment to limit mortality (Level 1 evidence)