Background
• Spectrum of heat-related illnesses including heat rash, cramps, syncope, stroke
Approach
• Careful hx: Determine etiology of hyperthermia: External (environmental) or internal (toxic/metabolic) factors, environmental hypothermia can occur even in absence of exertion (malnourished pt, chronically ill, elderly)
• Look for medication related hyperthermia: MH, NMS, etc.
• Use rectal thermometer to determine core temperature
EXTERNAL HEAT EMERGENCIES
Heat Cramps
History
• Brief, intermittent, severe muscle cramping usually following cessation of strenuous activity. Often in abdominal or calf muscles.
Findings
• Euthermic, clinical signs of dehydration
Evaluation
• Chem 7 (↓ Na, ↓ Cl), UA electrolytes optional (↓ urinary Na & Cl from sweating)
Treatment
• Oral salt or electrolyte repletion tablets or drinks (Gatorade); IV hydration rarely required
Disposition
• Home after observation for sx relief
Pearl
• Related to electrolyte deficiency; electrolyte enhanced sports drinks may be helpful although may cause diarrhea due to the high sugar content
Heat Edema
History
• Swollen feet/ankles after long periods of sitting/standing due to hydrostatic pressure, vasodilation & orthostatic pooling → vascular leak, interstitial fluid accumulation
• No underlying hepatic, lymphatic, cardiac, or venous dz
Findings
• Euthermic, B LE pitting edema w/o signs of CHF or renal failure
Evaluation
• Chem 7, UA for proteinuria, CXR for pulm edema, ECG for e/o LVH, RH strain
Treatment
• Elevate lower extremities, provide support hose
• No evidence that diuretics help
Disposition
• Home after reassurance, PCP f/u
Pearl
• Dx of exclusion
Heat Rash (Prickly Heat, Miliaria, Lichen Tropicus)
History
• Sweat-gland blockage w/ localized inflammatory response
• Often seen in pts newly arrived to subtropical/tropical areas or during heat waves
Findings
• Euthermic, erythema w/ pruritic vesicles, primarily in intertriginous areas, then becomes anhidrotic
• Occasionally will become superinfected, usually Staph
Evaluation
• None
Treatment
• Treat pruritus: Benadryl 25–50 mg PO or Atarax 25 mg PO
• Desquamate skin w/ chlorhexidine antibacterial soap or salicylate-containing topical scrub
Disposition
• Home, PCP f/u
Pearl
• Avoid routine talcum powder application, which may block sweat glands
Heat Syncope
History
• Syncopal event in warm/humid weather or following strenuous activity
• Heat → vasodilation → peripheral intravascular blood pooling, ↓ central venous return
Findings
• Euthermic, nl exam
Evaluation
• For other causes of syncope (see 1c)
• Syncope/presyncope sx should resolve w/i 30 min, if not consider further w/u
Treatment
• PO or IV hydration
Disposition
• Home, PCP f/u
Pearl
• Dx of exclusion, diagnose only in young healthy pts w/ no cardiac dz
Heat Exhaustion
History
• Gradual onset, extreme fatigue in warm/humid weather following strenuous activity, profuse sweating, dizziness, N/V; often pale w/ cool, moist skin
• Inadequate PO intake
Findings
• Mild hyperthermia, may reach 40°C (104°F), nl mental status
Evaluation
• Chem 7 for electrolyte imbalance, UA (rhabdomyolysis uncommon)
Treatment
• IV hydration (PO if pt tolerates), replace w/ NS (or alternate w ½ NS if ↑ Na)
Disposition
• Observation w/ continued hydration until normothermic w/ good UOP
Pearl
• No value w/ fever-reducing medications
Heat Stroke
History
• Acute onset when compared to heat exhaustion
• Classic: Occurs during heat waves, affects susceptible pts: Elderly, chronically ill, scleroderma, CF, burns, alcoholics, homeless, mentally ill, on diuretics or Anti-Chol
• Exertional: Occurs in pts who are overwhelmed by heat overproduction: Athletes, military recruits, thyroid storm, pheochromocytoma, sympathomimetic overdose
Findings
• Hyperthermia >41°C/106°F, CNS Dysfxn: Confusion, disorientation, delirium
• Classic: Anhidrotic, tachypnea
• Exertional: Diaphoretic until “sweat gland fatigue”
• Muscles usually flaccid in HS, if rigid consider NMS, etc.
Evaluation
• Chem 7 (electrolyte imbalance, ↓ blood sugar), LFTs (hepatic damage common), coags (DIC possible but uncommon), CK & UA (rhabdomyolysis common in exertional heat stroke)
Treatment
• Aggressive fluid resuscitation: Cooling procedures → vasoconstriction, ↑ BP so may need to guide fluid status by UOP, US, CVP, etc.
• Rapid cooling indicated, ↓ by 0.2°C/min → 39°C/102.2°F to avoid overshooting
• Ice water immersion: Can ↓ core temp in 10–40 min
• Evaporation: Spray water mist & use fan, maintains cutaneous vasodilation, avoids heat generation by shivering, 7× more efficient than ice packing but 2× as fast
• Adjunctive cooling strategies: Strategic ice packs near large blood vessels (ant neck, axilla, groin), ice water gastric lavage at NS 200 mL/h
• Mannitol 50–100 g IV ↑ renal blood flow, ↓ cerebral edema
• Treat rhabdomyolysis w/ IVF, HD if aneuric, tx coagulopathy w/ FFP
Disposition
• Admit for ongoing tx & cooling
Pearls
• Avoid alcohol sponge baths, dantrolene
• Avoid antipyretics (APAP damages liver, salicylates aggravate bleeding)
• Avoid α-adrenergic drugs (promote vasoconstriction, ↑ hepatic/renal damage, CO same)
• Avoid atropine/anticholinergics that ↓ sweating; use BZD to stop shivering
• Avoid neuroleptics (chlorpromazine): ↓ sz threshold, interfere w/ thermoregulation, etc.
INTERNAL HEAT EMERGENCIES
Malignant Hyperthermia (MH)
History
• Acute ↑ body temp after administration of inhaled anesthetic or succinylcholine
• Genetic abnlty of skeletal muscle sarcoplasmic reticulum → inappropriate Ca release → severe tetany & spasm (heat); often FH of adverse rxn to anesthesia
Findings
• Acute hyperthermia after anesthetic, hypercapnia (early sign), muscular rigidity, masseter muscle spasm, acidosis, tachycardia, rhabdomyolysis
Evaluation
• Check core temp, electrolytes, CK
Treatment
• Stop offending agent, increase ventilation rate, Dantrolene 2.5 mg/kg bolus IV, repeat doses of 1 mg/kg until sxs subside; (MH protocols)
Disposition
• Usually occurs in OR, admission for supportive care
Pearl
• MH hotline: 1-800-MH-HYPER (1-800-644-9737), ask for “Index Zero”
Neuroleptic Malignant Syndrome (NMS)
History
• Antipsychotic use (phenothiazines, butyrophenones, thioxanthenes, lithium, TCAs); recent initiation or dose ↑ (²⁄³ of cases in 1st wk)
• Antiparkinson medication withdrawal
• Dopamine receptor blockade → severe muscle spasticity & dystonia, heat overproduction, pathology similar to MH
Findings
• Triad: Hyperthermia, muscular rigidity (lead pipe), autonomic Dysfxn
• AMS, dyskinesia, tachycardia, dyspnea, diaphoresis, dysphagia, tremor, incontinence
Evaluation
• UA for myoglobin, CK for rhabdomyolysis, ↑ WBC, Chem, tox
Treatment
• Stop offending agent, dantrolene (as for MH), whole body cooling w/ evaporating fans
• Dopamine antagonists (bromocriptine 2.5 mg PO q8h, amantadine 200 mg PO q12h)
• Supportive tx: IVF, BP control, BZD
• Treat rhabdomyolysis w/ IVF, alkaline urine (pH > 6.5) to ↑ myoglobin excretion
• Keep Na in IVF close to 154 mEq/L; add NaHCO3
Disposition
• Admission; mortality 10–20%
Pearl
• NMS hotline: 1-888-667-8367
Serotonin Syndrome (SS)
History
• Drug & food interactions: MAOI + tyramine (found in aged cheese, wine, etc.); caused by excessive serotonin activity in spinal cord & brain
Findings
• Hunter criteria: Combination of clonus, hyperthermia, agitation, diaphoresis, ocular clonus, hyperreflexia, tremor, hypertonia
• Diarrhea, cramps, hypersalivation (similar to NMS), autonomic Dysfxn
Evaluation
• UA for myoglobin, CK for rhabdomyolysis, CBC, Chem, tox
• Clinical dx, must confirm h/o 2 serotonic agents, r/o toxic, metabolic, infection cause
Treatment
• Stop offending agent, supportive tx, control HTN, whole body cooling, treat rhabdomyolysis w/ IVF
• BZD: Ativan 2 mg IV q20–30min prn
• Dantrolene not recommended: May ↑ central serotonin metabolism & production
• Nonspecific serotonin inhib: Cyproheptadine 12 mg PO then 2 mg PO q2h
Disposition
• Admission; most resolve w/ no sequelae in 24–36 h after starting tx
Pearl
• Pts must stop MAOI for 6 wk prior to starting SSRI