Pocket Emergency Medicine (Pocket Notebook Series) 3rd Ed.

HYPERTHERMIA

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



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