HYPERTHERMIA

 

  1. Radiation (most important), convection, conduction, evaporation are modalities through which body dissipates heat.
     
  2. Heat illness is represented by continuum  of syndromes. The following are the entities:
     
    1. Heat Edema - presents with localized swelling  to the ankle, feet, hands. Occurs in the first few days of  acclimatization (period during which Na and H2O lost from sweat, cause ¯ plasma flow to the kidneys, and consequently there is  in aldosterone production with  consequent  Na and H2O retention). It is self limiting and resolves once  the acclimatization process is over.
       
    2. Heat Tetany - associated with heat exhaustion, heat stroke,  but it can  occur in the relatively asymptomatic pt. It  is believed  to be 2ry to hyperventilation and  respiratory alkalosis.
       Heat Cramps - cramps occur in exercised muscles. Pt sweats, loses NaCl, consumes tap water Þhyponatremia ®­ muscle irritability ® cramps.
       
      Treatment c/o NS replacement & cooling  body  temperature.
       
    3. Heat Exhaustion - occurs  as a consequence of both lyte and H2O loss with resultant    dehydration and ¯ in BP and ­in pulse. Pt experiences  HA,  N/V, myalgias, lightheadedness.    Mental Status is intact and temperature is < 39C  (normothermia is more common), which are important  clues  in distinguishing  this entity from  Heat Stroke. Pts are dehydrated with ¯ BP and ­ pulse.

      Treatment : rest, cooling, hydration, lytes correction.
       
    4. Heat Stroke - occurs  2ry to exertion, chronic illness, meds/drugs ( anticholinergic, sympathetic). Temperature rises and causes  oxidative phosphorylation and enzymatic system dysfunction.  Pt classically presents with high  temperature - > 40°C ( unless cooling was provided in prehospital setting), AMS. Generally, there are less signs of dehydration . Pt also shows tachycardia ( hyperdynamic state ) and usually is normotensive.  Skin can be both dry  and warm,  or  clammy and diaphoretic.  At greater risk for organ failure are: vascular endothelium, CNS (AMS), Liver,  lungs (ARDS/NCPE), muscles (rhabdomyalisis). DIC can  occur.

DX:

  • Pt may  present only with high temperature (> 40C) and AMS and labs can be normal if organ   damage didn't occur.
     
  • ­LFT, ­ CPK. Occasionally also ­ in amylase 2ry to pancreatitis.
     
  • Pt should have an Xray to R/O ARDS, SMA to  R/O renal failure  and   PT/PTT/plt  to r/o DIC
     
  • Hematological changes can occur (purpura, GI bleed)
     
  • CT may show cerebral edema that accounts for AMS

Treatment:

  • Outcome is directly related  to the treatment during the "golden hour".
     
  • Remove pt from the environment. Ice pack, wet sheets with airflow to increase heat loss with evaporation, NGT and/or Foley irrigation with ice water.
     
  • ASA and APAP are contraindicated since oxidative phosphorylation and liver are already affected.
     
  • Core temperature should be monitored constantly  with rectal probe.
     
  •  Avoid excessive  IVF since  pt is usually normovolemic.

Complications:

  • Hypotension: Occurs because cooling redistributes fluid/blood to the core. Avoid excessive  fluids and   -agonists to correct BP. If an inotropic to be used,  Dopamine appears to be the better choice.
     
  • ARDS
     
  • DIC
     
  • ARF: 2ry to rhabdomyalisis and  hypoperfusion.
     
  • SZ: use low doses of benzo, and preferably those not metabolized by liver  such as  chlordiapoxide ( Librium).
     
  • ­ K 2ry to muscular damage.
     
  •  ¯ Ca: this normalizes on its own in 2-3 days. Avoid Ca supplementation, unless EKG or CNS changes.
      
  • ­ LFTs: from shock liver  or heat denaturation. These are universal  findings. Rx is supportive.
     
  • Shivering: occurs during cooling. This causes paradoxical rise in temperature. Rx is with IV
     
  • Benzoes or IV Chlorpromazine.

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