Hyperthermia

OVERVIEW

Definitions

  • Hyperthermia is when core temperature exceeds that normally maintained by homeostatic mechanisms
  • Fever  or pyrexia is an elevation of body temperature above the normal range of 36.5–37.5 °C (97.7–99.5 °F) due to an increase in the temperature regulatory set point
  • Uncontrolled hyperthermia differs from fever in that the body temperature is elevated above the thermoregulatory set point due to excessive heat production and/or insufficient heat dissipation

PATHOPHYSIOLOGY

  • sensor-central controller effector mechanism involving autonomic nervous system
  • temperature sensors -> hypothalamus -> cold defenses (vasoconstriction, piloerection, behavioural, shivering, sweating)

CAUSES

  • endogenous
  • exogenous

OR

  • infections
  • non-infectious

OR

  • excessive heat production:
    exertional, MH, NMS, thyrotoxicosis, phaeochromocytoma, drug intoxication (sympathomimetic, serotonergic), seizures
  • diminished heat dissipation:
    heat stroke, dehydration, autonomic dysfunction, NMS, anticholinergic poisoning (may be exacerbated by heart failure)
  • hypothalamic dysfunction:
    CVA, encephalitis, trauma, granulomatous disease, NMS

EFFECTS

Fever

  • increased Q and HR
  • increased metabolic rate with O2 consumption and CO2 production

Heat stroke

  • altered mental state, seizures, coma
  • rhabdomyolysis
  • DIC
  • liver failure
  • renal failure

MANAGEMENT

Goals

(1) seek and treat underlying cause
(2) lower temperature if required (aim to cool to 39C in most settings)

> 40 C

  • potentially dangerous
  • treat if > 41 C (adults) or > 39 C (< 3 years of age)

Mild to Moderate hyperthermia

  • may be protective (e.g. in sepsis)
  • normalisation of temperature only required to avoid potential harm (e.g. stroke, TBI, hypoxic brain injury)

Practical Aspects

  • physical cooling:
    — surface (may cause shivering): take off clothes, tepid water sprays and fanning, ice packs (axillae, groin, neck), cooling garments and blanket
    — immersion is effective, but not suitable for sick patients and can cause vasoconstriction and impair central heat dissipation
    — cold IV fluids (see therapeutic hypothermia)
    — invasive: lavage (bladder, gastric, peritoneal, pleural), intravascular cooling catheters, RRT and ECMO/ bypass
  • pharmacological:
    — paracetamol, aspirin, NSAIDs (no evidence of benefit in heat stroke)
    — neuromuscular blockade if toxicological cause (e.g. serotonin syndrome) or increased muscular activity (e.g. seizure)
    — dantrolene for MH (not beneficial for heat stroke)

Supportive care and monitoring

  • oesophageal probe preferably in critically ill

Seek and treat underlying cause and complications


References and Links

LITFL

Journal articles

  • Grogan H, Hopkins PM. Heat stroke: implications for critical care and anaesthesia. Br J Anaesth. 2002 May;88(5):700-7. PMID: 12067009
  • Hadad E, Cohen-Sivan Y, Heled Y, Epstein Y. Clinical review: Treatment of heat stroke: should dantrolene be considered? Crit Care. 2005 Feb;9(1):86-91. Epub 2004 Aug 11. PMC1065088.
  • Leon LR, Helwig BG. Heat stroke: role of the systemic inflammatory response. J Appl Physiol. 2010 Dec;109(6):1980-8. PMID: 20522730.
  • Musselman ME, Saely S. Diagnosis and treatment of drug-induced hyperthermia. Am J Health Syst Pharm. 2013 Jan 1;70(1):34-42. PMID: 23261898

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health, a Clinical Adjunct Associate Professor at Monash University, and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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