Hyperthermia

Question 1

Fever vs Hyperthermia

Answer 1

=>Fever
* Elevation of body temperature due to hypothalamic set-point change
* Mediated by cytokines (infection / sterile inflammation)
* Thermoregulation -> intact (body actively generates and conserves heat to reach a new set point)

=>Hyperthermia
* Elevation of body temperature due to uncontrolled heat generation and/or impaired heat dissipation
* Examples: Muscular hyperactivity, Environmental heat exposure, Drug-induced thermogenesis
* Can reach higher temperatures than fever
* Associated with direct thermal tissue injury
* Complete loss of thermoregulatory control
* Antipyretics ineffective

Answer 2

Fever is regulated hyperthermia with a raised hypothalamic set point; hyperthermia is unregulated temperature rise with loss of thermal control. Heat stroke is the most severe form of hyperthermia, defined by hyperthermia plus CNS dysfunction.

Question 3

Heat stroke- types

Answer 3

2 Types:
* Exertional
* Nonexertional

=>Exertional heat stroke
* Caused by intense physical exertioneg-
Marathon runners, Military recruits, Firefighters
* Usually associated with hot weather but can occur in cooler climates depending on exertion and clothing

=>Clinical presentation
->Core temperature >40 °C
->Central nervous system dysfunction
* Nausea / vomiting
* Irritability
* Dizziness
* Ataxia
* Seizures
* Profuse sweating often present

Question 4

Non-exertional (classic) heat stroke

Answer 4

=>Due to failure of heat dissipation
* Typically occurs during heat waves
* Associated with:
* Poor hydration
* Lack of air conditioning

=>Risk factors
*	Older age
*	Obesity
*	Diabetes
*	Cardiac disease
*	Respiratory disease
*	Cognitive impairment
*	Blunted thirst response
*	Neurological or psychiatric disease
*	Substance use disorders

->Medications increasing risk
* Anticholinergics (including antihistamines)
* Antipsychotics
* Sympathomimetics
* Diuretics
* Laxatives

Question 5

D/D for hyperthermia

Answer 5

=>Malignant hyperthermia, Neutrolept malignant syndrome,Serotonin syndrome
=>Drug overdose- Anticholinergic, sympathomimetics
=>Drug withdrawal- GABA A/B
=>Endocrine causes- Hyperthyroidism, Pheochromocytoma
=>CNS causes- Meningitis/ Encephalitis/Pontine haemorrhage/ hypothalamic diseases
=>Sepsis

Question 6

Invx

Answer 6

• Immediate BGL
• CK- Rhabdo
• CBE- leukocytosis, thrombocytopaenia
• Se electrolytes – hyperkalaemia, hypophosphataemia, hyperglycaemia
• Organ functions- RFTs, LFTs-> risk of failure
• Coags- DIC
• Urine - Myoglobin, drug screen
• PCM, Salicylate levels
• TFTs, Metanephrines
• Blood, urine, sputum cultures- sepsis
  => If indicated/ diagnosis uncertain- CTbrain/ MRI
  LP

Question 7

Resuscitation

Answer 7

A – Intubation, Ventilation if obtunded
C – risk of shock state from dehydration and decreased myocardial function -> fluid boluses of Chilled fluid if available(20mL/kg + maintenance), inotropes
D – glucose management to normoglycaemia
E:
monitor core and skin temperature
remove clothes
active cooling to < 40 C (cool environment, ice water packs, ice water lavage, cold IV fluids, fans, dialysis)
anti-pyretics useless
may require sedation and paralysis

Question 8

Temprature Monitoring

Answer 8

=>Monitor Core temperature continuously to:
* Guide active cooling
* Prevent overshoot hypothermia

=>Preferred measurement sites
* Oesophageal probe –for intubated pts
* Bladder probe – for non-intubated
* Rectal temperature-> if no alternatives (Lags behind true core temperature)

Question 9

Temperature goals

Answer 9

1). Rapid initial cooling
* Reduce core temperature to ≤38 ° as quickly as possible
2). Avoid overshoot
* Stop active cooling at 38–39 °C
3). Ongoing vigilance
* Continue temperature monitoring for ≥6 hours
* Watch for recurrent thermal instability

Answer 10

Multimodal cooling strategies should be Initiated immediately & simultaneously:
=> Internal cooling with IV crystalloid
* Rationale-> Hyperthermic patients are frequently volume depleted
* IV crystalloid:
* Restores intravascular volume
* Contributes to internal heat removal
* Cooling effect enhanced if fluids are pre-chilled
* ~0.5 °C reduction per litre

Question 11

Cooling strategies

Answer 11

=>Surface cooling-
1) Immersive ice bath
* Most effective physical cooling method
* Cooling rate: ~0.2 °C per minute
* Particularly useful in:
* Exertional heat stroke
* Requires: Close monitoring & Airway vigilance
* Rapid transition to other methods once target temperature approached

=>Evaporative cooling (if ice bath unavailable) *	Technique
*	Fully undress the patient
*	Spray with lukewarm water using spray bottle
*	Do not use cold water (reduces evaporation)
*	Direct a fan at the patient
*	Efficacy-->Cooling rate ≈ 0.1 °C/min

Question 12

Surface cooling cont..

Answer 12

=>Ice packs to high-flow areas:
* Groin
* Axillae
* Neck
* Rationale:
* Conductive heat loss > evaporative
* As ice is added, approach becomes functionally similar to immersion
* Limitations
* Ineffective if ambient humidity >70%
* May fail in non–dehumidified environments

=> External water-based cooling pads (e.g. Arctic Sun)
* Setup time delays cooling

Question 13

Other cooling methods

Answer 13

• Intravascular cooling
• Respiratory cooling via dry air- NHF/ Nasal CPAP

Question 14

Rhabdomyolysis management

Answer 14

• Aggressive IV fluids
• Aim for high urine output
• Use continuous crystalloid infusion
• Monitor:
  
  • CK
  • Renal function
  • Electrolytes- maintain K, PO4 in normal range
  • Dialysis if fails to improve/ anuric/ hyperkalemic