Question 1

College answer

Syllabus topic/section:
2.1.14 Environmental Injuries and Toxicology in ICU: Thermal injury: L1

Discussion: 

Classic heatstroke is a multi-system disorder with a variety of risk factors encompassing societal, environmental, physiological and pathological causes. Candidates that did well in part a were able to provide a range of risk factors across these different domains in a structured approach.

Most candidates presented their answer to part b) by organ systems and were able to give a reasonable amount of information with this structure. The haematological and hepatic systems were frequently omitted in answers that had lower scores despite being more common complications than some of those listed. Rhabdomyolysis was almost universally included by candidates but tends to be less common in this situation as it occurs with exertional rather than classic heatstroke. Active cooling remains the mainstay of treatment for heatstroke and in preventing or managing complications. However, it was frequently omitted or lacking in detail from answers that scored less highly. Candidates who scored higher marks included detail around the management of the various complications as well as the methods to actively cool the patient in a detailed, prioritised, tiered approach to management.
 

Discussion

suggested that the best marks would have been achieved by structuring the risk factors into "societal, environmental, physiological and pathological causes", which suggests that factors such as global warming, capitalism and the Southern Oscillation Index would have attracted marks. 

Societal factors

• Low socioeconomic index (poverty, crowding, poor access to air conditioning or well-insulated shelter)
• Inadequate access to water (eg. Indigenous remote communities)
• Inadequate warning (limited access to internet, radio)

Environmental factors:

• High temperature (obviously)
• High humidity
• Low air movement 
• Enclosed spaces; or exposed spaces (no shade)

Patient factors:

• Failure of normal thermoregulatory mechanisms (eg. use of anticholinergic drugs leads to impaired sweating).
• Male gender (women are weirdly protected from heat stroke, particularly exertional heat stroke)
• Elderly,  very young (unable to relocate)
• Abrupt exposure (insufficiently acclimatised)

Pathological risk factors:

• Intoxicated (eg. unconscious)
• Increased thermogenesis (eg. exercise, hyperthyrodism, sepsis)
• Decreased volition or mobility (eg. dementia, delirium, physical disability)
• Depressed cardiac output (CCF, on diuretics, or beta-blocked)

Now, as to management. Active cooling is the most important strategy, but it is not a specific strategy to target a specific complicaiton - rather, it targets all of the complications at the same time. This may have resulted in many candidates completely forgetting about it when writing their organ-specific management answers. So: it should be mentioned at the top:

• Active cooling is the key to successful management
•  
• Unprotected airway due to encephalopathy
  • Prevents evaporative cooling by respiration
  • Requires intubation
• Respiratory failure
  • Ventilation failure - due to increased respiratory demand, higher metabolic rate (exacerbated by the effort of respiratory muscles)
  • Improves with mechanical ventilation and paralysis
  • Oxygenation failure due to capillary leak and systemic inflammatory response - improves with PEEP and lung-protective ventilation
• Circulatory failure
  • Increased cardiac output with reduced blood flow to the splanchnic organs, distributive shock
  • Potentially, decreased cardiac output due to cardiac dysfunction
  • Potentially, hypovolemia due to dehydration
  • Improves with vasoconstrictors and volume replacement
• CNS dysfunction
  • Decreased level of consciousness; seizures
  • Improves with cooling
  • Sedation +/- antiepileptic agents
• Electrolyte derangement
  • Lost through sweat: potassium
  • Elevated due to rhabdomyolysis: potassium, phosphate
  • Elevated due to dehydration: all, but especially sodium
• Fluid shifts
  • Volume loss both as sweat, an into third spaces
  • Responds to fluid resuscitation
• Renal function
  • ATN due to decreased renal perfusion and increased renal vascular resistance
  • Often, does not respond to IV fluids
  • May require dialysis
• Gastrointestinal function
  • Reduced splanchnic blood flow can lead to patchy gut ischaemia
  • Prolonged ileus usually follows
  • TPN and prokinetics are the solution
• Liver function
  • Microthrombotic hepatic damage
  • Decreased hepatic blood flow and therefore poor synthetic and metabolic function
• DIC and MAHA
  • Haemolysis and the consumption of clotting factors
  • Anecdotally, corticosteroids and thrombomodulin have been used
• Infectious complications
  • Bacterial translocation from the gut may require broad spectrum antibiotics