Hyperthermia

Question 1

Define hyperthermia

Answer 1

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

Question 2

Aetiology of hyperthermia

Answer 2

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

Question 3

Management for hyperthermia

Answer 3

Mild-moderate → only requires management to avoid potential harm e.g. stroke, TBI, hypoxic brain injury

Treat if > 41 C (adults) or > 39 C (< 3 years of age)

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)

Question 4

Define heat stroke

Answer 4

Heat stroke is hyperthermia with neurological dysfunction due to the failing thermoregulatory system

Rectal >40.6

Question 5

Clinical features of heatstroke

Answer 5

neurological dysfunction
hyperthermia
lack of sweating (may be present, especially in exertional heat stroke)
complications

hyperthermia
warm skin (or cool if shocked)
sweating often absent, but not always
CNS depression/excitation, focal neurology
vasodilatory shock decompensates as ongoing dehydration occurs
ATN causing renal failure
atraumatic rhabdomyolysis
electrolyte abnormalities: hyperglycaemia, low phosphate, high CK

Question 6

Management for heatstroke

Answer 6

rest in a cool, well-ventilated area
unlimited salted foods with cool water if drinking

A: obtain definitive airway if obtunded
B: ventilate
C: risk of shock state from dehydration and decreased myocardial function, fluid boluses 20mL/kg + maintenance, inotropes, ECMO
D: glucose management to normoglycaemia
E: monitor core and skin temperature
eliminate cause of hyperthermia
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 7

Management for rhabdomyolysis

Answer 7

maintain UO >2-3mL/kg/hr
crystalloid infusion
consider frusemide infusion 1mg/kg/h
consider mannitol 0.25-0.5g/kg
early RRT
maintain normal potassium, calcium and phosphate levels