Heat Stroke Associated Acute Kidney Injury

Heat stroke associated acute kidney injury is kidney failure complicating heat stroke, a life threatening illness defined by core temperature above 40 degrees Celsius with central nervous system dysfunction (delirium, seizures, coma). It occurs in 25% to 35% of exertional heat stroke and in 5% to 25% of classical (non-exertional) heat stroke, and is more common in older adults, children and workers or athletes exposed to prolonged heat. Mortality is high when cooling is delayed beyond 30 minutes.

Types:

• Exertional heat stroke: young, fit individuals (athletes, military recruits, labourers) with sudden onset during vigorous activity, often with sweating, rhabdomyolysis and early multi-organ failure
• Classical heat stroke: older adults, children, people with chronic illness or taking anticholinergics, diuretics, antipsychotics, beta blockers or stimulants, during heat waves; skin may be dry

Mechanisms of kidney injury:

• Severe volume depletion from sweating, reduced intake and vasodilation, with redirection of cardiac output to the skin
• Direct thermal injury to tubular cells and endothelium
• Rhabdomyolysis (exertional): myoglobin cast nephropathy and tubular toxicity
• Systemic inflammatory response, endotoxaemia from gut ischaemia, disseminated intravascular coagulation and thrombotic microangiopathy
• Hypotension, shock, hepatic failure with hepatorenal physiology
• Hyperuricaemia, hypokalaemia (chronic heat exposure) and chronic kidney disease of unknown aetiology in recurrent exposure (agricultural workers)

• Core temperature above 40 degrees Celsius (rectal or oesophageal), tachycardia, tachypnoea, hypotension
• Neurological: confusion, agitation, ataxia, seizures, coma
• Skin hot and flushed; sweating present or absent
• Oliguria, dark urine, muscle pain and swelling in exertional cases
• Vomiting, diarrhoea, hepatic injury with jaundice and transaminases above 1000 U/L at 24 to 72 hours
• Bleeding from disseminated intravascular coagulation; respiratory distress syndrome
• Electrolytes: hyperkalaemia, hypocalcaemia, hyperphosphataemia, lactic acidosis, hypernatraemia (classical) or hyponatraemia (exertional with water overload), hypoglycaemia

Red flags: core temperature above 41.5 degrees Celsius, Glasgow Coma Scale below 9, seizures, shock, creatine kinase above 20 000 U/L, potassium above 6.0 mmol/L, lactate above 5 mmol/L, INR above 2.0, platelets below 50 x 10^9/L, oliguria, hepatic encephalopathy.

• Clinical diagnosis: core temperature above 40 degrees Celsius with neurological dysfunction after heat exposure or exertion; measure rectal or oesophageal temperature, not oral or axillary.
• Creatinine, urea, electrolytes (sodium, potassium, calcium, phosphate, magnesium), glucose, bicarbonate, lactate, blood gas.
• Creatine kinase (peaks at 24 to 72 hours), liver function (ALT, AST), INR, fibrinogen, D-dimer, platelets, full blood count.
• Urinalysis for myoglobin and tubular casts; urine output hourly.
• ECG, troponin, chest radiograph, CT head if focal signs or atypical course.
• Toxicology screen (stimulants, anticholinergics, salicylates) and infection screen; exclude sepsis, malignant hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, thyroid storm, meningitis, cerebral malaria.

Differentials: sepsis, malaria, drug induced hyperthermia (cocaine, amphetamine, salicylate), thyroid storm, status epilepticus, intracranial haemorrhage.

Immediate cooling (the dominant intervention): cool first, transport second

• Cold water immersion (water at 1 to 15 degrees Celsius, with stirring) for exertional heat stroke, achieving a cooling rate above 0.15 degrees Celsius/min, until core temperature is 38.5 to 39 degrees Celsius; then stop to avoid overshoot hypothermia.
• If immersion is not possible: ice-water-soaked sheets and towels rotated every 2 to 3 minutes, ice packs to neck, axillae and groin, plus fans; evaporative cooling (spraying 25 to 30 degrees Celsius water with fans) is used in classical heat stroke and in older adults.
• Target treatment within 30 minutes of collapse.
• Antipyretics (paracetamol, aspirin) and dantrolene are ineffective and should not be used.
• Shivering and seizures: lorazepam 2 to 4 mg intravenously (0.1 mg/kg in children) or diazepam 5 to 10 mg intravenously; avoid phenothiazines.

Resuscitation

• Airway protection and oxygen; intubation for coma or respiratory failure.
• Isotonic crystalloid 500 mL aliquots with reassessment, titrated to blood pressure and urine output above 0.5 mL/kg/h (up to 1 mL/kg/h in rhabdomyolysis); avoid overload because of capillary leak and lung injury.
• Vasopressors for refractory hypotension after volume: noradrenaline 0.05 to 0.5 microg/kg/min; achieve cooling first where possible, since peripheral vasoconstriction impairs heat loss.
• Glucose monitoring: 50 mL of 50% glucose for hypoglycaemia.
• Exertional hyponatraemia (sodium below 130 mmol/L): hypertonic saline 3% 100 to 150 mL boluses for neurological signs; avoid hypotonic fluids.

Kidney specific management

• Rhabdomyolysis: isotonic crystalloid 200 to 300 mL/h targeting urine output 200 to 300 mL/h until creatine kinase is below 1000 U/L; avoid bicarbonate and mannitol routinely.
• Hyperkalaemia: calcium gluconate 10% 10 mL, insulin 10 units with glucose 25 g, salbutamol 10 to 20 mg nebulised; treat hypocalcaemia only if symptomatic.
• Avoid NSAIDs and nephrotoxins; dose adjust renally cleared drugs.
• Renal replacement therapy for refractory hyperkalaemia, pH below 7.15, overload, uraemic complications or persistent oliguria with rising creatinine; haemodialysis can be used for rapid heat extraction when other methods fail (cooled dialysate).

Other organ support

• Disseminated intravascular coagulation: fresh frozen plasma 15 mL/kg for INR above 2.0 with bleeding, platelets for counts below 20 x 10^9/L (below 50 x 10^9/L with bleeding), cryoprecipitate for fibrinogen below 1.5 g/L.
• Acute liver failure: N-acetylcysteine (150 mg/kg over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours) may be considered for transaminases above 1000 U/L with coagulopathy; early liver transplant assessment for progressive failure.
• Cerebral oedema: elevate head 30 degrees, osmotherapy (hypertonic saline) as indicated.

Follow up and return to activity. Creatinine and creatine kinase at 1, 4 and 12 weeks; creatinine and albumin:creatinine ratio at 3 months. Return to strenuous activity only after normal organ function and clinical clearance, gradually over several weeks with heat acclimatisation over 7 to 14 days. Prevent with acclimatisation, hydration to pale urine, rest breaks, work rest schedules and avoidance of exercise in extreme heat.

Special groups. Older adults: classical heat stroke needs evaporative cooling and cautious fluid; children: cool with cold water immersion where available, treat hypoglycaemia, and avoid hypothermia.