Heat Stroke: Kidney Impact And Recovery

Heat stroke is a life-threatening medical emergency that can lead to acute kidney injury (AKI). Heat stroke is the most severe heat-related illness and is characterised by a body temperature of over 40°C combined with neurologic dysfunction. It can be caused by strenuous exercise performed in a high-temperature and high-humidity environment.

AKI is a common manifestation in individuals presenting with heat stroke. Heat stroke can lead to rhabdomyolysis, which is a clinical and biochemical syndrome that occurs when skeletal muscle cells release creatine phosphokinase, lactate dehydrogenase, and myoglobin into the interstitial space and plasma. Rhabdomyolysis can lead to acute tubular injury, which can then develop into chronic kidney disease (CKD).

Heat stroke can also cause electrolyte abnormalities, such as hyponatremia, hypokalemia, hypophosphatemia, hypocalcemia, and hypomagnesemia. Some individuals with heat stroke-associated AKI may require dialysis.

There is evidence that the increase in heat waves caused by climate change is linked to the rise in kidney disease cases. Heat waves have become more common, with about three-quarters of the increase blamed on climate change.

Heat stroke and rhabdomyolysis

Rhabdomyolysis is a common complication of heat stroke. It is often combined with acute kidney injury (AKI), which is now recognised as a clear risk factor for chronic kidney disease (CKD). Heat stroke patients are at an increased risk of developing AKI, which in turn is associated with an increased risk of nephron death and can cause serious sequelae such as end-stage renal disease (ESRD).

Exertional heat stroke (EHS) is a life-threatening injury that can lead to AKI. A retrospective study of EHS patients admitted to the intensive care unit (ICU) from January 2008 to June 2019 found that 43.9% of patients developed AKI. Multivariate logistic analysis showed that lymphocyte, neutrophil, D-dimer and myoglobin (MB) levels were independent risk factors for AKI caused by EHS. In addition, the SOFA score and GCS score were risk factors for 90-day mortality in patients with EHS complicated with AKI.

Heat stroke and acute kidney injury

Heat stroke is a life-threatening medical emergency that can lead to acute kidney injury (AKI). AKI is a common manifestation in individuals presenting with heat stroke, with one study reporting that over 50% of those presenting with heat stroke had acute kidney injury.

Risk Factors

Heat stroke can occur during heat waves (termed epidemic or classic heat stroke) and also in association with exercise or labour in high temperatures (termed exertional heat stroke). Exertional heat stroke is especially common among military personnel, marathon runners, and workers in mines or agricultural fields. It is also more common among new workers who are not acclimatised and those who are overweight.

Types of Acute Kidney Injury

There appear to be two types of acute kidney injury. One form appears to be classical rhabdomyolysis, often associated with hyperuricemia and signs of dehydration. This form may be more common with exertional heat stroke. The other form is associated with normal or only mildly elevated creatine phosphokinase levels and is more common in epidemic heat stroke. Unlike rhabdomyolysis, where the injury appears more like an acute tubular injury, the second form of acute kidney injury clinically manifests more as an acute interstitial nephritis, with urinary leukocytosis and hematuria.

Treatment and Prognosis

If the patient survives the acute illness, kidney function usually returns to normal. However, some cases of heat stroke may progress to chronic kidney disease (CKD) months later with the presence of chronic tubulointerstitial nephritis on biopsy.

Heat Stress Nephropathy as a Cause of CKD

In recent years, epidemics of CKD have been identified in various hot regions of the world, where it affects workers who labour manually under extremely hot conditions. There is evidence that recurrent heat stress and dehydration can induce chronic inflammation and tubular injury, and that the development of CKD may result from repeated acute kidney injury driven by subclinical or clinical heat stroke.

Heat stress nephropathy

Heat-related illnesses can range from mild conditions such as dizziness, skin rashes, or cramps to more severe conditions like heat syncope and heat exhaustion. Heat stroke is characterised by a body temperature above 40°C, combined with neurological dysfunction, and it is considered a life-threatening condition that requires immediate medical attention.

Global climate change has led to a significant increase in temperatures, resulting in more frequent and severe heat-related illnesses. The consequences of heat injury include dehydration and rhabdomyolysis, which can lead to AKI and, subsequently, CKD. Studies have shown that individuals with heat stroke have an increased risk of developing CKD compared to those without heat-related injuries.

The underlying mechanisms of heat stress nephropathy include reduced blood volume, microthrombi in renal arteries, blockage of renal tubules by myoglobin, and renal interstitial cell inflammation. Inflammation and coagulation dysfunction play a crucial role in the development of heat stress nephropathy, as they can lead to endothelial injury and the activation of inflammatory cells.

Additionally, heat-induced peripheral vasodilation and dehydration can decrease intestinal and solid organ blood supply, leading to ischemia. This can cause permanent damage to the kidney tissues and increase the risk of acute or chronic renal failure.

Early treatment strategies, such as whole-body cold-water immersion and volume management, are crucial for improving the prognosis of heat stress nephropathy and reducing the risk of AKI and CKD.

Heat stress and kidney stones

Heat stress is a significant concern for people working outdoors or in hot environments, and it can have a range of adverse health effects, including kidney disease. Kidney stones, in particular, have been linked to heat stress and dehydration.

Kidney stones are solid clumps of material that form in the kidneys, consisting of crystal-forming substances such as calcium, oxalate, and uric acid. They can be extremely painful and sometimes require surgery to remove if they become too large. Dehydration is a well-known risk factor for kidney stone formation.

Heat Stress and Dehydration

Working in hot environments or during heatwaves can lead to dehydration as the body loses water and electrolytes through sweating. This dehydration can, in turn, lead to kidney stones as the concentration of minerals in the kidneys increases.

A study in Thailand found a significant association between occupational heat stress and self-reported doctor-diagnosed kidney disease. Male workers aged 35 or older in physical jobs with frequent heat stress had a 5.3 times higher risk of developing kidney disease compared to those without heat stress.

Similarly, a study in California found that for every additional inch of rain and each degree Fahrenheit increase in temperature, there was a small but significant increase in the number of kidney stone surgeries.

Preventing Kidney Stones

Drinking plenty of water is essential to prevent kidney stones, especially in hot and humid weather. Maintaining proper hydration helps dilute the minerals in the kidneys, reducing the risk of stone formation.

Other ways to prevent kidney stones include:

• Consuming more fruits and vegetables, as well as foods rich in magnesium and potassium, which can reduce urine acidity.
• Limiting foods high in oxalates, such as spinach, rhubarb, soy products, black tea, nuts, and chocolate, if you are prone to calcium oxalate stones.
• Ensuring adequate calcium intake, preferably from dairy products, as too much or too little calcium can increase the risk of stones.
• Maintaining a healthy weight, as obesity is a risk factor for kidney stones.
• Avoiding excessive alcohol consumption, as it can contribute to dehydration.

Global Warming and Kidney Stones

With global warming leading to rising temperatures and more frequent heatwaves, the prevalence of kidney stones is expected to increase worldwide. This highlights the importance of taking preventive measures and staying properly hydrated, especially for people living and working in hot and humid environments.

Heat stress and urinary tract infections

Heat stress can affect the kidneys and increase the risk of urinary tract infections (UTIs). Warmer weather increases the risk of UTIs in women treated in outpatient settings. A study found that on days when the temperature in the previous week was between 25 and 30°C, the incidence of UTIs increased by 20-30% compared to when the temperature was between 5 and 7.5°C.

UTIs are common bacterial infections, especially among women, and are caused mostly by the bacteria E. coli. While stress does not directly cause UTIs, it can lower the body's resistance to infection and illness. When stressed, the body produces cortisol, and if there is too much of it for too long, the body's ability to fight infection is reduced.

Stress can also amplify symptoms of lower urinary tract disorders, such as overactive bladder and interstitial cystitis. A study involving children and teens with lower urinary tract symptoms found that around 20% had significantly higher stress than those without symptoms, and this led to more severe symptoms.

To prevent UTIs, it is important to stay well-hydrated, especially during warmer weather, and to urinate as soon as you feel the need.

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