Prolonged sauna sessions may put bathers at risk of heat stroke, especially if they haven't consumed enough water beforehand, doctors have warned in the journal BMJ Case Reports.
The warning comes after medical professionals treated a woman in her early 70s who required hospital admission following an extended sauna session at her local gym. She had been performing stretching exercises in the sauna for around 45 minutes when she was found unconscious.
Heat stroke, although relatively rare, can be life-threatening, even in the absence of various underlying risk factors. It is defined as a sharp increase in core body temperature above 40°C that is associated with acutely impaired brain function. "Non-exertional" heat stroke results from prolonged exposure to high environmental temperatures.
Underlying risk factors for heat stroke include heart disease, lung disease, neurological disease, heavy drinking, or taking a cocktail of prescription medications. However, the woman had few of these risk factors. She had previously been diagnosed with type 1 diabetes and an underactive thyroid but wasn't a smoker or heavy drinker and was a regular gym-goer.
Upon arrival at the emergency department, her core body temperature was 42°C; normal temperature is 36.4°C. She had extremely low blood pressure and an extremely high heart rate. Shortly after, she experienced a seizure.
Medical staff rapidly cooled her with wet towels and a fan and administered intravenous fluids and blood products to stabilize her condition. Blood tests revealed malfunctioning kidneys and liver, evidence of a minor heart attack, and muscle tissue breakdown (rhabdomyolysis).
She regained consciousness within two hours of reaching a normal core temperature but remained confused and drowsy for two days. By day three, her confusion and drowsiness had resolved. She had no further seizures during her inpatient stay, which lasted 12 days. After 26 days, she had more or less fully recovered, although she experienced some mild fatigue and mild liver function disturbance.
As far as the authors are aware, only nine other similar cases have been reported, three of whom died as a result. "The prognosis of heat stroke varies according to patient factors, particularly extremes of age," the authors explain. They add, "Classical heat stroke in elderly people carries a mortality rate of [more than] 50%, and this increases further with each additional organ dysfunction."
The authors state, "Heat-related deaths spike during heat waves, as has been observed in multiple large international datasets." They add, "Deaths from heat stroke are expected to rise as global temperatures continue to increase." They emphasise, "Once heat stroke has occurred, the key determinate of outcome is how rapidly a patient is cooled, as the time spent with elevated core body temperature is correlated to the degree of cellular damage."
"My experience has emphasised the dangers of saunas and how important it is to be fully hydrated on entering a sauna, and for them to be regularly checked by staff," the woman in the study said.
"As a regular sauna user, I never suffered any issues and, on reflection, I believe I had not drunk enough water," she added.
This article was written in collaboration with generative AI company Alchemiq