SNOWMASS, COLO. — Exertional heat stroke in young athletes garners all the headlines, but most heat stroke cases occur in elderly housebound individuals with underlying chronic disease, Eric Johnson, M.D., said at the annual meeting of the Wilderness Medical Society.
The fatality rate of heat stroke in the elderly is high. The diagnosis is often missed during the critical first hours. That's because the differential diagnosis in the elderly nonathlete is lengthy, unlike in a young sports participant who collapses during an intensive hot weather workout.
“A lot of the time with geriatric patients we find that doctors immediately order CT scans, ECGs, blood tests, and so forth—and only 2 hours later someone finally takes a rectal temperature and finds out the patient has been 105° F. Then it's 'uh oh, this isn't meningitis, it wasn't a stroke, they're not septic, it wasn't a seizure,'” said Dr. Johnson, an emergency department physician in Boise, Idaho, and president-elect of the society.
“You have to think about those differential diagnoses, but the duration and magnitude of hyperthermia is the main determinant of outcome in heat stroke. When we miss it for 2 hours we have a very, very high mortality,” he said.
The diagnostic work-up often can be accelerated by speaking with paramedics to learn what the patient's environment was like. If it was stifling, Dr. Johnson thinks heat stroke; if the air conditioning was on and the room was comfortable, he may lean more toward other possibilities.
Part of the problem in diagnosing classic heat stroke promptly in the elderly is that it can be a challenge to obtain a reliable temperature reading from a patient with heat stroke. Measurements at the ear and rectum are “totally worthless” because they correlate poorly with core temperature in this situation, the physician said.
Instead, he obtains a bladder temperature if a Foley catheter is in place, or runs an esophageal probe to get a posterior retrocardiac temperature reading. Often he'll get both.
The concept of heat stroke lately has been redefined. Heat stroke is not primarily a dehydration issue; that's just one component. Heat stroke is a systemic inflammatory response to hyperthermia leading to a syndrome of multiorgan dysfunction in which encephalopathy is prominent.
Patients typically arrive at the hospital with agitation, combativeness, or other mental status changes, a temperature above 104° F, tachycardia, and tachypnea. Often they are bleeding due to disseminated intravascular coagulation because antithrombotic factors have stopped functioning at high body temperatures.
“There are a lot of complications. These folks that come in with heat stroke are going to spend a substantial time in your ICUs,” he continued.
A question that comes up all the time is how much intravenous fluid to give for resuscitation. Dr. Johnson noted that U.S. military medicine guidelines call for just 1–1.5 L, rather than the 3–4 L or more often still given in the civilian world. Israeli and Saudi physicians, whom Dr. Johnson considers the world's top experts in the management of heat stroke, also routinely use 1–1.5 L and have great success with it.
In his own practice he uses normal saline because of a theoretic concern that lactate may not be metabolized in the liver.