People do not typically think of themselves as at high risk of succumbing to heat or at greater risk than they once were, causing them to underestimate how a heat wave could lead them to the emergency room, said Kristie L. Ebi, a professor at the University of Washington who is an expert on the health risks of extreme heat.

“The heat you were asked to manage 10 years ago is not the heat you’re being asked to manage today,” she said. One of the first symptoms of heat illness can be confusion, she added, making it harder for someone to respond without help from others.

What Happens Next: States and hospitals are gearing up for another summer of extreme heat.

Dr. Srikanth Paladugu, an epidemiologist at the New Mexico Department of Health, said the state had nearly 450 heat-related emergency room visits in July last year alone and over 900 between April and September, more than double the number recorded during that stretch in 2019.

In preparation for this year’s warmer months, state officials are working to coordinate cooling shelters and areas where people can be splashed by water, Dr. Paladugu said.

Dr. Aneesh Narang, an emergency medicine physician at Banner-University Medical Center in Phoenix, said he often saw roughly half a dozen heat stroke cases a day last summer, including patients with body temperatures of 106 or 107 degrees. Heat illness patients require enormous resources, he added, including ice packs, fans, misters and cooling blankets.

“There’s so much that has to happen in the first few minutes to give that patient a chance for survival,” he said.

Dr. Narang said hospital employees had already begun evaluating protocols and working to ensure that there are enough supplies to contend with the expected number of heat illness patients this year.

“Every year now we’re doing this earlier and earlier,” he said. “We know that the chances are it’s going to be the same or worse.”