ICU admissions for out-of-hospital cardiac arrest rose on days above 90 degrees Fahrenheit, but those patients’ outcomes were similar to patients admitted on cooler days, according to preliminary research presented at the American Heart Association’s Resuscitation Science Symposium 2026.
About 90% of people with out-of-hospital cardiac arrest do not survive, and extreme heat is known to increase the risk of cardiac arrest, according to a Nov. 2 association news release.
“Heatwaves are becoming more frequent and intense nationally, causing additional strain on communities and emergency services, as well as on hospitals who must absorb the influx of climate-related illnesses,” Peter Graffy, PhD, a postdoctoral fellow in the section of pulmonary and critical care at the University of Chicago, said in the release. “This is important because ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready.”
Researchers analyzed data for more than 11,000 cardiac arrest patients admitted to the ICU at 10 health systems between 2018 and 2024 using the Common Longitudinal ICU Format Consortium, a network that standardizes electronic health record data across hospitals for research. Of those patients, 270 were admitted during extreme heat. Researchers also analyzed daily temperatures, humidity and air pollution near each hospital. The study defined extreme heat as temperatures over 90 degrees. The findings have not been peer-reviewed.
Here is what they found.
1. When temperatures climbed above 91 degrees, the rates of out-of-hospital cardiac arrest admissions to the ICU increased 45% than on days that peaked at 85 degrees. Admissions were 65% higher at 93 degrees and 102% higher at 98 degrees.
2. Older adults had a 48% higher admission rate and women had a 33% higher admission rate on days with extreme heat.
3. When temperatures reached 98 degrees, there were about 1.5 additional out-of-hospital cardiac arrest ICU admission across health systems.
4. Patients admitted after cardiac arrest on extreme heat days were more likely to require interventions for low blood pressure and continuous dialysis for kidney dysfunction.
5. But discharge status and survival were similar to those of patients admitted on days closer to 70 degrees, with no significant differences in rates of discharge home, transfer to an acute care hospital or in-hospital death.
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