As daily temperatures across the United States climb above 90 degrees Fahrenheit, hospitals are seeing a corresponding surge in intensive care unit admissions for out-of-hospital cardiac arrest (OHCA), according to new preliminary research presented at the American Heart Association's Resuscitation Science Symposium 2026. The findings, which have not yet been peer-reviewed, highlight a critical intersection of climate change and public health: extreme heat is not only triggering more cardiac emergencies but also placing added demand on already limited ICU beds, equipment and staff.
The study, led by Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow at the University of Chicago, analyzed data from more than 11,000 OHCA patients admitted to ICUs across 10 U.S. health systems between 2018 and 2024. Researchers compared daily temperatures near each hospital, adjusting for humidity and air pollution, to determine whether hotter days were associated with more cardiac arrest admissions. The results were striking: compared with days reaching 85 degrees F, OHCA admissions were 45% higher at 91 degrees F and 102% higher at 98 degrees F. People ages 65 and older had a 48% higher admission rate at 90 degrees F versus 67 degrees F, while women were admitted at a rate 33% higher on extreme heat days.
Cardiac arrest occurs when the heart's electrical system suddenly malfunctions, stopping blood flow to the brain and vital organs; approximately 90% of people who experience OHCA outside a hospital do not survive, as detailed by the American Heart Association's cardiac arrest resources. While previous research has linked heat to cardiac arrest using EMS calls or death records, this study is among the first to examine ICU-level impacts across multiple health systems.
Despite the increase in admissions, the research found no significant difference in discharge outcomes or survival rates for patients admitted during heat waves compared with cooler days. "We were surprised to find that outcomes were not that different between the two groups," Graffy said. "We had assumed that since extreme heat typically contributes to multi-organ system dysfunction that the rates of death would be higher... But this was not the case, and we think this is likely a testament to clinicians and care teams both in the emergency department and ICU." However, patients admitted on hotter days were more likely to require interventions for low blood pressure and continuous dialysis for kidney dysfunction, signaling greater clinical complexity during their ICU stay.
The implications for hospital capacity are significant. "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," Graffy said. "ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready." He suggested that hospitals could eventually use temperature forecasts to proactively allocate ICU beds and coordinate between emergency departments and intensive care units.
Ashish Panchal, M.D., Ph.D., FAHA, chair of the American Heart Association Emergency Cardiovascular Care Committee, emphasized the importance of public preparedness. "For the public and caregivers, especially those supporting older or medically vulnerable adults, heat warnings should be taken seriously because extreme heat can have consequences that extend from the home all the way through to the ICU," he said. "About 70% of cardiac arrests that happen outside of a hospital happen at home, and people need to be prepared: at a minimum, everyone should learn the lifesaving skills of CPR and seek medical care as quickly as possible." The Association offers resources such as Cardiac Arrest vs. Heart Attack and its Nation of Lifesavers initiative to improve bystander response.
The study is being presented at the Resuscitation Science Symposium 2026, held Nov. 7-8 in Chicago. As extreme heat events become more common globally, the findings underscore the need for healthcare systems to adapt. More information on the research is available in the release link, and the full abstract can be viewed via the Link to abstract. The American Heart Association's financial information is available here.
