Extreme Heat Pushed More Cardiac Arrest Patients Into the ICU
Out-of-hospital cardiac arrest admissions to intensive care units climbed as outdoor temperatures rose above 90 degrees Fahrenheit, with the sharpest increases seen in women and adults 65 and older. The pattern adds a new hospital-facing dimension to heat exposure: not just more emergency calls or excess deaths, but more critically ill patients requiring ICU-level care after resuscitation.
The study, presented as a preliminary abstract at the American Heart Association’s Resuscitation Science Symposium 2026, tracked ICU admissions across 10 U.S. health systems from 2018 through 2024. More than 11,000 patients with OHCA were admitted during that period, and 270 of those admissions occurred during extreme heat above 90 degrees Fahrenheit. Daily temperatures near each hospital were analyzed alongside humidity and air pollution, allowing investigators to examine whether hot days aligned with higher ICU admission rates and whether that exposure changed what happened after admission.
The rise was not subtle. Compared with days reaching 85 degrees Fahrenheit, daily OHCA ICU admissions were 45% higher at 91 degrees, 65% higher at 93 degrees, and 102% higher at 98 degrees. Relative to the median reference temperature of 67 degrees across the participating sites, people aged 65 and older had a 48% higher admission rate at 90 degrees, and women had a 33% higher admission rate on extreme-heat days.
One extra ICU admission per day may sound modest until it lands across a network of hospitals already running close to capacity.
At 98 degrees Fahrenheit, the heat burden translated to roughly 1.5 additional OHCA ICU admissions across the 10 health systems compared with days near the median temperature. For individual ICUs, even a small uptick in post-arrest admissions can complicate staffing, bed management, ventilator allocation, and the timing of advanced support. Cardiac arrest survivors often arrive unconscious and require ongoing resuscitation, hemodynamic monitoring, airway management, and neurologic assessment, turning each case into a resource-intensive admission that can last days or weeks.
More Organ Support, but No Clear Shift in Survival
Heat exposure changed the intensity of critical care, even when it did not change the final discharge disposition. Patients admitted after cardiac arrest on days at 90 degrees or warmer were more likely to need treatment for hypotension and, later in the ICU course, continuous dialysis for kidney dysfunction. They also showed markers of impaired circulation and metabolic stress while hospitalized, a physiologic profile consistent with systemic strain after severe heat exposure layered onto the already profound insult of cardiac arrest.
Still, the endpoint data did not separate the groups in a dramatic way. Deaths, hospice discharges, and hospital length of stay were about the same whether the arrest admission came during extreme heat or on days at 67 degrees or below. Rates of discharge home, transfer to another acute care hospital, and in-hospital death did not differ significantly by admission temperature. In practical terms, hotter days brought more critically ill patients and more organ-support needs, but they did not produce a clear worsening in the hospital outcomes measured here.
The finding is biologically plausible. Extreme heat can worsen dehydration, vasodilation, electrolyte instability, and circulatory stress, each of which can push a vulnerable person toward collapse or complicate recovery after resuscitation. Once the arrest has occurred, however, immediate ICU interventions may blunt the downstream effect of the original trigger. Post-arrest care can stabilize blood pressure, support failing kidneys, and maintain oxygenation while the brain and other organs recover, which may help explain why discharge outcomes remained similar despite the heavier burden of organ dysfunction.
Why Women and Older Adults Appeared More Vulnerable
Two subgroups carried a heavier admission burden: older adults and women. Adults 65 and older showed a 48% higher OHCA ICU admission rate at 90 degrees versus 67 degrees, and women had a 33% higher rate on extreme-heat days. The abstract did not dissect the mechanisms behind those differences, but the direction fits what clinicians already know about heat vulnerability in older adults, who often have less physiologic reserve, more chronic disease, and a reduced ability to dissipate heat. Social factors matter too, especially for people with limited access to air conditioning, transportation, or timely assistance when symptoms begin.
Women’s higher admission rate on hot days raises additional questions about exposure patterns, symptom recognition, and care-seeking behavior. The study does not provide a direct explanation, but the signal is clinically important because it suggests that heat-related cardiac arrest risk may not be evenly distributed across the population. A one-size-fits-all heat warning may miss the people most likely to deteriorate at home before emergency response arrives.
ICU Capacity Is Becoming Part of Heat Preparedness
Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow in pulmonary and critical care at the University of Chicago, said heatwaves are increasing strain on communities, emergency services, and hospitals that must absorb climate-related illness. He emphasized that ICU beds, equipment, and staff are limited, and sudden surges in critically ill patients can overwhelm resources if hospitals are not ready.
The study points to a straightforward operational lesson: temperature forecasts may eventually belong in ICU planning. A heat wave does not simply increase emergency department volume; it can also reshape the mix of patients who require invasive monitoring, vasopressor support, and dialysis after resuscitation. For hospitals, that means climate data could become part of bed forecasting, staffing plans, and coordination between emergency medicine and critical care teams.
Ashish Panchal, M.D., Ph.D., FAHA, said people caring for older or medically vulnerable adults should take heat warnings seriously because the consequences can extend from home to the ICU. He also pointed out that about 70% of cardiac arrests outside the hospital happen at home, making public preparedness essential. CPR training and rapid medical activation remain central, especially when extreme heat may be the upstream trigger.
Preliminary Data With Direct Bedside Implications
The abstract should be read as early evidence, not a final answer. Presentations at American Heart Association scientific meetings are not peer-reviewed, and the findings remain preliminary until published as a full manuscript. Even so, the signal is strong enough to influence how clinicians and hospital administrators think about heat as a driver of critical care demand.
The most important clinical message is not that heat changed survival after ICU admission; it is that heat increased the number of patients who arrived at the threshold of critical illness in the first place. More arrests during hotter days mean more families confronting sudden resuscitation, more ICU beds occupied by neurologically vulnerable patients, and more need for advanced support during periods when health systems are already strained by seasonal surges. The study leaves open whether earlier public health intervention, home cooling access, or targeted heat alerts could reduce those ICU admissions before they happen, but it makes the hospital burden difficult to ignore.