Extreme Heat Linked to Surge in Cardiac Arrest ICU Admissions

When the Thermometer Climbs, ICU Admissions for Cardiac Arrest Follow

As summer temperatures push past 90 degrees Fahrenheit, hospital intensive care units across the United States face a quiet, surging crisis. New preliminary research reveals that extreme heat sharply increases the rate of out-of-hospital cardiac arrest admissions, placing an immediate, heavy strain on critical care infrastructure. While emergency rooms prepare for heatstroke, the hidden cardiovascular toll of scorching weather is quietly filling ICU beds with patients requiring advanced life support.

The findings, scheduled for presentation at the American Heart Association’s Resuscitation Science Symposium 2026 in Chicago, quantify a danger that emergency physicians have long suspected. Researchers analyzed electronic health record data from 10 health systems participating in the Common Longitudinal ICU Format Consortium, evaluating how daily temperatures, humidity, and air pollution interacted with emergency cardiovascular admissions between 2018 and 2024. The results show a direct, steep escalation in out-of-hospital cardiac arrest admissions to the ICU as the mercury rises.

Tracking the Temperature Threshold

The data demonstrates a clear threshold where ambient heat begins to trigger a spike in severe cardiac events. Compared to days with a median reference temperature of 67 degrees Fahrenheit or below, the daily rate of out-of-hospital cardiac arrest admissions to intensive care units climbs steadily once temperatures cross the 90-degree mark.

When daytime highs reach 91 degrees Fahrenheit, admissions jump by 45 percent compared to days peaking at 85 degrees. At 93 degrees, the increase reaches 65 percent. On days hitting 98 degrees Fahrenheit, admissions spike by 102 percent, translating to roughly 1.5 additional critical care admissions for cardiac arrest across the studied health systems.

Certain populations bear the heaviest burden of this climate pressure. Adults aged 65 and older experience a 48 percent higher admission rate for out-of-hospital cardiac arrest on 90-degree days compared to 67-degree days. Meanwhile, women see a 33 percent increase in admissions during extreme heat.

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. 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, said Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow in the section of pulmonary and critical care at the University of Chicago.

Advanced Interventions and Hospital Strain

Once patients arrive at the hospital following a resuscitation, their treatment path changes depending on the environmental conditions surrounding their collapse. Individuals admitted during heat waves of 90 degrees Fahrenheit or warmer require more intensive medical interventions. Data shows these patients are more likely to need treatments for low blood pressure and, later in their ICU stay, continuous dialysis for kidney dysfunction, alongside markers of impaired circulation and metabolic stress.

Heat-related illnesses surge as extreme heat persists

Because these patients are often unconscious and unable to breathe independently, they require advanced life support for days or weeks. This extended care cycle strains already limited hospital resources.

Yet, the research uncovered an unexpected finding regarding patient survival. Despite requiring more complex physiological interventions, patients admitted during extreme heat experienced hospital discharge statuses and survival rates comparable to those admitted on cooler days. There were no significant statistical differences in rates of being discharged home, transferred to acute care facilities, or in-hospital death.

“We were surprised to find that outcomes were not that different between the two groups,” Graffy noted, attributing the stabilization success to the rapid, skilled interventions of emergency department and intensive care clinicians.

Preparing for the Heat-Driven ICU Surge

The disconnect between severe initial presentation and stable ultimate survival rates highlights a critical operational challenge for healthcare networks. Because recovery takes days to weeks, the connection between the ambient temperature at the time of the collapse and the patient’s long ICU stay is often obscured.

Public health experts emphasize that heat warnings demand the same urgency as severe weather advisories, particularly for vulnerable households lacking reliable air conditioning or transportation.

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, said Ashish Panchal, M.D., Ph.D., FAHA, volunteer chair of the American Heart Association Emergency Cardiovascular Care Committee, physician and professor of emergency medicine at The Ohio State University. We also know that about 70 percent 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.

As extreme heat events grow more frequent, researchers hope healthcare systems will eventually integrate local weather forecasts directly into operational planning. Anticipating temperature surges could allow hospitals to proactively manage ICU bed capacity, staffing levels, and resource coordination before the heat-driven wave of critical admissions reaches the emergency room doors.