Lead author Peter Mullins of George Washington University's School of Public Health and Health Services and colleagues found ICU admissions rose from 2.79 million in 2002-03 to 4.14 million in 2008-09. For the same time period, overall emergency department admissions grew by only 5.8 percent.
"These findings suggested emergency physicians were sending more patients on to the ICU," Mullins said in a statement. "The increase might be the result of an older, sicker population that needs more care."
However, the larger question, which this study couldn't answer, was whether there will be enough ICU capacity in the future to accommodate the growing number of patients, particularly the oldest of the old, the study authors said.
ICU admissions grew the most among patients age 85 and older -- increasing 25 percent every two years.
Utilization of tests and services provided to emergency department patients on their way to the ICU also spiked during the study period, with the largest rise occurring in computerized tomography or magnetic resonance imaging tests. In fact, CT and MRI tests provided while still in the emergency department increased from 16.8 percent to 37.4 percent, the study found.
The most common reasons for ICU admissions were symptoms such as chest pain or shortness of breath that can signal life-threatening conditions like heart attacks.
The researchers used data from the National Hospital Ambulatory Care Survey, a sample of U.S. hospital-based emergency departments. Their study was published in the journal Academic Emergency Medicine.