Covid-19 patients' risk of death may nearly double if they're admitted to an ICU that's operating at or near capacity, according to several recent studies—findings that reinforce health experts' warnings that fatality rates amid the pandemic can rise if hospitals become overwhelmed.

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For one study, published in JAMA, researchers looked at the mortality rates of 8,516 patients at 88 Veterans Affairs hospitals between March and November 2020 that each had at least 10 Covid-19 ICU patients.

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The researchers found that a patient's mortality risk from Covid-19 almost doubled when ICUs were at their busiest compared with when ICUs had fewer patients. Specifically, they found that patients admitted to an ICU where at least 75% of available beds were occupied by Covid-19 patients had an adjusted hazard ratio of 1.94 relative to times when Covid-19 patients occupied no more than 25% of beds.

In another analysis, which has yet to be peer-reviewed, researchers in the United Kingdom looked at data on the first wave of Covid-19 patients in the country and found that the risk of death from Covid-19 increased as ICU capacity filled.

For instance, the researchers found that once an ICU hit 85% capacity, a patient's risk of dying was about 20% higher compared with when occupancy was between 45% and 85%.

The same researchers conducted a related pre-print study using data from the United Kingdom's Covid-19 surge in the fall and found the same trend held: Mortality risk increased when admissions occurred during high occupancy, and decreased when admissions occurred in periods of low occupancy. For instance, the researchers found that a 40-year-old admitted to an ICU that's at more than 85% capacity had the usual mortality risk of someone 45 years old, whereas that same 40-year-old admitted to an ICU with low occupancy had the usual mortality risk of a 31-year-old.

Similarly, a pre-print paper from Israel assessed 19,336 Covid-19 patients hospitalized in that country between mid July of last year and early January and found—after adjusting for age, sex, and patients' health on the day of admission—the mortality rate for Covid-19 patients increases as ICU capacity fills. In fact, the mortality risk began increasing when just 500 patients nationwide were hospitalized for Covid-19, a level deemed manageable by the Israeli government.

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Discussion

Lewis Rubinson, CMO at Morristown Medical Center, who wrote an editorial accompanying the JAMA study, said if the study results "represent true causality, they provide additional support for public health strategies to 'flatten the curve.'"

However, neither the JAMA study nor the British pre-print studies established a cause behind mortality risk increasing as ICU capacity filled, and Rubinson noted that it's possible other trends could explain the correlation. For instance, he noted that ICUs may have admitted less severe cases when capacity rates were lower, or that health care providers during particularly busy times were forced to create makeshift ICUs and resort to other extraordinary measures.

"Did care change? That's really the question," Rubinson said. "This study doesn't show that. It suggests that may be going on." He added that if nothing else, the association between ICU capacity and mortality rates demonstrate that allowing hospitals to be overwhelmed is dangerous.

According to Lakshman Swamy, who works at the Cambridge Health Alliance, once hospitals start to reach capacity, "everything gets disrupted and a kind of 'soft rationing' kicks in." That means the ICU "has to raise the bar on how sick you need to be to get into the ICU. If you add stretched-out staff … you end up basically providing slower, less ideal care to everyone, including the sickest patients," he said.

Bilal Mateen—one of the co-authors of the UK studies and a clinician-researcher at the Wellcome Trust and Kings College Hospital—said he thinks expanding nurse-to-patient ratios and utilizing staff who weren't trained in critical care could be behind the mortality risk increase.

"I think the weight of evidence has gotten to the point where you can't really ignore the fact that as the hospital gets more full, something's going wrong," he said. "I would rather not do the experiments to find out why" (Stone, "Shots," NPR, 3/18; Belluz, Vox, 1/13; Phend, MedPage Today, 1/20).