Health care systems endured a stress test like no other over the past year as COVID-19 patients filled up hospital beds and intensive care units. Health care workers pleaded with the public to "flatten the curve," yet each surge in 2020 was worse than the next.
Now two recent studies quantify the consequences of flooding hospitals with COVID-19 patients and add urgency to continued efforts to keep cases and hospitalizations down.
The research, from both the United States and the United Kingdom, shows that when ICUs fill up, COVID-19 patients' chances of dying from the disease rise dramatically — despite improvements in treatment and care developed since last spring.
In the first study, published in JAMA, researchers at the Department of Veterans Affairs found a patient's chance of dying of COVID-19 nearly doubled if hospitalized when ICUs were busiest compared to times with fewer patients.
"We normally don't think about outcomes based on how many other people are sick," says Dr. Lewis Rubinson, chief medical officer at Morristown Medical Center, who wrote an editorial accompanying the JAMA study. "This reinforces that one of the best ways to improve survival is to reduce the overall pace of people coming into the ICU."
The study measured the mortality rate of more than 8,500 veterans at 88 VA hospitals between March and November.
As ICU demand increased, the mortality rate went up — a trend that was consistent at different times in the pandemic.
The study doesn't delve into why more people died when the ICU was busiest, but Rubinson says the association is — at the very least — a warning that letting hospitals get overloaded is perilous.
Critical care is labor intensive and hospitals took extraordinary steps during waves of COVID-19. Many created makeshift ICUs or relied on nurses caring for more patients in a shift than normal.
"Did care change?" asks Rubinson. "That's really the question. This study doesn't show that. It suggests that may be going on."
Rubinson says it makes sense that a resource mismatch can lead to worse outcomes, but other factors may have influenced mortality, as well. For example, the hospital may have placed sicker patients in the ICU when the demand was highest.
"A hospital is not a factory"
In the U.K., a group of researchers also discovered the risk of dying during a surge of COVID-19 hospitalizations rises incrementally as more patients are placed on ventilators in the ICU.
Once ICU occupancy hit 85% — a benchmark set by the Royal College of Emergency Medicine — the chance of dying was close to 20% higher compared to the baseline, when occupancy was between 45% and 85%.
"This risk doesn't occur above a specific threshold, but rather appears linear," the study's authors conclude in a paper released as a preprint that has not yet been peer-reviewed.
In the most extreme scenario, a patient admitted to an ICU where 99% of the beds are occupied has almost twice the risk of dying as a similar patient would when treated in an empty ICU.
That jump in mortality is based on data from the first wave of COVID-19 patients. The researchers ran their analysis using data from the fall surge in the U.K and found the trend held true: Mortality increased by about 70% when outcomes from the second wave were included in a second study also in preprint, says Dr. Bilal Mateen, one of the co-authors.
"It's madness," says Mateen, a clinical data science fellow at the Alan Turing Institute in the U.K. "We walked in expecting to see something. I don't think we expected the association to be that large."
Overall, in the second study, Mateen and his team analyzed nationwide data from more than 6,600 patients who were placed on mechanical ventilators (life support) from April to December.
The change in risk of dying can also be thought of in terms of age, which is a key predictor of survival with COVID-19.
For example, a 40-year-old admitted to an ICU with more than 85% occupancy essentially has the mortality risk of a 45-year-old. In contrast, a 40-year-old patient can actually mirror the survival of someone nine years younger when the ICU has low occupancy.
"This is something that is across all ages, across every demographic," says Harrison Wilde, who co-authored the report with Mateen.
"A hospital is not a factory and should not be operating at maximum capacity," he adds.
As with the VA study, the U.K. research can't directly pinpoint what led more patients to die when ICUs were full, but Mateen says the findings reflect the reality of how care changes when a hospital is overloaded.
"You have a finite set of resources that you can only slice into so small a piece before patients' care is going to be relatively compromised," says Mateen. "In the U.K., we've always known that quality of care starts to take a nosedive when you get above [85% occupancy]."
He suspects that expanding nurse-to-patient ratios and pulling in staff who are not trained in critical care could be key to why patients fared worse during the busiest times.
"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 says. "I would rather not do the experiments to find out why."
Slowing improvement in survival
After the initial spring surge last year, clinicians gained a better grasp on how to treat COVID-19 and the chance of hospitalized patients surviving improved. One study showed that hospitalized patients' mortality rates dropped from about 25% to under 8%.
It's a trend that holds true even when adjusting for characteristics like age and underlying health conditions, says Dr. Leora Horwitz, who has researched COVID-19 hospitalizations and was not involved in either the VA or U.K. study.
"Some of that is decreased volume, but some of it is also that we learned how to manage these patients and learned fast," says Horwitz, director of the Center for Healthcare Innovation and Delivery Science at NYU Langone Health.
Horwitz says there's no question hospital strain contributes to worse outcomes, but it's difficult to disentangle that from other forces that have also affected mortality during the pandemic.
While it appears the U.S. has turned a corner in the pandemic, the growing threat of new, more contagious coronavirus variants could spark another surge in hospitalizations, especially as more states remove mask mandates and social distancing requirements.
"We should keep doing everything possible to keep people out of hospitals, which means we should take the vaccine as soon as it's available, we should mask and we should social distance," she says.
"The bottom line is that having really crowded hospitals is bad for your health."
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