The number of COVID-19 patients expected to flood Ontario intensive care units has so far been more of a trickle, offering hope that there will be no overwhelming surge that will stretch the health-care system beyond capacity.

But clinicians say it's not only the number of patients posing a challenge for ICUs — it's how long they're typically staying.

While average patients spend just a few days in intensive care, COVID-19 patients often need resource-heavy critical care for a week or more, multiple experts told CBC News.

"It is a battlefield mentality," said Dr. Bram Rochwerg, the site lead at the Juravinski Hospital intensive care unit in Hamilton, Ont. and an associate professor at McMaster University. "We're all feeling it's our time to step up."

Right now, 254 patients are in Ontario ICUs, with 188 of those requiring ventilators to help them breathe, the latest provincial data shows.

The total has been trending downward from a high of 264 patients in ICUs reported on April 9, keeping the numbers below the best-case scenario anticipated by the province.

It's also well under the current available capacity, which clinicians attribute largely to thousands of non-emergency surgeries being put on hold.

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Dr. Rob Fowler, chief of Sunnybrook Hospital's trauma and critical-care program in Toronto, said dozens of COVID-19 patients have come through his ICU so far, and required care anywhere from "many, many days to many, many weeks.

"It seems like the majority are needing some time to get over the illness, on average in the range of a week or longer," echoed Rochwerg.

That's in contrast to the typical three-day average stay for ICU patients, according to the Canadian Institute of Health Information.

Those longer stays for Ontario COVID-19 sufferers echo early research from abroad, noted Dr. Hannah Wunsch, a professor of anesthesia and critical care medicine at the University of Toronto.

"That does have large implications for resources, because it's not just a question of counting patients, and how many come in requiring intensive care," she said.

"It is that multiplication out of how many days they're needing an ICU bed and ventilator, because that's what sort of adds up — and stacks up."

Severe cases, different supports

In some ways, those longer-term cases are not unlike other severe cases of pneumonia or acute respiratory distress syndrome — a form of respiratory failure marked by rapid, widespread lung inflammation — which ICU teams are well-versed in treating.

The difference now is where there was once a mix of people with different ailments, now ICUs are faced with many patients battling the same disease, needing days or weeks of care.

Dr. Niall Ferguson, head of critical care at Toronto's University Health Network and Sinai Health, said clinicians are watching patient reactions closely and adapting the principles for treating other respiratory conditions.

But it's a constant challenge, Fowler noted, since not every severely ill COVID-19 patient needs the same support.

"Some people will just need oxygen, some people will need ventilation, some people will have an inflammatory response that will result in low blood pressure," he said.

Dr. Hannah Wunsch, a professor of anesthesia and critical care medicine at the University of Toronto, says longer-than-average stays for Ontario COVID-19 sufferers echo early research from abroad. (Supplied by Dr. Hannah Wunsch)

What's also becoming clear, according to Ontario clinicians, is that patients requiring lengthy time on life support could suffer long-term consequences, from mental health and cognitive issues to lengthy physical recoveries.

"The longer you're on the ventilator, you lose muscle mass every day," Rochwerg said.

Despite the challenges in figuring out the best approaches to patient care amid this unprecedented pandemic, ICU teams are settling into this new reality — one that's been manageable so far.

Now questions are arising over what comes next if life starts gradually returning to normal.

Not time to 'breathe a sigh of relief'

What happens, for instance, if hospitals slowly begin rebooking elective surgeries, which typically require short post-operative ICU stays?

Ferguson said Toronto General, the hospital where he's currently practising, typically does four lung transplants a week, but he only knows of one booked in the last month or so amid the province-wide push to free up ICU beds for COVID-19 patients.

"The challenge will be once we start to ramp up other activity and try to figure out where that balance is," he said.

Dr. Niall Ferguson, head of critical care at the University Health Network and Sinai Health, says clinicians are watching patient reactions closely and adapting the principles for treating other respiratory conditions. (Supplied by Dr. Niall Ferguson)

Experts also warn that while COVID-19 patients may not be overwhelming ICUs, there is a staggering death toll among elderly residents in long-term care facilities who never make it into hospitals.

Untold numbers of people carrying the virus without symptoms could also be living in Canadian communities, which could fuel the disease's spread if physical distancing measures are loosened.

"There is substantial risk people will see the numbers levelling off and will receive the message that this is time to breathe a sigh of relief," Fowler said.

"If we hadn't instituted public-health measures," he added, "there is not necessarily a lot to separate us from other parts of the world."