For those who make it out the other side, their stay in intensive care is likely to be one of the most traumatic things they will ever experience. Being able to breathe is something we take for granted. But patients who have such difficulty breathing that they need to be intubated (which involves having a tube inserted into their mouth and down their airway) often believe they are going to die at some point during their stay in intensive care. Anecdotally, ICU doctors say patients with covid-19 tend to need a particularly large amount of sedation, which damages muscles and nerves, especially in the lungs. That damage can be permanent—which can in turn undermine the patient’s mental health.

“Their lives will never look exactly as they were before. Being admitted to an ICU is one of those ‘before and after’ life events, like having a child, or a parent dying,” says Megan Hosey, a psychologist who treats ICU patients.

Patients on ventilators often become delirious. They can drift in and out of consciousness, hallucinate, and become confused about what’s happening to them. It’s common for them to form delusions and misremember what’s occurred. “They can recollect that a nurse or doctor was trying to hurt them when they were doing a procedure to help them,” says Timothy Girard, associate professor of critical care medicine at the University of Pittsburgh Medical Center. It’s unsurprising, then, that so many ICU survivors go on to experience depression, anxiety, posttraumatic stress disorder, and other mental health issues.

A 2018 UK study of nearly 5,000 ICU survivors found that over half had developed at least one of these conditions a year after they left the hospital. A 2014 meta-analysis put this figure closer to one-fifth. Either way, “the research is clear that some people who have been hospitalized will develop PTSD,” says Antonis Kousoulis, research director at the Mental Health Foundation, a UK nonprofit.

It’s too early to know if people who’ve survived being hospitalized with coronavirus will experience similar rates of mental illness. Some will be affected more than others. And multiple studies suggest that ICU patients who have been heavily sedated, especially with high doses of benzodiazepines, are more likely to develop mental health issues, says Girard. This bodes badly given the high level of sedation required for covid-19 patients in ICUs.

“It will be traumatic for many, but everyone responds differently. Some will develop PTSD, but some won’t,” says psychologist Elizabeth Woodward. However, the first piece of research into this specific question, conducted in China and published in Psychological Medicine, suggests we need to prepare for a tsunami of poor mental health among survivors. The researchers found that 92% of the 714 patients they surveyed had “significant posttraumatic stress symptoms.” (There is a difference between symptoms and a diagnosable condition, to be sure. It’s very common for people to experience intrusive thoughts, flashbacks, and nightmares after a traumatic incident. It’s when those symptoms recur for months on end that it tips over into clinically recognized PTSD, says Woodward.)

While this serious secondary effect of the pandemic is undoubtedly heading our way, there is plenty we can do to mitigate its effects. Making sure those who are discharged from the ICU have ready access to medication and therapy, such as cognitive behavioral therapy, can help. Health-care workers can also keep an “ICU diary” while patients are on the ward—listing everything that happened to them and when—to help them make sense of their experience in the following months.

Interventions require education, organization, and money—a tall order at the best of times, but especially in the middle of a pandemic, when the health-care system is struggling to cope. However, the cost of doing nothing would be far greater, says Bienvenu. “There were World War II veterans who to their dying day still woke up screaming because they never talked about what they’d experienced,” he says. “We’d like to be able to prevent that, and we can.”