(HealthDay)

TUESDAY, March 18, 2014 (HealthDay News) -- Critically ill people who survive a stay in the intensive care unit face a heightened risk of mental health problems in the months after hospital discharge, a large new study suggests.

The study of more than 24,000 Danish ICU patients found that after discharge, people had an increased risk of developing depression, anxiety disorders or other psychiatric conditions.

The rates weren't high: About 0.5 percent of patients had a new diagnosis in the three months post-discharge. But that was 22 times the rate seen in the general population over the same time period, the findings showed.

Experts say the findings, reported in the March 19 issue of the Journal of the American Medical Association, highlight an emerging issue: As doctors get better at saving the lives of critically ill patients, more people will be at risk of longer-term problems beyond physical health.

"We've been worried for some time that we're discharging people who will be at risk of (mental health) problems, due to their illness and their experience in the ICU," said lead researcher Dr. Hannah Wunsch, of Columbia University Medical Center in New York City.

Based on her team's findings, that's the case.

For the study, the researchers used records from Denmark's system of medical databases. They focused on 24,000 ICU patients who were ill enough to be placed on a ventilator for complications ranging from lung failure to life-threatening infections.

Of those patients, almost 10,000 had no diagnosis of a mental health condition, or prescription for psychiatric drugs, in the prior five years. But in the three months after their discharge from the ICU, 0.5 percent received a new diagnosis, the researchers noted. Most often, that meant an anxiety disorder or "mood" disorder such as depression.

Many more -- 13 percent -- received a new prescription for a psychiatric medication, including antidepressants and drugs for anxiety and insomnia, according to the report.

Those rates were much higher than the ones among more than 80,000 Danish adults matched to the ICU patients for age and sex. Over the same time period, 0.02 percent were diagnosed with a mental health condition, and 0.7 percent were prescribed a psychiatric drug.

The ICU patients' risks also exceeded those of other hospital patients who didn't need intensive care. In that group, the study found, 0.2 percent were diagnosed with a psychiatric disorder in the three months after discharge, and 5 percent were prescribed a drug.

Those patterns aren't surprising, said Dr. Joseph Bienvenu, a psychiatrist at Johns Hopkins University School of Medicine in Baltimore.

"It's been known that many people who survive a critical illness have problems afterward, like depression, post-traumatic stress disorder and anxiety," said Bienvenu, who was not involved in the new study.

But these latest findings raise a big question, he said. Are the mental health issues specifically related to the ICU stay, or do those patients often have a history of psychiatric conditions?

Wunsch's team found that ICU patients did have a higher rate of past mental health conditions. Three percent had been diagnosed with a psychiatric disorder in the year before their ICU admission versus about 2 percent of other hospital patients and less than 1 percent of the general population.

But that didn't explain the post-discharge risks seen in the nearly 10,000 ICU patients with no signs of past mental health problems.

Bienvenu said it's not hard to imagine why those patients' mental health can suffer.

In the ICU, many patients become delirious, because of illness and the medications they're given. "They don't know what's going on," Bienvenu said. "And they often develop memories that are distorted -- kind of like a nightmare."

They may be aware of things happening around them, he noted, but have no understanding of it. Plus, patients on ventilators can't speak because of the breathing tube.

"All they know is that people are doing things to them," Bienvenu explained. "And they may think those people are trying to harm them, rather than help them."

Doctors don't routinely screen ICU patients for mental health problems. That's partly because the focus has been on, first, saving patients' lives, and then getting them into physical therapy or occupational therapy for any physical disabilities.

But there's a growing awareness that ICU survivors often have mental health issues and lingering "cognitive" effects, like problems with memory or thinking and planning, Bienvenu said.

And all of those problems can feed each other. "If you're depressed, it's hard to concentrate," Bienvenu noted. "If you can't walk, you're probably going to feel depressed. It's very important that we try to take care of the whole patient."

More information

The Society of Critical Care Medicine has information for ICU patients and families.