THURSDAY, May 1 (HealthDay News) -- About one-third of children in pediatric intensive care units experience delusions, and those delusional memories put youngsters at a higher risk of developing post-traumatic stress syndrome after their hospital stay.

Delusions were more common in children who had to be sedated for more than two days, and in youngsters who were admitted on an emergency basis, according to a study in the first May issue of the American Journal of Respiratory and Critical Care Medicine.

"In the majority of cases, these delusional memories consisted of one or more hallucinations which were often frightening and which the children could still recall vividly," said study author Gillian Colville, a consultant clinical psychologist and head of the pediatrics psychology service at St. George's Hospital in London. "[Children] reported seeing rats, cats, scorpions on the walls and, in some cases, crawling on the bed, and a couple of children were convinced that their parents had been replaced by imposters."

The timing of these hallucinations was usually around the time the children were being weaned off sedatives. Such medications are used to help control pain and anxiety in children, and in adults, who need intensive medical care.

"Sedatives, and benzodiazepines in particular, interfere with the ability to form new memories, and part of what they do is alter how you remember what's going on," said Dr. Scott Watson, a pediatric intensivist in the division of critical care medicine at Children's Hospital of Pittsburgh. "Sedating medications also interfere with normal sleep, so processing information and memory is more difficult."

However, because being in intensive care is a stressful experience itself, the authors aren't recommending that the use of sedatives be discontinued but suggest that additional studies be done in children to see if periods of interrupted sedation might lower rates of delirium.

The current study included 102 children between the ages of 7 and 17 who were asked about their experience in the PICU three months after they had been discharged.

Sixty-three percent of the children reported at least one factual memory of their hospital stay, such as seeing their parent at their bedside when they woke, or seeing the video monitors in the PICU.

Thirty-two percent of the youngsters reported having delusional memories. If they were sedated for more than two days, the odds of having a delusional memory increased nearly fivefold, according to the study.

Twenty-seven children had scores high enough to be considered as having "probable" post-traumatic stress disorder (PTSD), and the risk of PTSD was significantly higher for children who reported having delusional memories.

"Some of the symptoms that define PTSD involve the person reexamining what happened in the form of intrusive memories, sometimes known as flashbacks," explained Colville. "These memories are likely to be of the particularly distressing parts of what happened and are associated with strong emotions of fear and threat. On the whole, the children interviewed were much more distressed by their delusional memories than by the factual memories they experienced."

Colville recommended that parents and caregivers be clear and honest with children, in an age-appropriate manner, about what's going on both during their hospital stay and after. She said it's reassuring for children to know that other children have experienced the same types of hallucinations. "Sometimes, [children] have thought they were going mad," she said.

Watson agreed, adding "Children are likely to have confused and potentially disturbing memories of an ICU stay. Despite this, most children appear to recover well and don't suffer from PTSD. If your child is having difficulty or shows signs of PTSD, talk to your provider about getting help."

Symptoms of PTSD include recurrent, intrusive memories or flashbacks of the event, difficulty concentrating, sleeping problems, irritability and lack of enjoyment of normal activities, according to the National Library of Medicine.

More information

To read more about what to expect from a stay in the pediatric intensive care unit, visit the Nemours Foundation's KidsHealth.