Being admitted to a hospital intensive care unit can be frightening.

In addition to concerns about a serious physical ailment, the frenetic atmosphere disturbs the patient’s sleep-wake cycle and can agitate the most even-tempered person.

A study published in the New England Journal of Medicine showed that two out of three ICU patients experienced mental impairments as a result of being in the unit.

Four months after their hospitalization, 40 percent of these patients had cognitive decline comparable to that observed from a traumatic brain injury, and approximately 25 percent had symptoms similar to mild Alzheimer’s disease.

Six out of 10 patients still had cognitive symptoms one year after their ICU admission.

If patients experienced delirium during an ICU stay (for instance, confusion, unstable attention, or distorted thinking), they were more likely to develop post-ICU mental symptoms.

Taking painkillers did not seem to be linked to mental symptoms.

Delirium is linked to brain inflammation, which could contribute to mental decline.

This suggests that doctors should use aggressive treatment of this condition when it occurs, especially in an ICU setting.