Disturbed memory and amnesia related to intensive care

Patients, when admitted to an intensive care unit (ICU), have one thing in common: their illness is life-threatening. Patients may remain on ICU in a critical condition, needing support with their breathing, circulation, and/ or kidneys for varying lengths of time, from days to weeks. During that tim e the patients will receive sedative and analgesic drugs to ensure complian ce with artificial ventilation. Patients recovering from critical illness f requently have little or no recall of their period in ICU, or remember nigh tmare, hallucinations, or paranoid delusions. The nature, extent and reason for these difficulties, have been under-reported and consequently our purp ose was to conduct a review of memory problems experienced by ICU patients. A systematic literature review of computer databases (Medline, PsycLit, an d CINAHL) identified 25 relevant papers. In addition, other relevant articl es were obtained, citation lists and associated articles retrieved. Due to lack of research on processes underlying memory problems in ICU patients al l articles that introduced an insight into possible mechanisms were include d in the review. There seem to be two possible processes contributing to memory problems in ICU patients. First the illness and treatment may have a general dampening effect on memory. Delirium and sleep disturbance are both common in ICU pat ients. Delirium can result in a profound amnesia for the period of confusio n. Sleep deprivation exacerbates the confusional state. Slow wave sleep is important for the consolidation of episodic memories. Treatment administere d to patients in ICU can have effects on memory. Opiates, benzodiazepines, sedative drugs such as propofol, adrenaline, and corticosteroids can all in fluence memory. In addition, the withdrawal of drugs, such as benzodiazepin es, can cause profound withdrawal reactions, which may contribute to deliri um. Second, we hypothesise that there is a process that affects memory nega tively for external events but enhances memory for internal events. The phy sical constraints and social isolation experienced by ICU patients and the life-threatening nature of the illness may increase the experience of hypna gogic hallucinations. Attentional shift during hypnagogic images from exter nal stimuli to internally generated images would explain why ICU patients h ave such poor recall of external ICU events, but can clearly remember hallu cinations and nightmares. Patients describe these memories as being very vi vid and this is explored in terms of flashbulb memory formation. The absence of memories for real events on ICU can result in ICU patients r emembering paranoid delusions of staff trying to kill them, with little inf ormation to reject these vivid memories as unreal. This has implications fo r patients' future psychological health.