To promote successful recovery after a hospitalization, health care professionals often focus on issues related to the acute illness that precipitated the hospitalization. Their disproportionate attention to the hospitalization's cause, however, may be misdirected. Patients who were recently hospitalized are not only recovering from their acute illness; they also experience a period of generalized risk for a range of adverse health events. Thus, their condition may be better characterized as a post-hospital syndrome, an acquired, transient period of vulnerability. This theory would suggest that the risks in the critical 30-day period after discharge might derive as much from the allostatic and physiological stress that patients experience in the hospital as they do from the lingering effects of the original acute illness. At the time of discharge, physiological systems are impaired, reserves are depleted, and the body cannot effectively defend against health threats.

Nearly one fifth of Medicare patients discharged from a hospital — approximately 2.6 million seniors — have an acute medical problem within the subsequent 30 days that necessitates another hospitalization. These recently discharged patients have heightened risks of myriad conditions, many of which appear to have little in common with the initial diagnosis. The causes of readmission, regardless of the original admitting diagnosis, commonly include heart failure, pneumonia, COPD, infection, gastrointestinal conditions, mental illness, metabolic derangements, and trauma (see graphProportions of Rehospitalizations for Causes Other Than the Condition at Initial Discharge.). The breadth of these readmission diagnoses has been shown in studies using administrative claims and those using chart reviews. Thus, this observation is not likely to be merely the result of variation in coding. 

How might the post-hospital syndrome emerge? Hospitalized patients are not only enduring an acute illness, which can markedly perturb physiological systems, but are experiencing substantial stress. During hospitalization, patients are commonly deprived of sleep, experience disruption of normal circadian rhythms, are nourished poorly, have pain and discomfort, confront a baffling array of mentally challenging situations, receive medications that can alter cognition and physical function, and become deconditioned by bed rest or inactivity. Each of these perturbations can adversely affect health and contribute to substantial impairments during the early recovery period, an inability to fend off disease, and susceptibility to mental error.

Researchers have documented the prevalence and risk of these stressors. For example, hospitalized patients often experience disturbance of sleep, and studies have revealed polysomnographic abnormalities in hospitalized patients, including reductions in sleep time and stages R (rapid eye movement [REM]) and N3 (slow wave) and an increase in stage N1 (non-REM). This disruption can have debilitating behavioral and physiological effects: sleep deprivation adversely affects metabolism, cognitive performance, physical functioning and coordination, immune function, coagulation cascade, and cardiac risk.