A case-control study of patients readmitted to the intensive care unit.

OBJECTIVE: To determine characteristics of patients requiring readmission to an intensive care unit (ICU).

DESIGN: Retrospective case-control chart review.

SETTING: Adult patients in an 8-bed medical and 16-bed surgical ICU in a 650-bed university teaching hospital during an 18-month period.

INTERVENTIONS: None.

METHODS: Each patient readmitted to either ICU was compared to a single control patient matched for age, sex, unit, and diagnosis. A total of 117 variables were obtained from chart review. The last value for each variable before ICU discharge was used. Chi-square analysis, linear regression factor analysis, correlation, and Student's t-test were used to identify significant factors predicting the patient's return to an ICU. Descriptive statistics were used to describe various subgroups.

RESULTS: Mortality rate was 41.5% in the 82 readmitted patients (comprising 4.6% of the total ICU admissions) and only 7.3% in the controls. Mean (+/- SD) hospital length of stay was 47.8 +/- 42.0 days in the study group and 20.8 +/- 14.2 days (p < .0009) in the controls. Initial ICU length of stay was 8.3 +/- 16.1 days in the readmitted group and 4.0 +/- 5.0 days (p = .02) in the controls. Variables that predicted readmission to the ICU were: increased respiratory rate (24.2 vs. 20 breaths/min, p < .002), lower hematocrit value (31.9% vs. 34.4%, p = .01), positive fluid balance (p < .03), and positive blood cultures (six in the readmitted group, none in the controls, p = .002). More than 30% of readmissions were for a recurrence or worsening of the original problem. Fifty-four percent of the patients were readmitted with pulmonary failure. Mortality rate in both groups was related to advanced age, Acute Physiology and Chronic Health Evaluation (APACHE II) scores at ICU discharge, and increased blood urea nitrogen concentrations. Mortality rate in the control group, but not in the readmitted group, correlated with the level of consciousness, serum creatinine concentration, and use of hemodialysis.

CONCLUSIONS: Readmission to an ICU carries a risk of high mortality rate and increased length of stay and may represent premature discharge in at least 30% of patients. Pulmonary failure is the immediate cause of readmission in more than half of the readmitted patients. Increased respiratory rate correlates with ICU readmission. Intermediate care areas for patients with poor pulmonary function may help to avoid readmission to an ICU, prevent death, and conserve hospital resources.