An empirical derivation of the optimal time interval for defining ICU readmissions

Abstract

Background: Intensive care unit (ICU) readmission rates are commonly viewed as indicators of ICU quality. However, definitions of ICU readmissions vary, and it is unknown which, if any, readmissions are associated with ICU quality.

Objective: Empirically derive the optimal interval between ICU discharge and readmission for purposes of considering ICU readmission as an ICU quality indicator.

Research design: Retrospective cohort study.

Subjects: A total of 214,692 patients discharged from 157 US ICUs participating in the Project IMPACT database, 2001-2008.

Measures: We graphically examined how patient characteristics and ICU discharge circumstances (eg, ICU census) were related to the odds of ICU readmissions as the allowable interval between ICU discharge and readmission was lengthened. We defined the optimal interval by identifying inflection points where these relationships changed significantly and permanently.

Results: A total of 2242 patients (1.0%) were readmitted to the ICU within 24 hours; 9062 (4.2%) within 7 days. Patient characteristics exhibited stronger associations with readmissions after intervals >48-60 hours. By contrast, ICU discharge circumstances and ICU interventions (eg, mechanical ventilation) exhibited weaker relationships as intervals lengthened, with inflection points at 30-48 hours. Because of the predominance of afternoon readmissions regardless of time of discharge, using intervals defined by full calendar days rather than fixed numbers of hours produced more valid results.

Discussion: It remains uncertain whether ICU readmission is a valid quality indicator. However, having established 2 full calendar days (not 48 h) after ICU discharge as the optimal interval for measuring ICU readmissions, this study will facilitate future research designed to determine its validity.

Figure 1

Cumulative Events 24–168 hours post-ICU discharge

Figure 2. Patient Variables

All models adjusted for year of ICU admission, whether patient received a critical care consult, patient race (black, white, other), ICU admission location (Emergency Department, Another Hospital, General Care Floor, Step Down, Procedure, SNF, Rehab or LTAC, Another ICU, Other) discharge from the ICU to a general care floor or step down unit, DNR status at the time of ICU discharge, duration of mechanical ventilation, receipt of mechanical ventilation, receipt of vasopressors while in the ICU, functional status at the time of ICU admission (independent, partially dependent, fully dependent), patient insurance status (private, medicare, Medicaid, self pay, other) patient age (<65, 65–74, 75–84, 85+), admission to the ICU for treatment vs. monitoring, MPM, ICU length of stay, number of comorbidities, and the presence of chronic respiratory or cardiovascular illness, chronic renal failure, requiring of dialysis, solid organ cancer in the past 5 years, and proven metastatic cancer, % new ICU admissions, ICU census, and acuity of other patients in the ICU on the day of ICU discharge, duration of time between extubation or pressor discontinuation and ICU discharge. *Log transformed exposure

Figure 3. ICU Discharge Circumstance Variables

All models adjusted for year of ICU admission, whether patient received a critical care consult, patient race (black, white, other), ICU admission location (Emergency Department, Another Hospital, General Care Floor, Step Down, Procedure, SNF, Rehab or LTAC, Another ICU, Other) discharge from the ICU to a general care floor or step down unit, DNR status at the time of ICU discharge, duration of mechanical ventilation, receipt of mechanical ventilation, receipt of vasopressors while in the ICU, functional status at the time of ICU admission (independent, partially dependent, fully dependent), patient insurance status (private, medicare, Medicaid, self pay, other) patient age (<65, 65–74, 75–84, 85+), admission to the ICU for treatment vs. monitoring, MPM, ICU length of stay, number of comorbidities, and the presence of chronic respiratory or cardiovascular illness, chronic renal failure, requiring of dialysis, solid organ cancer in the past 5 years, and proven metastatic cancer, % new ICU admissions, ICU census, and acuity of other patients in the ICU on the day of ICU discharge, duration of time between extubation or pressor discontinuation and ICU discharge. *Odds ratios for a 10% change in the exposure †ICU census is standardized and normalized