AACN Advanced Critical Care Volume 27, Number 1, pp. 29-39 © 2016 AACN

Risk Factors and Outcomes Associated With Readmission to the Intensive Care Unit After Cardiac Surgery Young Ae Kang, RN, MSN, CCN, CNS

ABSTRACT mechanical ventilation time, new-onset arrhythmia, unplanned reoperation, massive blood transfusion, prolonged inotropic infusions, and complications. Other factors were high blood glucose level, hemoglobin level, and score on the Acute Physiology and Chronic Health Evaluation II. In-hospital stay was longer and late mortality was higher in the readmitted group. These data could help clinical practitioners create improved ICU discharge protocols or treatment algorithms to reduce length of stay or to reduce readmissions. Keywords: readmission, cardiac surgery, intensive care unit, risk factor

Unplanned readmission to the intensive care unit (ICU) is associated with poor prognosis, longer hospital stay, increased costs, and higher mortality rate. In this retrospective study, involving 1368 patients, the risk factors for and outcomes of ICU readmission after cardiac surgery were analyzed. The readmission rate was 5.9%, and the most common reason for readmission was cardiac issues. Preoperative risk factors were comorbid conditions, mechanical ventilation, and admission route. Perioperative risk factors were nonelective surgery, duration of cardiopulmonary bypass, and longer operation time. Postoperative risk factors were prolonged


o accommodate greater consumer interest in the quality of medical services that has resulted from the changing medical marketplace and higher incomes, the US Department of Health and Human Services has begun efforts to improve health care by evaluating the quality of health care services offered by hospitals. Performance indicators that can be used to directly assess the outcomes of health care services, such as mortality, morbidity, incidence of sequelae, and reutilization of services, are useful general measures. These objective indicators may be effectively used to evaluate treatment outcomes quantitatively and are thus considered useful measures of health care quality and effectiveness.1 According to the Quality Indicators Committee of the Society of Critical Care Medicine, intensive care unit (ICU) readmission, which is an unplanned admission within 48 hours

after previous discharge, is one of the indicators of health care quality and effectiveness.2 Unplanned ICU readmissions may reflect insufficient treatment of patients during the previous ICU episode or premature discharge.2 However, ICU readmission has been more associated with patients’ characteristics and in particular with illness severity than with the quality of treatment.3 Given the effect of an ICU readmission on patients, unplanned readmissions can be an important indicator of health care quality.1 Moreover, ICU readmission is highly related to mortality and Young Ae Kang is Clinical Nurse Specialist, Cardiovascular Surgery ICU, Asan Medical Center, 88, Olympic-ro, 43-gil, Songpa-gu, Seoul, 138-736, Korea ([email protected]). The author declares no conflicts of interest. DOI: http://dx.doi.org/10.4037/aacnacc2016451




factors such as underlying condition, age, and disease severity.8,14,15 Most patients were readmitted to the ICU because of hemodynamic problems such as respiratory and cardiac insufficiency, and the duration of mechanical ventilation during the initial ICU admission was longer in readmitted patients.4,15 Several Korean studies have addressed ICU readmission, and most of the previous studies targeted patients in integrated ICUs. In a few international studies, researchers compared ICU readmission in patients who had undergone cardiac surgery with readmission rates of all ICU patients. Therefore, an assessment of the prognosis and readmission-related factors according to diseases and departments in large hospitals equipped with specialized ICUs could help to target interventions in subsets of patients at risk for readmission and to create decision algorithms for optimal ICU discharge time. Furthermore, the rate of premature ICU discharge could potentially be decreased. By targeting patients who underwent cardiac surgery, the present study was intended to help decrease ICU readmissions by analyzing the factors associated with unplanned ICU readmission and patients’ prognosis, particularly to clarify patients’ predischarge risk factors. In addition, a secondary purpose of this study was to lay a foundation for the optimal assessment of patients’ status before ICU discharge for future use in establishing standardized protocols for determining the appropriate ICU discharge time for cardiac surgical patients.

morbidity,4 and when patients are readmitted, the increased length of stay due to the patient’s worsening illness increases overall health care costs. ICU treatment is reportedly 3 times more expensive than is care in general patient care units.5 To shorten the ICU hospitalization period, protocols that include initiatives such as early extubation have been developed and executed.6 However, readmission rates are growing along with an increased incidence of reintubations and complications, drawing focused attention to the problems associated with potential premature discharge from the ICU.7 Background Most patients who undergo cardiac surgery receive immediate postoperative care in the ICU without being transferred to a post­anesthesia recovery room.8 Upon discharge from the ICU, they are transferred to general care units, where the patients may be exposed to a treatment environment that is less than optimal to address the complex needs of patients recovering from cardiac surgery. In general patient care units where patients cannot be intensively monitored, it may not be possible to rapidly detect changes in the patient’s condition or to implement early treatment appropriate to the patient’s status. Accordingly, readmission to the ICU from general care units is always a possibility. Unplanned ICU admission is an unfortunate experience for both patients and their families. Most patients who are readmitted to the ICU with deteriorating health have a poor prognosis,9 require more time and effort from medical teams,10 and show significantly higher in-hospital mortality and longer hospital stays than patients admitted for the first time.11 Most patients are readmitted to the ICU because they require intensive care.12 However, Nishi et al13 reported that 20.8% of the readmitted patients in a surgical ICU would not have been readmitted if they had received proper treatment after a previous discharge and that 4.6% were readmitted because of premature discharge. Thus, ICU readmission could be prevented or reduced if the factors associated with ICU readmission were identified and the discharge time more appropriately determined. Researchers in previous studies have reported that readmissions to the ICU after a previous discharge were associated with

Methods Design

This retrospective observational cohort study was done to analyze the risk factors associated with unplanned ICU readmission after cardiac surgery and patients’ prognosis. This study was approved by the institutional review board of Asan Medical Center, Seoul, Korea, and permitted by the relevant medical department. Study Population

Ultimately, the present study included 1368 patients who had undergone cardiac surgery and were hospitalized in the cardiovascular surgery ICU of a tertiary hospital in Seoul, Korea, between January 1, 2012, and June 30, 2013. ICU readmission was defined as readmission of a patient to the same ICU after discharge 30




All patients admitted to cardiovascular surgery intensive care unit (n = 1520) Excluded Not meeting inclusion criteria (n = 148)


Included (n = 1372)

Nonreadmitted group (n = 1287)

Readmitted group (n = 85)

Nonreadmitted group (n = 1287)

Unplanned readmitted group (n = 81)

Excluded Planned readmissions due to staged operations during same hospitalization (n = 4)

Figure 1: Enrollment flow diagram.

to a general care unit during the same hospitalization.1,10,11,16 Patients who were unexpectedly readmitted to the cardiovascular surgery ICU because of a deterioration or change in their condition were included in the analyses as “readmitted.” All selected patients were older than 18 years and had been admitted to the ICU after major cardiac surgery during the specified study time frame, including all surgeries that involved cardiopulmonary bypass (CPB), off-pump coronary artery bypass graft (CABG), and pericardectomy without CPB. The exclusion criteria were as follows: (1) patients whose readmission length of stay was less than 4 hours, (2) patients who died in the ICU during treatment or were transferred to another hospital, and (3) patients transferred to a different ICU to have continuous treatment for a noncardiac illness after cardiac surgery. Patients readmitted to the ICU at different times of the study period because of sequential surgery or treatments were also included because they were regarded as individual hospitalization cases, in accordance with the above inclusion and exclusion criteria. The flow diagram describing selection of study participants is presented in Figure 1, and the general characteristics of participants are listed in Table 1. Of the 1368 patients, 806 (58.9%) were male, and the mean age was 58.7 (SD, 13.3) years. A total of 134 patients (9.8%) had a history of 2 or more cardiac surgeries, and a previous cardiac problem was seen in 24.0%.

CABG surgery was performed in 29.6%, valve surgery in 40.6%, aorta surgery in 11.2%, and combined surgery (CABG/valve surgery, CABG/aorta surgery) in 4.7%. The remaining operations included heart transplant, pulmonary thromboembolectomy, cardiac myxoma excision, and congenital heart disease repair. Data Collection

Data were collected from the electronic medical records by using a standardized form designed by the author. The preoperative clinical information of patients included ICU admission routes, diagnoses, type of operation, preoperative arrhythmia, ejection fraction, urgency of operation (elective or emergent), operation time, and CPB time. Postoperative information included mechanical ventilation time, infusion time of inotropic drugs, newonset arrhythmia, newly developed complications, new implantation of cardiac support devices, and blood transfusion. Laboratory data, scores on the Acute Physiology and Chronic Health Evaluation (APACHE) II, and support drugs or devices at the time of ICU discharge also were examined. Statistical Analysis

Data were analyzed by using IBM SPSS 20.0 in both univariate and multivariate models. Continuous data are presented as mean (SD) or median (interquartile range [IQR]), and categorical data are presented as number (percentage). Logistic regression testing was used to analyze risk factors 31



Table 1: General Characteristics of the Study Patients (N = 1368) Characteristic

Table 2: Clinical and Therapeutic Characteristics of the Study Patients (N = 1368) a





Age, mean (SD), y

58.7 (13.3)

55.6 (12.9)

Sex Male Female

Preoperative ejection fraction, mean (SD), %

806 (58.9) 562 (41.1)

Preoperative arrhythmia

320 (23.4)

Body surface area, mean (SD), m2

1.69 (0.19)

Diabetes mellitus

311 (22.7)


554 (40.5)


Preoperative device Ventilator IABP, ECMO

25 (1.8) 22 (1.6)

466 (34.1)

Admission route General care area ICU/ER

1206 (88.2) 162 (11.8)

Smoking Current Former

280 (20.5) 313 (22.9)

Surgery type Elective Emergency

1151 (84.1) 217 (15.9)

ICU admission history

426 (31.1)

Operation time, mean (SD), h

Cardiac surgery history

134 (9.8)

Comorbid condition Cardiac problems Cerebrovascular disease Respiratory disease Azotemia ESRD or hemodialysis Cancer

329 (24.0) 142 (10.4) 78 (5.7) 94 (6.9) 24 (1.8) 54 (3.9)

CPB Operation with CPB use CPB time, mean (SD), min

Surgery classification CABG Valve surgery Aorta surgery Combined surgery Heart transplant Other

405 (29.6) 556 (40.6) 153 (11.2) 64 (4.7) 62 (4.5) 128 (9.4)

Mechanical ventilation time, median (IQR), h Inotropic drugs Patients receiving Infusion time, median (IQR), h

Values are number (percentage) of patients unless otherwise specified in first column.

associated with unplanned readmission. The nonreadmission and readmission groups were compared by using c2 and Fisher exact tests. A P value of .05 or less was considered statistically significant.

10.0 (1.6-8050.2)

944 (69) 38 (0.2-932.1) 36 (2.6) 235 (17.2)

New-onset arrhythmia

553 (40.4)

Complication Cardiac Cerebrovascular Respiratory Bleeding New-onset CRRT or HD


1042 (76.2) 148 (67.3)

Cardiac device support IABP, ECMO Pacemaker

ICU events Reoperation CPCR

Abbreviations: CABG, coronary artery bypass graft; ESRD, end-stage renal disease; ICU, intensive care unit.

4.8 (1.6)

58 (4.2) 13 (1.0) 79 58 46 152 23

(5.8) (4.2) (3.4) (11.1) (2.6)

Abbreviations: CPB, cardiopulmonary bypass; CPCR, cardiopulmonary cerebral resuscitation; CRRT, continuous renal replacement therapy; ECMO, extracorporeal membrane oxygenator; ER, emergency room; HD, hemodialysis; IABP, intra-aortic balloon pump; ICU, intensive care unit; IQR, interquartile range.


Values are number (percentage) of patients unless otherwise specified in first column.

Clinical and therapeutic characteristics of the study participants are listed in Table 2. Briefly, 11.8% of patients were admitted via the ICU or emergency department, preoperative arrhythmias were seen in 23.4% of patients, and 1.8% of patients required mechanical ventilation during preoperative

care. Two hundred seventeen patients (15.9%) had emergent or urgent surgery, and the mean operation time was 4.8 (SD, 1.6) hours. CPB was used in 76.2% of patients, and the mean CPB time was 148 (SD, 67.3) minutes. During postoperative care, the median duration of mechanical ventilation was 10


Clinical and Therapeutic Characteristics of the Study Patients




Table 3: Characteristics and Outcomes of Patients Readmitted to the Intensive Care Unit (n = 81) Valuea Characteristic Reason for readmission Cardiac Respiratory Cerebrovascular Gastrointestinal Sepsis Reoperation Wound infection Time interval between readmission and ICU discharge, median (IQR), h ≤ 72 h 72 h-7 d 7-14 d 14-21 d 21-28 d > 28 d Second ICU LOS, median (IQR), h


17 20 10 27 4 3

Risk Factors and Outcomes Associated With Readmission to the Intensive Care Unit After Cardiac Surgery.

Unplanned readmission to the intensive care unit (ICU) is associated with poor prognosis, longer hospital stay, increased costs, and higher mortality ...
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