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Eur J Cardiothorac Surg 2003;23:354-359
© 2003 Elsevier Science NL
Division of Cardiac Surgery, New Halifax Infirmary, Halifax, Nova Scotia, Canada
Received 10 July 2002; received in revised form 20 November 2002; accepted 21 November 2002.
* Corresponding author. New Halifax Infirmary, QEII HSC, Division of Cardiac Surgery, 1796 Summer Rm. 2269, Halifax, Nova Scotia, B3H 3A7, Canada. Tel.: +1-902-473-7597; fax: +1-902-473-4448
e-mail: imtiaz.ali{at}dal.ca
| Abstract |
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Key Words: Cardiac surgery Intensive care unit Readmission
| 1. Introduction |
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ICU readmission is believed to be associated with higher in-hospital mortality and may predict poor outcomes [11]. Only a few studies have considered the issue of readmission to the ICU in surgical patients [1214]. These have produced variable results because of the heterogeneity of patients evaluated, presumably related to the varied nature of the operations typically performed at the respective institutions. Taken together, the most reliable predictor of readmission reported by these studies was unstable vital signs at the time of ICU discharge [11].
We are aware of only one study that examined cardiac surgery patients specifically [10]. In that study, Cohn et al. found an increase in cardiac surgery ICU readmissions over a 4 year time frame. Their study was motivated by a concern that the increase in ICU readmissions may have resulted from an observed decrease in initial ICU length of stay during the same period. Instead they found that patients discharged earlier from the ICU generally were not readmitted as often as those who had prolonged initial ICU stays. This begs the questions, why was their rate of ICU readmission increasing, and if ICU readmissions are not a result of shorter initial ICU stays, what are the causes?
In the present study we sought to determine predictors of ICU readmission in a large group of patients undergoing coronary artery bypass surgery (CABG) at a single institution, and to evaluate their longitudinal follow-up in terms of mortality over time. The ability to predict who is at risk for ICU readmission may set the stage for preemptive strategies.
| 2. Methods |
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2.2. Data collection
Perioperative patient variables were collected on Society of Thoracic Surgeons (STS) forms by three full time research assistants and maintained in a computer database format (Summit Medical Systems, Inc. MN, USA, 1997). This has been standard practice at this institution for all cardiac surgical cases since 1995 with data element validation. Urgency status was also determined using the standard STS Cardiac Surgery Database definitions. An elective case was defined as one in which the patient was stable for more than 24 h prior to the procedure. Urgent operations were those that required a procedure to be performed within 24 h to prevent further clinical deterioration, and emergent/salvage cases were those patients who required an immediate operation. The variables evaluated included: age, chronic obstructive pulmonary diseases (COPD), cross-clamp time, diabetes, ejection fraction (EF), gender, hypertension, intra-aortic balloon counter-pulsation use, New York Heart Association class (NYHA), perioperative myocardial infarction (MI), preoperative hospitalization, preoperative renal failure (renal failure was defined as a serum creatinine greater or equal to 177 mmol/l), prolonged ventilation, pump time, reoperation, stroke, and urgency status.
2.3. Clinical decision making
All postoperative cardiac surgery patients were taken to a dedicated cardiovascular intensive care unit (CVICU), not a post-anesthesia recovery care unit. The decision to discharge patients from the ICU was made on an individual, patient-by-patient basis by one of the seven attending cardiovascular surgeons, two cardiac anesthetists, and/or supporting resident house-staff taking care of the patient. Patients were generally not transferred from the ICU if they were considered at risk clinically for decreased oxygen delivery. This included patients with signs of inadequate tissue perfusion (lactate levels >4 mmol/l, mixed venous oxygen saturation <50%, urine output <0.5 ml/kg per h, cardiac index <2 l/min per m2), significant hemodynamic instability, patients requiring inotropes other than low dose dopamine (<3 µg/kg per min), utilization of a intra-aortic balloon pump (IABP) or a ventricular assist device (VAD), and patients with multi-organ dysfunction.
Discharged patients were transferred to an intermediate care or general care ward under the care of the same surgeons and house-staff team. Patients readmitted to the ICU were identified by reviewing the ICU logbook. Note that a few patients were readmitted to a medical ICU when no beds were available in CVICU and were considered readmissions in this study. The reasons for readmission were determined by reviewing the physician's progress notes, the nurse's progress notes and the discharge summary.
2.4. Statistics
Descriptive statistics were obtained for all variables using the SAS software package (SAS, Version release 6.12, SAS Institute Inc., Cary, NC). These included continuous and discrete variables which were analyzed with Student's t-test, the chi-squared test, or Fisher's exact test where appropriate. A stepwise logistic regression model was developed to identify predictors of ICU readmission for patients undergoing CABG. Univariate predictors of ICU readmission were entered into the model if the P value was less than or equal to 0.05. KaplanMeier survival analysis was used to evaluate all cause mortality. Mortality data were obtained from vital statistics (Government of Nova Scotia), by contacting the family physicians of the individual patients to obtain the last known follow-up, and by attempting to contact the patients directly.
| 3. Results |
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| 4. Discussion |
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Cohn et al. [10] attempted to predict a return to ICU by identifying several clinical variables related to ICU readmission which included: longer initial ICU length of stay, poor left ventricle (LV) function, a history of congestive heart failure (CHF), longer initial intubation time, and postoperative weight gain. Similarly, we found COPD, renal failure, age >70, NYHA IV, redo surgery, low EF, prolonged initial mechanical ventilation and longer preoperative hospitalization all to be univariate predictors of ICU readmission. However, only preoperative renal failure and prolonged mechanical ventilation were shown to be independent predictors of readmission to ICU after multivariate analysis.
Both of these multivariate predictors of ICU readmission fit well with our understanding of perioperative morbidity. Patients with renal failure are at greater risk of complications related to poor nutrition, fluid overload and respiratory dysfunction, metabolic and electrolyte abnormalities, and problems of drug overdose and toxicities, all of which can necessitate a return to the ICU. Preoperative renal failure and the need for postoperative dialysis have both been associated with increased perioperative mortality [16]. While prolonged mechanical ventilation defined as greater than 24 h is required in less than 10% of patients who undergo CABG surgery [4], it was shown in the present study to be the strongest predictor of a return to ICU with an odds ratio of 10. Prolonged ventilation is a surrogate for poor outcome and is known to be associated with several important variables including preoperative low EF, renal failure, COPD, age, gender, and unstable angina [4]. Despite the inherent limitations of a retrospective study we have identified two important clinical variables that appear to predict a return to ICU and on which adjustments to patient care can be focused.
There is considerable debate regarding how information on ICU readmission rates can best be used. It may be that centers with high rates of readmission are delivering sub-standard care. Alternatively, these centers may be more aggressive with respect to early discharge from ICU in an attempt to reduce costs. While patients readmitted to the ICU have a worse course in general, there is no evidence that patients readmitted to the ICU would have had a better outcome had the event that brought them back to the ICU occurred in the ICU rather than on the wards [17]. Furthermore, the role of intensive care itself may be in question. ICU practice patterns vary widely, with one study estimating ICU utilization in the United States to be 2.5 times that in Canada [18]. What is well established is that those who return to the ICU fair worse, making the prediction of this event worthwhile. In clinical practice, attention should be paid to optimizing the recovery of patients that have undergone prolonged ventilation or those in renal failure before discharging them from the ICU. Further research into methods of avoiding these complications may help to decrease the rate of ICU recidivism.
Considerable effort has been invested in reducing the length of hospital stays using fast-tracking protocols in an attempt to reduce cost [19]. It would appear that discharging patients earlier from the ICU does not affect the rate of readmission [10]. In fact more than two-thirds of patients readmitted to ICU in the present study had been discharged for 2 or more days suggesting that too early an original discharge was not likely the cause for readmission. The economic impact of discharge and readmission to the ICU versus remaining in the ICU has not been determined. It has been suggested that the former may be more costly, as the greatest proportion of ICU costs are accrued on the first day, and presumably a readmission to the ICU would be like a second first day [20]. This may not be true in other institutions within different healthcare systems. One method that has been proposed to reduce readmission rates to ICUs is to include the appointment of a follow-up nurse [21].
In summary, identification of patients that have preoperative renal failure or that have undergone ventilation for more than 24 h after CABG may help to identify patients at risk of ICU readmission. Careful optimization of these high-risk patients and caution before discharging them from the ICU may help to reduce the rate of ICU readmission, with a possible decrease in mortality, length of stay, and cost.
| References |
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