During the last decade, cardiac surgery has faced a

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1 Determinants of Early Discharge From the Intensive Care Unit After Cardiac Operations Marco Ranucci, MD, Carmen Bellucci, MD, Daniela Conti, MD, Anna Cazzaniga, MD, and Bruno Maugeri, MD Departments of Cardiovascular Anesthesia and Intensive Care and Internal Medicine, IRCCS Policlinico S. Donato, Milan, Italy Background. The length of stay in the intensive care unit is one of the factors limiting operating room utilization in cardiac surgery. We investigated the impact of a goal-oriented program aimed at discharging the patients from the intensive care unit the morning after the operation within a comprehensive model including other explanatory variables. Methods. A multivariable predictive model for early discharge from the intensive care unit was established using a stepwise forward logistic regression. The analysis was retrospectively conducted on 9120 consecutive patients undergoing cardiac surgical procedures at our institution. Results. A total of 1874 patients were discharged early from the intensive care unit. Factors associated with early discharge were ejection fraction, lowest hematocrit on cardiopulmonary bypass, lowest temperature on cardiopulmonary bypass, and the presence of the goal-oriented strategy (odds ratio, 5.5; 95% confidence interval, 4.8 to 6.3). Factors associated with late discharge were age, preoperative serum creatinine value, unstable angina, congestive heart failure, redo operation, combined operation, and cardiopulmonary bypass duration. An extubation time of 4 hours after the arrival in the intensive care unit was associated with the peak rate of early discharge. Patients being early discharged according to the goal-oriented strategy did not demonstrate a different complication rate compared with patients treated with a standard strategy. Conclusions. Early discharge from the intensive care unit depends on a combination of preoperative and intraoperative factors, but most of all on the presence of a goaloriented strategy. A very early extubation is not required for an early discharge from the intensive care unit. (Ann Thorac Surg 2007;83: ) 2007 by The Society of Thoracic Surgeons During the last decade, cardiac surgery has faced a growing interest for fast extubation and early discharge from the intensive care unit (ICU) after the operation. The main determinant of this increased demand for fast-track cardiac surgery is the need for containing the burgeoning costs involved in cardiac operations, saving resources, and ICU costs. Cheng and associates [1] showed that the application of fast-track cardiac anesthesia results in a decreased intubation time, resource usage, and costs in patients undergone coronary artery bypass graft (CABG) surgery. Early extubation is classically considered one of the main steps in a fast-track process [2], and different anesthesia protocols have been proposed to achieve this goal. In the 1990s, the common procedure for fast-track cardiac anesthesia included a limited intravenous opioid dose with the concomitant use of volatile anesthetics or propofol, or both [3, 4]. Subsequently, many authors proposed the use of a totally intravenous anesthesia [5 8]. Regardless of the anesthetic regimen, there is still an open debate about the optimal extubation time after cardiac operations, even if it is generally accepted that early extubation is one of the main determinants of early discharge from the ICU [1, 2, 4, 6, 9]. Accepted for publication Oct 2, Address correspondence to Dr Ranucci, Cardiovascular Anesthesia Department, IRCCS Policlinico S. Donato, Via Morandi 30, San Donato Milanese, Milan, Italy; cardioanestesia@virgilio.it. Many studies have addressed the success rate of a fast-track program in different conditions; however, nearly all of the studies (1) included only patients who had undergone isolated CABG operations [7, 9 12]; (2) were powered to compare different fast-track cardiac anesthesia techniques [5 7, 10]; (3) were powered to compare different postoperative analgesia managements [8, 12], and (4) with few exceptions [13], fewer than 600 patients were analyzed. The primary end point of this study was to determine the predictors for an early discharge (the morning after the operation) from the ICU after cardiac operations, with specific respect to the application of a goal-oriented strategy. The role of extubation time in this process and the outcome profile in patients being discharged early from the ICU are secondary end points. Patients and Methods The present study is based on a retrospective analysis of the cardiac surgical activity at our institution during the last 6 years. Patients A series of 9120 consecutive patients who had cardiac operations at our institution in the period May 1, 2000, through March 31, 2006, was retrospectively analyzed using the local computerized database. Data before the 2007 by The Society of Thoracic Surgeons /07/$32.00 Published by Elsevier Inc doi: /j.athoracsur

2 1090 RANUCCI ET AL Ann Thorac Surg EARLY DISCHARGE FROM THE ICU 2007;83: year 2000 were unavailable owing to the lack of a systematic data collection. All patients gave a written consent to the anonymous scientific treatment of their data. The local ethical committee waived the need for approval. The database includes all the adult ( 18 years) patients undergoing cardiac surgical procedures. Every kind of cardiac operation was included, excepted cardiac transplantation, which is not performed in our institution. The only exclusion criterion was death during the operation or within the first 24 hours after the operation (66 patients). A final series of 9054 adult patients was admitted to the statistical analysis. Intraoperative Anesthetic Management, Monitoring, and Cardiopulmonary Bypass Premedication included atropine sulphate (0.5 mg), promethazine (50 mg), and fentanyl (50 to 100 g, according to the patient s weight). Anesthesia was induced with an intravenous infusion of remifentanil at a starting dose of 0.5 g kg 1 min 1 and a midazolam bolus of 0.2 mg/kg. Cisatracurium besylate (0.2 mg/kg) was administered to allow tracheal intubation. The anesthesia was maintained with a continuous infusion of remifentanil at a dose of 0.05 g kg 1 min 1 to 1 g kg 1 min 1 (titrated on the basis of the hemodynamic response) and midazolam at 0.1 mg kg 1 h 1. All the operations were performed with cardiopulmonary bypass (CPB). CPB was conducted using closed or open circuits, standard or phosphorylcholine coated hollow-fiber oxygenators, and roller or centrifugal pumps, according to availability. Regardless of the circuit used, the priming volume was always minimized to 800 to 1000 ml. Intraoperative standard monitoring included the usual invasive arterial blood pressure monitoring at the radial site plus a triple lumen central venous catheter for central venous pressure measurement. In patients with a reduced ejection fraction ( 0.30), a pulmonary artery catheter was inserted, and in case of a valve procedure or combined operations, transesophageal echocardiographic monitoring was applied. After CPB discontinuation and protamine administration, an intramuscular dose of 10 to 15 mg of morphine (according to the patient s weight) was administered, and an intravenous infusion of ketorolac (30 mg) and tramadol (100 mg) was started and continued until the end of the operation. Simultaneously, the remifentanil infusion was decreased, to be stopped at the end of the operation. At the skin closure, an elastomeric pump was connected to a peripheral venous catheter to guarantee a continuous infusion of ketorolac (0.05 mg kg 1 h 1 ) and tramadol (0.15 mg kg 1 h 1 ) throughout the first 24 hours of the postoperative course. The last cisatracurium besylate bolus was administered at the sternal closure. Patients were transferred to the ICU with the midazolam infusion at 0.05 mg kg 1 h 1. Postoperative Management All the patients were admitted to the adult postcardiac surgery ICU, where the nursing ratio is 1:2 patients. Postoperative analgesia was maintained with the elastomeric pump infusion and, if needed, with an intravenous dose of morphine (5 mg). The midazolam infusion was maintained during the first hour, considered as the observation period. Criteria for starting the extubation process were at least 2 hours from the arrival in ICU, temperature higher than 36 C, hemodynamically stable, chest tube drainage of less than 100 ml/h, and hourly urine output exceeding 0.5 ml/kg. Once this profile was established, the midazolam infusion was stopped if it was still being used. Patients were considered eligible for extubation when they met the following criteria: responds to command, pulse oximetry oxygen saturation (Spo 2 ) exceeding 95% at a fraction of inspired oxygen (Fio 2 ) of less than 0.5; ph exceeding 7.3; Paco 2 of less than 50 mm Hg, and adequate respiratory mechanics. Patients were considered eligible for ICU discharge when they met the following criteria: no mental confusion; Spo 2 exceeding 90% at a Fio 2 of less than 0.5; no uncontrolled arrhythmia; no active chest tube drainage; hourly urine output exceeding 0.5 ml/kg, and no vasopressors or inotropic agents of any kind. Intensive Care Unit Discharge Strategy From 2000 through 2003, no specific strategy for discharging patients the morning after the operation was applied. At the beginning of 2004, a specific goal-oriented strategy, aimed to discharge patients the morning after the operation was applied. This strategy was based on a series of changes in the ward and ICU organization and protocols that are listed and compared with the standard strategy in Table 1. Data Collection and Definitions All the variables collected are presented in Table 2. The following definitions have been applied: recent myocardial infarction (within the previous 30 days); cardiogenic shock: patients treated emergently, under inotropic support, or with intraaortic balloon pump for low cardiac output state, or both; chronic renal failure: requiring renal replacement treatment; chronic obstructive pulmonary disease (COPD): on specific medication; type of operation: isolated CABG, isolated valve procedure, combined operation; perioperative myocardial infarction: new Q waves plus enzymatic criteria; low cardiac output syndrome: need for inotropic support for more than 24 hours; acute renal failure: requiring renal replacement therapy; stroke, transient neurologic dysfunction: psychotic behavior, agitation; severe pulmonary dysfunction: requiring prolonged ( 48 hours) mechanical ventilation owing to poor gas exchange;

3 Ann Thorac Surg RANUCCI ET AL 2007;83: EARLY DISCHARGE FROM THE ICU Table 1. Characteristics of Standard and Goal-Oriented Strategies Standard Strategy (years ) Goal-Oriented Strategy (years ) Operating room Short-acting totally IV anesthetic protocol; elastomeric pump IV analgesic treatment Intensive Care Unit Extubation: based on standard hemodynamic, respiratory, neurologic criteria (see text). Rarely performed from AM through 6.00 AM Postextubation ICU observation time: 6 hours ICU discharge: based on standard hemodynamic, respiratory, neurologic criteria (see text) Ward No dedicated beds for early discharged patients Nurse/patient ratio 1:6 No routine continuous hemodynamic parameters monitoring 1091 Short-acting totally IV anesthetic protocol; elastomeric pump IV analgesic treatment Extubation: based on standard hemodynamic, respiratory, neurologic criteria. Performed whenever feasible regardless of night hours Postextubation ICU observation time: 2 hours ICU discharge:based on standard hemodynamic, respiratory, neurologic criteria Six dedicated beds for early discharged patients. At least three available early in the morning Nurse/patients ratio 1:4 for early discharged patients Bedside or telemetric hemodynamic parameters monitoring available in the six dedicated beds Changes applied indicated in Bold. ICU intensive care unit; IV intravenous. mortality rate: death occurring after 24 hours from the operation; goal-oriented strategy: application of the abovedescribed protocol aimed to discharge patients the day after the operation. Based on the purpose of the study, patients were placed in the early discharge or late discharge group according to the ICU discharge time. Early discharge was defined as a discharge within the morning after the operation day (from 8.00 am to 12:00 pm). Considering that the patients were usually admitted in the ICU on the operation day from pm to pm, patients being discharged early had a length of stay in the ICU of 10 to 24 hours. Statistical Analysis The primary outcome variable was considered the early discharge from the ICU. No distinction was made with respect to the eligible or actual day of discharge. Table 2. Data Collection Preoperative Intraoperative Postoperative Age (ys) Type of operation Mechanical ventilation time (hrs) Gender Cardiopulmonary bypass duration (min) Intensive care unit stay (days) Weight (kgs) Lowest hematocrit (%) on CPB Postoperative hospital stay (days) Height (cms) Lowest temperature ( C) on CPB Need for surgical revision LVEF Use of closed or open circuits Peak serum creatinine (mg/dl) NYHA class Use of standard or biocompatible circuits Acute renal failure Recent MI Use of roller or centrifugal pumps Low cardiac output syndrome Unstable angina Redo surgery Atrial fibrillation (not preexisting) CHF Urgent surgery Ventricular arrhythmias Previous vascular surgery MI Cardiogenic shock Cardiac arrest Intraaortic balloon pump Severe pulmonary dysfunction Active endocarditis Transient neurologic dysfunction Chronic renal failure Stroke Diabetes on medication Sepsis COPD Mortality Cerebrovascular accident Goal-oriented strategy Serum creatinine (mg/dl) Hematocrit (%) CHF congestive heart failure; COPD chronic obstructive pulmonary disease; CPB cardiopulmonary bypass; LVEF left ventricular ejection fraction; MI myocardial infarction; NYHA New York Heart Association.

4 1092 RANUCCI ET AL Ann Thorac Surg EARLY DISCHARGE FROM THE ICU 2007;83: Table 3. Demographics and Preoperative Profile of the Patient Population Variable Without the goal-oriented strategy (n 5,549) (%) a With the goal-oriented strategy (n 3,505) (%) a Age (ys) NS Weight (kgs) NS Height (cms) NS Gender male 3,810 (68.6) 2,383 (67.9) NS Serum creatinine (mg/dl) NS Haematocrit (%) NS LVEF NS Recent MI 1,027 (18.5) 677 (19.3) NS Unstable angina 339 (6.1) 228 (6.5) NS Congestive heart failure 228 (4.1) 182 (5.2) 0.03 Cardiogenic shock 333 (0.6) 281 (0.8) NS Previous cardiac surgery 272 (4.9) 237 (6.8) Previous vascular surgery 255 (4.6) 168 (4.8) NS Chronic renal failure 39 (0.7) 25 (0.7) NS Diabetes on medication 722 (13) 446 (12.7) NS COPD 383 (6.9) 270 (7.7) NS Previous CVA 233 (4.2) 176 (5.0) NS p a Data presented as count and percentage for categoric variables; mean standard deviation for continuous variables. COPD chronic obstructive pulmonary disease; CVA cerebral vascular accident; LVEF left ventricular ejection fraction; MI myocardial infarction; NS not significant. Preoperative and intraoperative variables were initially tested for association with early discharge using univariate analysis. Continuous variables were tested using the Student t test for unpaired data, and categoric variables were tested using a relative risk analysis with 95% confidence intervals (CI). The variables associated with an early discharge from the ICU were included in a multivariable analysis (stepwise forward logistic regression) to identify the independent predictors of early discharge and their respective power within the model. To avoid overfitting of the model, the number of independent variables admitted to the model was limited to 1 for every 100 events; multicollinearity was controlled using a correlation matrix for the independent variables, considering a value of correlation 0.8 as the highest acceptable limit [14]. Tolerance statistics were applied to confirm the absence of multicollinearity, considering a tolerance value 0.3 for excluding multicollinearity [14]. Model performance was assessed using a receiver operating characteristic curve analysis for discrimination and the Hosmer-Lemeshow goodness-of-fit test for calibration. Subsequent analyses applied to the association between early discharge from the ICU and mechanical ventilation duration, and to the outcome profile of early discharged patients included Pearson 2 test, relative risk analysis, and Student t test for unpaired data. Data in tables are reported as mean standard deviation of the mean or as count and percentage. A p 0.05 was considered significant for all the statistical tests. Statistical calculations were performed using the SPSS 11.0 (SPSS Inc, Chicago, IL) statistical program. Results Main Group Demographics and preoperative profile of the patient population are reported in Table 3, with separate values according to the existence of the strategy oriented to early discharge from the ICU. There are significant differences in the number of patients with congestive heart failure and previous cardiac surgery that reflect an increased risk profile of the patients operated on in the most recent period. An early discharge from the ICU the day after the operation was achieved in 1874 patients (21%). Seven continuous variables and 10 categoric variables were significantly associated with an early discharge from the ICU. Age, serum creatinine levels, unstable angina, previous vascular surgery, congestive heart failure, cardiogenic shock, chronic renal failure, COPD, diabetes on medication, redo operation, combined operation, and CPB duration were significantly associated with late discharge. Ejection fraction, baseline hematocrit, lowest hematocrit on CPB, and lowest temperature on CPB were significantly associated with early discharge. The presence of a goal-oriented strategy was significantly (p 0.001) associated with the early discharge (odds ratio [OR] 4.3; 95% CI, 3.9 to 4.8). All the above-mentioned variables were included into a multivariable stepwise forward logistic regression with the early discharge as the dependent variable. The multivariable model excluded factors that were significant at the univariate analysis, owing to the presence of intercorrelation between independent variables (the baseline

5 Ann Thorac Surg RANUCCI ET AL 2007;83: EARLY DISCHARGE FROM THE ICU Table 4. Multivariable Model (Logistic Regression) for Early Discharge From the Intensive Care Unit Factors b SE p OR 95% CI Age (ys) Ejection fraction Serum creatinine (mg/dl) Unstable angina Congestive heart failure Redo operation Combined operation CPB duration (min) Lowest HCT on CPB (%) Lowest T on CPB ( C) Goal-oriented strategy Constant b regression coefficient; CI confidence interval; CPB cardiopulmonary bypass; HCT hematocrit; OR odds ratio; SE standard error; T temperature. hematocrit was intercorrelated with the lowest hematocrit on CPB; previous vascular surgery with age; chronic renal failure with serum creatinine value; COPD with age; diabetes on medication with age and serum creatinine value) or to the few number of events (cardiogenic shock). The final multivariable model (Table 4) included the six continuous variables of age, ejection fraction, baseline hematocrit, serum creatinine level, lowest hematocrit on CPB, and lowest temperature on CPB, and the five categoric variables of unstable angina, congestive heart failure, redo operation, combined operation, and goaloriented strategy. The presence of the goal-oriented strategy was associated with a successful early discharge from the ICU with an OR of 5.5 (95% CI, 4.8 to 6.3). The discrimination properties of the predictive model for early discharge from the ICU were confirmed by a receiver operating characteristics under the curve area 0.79 (95% CI, 0.78 to 0.81; p 0.001) and the calibration was considered adequate according to the Hosmer- Lemeshow goodness-of-fit test ( , p 0.7). Extubation Time, Early Discharge From the ICU, and Outcome In a separated post hoc analysis, we considered the extubation time in patients with or without a goaloriented strategy. In this analysis, we considered only patients being extubated within 12 hours (2082 in the goal-oriented strategy group and 2783 in the other group) to avoid the inclusion of patients who needed prolonged intubation owing to postoperative problems. Mean extubation time (hours) was for the group without a goal-oriented strategy and for the group with a goal oriented strategy (p 0.001), and the distribution of extubation times significantly differed between groups (Fig 1). The rate of successful early discharge from ICU (Fig 2) was significantly higher at each extubation time in the goal-oriented strategy group, with a peak at 4 hours for both groups. Patients extubated 2 or 3 hours after their arrival in the ICU had a lower success rate than patients extubated at the fourth hour (49.7% versus 60.2%, p 0.05). To investigate the reasons for this difference, we analyzed the presence of postextubation complications leading to a delayed discharge from the ICU in patients being extubated 2 to 3 hours or 4 hours after the arrival in the ICU (Table 5). The overall postextubation complication rate was significantly higher for patients being extubated after 2 or 3 hours, and significant differences were noticed for the surgical revision and the transient neurologic damage rates. Finally, we analyzed the general outcome variables in the subgroup of patients successfully discharged from the ICU the morning after the operation (n 1865) with (n 1243) or without (n 622) a goal-oriented strategy. Fig 1. Extubation time distribution with (filled bars) or without (clear bars) a goal-oriented strategy.

6 1094 RANUCCI ET AL Ann Thorac Surg EARLY DISCHARGE FROM THE ICU 2007;83: Fig 2. Success rate in early discharge from the ICU as a function of extubation time, with (open circles) or without (filled squares) a goal-oriented strategy. Dashed lines are 95% confidence intervals. No significant differences were noticed, except for a lower peak serum creatinine level ( mg/dl versus mg/dl, p 0.01) and a lower rate of ventricular arrhythmias (0.08% versus 0.8%; relative risk, 0.42; 95% CI, 0.27 to 0.57) in the goal-oriented strategy group. However, once corrected for other covariates (ejection fraction and perioperative myocardial infarction), the difference in ventricular arrhythmias rate became not significant. Comment The main finding of our analysis is that the application of a well-defined strategy is the most important step in a process aimed at the early discharge of patients from the ICU after cardiac operations. After correction for all of the other patient-related and operation-related covariates, the presence of this strategy is independently associated with a fivefold higher rate of early discharge. From a practical standpoint, it is worthwhile to notice that the strategy applied does not include any changes in the intraoperative management and only minor changes in the ICU management, conversely concentrating resources and technical equipment in the ward. This enhanced level of patient care in the ward makes the ICU staff more confident in discharging patients early, after 2 hours from the extubation, and is not associated with an increased reentry rate or adverse events in the ward, even though this strategy was applied to a patient series with a more severe preoperative risk profile. Within this context, the extubation time has a limited role. Patients treated with the goal-oriented strategy had significantly lower extubation times, but the difference in clinical terms is negligible (1.4 hours). Conversely, the success rate with respect to the extubation time is almost parallel in the groups with or without the goal-oriented strategy, being always significantly higher for each extubation time in the goal-oriented strategy group. The peak of success in both groups was obtained at an extubation time of 4 hours: before and after this timing, the success rate declines. It seems reasonable that the reason for a lower rate of early discharge from the ICU in patients being very early extubated could be a higher rate of postextubation complications, leading the ICU staff to postpone the discharge. Our analysis confirms this hypothesis, revealing a significant higher rate of postextubation complications in patients extubated after 2 or 3 hours versus patients extubated after 4 hours. The interpretation of this data is speculative, because our work is a retrospective analysis and we have no explanation for the higher rate of surgical revisions in patients being very early extubated. Conversely, there is a combination of events (need for inotropic support, decreased urine output, ventricular arrhythmias) that may be interpreted as a moderate low cardiac output state not present before the extubation but possibly triggered by the increased cardiac work load to sustain the spontaneous ventilation. Most importantly, the presence of a higher rate of transient neurologic dysfunctions in these patients may explain the delayed discharge from the ICU and could be related to our intraoperative anesthetic protocol, which is based on midazolam as the hypnotic agent. This management has been already used in fast-track cardiac anesthesia [5, 15] with successful early extubation and discharge from the ICU. One study [5], however, demonstrated that propofol-based anesthesia was associated with a shorter intubation time, whereas midazolambased anesthesia in elderly patients was associated with a higher rate of mental function impairment. Therefore, a different anesthetic management more oriented to early extubation could induce different results, and we cannot exclude that by using shorter-acting intravenous hypnotic drugs, a different optimal timing for extubation could be established. Our study confirms the role of other covariates within Table 5. Postextubation Complications Leading to a Late Discharge From the Intensive Care Unit Event Extubation Time After Arrival in ICU 4 hours (n 181) (%) 4 hours (n 156) (%) p Surgical revision 5 (2.8%) Need for inotropic support 5 (2.8%) 3 (1.9%) Myocardial infarction 0 1 (0.6%) Ventricular arrhythmias 3 (1.6%) 1 (0.6%) Transient neurologic 8 (4.4%) 1 (0.6%) dysfunction Decreased urine output 2 (1.1%) 1 (0.6%) Poor respiratory gas 4 (2.2%) 1 (0.6%) exchange Total complications 27 (15%) 8 (5.1%) ICU intensive care unit.

7 Ann Thorac Surg RANUCCI ET AL 2007;83: EARLY DISCHARGE FROM THE ICU a fast-track program in cardiac surgery. In a study addressing the role of preoperative risk factors in determining the success of a fast-track program, Cheng and associates [10] demonstrated that the success rate decreased as a function of preoperative risk score and age. Brucek and associates [8], in a model of ultra-fast track extubation, found that surgery duration and preoperative lung dysfunction were significant predictors of failure in extubation immediately after surgery. In our model, both the patient risk profile and operation-related factors significantly contribute in determining the discharge time from the ICU. In addition to the already mentioned variables, we found that severe hemodilution was an independent predictor of late discharge from the ICU. Many articles have recently addressed this topic, demonstrating that severe hemodilution during CPB is associated with a number of postoperative complications, mainly related to renal dysfunction [16 19], but also to many other organ dysfunctions and death [20, 21]. We recently demonstrated that the reason for this association is a low oxygen delivery during CPB [22]; however, the role of hemodilutiontriggered homologous blood transfusions must be mentioned in the determinism of hemodilution-related complications [23]. The main strength of our study relies on the number of patients and variables considered. We are, however, aware of the limitations of our approach. The study is not prospective, and the patients have not been randomized for the goal-oriented strategy. Moreover, our model is not validated in a second series of patients. In conclusion, a successful program of early discharge from the ICU depends on the (1) preoperative risk profile of the patients, (2) type of operation, temperature, and duration of CPB, (3) application of strategies aimed to reduce hemodilution during CPB; and, the most important point, (4) on the application of a goal-oriented strategy with increased resources in the ward and a short postextubation observational period in the ICU. The extubation time is correlated to success only after the fourth postoperative hour. In our model, a very early extubation is not a guarantee of higher success rate in early discharging patients from the ICU. References 1. Cheng DHC, Karski J, Peniston C, et al. Early tracheal extubation after coronary artery bypass graft surgery reduces costs and improves resource use: a prospective randomized controlled trial. Anesthesiology 1996;85: Cheng DCH. Fast-track cardiac surgery pathways: early extubation, process of care, and cost containment. 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Readmission to the intensive care unit after fast-track cardiac surgery: risk factors and outcomes. Ann Thorac Surg 2003;76: Katz MH. Multivariable analysis. 2nd ed. Cambridge: Cambridge University Press, Sulzer CF, Chiolero R, Chassot PG, Mueller XM, Revelly JP. Adaptive support ventilation for fast tracheal extubation after cardiac surgery: a randomized controlled study. Anesthesiology 2001;95; Ranucci M, Pavesi M, Mazza E, et al. Risk factors for renal dysfunction after coronary surgery: the role of cardiopulmonary bypass technique. Perfusion 1994;9: Swaminathan M, Phillips-Bute BG, Conlon PJ, Smith PK, Newman MF, Stafford-Smith M. The association of lowest hematocrit during cardiopulmonary bypass with acute renal injury after coronary artery bypass surgery. Ann Thorac Surg 2003;76: Karkouti K, Beattie WS, Wijeysundera DN, et al. Hemodilution during cardiopulmonary bypass is an independent risk factor for acute renal failure in adult cardiac surgery. 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