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Ann Thorac Surg 2003;76:503-507
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Readmission to the intensive care unit after "fast-track" cardiac surgery: risk factors and outcomes

^a Cardiothoracic Surgery, Rabin Medical Center, Beilinson Campus, Petah Tiqva, affiliated with the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel,
^b Department of General Intensive Care, Rabin Medical Center, Beilinson Campus, Petah Tiqva, The Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel

Accepted for publication March 4, 2003.

^* Address reprint requests to Dr Kogan, Department of Cardiothoracic Surgery, Rabin Medical Center, Beilinson Campus, Petah Tiqva 49 100, Israel
e-mail: akogan{at}clalit.org.il

	Abstract

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
BACKGROUND: The introduction of "fast-track" management into cardiac surgery has significantly shortened the intensive care unit (ICU) length of stay. Readmission to the ICU, traditionally used as a quality index, has not been investigated in these patients. The aim of this study was to assess the causes, risk factors, and outcomes associated with readmission to the ICU.

METHODS: All patients undergoing open-heart surgery in a tertiary care, university-affiliated center were included in this prospective observational study. Preoperative and intraoperative data as well as ICU outcome were noted in all patients.

RESULTS: Over the 27-month study period,1,613 patients were targeted for fast track management (discharge from ICU on the first postoperative day). The readmission rate was 3.29% (53 patients). Forty-three percent of readmissions occurred within 24 hours of discharge usually because of pulmonary problems (43%) or arrythmias (13%). Readmission was associated with a prolonged ICU stay (105 ± 180.0 versus 19.2 ± 2.4 hours of initial ICU stay) and worse outcome: the only patients who died (6 of 53, 11.3%) were in this group. On multivariate analysis, a Bernstein-Parsonnet risk estimate more than 20 strongly predicted readmission (odds ratio, 3.08; 95% confidence interval, 1.43 to 6.69).

CONCLUSIONS: Among a homogeneous group of patients targeted for fast-track management after cardiac surgery, readmission although uncommon is associated with a longer second ICU stay and significant mortality. The recognition of specific risk factors may allow for appropriate modification of the postoperative course.

	Introduction

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Interventions designed to improve intensive care unit (ICU) utilization have become an important part of patient management. In the field of cardiac surgery, studies have shown that modifying anesthetic techniques and postoperative sedation protocols may allow for early extubation and thereby early ICU discharge—so-called "fast-track" management [1, 2]—with no significant additional morbidity or mortality [3, 4]. However the end-points used to define the success of this intervention have typically included critical events related to the initial ICU stay. Readmission to the ICU, traditionally used as a quality index [5, 6], has not been investigated in this respect nor has the outcome of these patients been described.

We performed a prospective study among patients targeted for early extubation after cardiac surgery to assess the number of patients requiring readmission to the ICU, the factors predicting readmission, and in particular, patient outcome.

	Material and methods

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
All patients undergoing open-heart surgery in our tertiary care, university-affiliated center over a 27-month period were included in this prospective observational study. Patients undergoing heart, lung, or heart-lung transplantation and patients undergoing aortic aneurysm or aortic dissection repair were excluded. Ethics committee approval was not obtained as fast-track management has been part of the standard care policy at our institution for the past 4 years. All patients received standardized anesthesia. Premedication consisted of midazolam syrup 0.1 mg/kg and anesthesia was induced with fentanyl 10 to 15 µg/kg and midazolam 0.02 to 0.04 mg/kg. Pancuronium bromide was given to facilitate endotracheal intubation and the lungs were then ventilated with an oxygen/air mixture to maintain normocapnia. Anesthesia was maintained with isoflurane, fentanyl, and midazolam. The total dose of fentanyl was 20 to 40 µg/kg and that of midazolam, 0.15 to 0.2 mg/kg. Cardiopulmonary bypass was performed using a membrane oxygenator. Cardiac arrest was achieved by multiple administrations of anterograde or retrograde blood cardioplegia. Topical cooling was not mandatory. In almost all cases core temperature was approximately 30°C. All patients were rewarmed to 37°C before discontinuation of cardiopulmonary bypass. After completion of surgery all patients were returned to the cardiothoracic ICU while still intubated

The ICU is a 12-bed unit run by a full-time intensivist; the staff to patient ratio is 2:1. Patients were targeted for fast-track management, defined as early extubation enabling discharge from the ICU on the first postoperative day, upon their arrival in the ICU. Exclusion criteria were the requirement for intraortic balloon pump, poor general condition, severe hemodynamic instability requiring increasing doses of cardioactive drugs, and the anticipated need for prolonged respiratory support (severe chronic obstructive pulmonary disease, requirement for fractional concentration of inspired oxygen greater than 0.6 and high positive end-expiratory pressure). Standard postoperative care consisted of mechanical ventilation in the assist-control mode, cardioactive drugs where indicated, the use of warm air heaters to maintain normothermia, and analgesia with intravenous morphine boluses as required. Criteria for weaning from the ventilator included hemodynamic stability (no or decreasing use of cardioactive drugs), absence of significant bleeding (< 100 mL/h), absence of significant arrhythmias, adequate urine output (> 1 mL · kg^-1 · h^-1), and oxygen saturation more than 95% with fractional concentration of inspired oxygen less than 0.50; the patient also needed to be sufficiently awake to follow commands. Patients fulfilling these criteria were placed on pressure support ventilation for 20 to 30 minutes, and in the absence of respiratory or cardiac distress, extubation was performed immediately thereafter. Patients were discharged from the ICU to the adjacent cardiothoracic ward at least 4 to 6 hours after extubation. During this period, any increasing requirement for cardioactive drugs, or significant decrease in oxygen saturation (<90% despite oxygen mask), urine output, or level of consciousness, was considered a contraindication for discharge. The staff to patient ratio on the ward is 1:6 and all patients are monitored with telemetry (heart rate and rhythm) for the first 24 hours. There is no intermediate care facility at our hospital.

The following data were recorded: preoperative age, sex, type of surgery, the 2000 Bernstein-Parsonnet risk estimate [7]; intraoperative duration of cross-clamping and bypass; and postoperative duration of mechanical ventilation, duration of initial ICU stay, timing and cause of readmission, duration of ICU readmission, and hospital mortality. Reasons for readmission were classified as (1) pulmonary (respiratory distress characterized by tachypnea more than 30 breaths per minute, decrease in arterial saturation to <90%, use of accessory muscles or abdominal paradox, inability to clear secretions); (2) renal (decrease in urine output to < 0.5 mL/kg for more than 4 hours despite fluid resuscitation); (3) new onset atrial fibrillation severe or persistent enough to require pharmacologic treatment or cardioversion; (4) bleeding (new-onset bleeding of more than 200 mL/h); (5) new cerebrovascular accident; (6) hemodynamic instability (any decrease in blood pressure requiring increasing use of cardioactive drugs); (7) gastrointestinal (upper gastrointestinal bleeding); (8) severe agitation (requiring intravenous sedation); (9) sepsis (characterized by two or more of the following features: temperature > 38°C or < 36°C, respiratory rate > 28 breaths per minute or partial pressure carbon dioxide in alveolar gas < 32 mm Hg, white cell count > 12,000/mm³ or < 4,000/mm³, and heart rate > 90 beats per minute together with a source of infection); and (10) and pericardial tamponade (demonstrated on echocardiography). Multiorgan dysfunction syndrome was defined as the presence of altered organ function in an acutely ill patient and the inability to maintain homeostasis without support.

Statistical analysis
Numerical data are expressed as mean (±SD). The ² test or Fisher’s exact test if appropriate was used to compare the distribution of categorical variables between patients readmitted and not readmitted to the ICU. Student’s t test was used to compare continuous variables between the two groups. Univariate analysis was performed to identify risk factors associated with readmission on ² analysis. A p value of less than 0.05 was considered statistically significant. These values were then entered into a multiple logistic regression model to identify independent risk factors. The odds ratio (OR), 95% confidence interval (CI), and p values were calculated for each risk factor. A p value of less than 0.05 was considered statistically significant. Statistical analysis was performed using SPSS 8.0 for Windows (SPSS, Chicago, IL).

	Results

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
During the study period, 2,550 patients underwent cardiac surgery. Of these, 68 patients were excluded from the study because they had undergone either organ transplantation or aneurysm repair, and another 869 patients were excluded after initial assessment in the ICU. Of the remaining 1,613 patients included in the study, 53 (3.29%) required readmission after initial fast-track management. The demographic characteristics of the readmitted and not readmitted groups are shown in Table 1. The only significant difference between the groups was a higher 2000 Bernstein-Parsonnet risk estimate score in the group requiring readmission (20.1 ± 10.0 versus 12.9 ± 8.4, p < 0.05). Factors accounting for the higher risk estimate were age more than 70 years, female sex, and left ventricular ejection fraction less than 30%. Twenty-one patients were taken off fast track in the ICU due to active bleeding, of whom 8 required resternotomy.

Factors associated with readmissions are shown in Table 4. On multivariate analysis, age more than 70 years, female sex, a 2000 Bernstein-Parsonnet risk estimate of more than 20, and operation other than first isolated coronary artery bypass graft were independently associated with the need for readmission. As age, sex, and type of operation are components of the 2000 Bernstein-Parsonnet risk estimate, a separate analysis was performed to exclude collinearity. The variance inflation factor (VIF) was less than 10, suggesting that the collinearity was not significant.

	Comment

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

Numerous studies have shown that fast-track management is a safe and effective option for patients undergoing cardiac surgery [3, 4]. It results in a decreased duration of ventilation and a decreased ICU and hospital stay [8, 9] with benefits to both the patient (decreased intubation-associated complications) and the health-care system (decreased costs and better ICU utilization). Importantly it apparently does not significantly compromise quality of care; that is, it does not lead to increased rates of reintubation [4], perioperative myocardial ischemia and infarction [8], arrhythmias [9], or mortality [2]. Although the safety of early extubation in these patients has not been unequivocally established the serious adverse event rate remains so low that a trial of thousands of patients would be required to do so [10].

Any intervention targeting early ICU discharge must take into account the possibility of subsequent patient deterioration and the need for readmission. This outcome variable is especially relevant as series examining the course of patients requiring unexpected readmissions to medical and surgical ICUs have reported increased length of hospital stay and mortality [11, 12]. However in a review of risk factors and outcomes of patients readmitted to ICUs, Rosenberg and Watts [13] stressed that the heterogeneity of the patients in these studies makes it difficult to identify specific types of ICUs and patient groups. We were unable to find any study addressing this issue in fast-track patients. In the paper of Rosenberg and Watts [13] the decision to transfer patients from the ICU was protocol driven and measurement based—not time based. The patients readmitted to the ICU were those with a longer initial length of ICU stay; a decreased initial stay did not appear to account for increased ICU recidivism. In the only other related study patients readmitted to the cardiac surgical ICU had high morbidity and mortality rates (31%) [14]. However no mention was made of their initial ICU course and whether fast-track management was used. In our series discharge was by definition time-based and the results showed that the second duration of ICU stay was prolonged compared with the initial stay and that all the patients who died were in this group.

Readmissions occurred within 24 hours of the initial ICU discharge in 47.2% of all readmitted cases, a rate similar to other series of ICU readmissions [5, 13, 14]. The most common reason was pulmonary problems, as in other series [13–15]. It is these early readmissions that may indeed reflect the quality of the discharge decision. Our patients are weaned from the ventilator and discharged from the ICU according to strict protocols. It is thus likely that the lower intensity of respiratory support possible in a general medical ward, combined with inadequate analgesia (resulting in decreased coughing and clearing of secretions) and poor ventilatory reserves (patients with chronic obstructive lung disease and obesity), results in the early appearance of respiratory distress. The decision to discharge is usually made when the physiologic status is considered stabilized and ICU monitoring and care are no longer deemed necessary [16]. It would be preferable to be able to identify and focus on specific groups of patients at risk of readmission before initial discharge. Their postoperative course could then be modified by a number of strategies. Firstly, it has recently been shown in a study conducted in 20 United Kingdom general intensive care units that the discharge mortality of at risk patients may be reduced by 39% if they remain in intensive care units for another 48 hours [17]. The discharge triage model predicting patients at risk in this study included age, Acute Physiology and Chronic Health Evaluation (APACHE) II score (both chronic health and acute physiology points), length of ICU stay, and significantly, cardiac surgery. While this study included a heterogeneous group of patients in general ICUs, it suggests that prolonging ICU stay in at-risk patients may decrease the occurrence of complications necessitating readmission. Discharging high risk patients to an intermediate or high dependency unit has also been shown to reduce to nil the number of patients requiring readmission to the ICU [18] and to result in significant cost savings. In the event that the above options are not available, and patients are discharged to a general ward, the possibility of providing preemptive cardiorespiratory support such as noninvasive ventilation (bilevel positive airway pressure) could be considered. An active follow-up of high-risk patients after ICU discharge by a dedicated team of respiratory therapists has also been shown to decrease mortality [19].

Specific risk factors for readmission have been described in post–cardiac surgery patients, not necessarily those targeted for fast-track management. They include female sex, poor cardiac function, and several intraoperative and postoperative factors, particularly large fluid requirements and prolonged ventilator use [15]. We identified age more than 70 years, female sex, a 2000 Bernstein-Parsonnet risk estimate more than 20, and operation other than first isolated coronary artery bypass graft as factors significantly associated with the need for readmission. The risk estimate model [7], which takes into consideration 47 potential risk factors, was devised to estimate preoperative risk for open-heart surgery. It is simple and rapidly completed at the patient bedside, and has been found to have a high predictive value for readmission [14].

In conclusion we have shown that in a homogeneous group of patients targeted for fast-track management after cardiac-surgery, readmission although uncommon is associated with a longer second ICU stay and significant mortality. We suggest that additional studies performed in this group of patients to identify specific risk-factors would allow for improved clinical decision making and allow for the appropriate modification of the postoperative course.

	Acknowledgments

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
We thank Gloria Ginzach and Hanni Penn for their editorial and secretarial assistance.

	References

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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