Determinants of Length of Stay After Coronary Artery Bypass Graft Surgery
Background Rising healthcare costs have prompted limitations in the length of stay (LOS) for patients undergoing coronary artery bypass graft surgery (CABG). Because not all patients are candidates for early discharge, in the present study our aim was to determine factors that prolong LOS.
Methods and Results In 194 consecutive patients undergoing CABG procedures, LOS was >7 days in 37%. Stepwise multiple regression procedures and χ2 testing were used to determine what factors prolonged LOS for >7 days. Preoperative factors that significantly (P<.05) prolonged LOS included repeat CABG, CABG plus valve surgery, congestive heart failure, preoperative coronary care unit stay, renal failure, and insulin-dependent diabetes mellitus. Patients with at least one risk factor had a significantly higher incidence of LOS of >7 days (47% versus 17%; P<.001). Significant (P<.05) postoperative factors prolonging LOS included arrhythmias, respiratory insufficiency, pneumonia, and wound infection. Of patients with at least one risk factor, 83% had LOS of >7 days (P<.001).
Conclusions The presence of certain preoperative and postoperative risk factors can be predicted to prolong LOS after CABG surgery. This should be taken into consideration when defining reimbursement policies.
Rising health care costs have prompted physicians and third-party payors to attempt to limit the length of stay after major surgical procedures.1 This is especially true for patients who undergo coronary artery bypass graft surgery (CABG), which is the most commonly performed major operation in the United States and accounts for considerable expenditure of health care costs.2 3 4 Currently, the majority of CABG patients are already hospitalized with unstable angina syndromes, so the preoperative length of stay is more difficult to control. Therefore, attention has been directed to curtailing the postoperative length of stay.
In 1986, we reported on the determinants of length of stay for 177 patients undergoing isolated CABG at The Boston University Medical Center.5 At that time, only 28% of CABG patients were discharged before the eighth postoperative day. Since that time, changes in health care reimbursement policies have prompted us to introduce programs such as same-day admissions, early extubation, critical pathways, and “fast-tracking” in an attempt to shorten the length of stay after CABG. Concomitantly, the profiles of patients undergoing CABG have changed, resulting in more older patients with more extensive coronary disease and unstable symptoms, increasing comorbid diseases, and a higher incidence of repeat surgery. Therefore, not all patients will be candidates for early discharge. We undertook the present study to determine what preoperative and postoperative variables would contribute to prolonged length of stay after CABG. Furthermore, we were interested to see whether the presence of certain preoperative and postoperative risk factors could predict which patients were more likely to require longer hospitalization after CABG.
The records of 194 consecutive patients who had undergone a CABG-related procedure and were discharged alive from The Boston University Hospital between January 1993 and April 1993 were retrospectively reviewed. During this time, fast-track and early extubation protocols were developed in an attempt to discharge patients by the seventh postoperative day. Patients discharged after the seventh postoperative day were considered to have a prolonged length of stay. Data sheets were developed to evaluate preoperative and postoperative variables that might prolong length of stay (Tables 1⇓ and 2⇓).
All surgical procedures were performed with a membrane oxygenator at systemic temperatures of 34°C. Multidose cold blood cardioplegic solutions were given antegrade, retrograde, or antegrade/retrograde at the surgeon’s discretion. Cell-saving techniques were routinely used in all patients.
Inotropic agents were used as necessary to maintain a cardiac index of at least 2.0 L/m2. Patients were extubated as soon as possible. Candidates for early extubation (6 to 8 hours after surgery) included patients with stable hemodynamics and no significant mediastinal bleeding and patients who were awake and alert with normal arterial blood gases. All extubated patients were transferred from the intensive care unit on the first postoperative day unless the use of inotropic or vasodilator drugs was necessary. β-Blocking agents were instituted on the first postoperative day in all patients with an ejection fraction of >40%. Criteria for discharge from the hospital included stable cardiac rhythm, an oral temperature of <99°F, hematocrit of ≥25%, oral intake of at least 1000 calories per day, successful completion of an exercise test that included independent ambulation and the ability to climb one flight of stairs, no significant wound complications, and adequate home support systems.
Values are given as mean±SD. An association between a risk factor and length of stay in days was analyzed with the independent-sample t test, which was used to compare mean length of stay for those with and those without the risk factor. The association between risk factor and a stay of >7 days was analyzed with the χ2 test, which was used to compare the proportion of patients with extended stays among those with and those without the risk factor. In addition, summary categorizations were made for any preoperative risk factor and any postoperative risk factor. The effects of these summary risk categories were analyzed with two-factor ANOVA (for the outcome of length of stay in days) and multiple logistic regression (for the outcome of length of stay of >7 days). Stepwise multiple regression (for length of stay in days) and stepwise logistic regression (for the categorical outcome of length of stay of >7 days) were used to identify risk factors that had an independent effect on outcome. For both versions of the outcome, a model was first fit using early preoperative risk factors as predictors. A second model was then fit to determine which postoperative risk factors contribute additional information toward predicting length of stay while controlling for the identified preoperative factors. All statistical analyses were performed by Dr Timothy Heeran (Department of Epidemiology, The Boston University School of Public Health, Boston, Mass). Differences were considered significant at the P<.05 level.
The results of the present study are summarized in Tables 1 through 4⇑⇑⇓⇓ and the Figure⇓. Of the 194 study patients, the age range was from 32 to 86 years (mean±SD, 65±11.7). There were 137 men (71%) and 57 women (29%). The most frequently performed procedure was CABG (173 patients [84%]); 18 patients (9%) underwent repeat CABG; 8 patients (4%) underwent CABG with aortic valve replacement, and 5 patients (3%) underwent CABG with mitral valve replacement.
The length of stay ranged from 4 to 47 days (mean±SD, 8.7±5.9 days [Figure⇑]). In 69 patients (37%), the length of stay was >7 days. The preoperative factors that significantly prolonged length of stay are summarized in Table 1⇑. Univariate analyses with χ2 testing identified patients with repeat CABG, CABG plus valve surgery, congestive heart failure, insulin-dependent diabetes mellitus, a preoperative length of stay of >8 days, emergency surgery, creatinine level of ≥1.5, transfer to the operating room from the coronary care unit, and the need for intravenous nitroglycerin as significant independent variables that prolonged length of stay. When multivariate analyses were applied, significant variables prolonging length of stay included repeat CABG (P<.05), CABG plus valve surgery (P<.001), congestive heart failure (P<.01), insulin-dependent diabetes mellitus (P<.05), creatinine level of ≥1.5 (P<.001), and transfer to the operating room from the coronary care unit (P<.001).
Postoperative factors that significantly prolonged length of stay are summarized in Table 2⇑. Univariate analysis identified patients with arrhythmias, intubation for ≥48 hours, lobar pneumonia, wound infection, weight gain of ≥20 lb, inotropic support for ≥48 hours, and myocardial infarction as significant variables prolonging length of stay. When multivariate analyses were applied, significant risk factors included arrhythmia (P<.01), intubation for ≥48 hours (P<.05), lobar pneumonia (P<.001), and wound infection (P<.001).
The effects of both preoperative and postoperative risk factors in prolonging the length of stay are shown in Table 3⇑. In patients with no preoperative risk factors (66), the mean length of stay was 6.6 days, and only 18% of patients remained hospitalized for >7 days. However, in patients with at least one preoperative risk factor, the mean length of stay increased to 9.8 days, and 45% of these patients remained hospitalized for >7 days (P<.001). The group of patients without any preoperative or postoperative risk factors had the shortest length of stay (mean, 6.3 days; 13% of patients had a length of stay of >7 days). Patients with at least one preoperative and one postoperative risk factor had the longest length of stay (mean, 14.2 days; 73% of patients had a length of stay of >7 days [P<.001]). Development of a postoperative risk factor significantly prolonged length of stay (mean, 8.2 days; 45% of patients had a length of stay of >7 days [P<.001]), whereas avoidance of postoperative risk factors despite the presence of a preoperative risk factor significantly decreased length of stay (mean, 7.1 days; 30% of patients had a length of stay of >7 days [P<.05]).
The reason for the prolonged length of stay in the 37% of patients hospitalized for >7 days postoperatively is shown in Table 4⇑. The most common cause was respiratory insufficiency, followed closely by the development of an arrhythmia. In the 21 patients in whom an arrhythmia extended the length of stay, 17 experienced atrial fibrillation. Wound infection, stroke, and postoperative myocardial infarction were the next most common variables prolonging length of stay.
In 1986, only 28% of patients undergoing CABG at The Boston University Medical Center were discharged by the 8th postoperative day.5 The majority (45%) were discharged between the 9th and 11th postoperative days, and in 79% of these patients, no identifiable reason could be determined to account for the prolonged length of stay. In the past 3 years, changes in health care reimbursement policies have prompted the introduction of various changes in the practice of cardiac surgery that have had a dramatic impact on the length of stay. All elective cases are now admitted on the same day of surgery. Anderson et al6 have shown that patients admitted for same-day surgery have a length of stay that is 1.5 days less than that for patients admitted the day before CABG. Loop et al7 also showed that same-day patients had a decreased length of stay and a significantly lower hospital bill. We continue to use blood cardioplegia with both antegrade and antegrade/retrograde techniques in the vast majority of our patients. A recent study from the Cleveland Clinic compared the use of blood cardioplegia techniques with crystalloid cardioplegia.8 Time in the intensive care unit, length of hospitalization, and length of stay outlier status were significantly decreased in the blood cardioplegia group. The net savings in hospital cost was $2196 per patient. By introducing an early extubation program, we also decreased the length of stay in the intensive care unit, which accounts for a significant percentage of hospital costs for CABG.6 9 Several factors led to a reduction in hospital stay once the patient leaves the intensive care unit. The introduction of “critical pathways” and “fast-tracking” has helped to focus on potential complications before they occur. Patients are mobilized faster, increased weight gain is treated aggressively with diuretics, and discharge planning is instituted as soon as the patient is discharged from the intensive care unit. Recent studies have shown that fast tracking results in a significant reduction in length of stay after CABG.10 11 We and others have found that nurse case managers are invaluable in making sure that patients stay “on track” on their critical pathways.12 13 In addition to tracking patients for discharge, they coordinate and screen patients for transfer to rehabilitation and chronic care units, thus minimizing length of stay in acute care facilities.
The results of the present study show that these interventions have had a dramatic impact on the length of stay at our institution. Compared with our earlier series, only 37% of patients remained hospitalized past the seventh postoperative day. Similarly, there has also been a change in preoperative risk factors that prolong length of stay. In our earlier study, univariate analyses identified female sex, age of ≥65 years, unstable angina, and congestive heart failure as predictors of prolonged length of stay. Because the profiles of patients who undergo CABG have changed, age and female sex are no longer predictors of prolonged length of stay in our present study. However, congestive heart failure and symptoms of unstable angina, including preoperative coronary care unit stay and the need for intravenous nitroglycerin, continue to be predictive of prolonged length of stay. Repeat CABG, CABG plus valvular surgery, insulin-dependent diabetes mellitus, and creatinine level of >1.5 have also emerged as predictors of prolonged length of stay. As in our earlier series, patients who develop major postoperative complications, including wound infection, pneumonia, and respiratory insufficiency, as well as arrhythmias tend to remain hospitalized longer. Similar findings were noted by Weintraub et al14 and Welsh et al,15 who noted that the development of postoperative complications was a significant contributor to prolonged length of stay.
In contrast to earlier studies, our results indicate that the presence or absence of certain preoperative and postoperative risk factors can be used to predict which patients will require prolonged length of stay.14 Patients without preoperative risk factors who do not develop postoperative risk factors have the shortest length of stay and are more likely to be candidates for fast-track pathways. In contrast, patients with preoperative risk factors who develop postoperative complications will have the longest length of stay. However, patients with preoperative risk factors who do not develop postoperative risk factors will still have significantly shorter lengths of stay. It is this group of patients who should be targeted in an attempt to decrease postoperative length of stay. In the present study, the two most common reasons for prolonged length of stay were pulmonary insufficiency and atrial arrhythmias. To decrease postoperative respiratory complications, we have made an attempt to have all patients stop smoking for at least 1 week before surgery when possible. All in-house patients are seen before surgery by a physical therapist. Patients are mobilized by the morning after surgery; intensive pulmonary physiotherapy is instituted, and inhalant and bronchodilator therapy is used when necessary. Diuretics are used to decrease early weight gain, which may compromise pulmonary function. In an attempt to decrease the incidence of atrial arrhythmias, β-blocking agents are instituted on the first postoperative day in patients with ejection fractions of >40%.
Despite the tremendous gains made in lowering the length of stay after CABG procedures, there still will be groups of patients who will require longer lengths of stays. Our study shows that the presence or absence of certain preoperative and postoperative risk factors can be used to predict which patients will require longer hospitalizations. Furthermore, due to the profiles of patients having surgery continuing to change as a result of increasing age and comorbid disease and the influence of invasive cardiology interventions, variables that influence the length of stay may also change. Health care providers must take these factors into consideration when defining reimbursement policies for CABG procedures.
The secretarial assistance of Ellie LaBombard and the administrative support of Elizabeth Clifford are greatly appreciated.
- Copyright © 1995 by American Heart Association
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