Ann Thorac Surg 2004;78:1972-1978
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
Risk Factors for Readmission After Neonatal Cardiac Surgery
Andrew S. Mackie, MDa,c,*,
Kimberlee Gauvreau, ScDa,c,
Jane W. Newburger, MDa,c,
John E. Mayer, MDb,d,
Lars C. Erickson, MDa,c
a Department of Cardiology, Harvard Medical School, Boston, Massachusetts, USA
b Department of Cardiac Surgery, Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
c Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
d Department of Surgery, Harvard Medical School, Boston, Massachusetts, USA
Accepted for publication May 18, 2004.
* Address reprint requests to Dr Mackie, Division of Cardiology, Montreal Children's Hospital, Room D-371, 2300 Tupper St, Montréal QC H3H 1P3, Canada
andrew.mackie{at}muhc.mcgill.ca
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Abstract
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BACKGROUND: Repeat hospitalizations place a significant burden on health care resources. Factors predisposing infants to unplanned hospital readmission after congenital heart surgery are unknown.
METHODS: This is a single-center, case-control study. Cases were rehospitalized or died within 30 days of discharge following an arterial switch operation (ASO) or Norwood procedure (NP) between 1992 and 2002. Controls underwent an ASO or NP between 1992 and 2002, and were neither readmitted nor died within 30 days of discharge. Patients and controls were matched by gender, year of birth, and procedure. Potential risk factors examined included indices of medical status at the time of discharge, determinants of access to health care, and provider characteristics.
RESULTS: Forty-eight patients were readmitted; 19 of 498 (3.8%) following an ASO and 29 of 254 (11.4%) after a NP (p < 0.001). Six infants died within 30 days of discharge; 1 after an ASO and 5 after a NP. In multivariate analysis, predictors of readmission or death were: residual hemodynamic problem(s) (odds ratio [OR] 4.10 [1.18, 14.3], p = 0.026); an intensive care unit stay greater than 7 days (OR 5.17 [1.12, 23.9] p = 0.035) (ASO); residual hemodynamic problem(s) (OR 5.84 [1.98, 17.2], p = 0.001); and establishment of full oral intake less than 2 days before discharge (OR 5.83 [1.83, 18.6], p = 0.003) (NP). Combining both groups, living in a low income Zip Code (< $30,000/annum) was associated with a lower likelihood of readmission (OR 0.25 [0.07, 0.85], p = 0.027).
CONCLUSIONS: Residual hemodynamic problem(s) predispose to hospital readmission after the ASO and NP. Low socioeconomic status may reduce the likelihood of readmission even when problems arise.
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Introduction
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Repeat hospitalizations in children impose an important emotional and financial burden on affected families and consume significant health care resources [1]. Such patients account for a disproportionate number of inpatient days [2]. Although hospital readmission has been studied in children with asthma [3, 4], in newborns after early neonatal discharge [5, 6], and in adults with congestive heart failure [7], there is a paucity of data regarding factors that predispose children with heart disease to repeated hospitalizations.
Williams and colleagues [8] identified indications for readmission in a group of infants and children with hypoplastic left heart syndrome (HLHS). Among 72 infants surviving to hospital discharge after Norwood palliation, there were 26 nonelective readmissions, of which 22 were for infectious illnesses. Vricella and colleagues [9] studied 198 children between the ages of 0 to 18 years undergoing elective cardiac surgical procedures. Nineteen patients (9.7%) were readmitted, and an additional eleven patients (5.6%) made unscheduled visits to emergency rooms or clinics but were managed as outpatients. Postpericardiotomy syndrome and pleural effusions were the most common diagnoses, accounting for 14 (47%) of these 30 patients. Turley and colleagues [10] reported the outcomes of 286 consecutive patients managed by a single pediatric cardiac surgeon. Readmission within 14 days was necessary because of infection in 3 (1.0%), postpericardiotomy syndrome in 3 (1.0%), and arrhythmia in 1 (0.3%).
Although these studies cite diagnoses responsible for readmission, readmission was not the primary focus of these reports. We have found no studies examining factors predisposing to nonelective hospital readmission in children after surgery for congenital heart disease. The objective of this study was to identify risk factors for hospital readmission or death within 30 days of discharge after the arterial switch and Norwood procedures in newborn infants.
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Patients and Methods
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Patients
The patients (cases) were identified using the computerized database of the Cardiovascular Program at Children's Hospital, Boston. Cases were defined as neonates who were either (a) nonelectively readmitted to Children's Hospital, Boston between September 1992 and September 2002, within 30 days of discharge following an arterial switch or Norwood procedure, or (b) died within 30 days of discharge after one of the above operations. Cases were excluded if they were greater than one month of age at the time of surgery or if they were transferred to another hospital before discharge home.
The controls arose from the population of infants that had undergone either an arterial switch or Norwood procedure between September 1992 and September 2002, survived to discharge, and had not been readmitted to any hospital or died within 30 days of discharge. The controls were chosen without knowledge of their medical history and were matched to patients by operation type, gender, and year of surgery, with a 2:1 ratio of controls to patients. To ensure that controls were not readmitted to another hospital within 30 days of discharge from our institution, clinic notes of physicians providing follow-up care for at least the first two months after discharge were reviewed for reference to hospital readmission. Written parental consent for release of medical records was obtained before contacting referring physicians. Controls were excluded if they were more than one month of age at the time of surgery or if they were transferred to another hospital before discharge home. One infant with pyloric stenosis, readmitted at three weeks of age to a referring hospital, was also excluded as this reason for readmission was felt to be unrelated to the prior heart surgery.
Study Design
We used a matched case-control design. Medical records were reviewed for potential risk factors for hospital readmission (Table 1). Ward census at the time of hospital discharge was obtained from the hospital's office of patient statistics. Distance between patient residence and Children's Hospital Boston were calculated from the Zip Code centroids published by the Bureau of the Census [11]. Residential Zip Code median family income and residential urban versus rural dwellers was drawn from the 1990 U.S. Census [12]. The Committee on Clinical Investigation at our hospital granted permission for a database and medical record review (October 16, 2002).
Statistical Analysis
Fisher's exact test was used to examine relationships between categorical variables. Univariate and multivariate analyses of each potential risk factor were performed to identify factors predicting an increased risk for readmission, using conditional logistic regression for matched case-control designs. A p value less than 0.05 was required for retention in the final multivariate model. Odds ratios for readmission and 95% confidence intervals were generated. Analyses were repeated for each surgical subgroup, and repeated excluding controls for whom freedom from readmission to another hospital was not confirmed. A commercially available statistical package (Stata version 8, College Station, TX) was used.
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Results
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Forty-eight patients were readmitted within 30 days of discharge; 19 of 498 (3.8%) patients discharged after an arterial switch and 29 of 254 (11.4%) patients discharged after Norwood surgery (p < 0.001). Indications for hospital readmission are listed in Table 2. Median time until readmission was 9 days (interquartile range, 5 to 15.5 days). An additional 6 infants died within 30 days of discharge; 5 after Norwood surgery and 1 after arterial switch surgery. Anatomic diagnoses are summarized in Table 3. Patient characteristics are listed in Table 4.
We reviewed our institutional medical records to ascertain freedom from readmission in all controls. In addition, independent confirmation was achieved in 79 of 108 (73%) controls through written or telephone contact with primary care physicians after obtaining patient consent. The remaining 29 controls had no available contact information (n = 27) or did not reply to our written request granting permission to contact their primary care physician (n = 1), or were not contacted because the patient was known to have died (n = 1). The majority of the controls for whom we could not determine contact information were followed by a cardiologist outside our institution (26 of 27, 96.3%). All patient characteristics cited in Table 4 were compared between controls verified as having not been readmitted with those controls for whom we had no confirmation, and no significant differences were found.
On univariate analysis (Table 5), factors associated with an increased risk of readmission were: living in an urban residential area, intensive care unit (ICU) course greater than 7 days, total postoperative length of stay greater than 12 days, establishment of full oral feedings less than 2 days before discharge, medical comorbidity, and residual hemodynamic problem(s). Factors associated with a reduced likelihood of readmission were Zip Code median family income less than $30,000 and distance between home and hospital greater than 100 miles.
On multivariate analysis (Table 6), independent factors predicting an increased risk of readmission were the presence of a residual hemodynamic problem(s) and the establishment of full oral feedings less than 2 days before discharge. Having a Zip Code median family income less than $30,000 predicted a lower likelihood of readmission.
A separate analysis was performed for each of the Norwood and arterial switch groups. On univariate analysis (Table 7), factors associated with an increased risk of readmission after Norwood surgery were: total postoperative length of stay greater than 12 days, establishment of full oral feedings less than 2 days before discharge, and residual hemodynamic problem(s); whereas living greater than 100 miles from the hospital predicted a lower likelihood of readmission. On multivariate analysis of the Norwood group (Table 8), establishment of full oral feedings less than 2 days before discharge and residual hemodynamic problem(s) were both independent predictors of readmission. However, after arterial switch surgery, univariate predictors of readmission (Table 9) were ICU stay greater than 7 days, total postoperative length of stay greater than 12 days, medical comorbidity, and having residual hemodynamic problem(s). On multivariate analysis of the arterial switch group (Table 10), both an ICU stay greater than 7 days and residual hemodynamic problem(s) were independent predictors of readmission. Median total postoperative length of stay was longer in Norwood as compared to arterial switch patients (16 vs 10 days, p < 0.0001).
A subanalysis was performed to explore the nature of the relationship between socioeconomic status and readmission. Of note, 62% of patients living in low-income Zip Codes (< $30,000/annum) resided at least 100 miles from the hospital, as compared to 20% of those living in higher-income Zip Codes (
$30,000/annum) (p < 0.001). However, there were no differences between patients living in low versus high-income Zip Codes with regards to median ICU length of stay (8 vs 7 days, p = not significant [NS]), median total postoperative length of stay (13 vs 14 days, p = NS), rate of comorbid condition(s) (24% vs 23%, p = NS), or rate of residual hemodynamic problem(s) (28% vs 32%, p = NS).
Univariate and multivariate analyses were repeated using only the 79 control patients for whom freedom from readmission in another hospital was confirmed by the patient's physician. With both arterial switch and Norwood patient groups combined, the multivariate model was similar to that in Table 6; both residual hemodynamic problem(s) and Zip Code median family income remained independent predictors of hospital readmission. However, ICU stay greater than 7 days (OR 3.75 [1.29, 10.9], p = 0.015) replaced establishment of full oral feedings less than 2 days before discharge as an independent predictor of readmission. Among arterial switch patients, ICU stay greater than 7 days remained an independent predictor of readmission. For patients who underwent Norwood surgery, the multivariate model was unchanged, with both residual hemodynamic problem(s) and establishment of full oral feedings less than 2 days before discharge remaining independent predictors of readmission.
Analyses were then repeated omitting the six patients who died within 30 days of discharge and their corresponding controls. On multivariate analyses, variables that were significant in this subgroup were identical to those significant in the multivariate models above.
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Comment
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This study examined reasons and potential risk factors for nonelective hospital readmission after complex neonatal cardiac surgery, including risk factors that reflect patient well being at discharge, provider characteristics, and access to health care services. Indications for readmission differed following the arterial switch procedure as compared to Norwood surgery. Known complications of the Norwood procedure, including shunt obstruction with hypoxemia, arch obstruction, and pulmonary overcirculation with poor weight gain and vomiting, were responsible for many of the readmissions that we observed in this group (Table 2) [8]. These problems are consistent with the independent risk factors for readmission identified in Norwood patients, namely the presence of residual hemodynamic problems and establishment of full oral intake less than 2 days before discharge. The readmission rate in the Norwood group was higher than in the arterial switch group (11.4% vs 3.8%, respectively), consistent with the inherently unstable parallel circulation after Norwood surgery as compared to the physiologically corrected circulation after the arterial switch operation.
Infections were responsible for only 28% of readmissions after Norwood surgery, as compared to the arterial switch group for which almost two-thirds of readmissions were for infectious reasons, the majority being wound infections. Presumably this is because wound infections in the Norwood group were diagnosed and treated before hospital discharge, as these patients had greater postoperative lengths of stay than the arterial switch patients, who were perhaps more likely to be home by the time wound infections appeared.
Zip Code median annual family income less than $30,000 was a factor that lacked sufficient power to predict a decreased likelihood of readmission when the Norwood and arterial switch subgroups were analyzed separately. However, when all readmitted patients were analyzed together, independent of operation performed, low Zip Code median family income predicted a lower likelihood of readmission. There are several potential explanations for this finding. For example, low income families may have reduced access to transportation and be less able to return to the hospital at times of medical need, seeking other sources of care or no care at all. Low socioeconomic status is highly correlated with reduced access to medical care [13–16]. As well, we found that patients living in low-income Zip Codes lived further away from the hospital. Goodman and colleagues [17] demonstrated that children living 30 minutes from the nearest hospital were less likely to be hospitalized than children living in close proximity to a hospital.
Our findings suggest that hospital readmission in some patients is a preventable complication of inpatient care. For example, ensuring that full oral intake has been established for 2 days or longer before discharge may prevent readmissions related to failure to gain weight or vomiting of uncertain etiology.
These results must be interpreted in light of the study design. It is possible that some patients were readmitted to other hospitals without our knowledge, particularly patients transferred to hospitals closer to home as compared to patients discharged directly to home from our institution. Therefore, the number of readmissions that we observed is likely an underestimate of the true incidence of hospital readmissions. As well, the readmitted patients in our study could somehow be different from readmitted patients that we failed to identify, though there is little reason to suspect this to be the case. A third limitation is our lack of data on home nursing care and unscheduled emergency department and physician office visits. Such encounters may serve to prevent hospital readmission in some circumstances. However, unscheduled emergency department and physician office visits also increase the overall burden of health care delivery and may be preventable. Fourth, readmission to another hospital was not independently excluded for all control patients. However, no differences were found among characteristics of controls for whom we had thorough follow-up as compared to those having incomplete follow-up; during the process of verifying that control patients were not admitted to another hospital, no potential controls were found to have been readmitted with the exception of one infant readmitted with pyloric stenosis at 3 weeks of age. Furthermore, if any controls were in fact readmitted, then our point estimates of effect underestimate the truth, meaning that our results are a conservative interpretation of the true risk of hospital readmission. Finally, this is a single-center study and the results may not be generalized to other institutions.
Six patients who died suddenly within 30 days of discharge were included in this analysis, as this group was too small to make meaningful conclusions from in isolation. Including this group allowed us to capture all patients having a serious clinical event within 30 days of discharge. Although risk factors for sudden death could be different from those that result in hospital readmission, removing these patients had no influence on the multivariate models.
In conclusion, hospital readmission after Norwood surgery was more likely in patients who had established full oral intake less than 2 days before discharge or had significant residual hemodynamic problems. An ICU stay greater than 7 days or the presence of residual hemodynamic problems predicted readmission in infants after arterial switch surgery. Readmission was less likely to occur in patients living in low-income Zip Codes for undefined reasons, which we speculate may be related to reduced access to care. The optimal postoperative management of these patients, balancing the risk of readmission with the financial and psychosocial costs of longer initial hospitalization or extended outpatient services, remains a matter of individualized patient care and physician judgment.
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Abstract
Introduction
