STS: Risk score predicts rehospitalization after heart surgery

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Rehospitalization risk models show marginal performance

Identifying the factors that determine whether a patient will need rehospitalization following discharge after heart surgery is a huge and unresolved problem. Risk models for the rate of hospital readmission following cardiothoracic surgery have historically performed poorly. Perhaps that’s because the models often fail to include factors with the strongest impact on readmissions. Most of the factors that appear to drive readmissions seem to be out of the direct control of hospital staffs, such as a lack of support for patients once they leave the hospital. Socioeconomic factors like this have usually not been included in risk models.

Dr. David M. Shahian

The C statistic (area under the receiver operating characteristic curve) for the model reported by Dr. Kilic was 0.66, very close to the 0.648 that my colleagues and I reported in 2014 for a risk model of 30-day hospital readmission following isolated coronary artery bypass grafting that used data from more than 162,000 Medicare patients who underwent surgery during 2008-2010 (Circulation. 2014 July 29;130[5]:399-409). This means that both models accounted for roughly two-thirds of the variability in readmission rates, which makes our model as well as Dr. Kilic’s model marginal in its ability to identify patients at greatest risk. Similar limitations exist for the other reported models for assessing the readmission risk following heart surgery.

One strength of the model reported by Dr. Kilic was its inclusion of patient factors that developed following the start of the index admission, such as postoperative acute renal failure.

Dr. David M. Shahian is a professor of surgery at Harvard Medical School and associate director of the Codman Center for Clinical Effectiveness in Surgery at the Massachusetts General Hospital, both in Boston. He made these comments during the discussion of Dr. Kilic’s report. Dr. Shahian had no relevant financial disclosures.




PHOENIX – A simple, five-element formula can help identify the patients undergoing heart surgery who face the greatest risk for a hospital readmission within 30 days following discharge from their index hospitalization.

The surgeons who developed this formula hope to use it in an investigational program that will target intensified management resources in postsurgical patients who face the highest readmission risk, to cut rehospitalizations and better improve their clinical status and quality of life.

The analysis that produced this formula also documented that the worst offender for triggering rehospitalizations following heart surgery is fluid overload, the proximate readmission cause for 23% of postsurgical patients, Dr. Arman Kilic said at the annual meeting of the Society of Thoracic Surgeons. The next most common cause was infection, which led to 20% of readmissions, followed by arrhythmias, responsible for 8% of readmissions, said Dr. Kilic, a thoracic surgeon at the University of Pennsylvania in Philadelphia.

Dr. Arman Kilic Mitchel L. Zoler/Frontline Medical News

Dr. Arman Kilic

Because fluid overload, often in the form of pleural effusion, is such an important driver of rehospitalizations, a more targeted management program would include better titration of diuretic treatment to patients following heart surgery, thoracentesis, and closer monitoring of clinical features that flag fluid overload such as weight.

“The volume overload issue is where the money is. If we can reduce that, it could really impact readmissions,” Dr. Kilic said in an interview.

An investigational program to target rehospitalization risk in heart surgery patients is planned at Johns Hopkins Hospital in Baltimore, where Dr. Kilic worked when he performed this analysis. Surgeons at Johns Hopkins are now in the process of getting funding for this pilot program, said Dr. John V. Conte Jr., professor of surgery and director of mechanical circulatory support at Johns Hopkins and a collaborator with Dr. Kilic on developing the risk formula.

Dr. John V. Conte Jr.

Dr. John V. Conte Jr.

“We’ll tailor postoperative follow-up. We’ll get high-risk patients back to the clinic sooner, and we’ll send nurse practitioners to see them to make sure they’re taking their medications and are getting weighed daily,” Dr. Conte said in an interview. “When a patient has heart surgery, they typically retain about 5-10 pounds of fluid. Patients with good renal function give up that fluid easily, but others are difficult to diurese. Many patients go home before they have been fully diuresed, and we need to follow these patients and transition them better to out-of-hospital care.”

He noted that other situations also come up that unnecessarily drive patients back to the hospital when an alternative and less expensive intervention might be equally effective. For example, some patients return to the hospital out of concern for how their chest wound is healing. Instead of being rehospitalized, such patients could be reassured by having them send a nurse a photo of their wound or by coming to an outpatient clinic.

“We need to engage more often with recently discharged patients,” Dr. Conte said in an interview. “Discharging them doesn’t mean separating them from the health care system; it should mean interacting with patients in a different way” that produces better outcomes and patient satisfaction for less money. Developing improved ways to manage recent heart surgery patients following discharge becomes even more critical later this year when, in July, the Centers for Medicare & Medicaid Services adds 30-day readmissions following coronary artery bypass grafting (CABG) to its list of procedures that can generate a penalty to hospitals if they exceed U.S. norms for readmission rates.

The risk model developed by Dr. Kilic, Dr. Conte, and their associates used data collected from 5,360 heart surgery patients treated at Johns Hopkins during 2008-2013. Nearly half the patients underwent isolated CABG, and 20% had isolated valve surgery. Overall, 585 patients (11%) had a hospital readmission within 30 days of their index discharge. One limitation of the analysis was it used data only on readmissions back to Johns Hopkins Hospital.

The researchers used data from three-quarters of the database to derive the risk formula, and from the remaining 25% of the database to validate the formula. A multivariate analysis of demographic and clinical characteristics that significantly linked with an elevated risk for readmissions identified five factors that independently made a significant contribution to readmission risk. The researchers assigned each of these five factors points depending on its relative contribution to readmission risk in the adjusted model: Severe chronic lung disease received 6 points; placement of a ventricular assist device received 5 points, while other types of heart surgery that was not CABG or valve surgery received 4 points (isolated CABG, isolated valve, or combined CABG and valve surgery received 0 points); development of acute renal failure postoperatively but before index discharge received 4 points; an index length of stay beyond 7 days received 4 points; and African American race received 3 points. The maximum number of points a patient could receive was 22.


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