Volume Cuts Renal Artery Bypass Deaths in Low-Risk Patients

TUCSON, ARIZ. — In-hospital mortality for renal artery bypass in low-surgical-risk patients was more than fourfold greater at low-volume than at high-volume hospitals across the nation during a recent 6-year period.

However, among patients at intermediate or high surgical risk, in-hospital mortality for renal artery bypass (RAB) did not vary significantly based on a hospital's RAB volume, Dr. J. Gregory Modrall reported at the annual meeting of the Southern Association for Vascular Surgery.

This latter finding came as a surprise. The study hypothesis was that a high hospital RAB volume is a proxy for greater surgical team expertise, which was expected to translate into improved outcomes, explained Dr. Modrall of the department of surgery, University of Texas at Dallas.

He and his coinvestigators analyzed the Healthcare Cost and Utilization Project Nationwide Inpatient Sample, the nation's largest all-payer inpatient database, with more than 1,000 participating U.S. hospitals. During the years 2000–2005, they identified 7,413 patients who underwent RAB. The frequency of the operation was 3.2 cases per 100,000 discharges.

Dividing the hospitals into tertiles based on annual RAB volume, the investigators defined low-volume centers as those doing fewer than two per year, medium-volume hospitals as those doing two to five annually, and high-volume hospitals as those doing more than five.

For decades RAB has been a treatment mainstay for renal artery stenosis with presumed renovascular hypertension or ischemic nephropathy. However, according to Dr. Modrall's Nationwide Inpatient Sample analysis, the annual number of RABs performed plummeted by 49% between 2000 and 2005.

Overall national in-hospital mortality for RAB was 9.6%. There was no significant difference in crude rates based on hospital volume: 9.9% in low-volume, 10.5% in medium-volume, and 8.2% in high-volume centers.

However, it was a different story after adjustment for patient risk profile. In an earlier study, Dr. Modrall and his colleagues identified five independent risk factors for in-hospital mortality with RAB: advanced age, female sex, and a history of chronic renal failure, heart failure, or chronic lung disease.

When the investigators adjusted for risk factor level, patients in the lowest-risk quartile had an in-hospital mortality of 6.4% in low-volume hospitals, 3.7% in medium-volume hospitals, and 1.5% in high-volume hospitals.

In the remaining quartiles of patient risk, however, there was no significant difference in mortality based on hospital volume. For example, patients in the second-highest risk quartile had an in-hospital mortality of 9.9% in low-, 7.8% in medium-, and 11.9% in high-volume hospitals. Among those in the highest-risk quartile, the rates were 15.2%, 20.2%, and 16.3%, respectively.

In a separate multivariate analysis with hospital RAB volume as a continuous variable, there was a 2% decrease in the risk of in-hospital mortality for each additional RAB done per year at a hospital.

“If you have two hospitals operating on precisely the same patient population and one does six cases per year and the other does five, the hospital that does six bypasses per year will have a 2% lower risk of in-hospital mortality,” Dr. Modrall said.

These findings have important implications for patient management, the surgeon stressed. “Surgeons who practice in a low-volume hospital may want to consider lower-risk alternatives: transferring the patient to a high-volume referral center with documented expertise in renovascular surgery, or performing renal artery stenting, or even medical management. And certainly if you do contemplate doing renal artery bypass operations, I would strongly urge you to consider the five components of patient risk,” he said.

Dr. Bruce A. Perler, a study discussant, observed that Dr. Modrall's “somewhat sobering study” illustrates a key point: “There's no area of vascular surgery where percutaneous angioplasty has had a more profound impact than in renal artery occlusive disease.”

It's counterintuitive that high-volume hospitals, which do so much better with low-risk patients, don't also achieve better results with higher-risk patients, noted Dr. Perler, professor of surgery and chief of vascular surgery at Johns Hopkins University, Baltimore.

Dr. Modrall said he thinks patient risk factors are the major determinant of in-hospital mortality. In low-risk patients, surgical expertise as reflected in hospital RAB volume can make a big impact. Not so in heavily risk-laden patients.

“Patients who are high risk have so many risk factors that it really doesn't matter where they have their operation—they're probably going to have relatively poor outcomes,” he explained.

The lowest-risk patients had a mortality of 6.4% in low-volume hospitals and 1.5% in high-volume hospitals. DR. MODRALL

ELSEVIER GLOBAL MEDICAL NEWS

TUCSON, ARIZ. — In-hospital mortality for renal artery bypass in low-surgical-risk patients was more than fourfold greater at low-volume than at high-volume hospitals across the nation during a recent 6-year period.

However, among patients at intermediate or high surgical risk, in-hospital mortality for renal artery bypass (RAB) did not vary significantly based on a hospital's RAB volume, Dr. J. Gregory Modrall reported at the annual meeting of the Southern Association for Vascular Surgery.

This latter finding came as a surprise. The study hypothesis was that a high hospital RAB volume is a proxy for greater surgical team expertise, which was expected to translate into improved outcomes, explained Dr. Modrall of the department of surgery, University of Texas at Dallas.

He and his coinvestigators analyzed the Healthcare Cost and Utilization Project Nationwide Inpatient Sample, the nation's largest all-payer inpatient database, with more than 1,000 participating U.S. hospitals. During the years 2000–2005, they identified 7,413 patients who underwent RAB. The frequency of the operation was 3.2 cases per 100,000 discharges.

Dividing the hospitals into tertiles based on annual RAB volume, the investigators defined low-volume centers as those doing fewer than two per year, medium-volume hospitals as those doing two to five annually, and high-volume hospitals as those doing more than five.

For decades RAB has been a treatment mainstay for renal artery stenosis with presumed renovascular hypertension or ischemic nephropathy. However, according to Dr. Modrall's Nationwide Inpatient Sample analysis, the annual number of RABs performed plummeted by 49% between 2000 and 2005.

Overall national in-hospital mortality for RAB was 9.6%. There was no significant difference in crude rates based on hospital volume: 9.9% in low-volume, 10.5% in medium-volume, and 8.2% in high-volume centers.

However, it was a different story after adjustment for patient risk profile. In an earlier study, Dr. Modrall and his colleagues identified five independent risk factors for in-hospital mortality with RAB: advanced age, female sex, and a history of chronic renal failure, heart failure, or chronic lung disease.

When the investigators adjusted for risk factor level, patients in the lowest-risk quartile had an in-hospital mortality of 6.4% in low-volume hospitals, 3.7% in medium-volume hospitals, and 1.5% in high-volume hospitals.

In the remaining quartiles of patient risk, however, there was no significant difference in mortality based on hospital volume. For example, patients in the second-highest risk quartile had an in-hospital mortality of 9.9% in low-, 7.8% in medium-, and 11.9% in high-volume hospitals. Among those in the highest-risk quartile, the rates were 15.2%, 20.2%, and 16.3%, respectively.

In a separate multivariate analysis with hospital RAB volume as a continuous variable, there was a 2% decrease in the risk of in-hospital mortality for each additional RAB done per year at a hospital.

“If you have two hospitals operating on precisely the same patient population and one does six cases per year and the other does five, the hospital that does six bypasses per year will have a 2% lower risk of in-hospital mortality,” Dr. Modrall said.

These findings have important implications for patient management, the surgeon stressed. “Surgeons who practice in a low-volume hospital may want to consider lower-risk alternatives: transferring the patient to a high-volume referral center with documented expertise in renovascular surgery, or performing renal artery stenting, or even medical management. And certainly if you do contemplate doing renal artery bypass operations, I would strongly urge you to consider the five components of patient risk,” he said.

Dr. Bruce A. Perler, a study discussant, observed that Dr. Modrall's “somewhat sobering study” illustrates a key point: “There's no area of vascular surgery where percutaneous angioplasty has had a more profound impact than in renal artery occlusive disease.”

It's counterintuitive that high-volume hospitals, which do so much better with low-risk patients, don't also achieve better results with higher-risk patients, noted Dr. Perler, professor of surgery and chief of vascular surgery at Johns Hopkins University, Baltimore.

Dr. Modrall said he thinks patient risk factors are the major determinant of in-hospital mortality. In low-risk patients, surgical expertise as reflected in hospital RAB volume can make a big impact. Not so in heavily risk-laden patients.

“Patients who are high risk have so many risk factors that it really doesn't matter where they have their operation—they're probably going to have relatively poor outcomes,” he explained.

The lowest-risk patients had a mortality of 6.4% in low-volume hospitals and 1.5% in high-volume hospitals. DR. MODRALL

ELSEVIER GLOBAL MEDICAL NEWS

TUCSON, ARIZ. — In-hospital mortality for renal artery bypass in low-surgical-risk patients was more than fourfold greater at low-volume than at high-volume hospitals across the nation during a recent 6-year period.

However, among patients at intermediate or high surgical risk, in-hospital mortality for renal artery bypass (RAB) did not vary significantly based on a hospital's RAB volume, Dr. J. Gregory Modrall reported at the annual meeting of the Southern Association for Vascular Surgery.

This latter finding came as a surprise. The study hypothesis was that a high hospital RAB volume is a proxy for greater surgical team expertise, which was expected to translate into improved outcomes, explained Dr. Modrall of the department of surgery, University of Texas at Dallas.

He and his coinvestigators analyzed the Healthcare Cost and Utilization Project Nationwide Inpatient Sample, the nation's largest all-payer inpatient database, with more than 1,000 participating U.S. hospitals. During the years 2000–2005, they identified 7,413 patients who underwent RAB. The frequency of the operation was 3.2 cases per 100,000 discharges.

Dividing the hospitals into tertiles based on annual RAB volume, the investigators defined low-volume centers as those doing fewer than two per year, medium-volume hospitals as those doing two to five annually, and high-volume hospitals as those doing more than five.

For decades RAB has been a treatment mainstay for renal artery stenosis with presumed renovascular hypertension or ischemic nephropathy. However, according to Dr. Modrall's Nationwide Inpatient Sample analysis, the annual number of RABs performed plummeted by 49% between 2000 and 2005.

Overall national in-hospital mortality for RAB was 9.6%. There was no significant difference in crude rates based on hospital volume: 9.9% in low-volume, 10.5% in medium-volume, and 8.2% in high-volume centers.

However, it was a different story after adjustment for patient risk profile. In an earlier study, Dr. Modrall and his colleagues identified five independent risk factors for in-hospital mortality with RAB: advanced age, female sex, and a history of chronic renal failure, heart failure, or chronic lung disease.

When the investigators adjusted for risk factor level, patients in the lowest-risk quartile had an in-hospital mortality of 6.4% in low-volume hospitals, 3.7% in medium-volume hospitals, and 1.5% in high-volume hospitals.

In the remaining quartiles of patient risk, however, there was no significant difference in mortality based on hospital volume. For example, patients in the second-highest risk quartile had an in-hospital mortality of 9.9% in low-, 7.8% in medium-, and 11.9% in high-volume hospitals. Among those in the highest-risk quartile, the rates were 15.2%, 20.2%, and 16.3%, respectively.

In a separate multivariate analysis with hospital RAB volume as a continuous variable, there was a 2% decrease in the risk of in-hospital mortality for each additional RAB done per year at a hospital.

“If you have two hospitals operating on precisely the same patient population and one does six cases per year and the other does five, the hospital that does six bypasses per year will have a 2% lower risk of in-hospital mortality,” Dr. Modrall said.

These findings have important implications for patient management, the surgeon stressed. “Surgeons who practice in a low-volume hospital may want to consider lower-risk alternatives: transferring the patient to a high-volume referral center with documented expertise in renovascular surgery, or performing renal artery stenting, or even medical management. And certainly if you do contemplate doing renal artery bypass operations, I would strongly urge you to consider the five components of patient risk,” he said.

Dr. Bruce A. Perler, a study discussant, observed that Dr. Modrall's “somewhat sobering study” illustrates a key point: “There's no area of vascular surgery where percutaneous angioplasty has had a more profound impact than in renal artery occlusive disease.”

It's counterintuitive that high-volume hospitals, which do so much better with low-risk patients, don't also achieve better results with higher-risk patients, noted Dr. Perler, professor of surgery and chief of vascular surgery at Johns Hopkins University, Baltimore.

Dr. Modrall said he thinks patient risk factors are the major determinant of in-hospital mortality. In low-risk patients, surgical expertise as reflected in hospital RAB volume can make a big impact. Not so in heavily risk-laden patients.

“Patients who are high risk have so many risk factors that it really doesn't matter where they have their operation—they're probably going to have relatively poor outcomes,” he explained.

The lowest-risk patients had a mortality of 6.4% in low-volume hospitals and 1.5% in high-volume hospitals. DR. MODRALL

ELSEVIER GLOBAL MEDICAL NEWS