Ann Thorac Surg 2006;81:553-554
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Karl F. Welke, MD
Division of Cardiothoracic Surgery, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239-3098
(Email: welkek{at}ohsu.edu).
Initial studies using administrative databases reported an inverse relationship between cardiac surgery procedural volume and mortality. More recent studies using both administrative and clinical databases have questioned the strength of this relationship. The enthusiasm for volume as a marker for quality has been tempered in part due to (1) the range of mortality rates in both low-volume and high-volume hospital groups, and (2) the much weaker relationship demonstrated in clinical databases. Although on average, high-volume hospitals have lower coronary artery bypass grafting (CABG) mortality rates than low-volume hospitals, wide variation in mortality rates exists among hospitals within similar volume categories. The volume–mortality relationship may be mitigated in clinical data due to the superiority of clinical data in adjusting for severity of illness. The Medicare dataset was designed for reimbursement purposes and omits many of the strongest predictors of mortality identified in clinical datasets (ie, left ventricular ejection fraction, multiple prior cardiac procedures, left main coronary artery disease, three-vessel coronary artery disease). In addition, the timing of important events such as how long before surgery a preoperative myocardial infarction occurred cannot be determined. This decreases the utility of such variables. While addressing the previously mentioned issues, clinical databases are limited in their scope and therefore contain select samples rather than complete national coverage.
In the current article, Plomondon and colleagues [1] analyzed the relationship between procedural volume and morbidity and mortality after off-pump CABG at 44 Veterans Affairs (VA) hospitals from 1998 to 2003. They found no association between either hospital total CABG volume or hospital off-pump CABG volume and morbidity or mortality. The results are in agreement with a previous article that examined the relationship between hospital total CABG volume and mortality in VA hospitals [2]. The inclusion of morbidity as an outcome measure increases the importance of the present study. Results from the VA may not be applicable to the general population due to the small volumes of all involved centers and the unique systems of care in VA hospitals, including surgical staff shared with affiliated academic medical centers. However they are important in and of themselves, as the VA is the largest health care system in the United States.
Volume is not a measure of quality of care, but rather an easily obtained structural attribute often associated with quality. If a comparison was made of high-volume and low-volume hospitals with good outcomes to high-volume and low-volume hospitals with poor outcomes, there would likely be characteristics common to good performing hospitals that explained the apparent influence of volume. These factors are apt to be process measures and characteristics of the systems of care not currently captured in either administrative or most clinical databases (ie, adherence to known best practices, preoperative preparation, experience and ability of all members of the patient care team, teamwork, postoperative care). Rather than focus on an imperfect surrogate, we need to begin the more difficult task of identifying these fundamental elements that explain the variation in medical outcomes.
 |
References
|
|---|
- Plomondon ME, Casebeer AW, Schooley LM, et al. Exploring the volume-outcome relationship for off-pump coronary artery bypass graft procedures Ann Thorac Surg 2006;81:547-554.[Abstract/Free Full Text]
- Shroyer ALW, Marshall G, Warner BA, et al. No continuous relationship between Veterans Affairs Hospital coronary artery bypass grafting surgical volume and operative mortality Ann Thorac Surg 1996;61:17-20.[Abstract/Free Full Text]
Top
References