knee arthroplasty (Lavernia and Guzman, 1995), carotid endarterectomy (Ruby et al., 1996), thyroidectomy (Sosa et al., 1998), colorectal surgery (Rosen et al., 1996), and HIV/AIDS treatment (Kitahata et al., 1996). In these cases, the more procedures carried out, the better are the results, in at least some dimensions.

Although most of the published studies of volume-outcome relationships have demonstrated better outcomes with higher volumes, this finding has not been universal. Conflicting results have been reported for trauma centers, for example, with at least two reports of better results with higher volumes (Konvolinka et al., 1995; Smith et al., 1990), one with poorer results with higher volumes (Tepas et al., 1998), and one study of trauma surgeon case volume showing no difference between high and low volumes (Richardson et al., 1998). A study of 28-day mortality rates for very low birth weight infants reported no difference associated with the number of such infants treated in the neonatal intensive care unit (Horbar et al., 1997).

Within a hospital, processing a high volume of one type of service can lead to organizational efficiency, establishment of multidisciplinary teams, use of guidelines, and evaluation of outcomes. These aspects of specialization can all contribute to success. Alternatively, it may be that the experience gained by individual providers is the key to improving outcomes. Variations in mortality and complications are influenced more by patient variables than by organizational factors (e.g., volume, nursing surveillance, quality of interaction among professionals) according to a recent review of studies of the effects of these factors on patient outcomes (Mitchell et al., 1997).

High-Risk Cancer Surgery

The treatment of several cancers involves surgery that is complex and has high short-term risks for patients. One common cancer in this category is non-small-cell lung cancer (NSCLC). Three others that occur infrequently are pancreatic, esophageal, and gastric cancers.

There is no effective screening procedure for NSCLC, and about one-half of NSCLC patients present with metastatic disease. About one-third of all NSCLC patients have their disease diagnosed at a stage where surgery is recommended as part of initial care. In a procedure called pulmonary resection, diseased portions of the lung are removed. Surgery is more commonly performed on younger patients and those with local or regional disease. Fewer than one in ten individuals with distant NSCLC receives surgery; these patients are more often treated with radiation (Table 5.1). The expected perioperative or 30-day mortality in university medical centers varies with the extent of the primary surgery, ranging from about 1 to 6 percent (Ginsberg et al., 1997). These absolute mortality risks are known to vary with patient characteristics (e.g., age, stage of disease, and comorbidity). A 30-day mortality rate of 17 percent after pneumonectomy (removal of part or all of the lung) was observed in an evaluation of a national sample of Medicare claims from the early 1980s (Whittle et al., 1991).

Two studies have shown a relationship between high hospital volume and lower mortality for NSCLC. Romano and Mark (1992) used hospital discharge abstracts to assess the outcome of surgery for all adults (n = 12,439) who underwent pulmonary resections in 1983-1986 in 499 nonfederal California hospitals. Hospital volume was defined by the total number of resections for lung cancer per year and was divided into quartiles. In-hospital mortality was 3.8 percent after wedge resection, 3.7 percent after segmental resection, and 11.6 percent after

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