Het volume van chirurgische ingrepen en de impact ervan op ... - KCE

138 Volume Outcome KCE reports 113
OUTCOME
In-hospital mortality was 0.98% after CEA (Table 6.5). This is slightly lower than the
mean in-hospital mortality of 1.6% (range 0.3 to 5.2%) reported by Holt and
associates. 61 The funnel plot (Figure 2.1) revealed two outlying centres with a higher
mortality. We would need additional information to investigate and explain these
observed results.
The observed in-hospital and approximate 30-day mortality is higher after CAS (2.0%)
than after CEA (1.1%) (see Table 6.5). Mas et al. had to prematurely stop their trial
when it became clear that the 30-day incidence of any stroke or death was 3.9% after
endarterectomy (95% CI, 2.0 to 7.2) and 9.6% after stenting (95% CI, 6.4 to 14.0). 260
Stroke rate after CEA was 1.51% in Belgian centres (Table 6.5). This is lower than in
Holt’s meta-analysis which showed a stroke rate of 2.7% (range 0.23 to 6.1%). 61 There
is, however, a problem in the coding of post-operative stroke since it is impossible to
distinguish between patients who are admitted due to a stroke, and patients who suffer
from a stroke post-operatively. Either of these may be miscoded, as Holt points out. 61
Therefore, he suggests that post-operative death is a more valid measure for CEA
outcome than stroke.
AMI rate after CEA was 0.66% in Belgium (Table 6.5). This outcome measure has a
limited value since the abovementioned coding problem applies in the same way to AMI.
In addition, it has to be acknowledged that, in practice, surgeons might miss an AMI
because they are not looking for it. Yadav et al., for example, found a 1-year AMI rate of
3.0 and 7.5% after, respectively, CAS and CEA. 261 They defined AMI as an increase of
creatinine kinase higher than two times the upper limit with a positive MB fraction.
Christian et al. pointed out that complication rate would actually be a better end point
than mortality for procedures such as CEA where death is a rare outcome. The
difficulty is, however, the unreliability of the coding of complication data in
administrative databases. 93
PATIENT CASE MIX
Belgian patients with a CEA or CAS procedure were on average 71 years old and
predominantly male (66%). One out of five patients (19.5%) had a Charlson score of at
least three. Even when AMI and cerebrovascular diseases are excluded from the
calculation of the Charlson score (modified Charlson score, explained in section
4.3.2.1), this percentage decreases only slightly to 18%. See Table 6.6.
While age and sex seem comparable with other studies, the percentage of patients with
Charlson score >3, on the other hand, is only 10% in Birkmeyer’s study. 115
Information on the symptomatic status of the patient and the degree of carotid stenosis
are supplementary risk factors that are often used for further risk adjustment, but that
61, 115, 256
are not available in the administrative MCD.
VOLUME OUTCOME ASSOCIATION
The meta-analysis performed by Holt et al. showed persistent and reproducible
evidence for an inverse relationship between hospital volume and mortality: death
attributable to CEA occurred less frequently in higher-volume hospitals (odds ratio 0.76
[0.74-0.81]). 61 The validity of this result was supported by the fact that exclusion of the
largest study did not change the pooled effect estimate.
In Belgian data, a CEA volume increase of 10% is associated with a decrease of 6% in the
odds of death. The validity of this result is, however, undetermined by the fact that the
volume outcome relationship is influenced by three centres (see Table 6.8).
RELATIONSHIP BETWEEN CASE MIX AND VOLUME
Our results (see Table 6.7) show that differences in case-mix between higher- and
lower-volume hospitals do not underlie the volume-outcome relationship. This is
supported by the analysis by Birkmeyer where significant crude results also remain
significant after case mix adjustment. 115