- © 2004 Canadian Medical Association or its licensors
Appropriate access time for surgery is often determined on the basis of expert opinion. However, in our study,1 we used surgery records to assess the risk of undergoing emergency surgery in relation to the duration of the wait for elective cholecystectomy. Given the magnitude of the effect that we observed,1 we assumed that there might be policy implications.
Alexander Tsai brings attention to articles that might be relevant in other circumstances, but for the purposes of our research,1 it is difficult to see how results concerning length of stay and death after hip fracture surgery could help the reader to better interpret our findings on the risk of emergency admission while awaiting elective cholecystectomy.
Tsai suggests that “the patients who ended up on the waiting list might have been sicker.” In our study1 we assessed the frequency of emergency surgery after registration on the waiting list. Patients who underwent emergency surgery without placement on the list might have been less or more sick, but they were not included in the study. For patients on the list, coexisting illnesses might indeed have caused additional delay in surgery. However, whether biliary complications, such as acute cholecystitis, obstructive jaundice, cholangitis or pancreatitis, occur more frequently in patients with comorbid conditions is unclear.
There is no doubt that risk selection (the process whereby the makeup of a population changes over time through removal of subjects at higher risk) may bias the observed risk, because of unobserved heterogeneity.2 For instance, when the risk of symptoms worsening is constant over the duration of the wait, risk estimates without adjustment for heterogeneity of individual patients will probably underestimate the true risk associated with longer waiting time, and the risk associated with longer relative to shorter waits may also be underestimated. Therefore, our message to health policy-makers should be that the risk of emergency surgery while waiting for elective cholecystectomy increased by a factor of almost 3 after 20 weeks on the waiting list, and that this is perhaps an underestimate.
Boris Sobolev Mark FitzGerald The Centre for Clinical Epidemiology and Evaluation Vancouver, BC Dale Mercer Queen's University Kingston, Ont.
References
- 1.
- 2.