We thank Xue and colleagues1 for their interest in our article. We agree with these authors that multivariable modelling of observational data may be vulnerable to confounding2 and have already acknowledged this in our article.3 Unfortunately, some of the perioperative factors suggested by Xue and colleagues are not available in this dataset and hence we cannot perform further analyses based on these factors. This is similar to many other epidemiological studies,4–6 and may be an important limitation provided the omissions constitute independent confounders not mediators of the outcome. We are interested in preoperative anaemia and plan to undertake future studies to explore its relationship with postoperative mortality. However, we disagree that inclusion of postoperative complications would be pertinent to our study as these may be mediators of the effect of drug on mortality, rather than independent confounders. Nonetheless, our analyses, as published, are novel as they explore class and dose effects of statins, as well as exploring the effects of other cardiovascular medications, in several different statistical models. The strength of the effect of statins on postoperative mortality warrants further investigation.
Acknowledgements related to this article
Assistance with the reply: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
1. Xue F-S, Liu G-P, Sun C, Yang G-Z. Association of preoperative cardiovascular drugs with short-term mortality after coronary artery bypass grafting. Eur J Anaesthesiol
2. Okoli GN, Sanders RD, Myles P. Demystifying propensity scores. Br J Anaesth
3. Venkatesan S, Okoli GN, Mozid AM, et al. Effects of five preoperative cardiovascular drugs on mortality after coronary artery bypass surgery: a retrospective analysis of an observational study of 16 192 patients. Eur J Anaesthesiol
4. Bottle A, Mozid A, Grocott HP, et al. Preoperative risk factors in 10 418 patients with prior myocardial infarction and 5241 patients with prior unstable angina undergoing elective coronary artery bypass graft surgery. Br J Anaesth
5. Bottle A, Mozid A, Grocott HP, et al. Preoperative stroke and outcomes after coronary artery bypass graft surgery. Anesthesiology
6. Sanders RD, Bottle A, Jameson SS, et al. Independent preoperative predictors of outcomes in orthopedic and vascular surgery: the influence of time interval between an acute coronary syndrome or stroke and the operation. Ann Surg