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LETTER TO THE EDITOR

Nonignorable Covariates

Department of Anesthesiology and Critical Care; Centre Hospitalier Universitaire Pitié Salpêtrière; Assistance Publique des hôpitaux de Paris; Université Pierre et Marie-Paris 6., 47 bld de l'hôpital, 75013; Paris, France; yannick.le-manach{at}psl.ap-hop-paris.fr

In Response:

We agree with Dr. Pace1 that the nonrandomized design is probably the main weakness of our study2; nevertheless, the bias reduction has been our main concern. Indeed, three different statistical methods were used, but we assume that the unknown (or not recorded) variables could not have been taken into account. This limitation is observed in each nonrandomized study. Furthermore, the comment about a potential bias related to the before-after design has been assessed by a pooled analysis, which is presented and discussed in the original publication.2

Our study does not demonstrate that the postoperative withdrawal of a chronic statin therapy induces postoperative cardiac events, because this causality could only be proven by randomized studies. However, this causality link has never been asserted, and the well-recognized limitations of a retrospective study have been acknowledged. Nevertheless, the observed association remains important and should be considered in clinical practice, especially since these results had been reported by other groups in the same3 or similar4 conditions.

REFERENCES

1. Pace NL. Nonignorable covariates. Anesth Analg 2008;106:673[Free Full Text]
2. Le Manach YL, Godet G, Coriat P, Martinon C, Bertrand M, Fléron M-H, Riou B. The impact of postoperative discontinuation or continuation of chronic statin therapy on cardiac outcome after major vascular surgery. Anesth Analg 2007;104:1326–33[Abstract/Free Full Text]
3. Schouten O, Hoeks SE, Welten GM, Davignon J, Kastelein JJ, Vidakovic R, Feringa HH, Dunkelgrun M, van Domburg RT, Bax JJ, Poldermans D. Effect of statin withdrawal on frequency of cardiac events after vascular surgery. Am J Cardiol 2007; 100:316–20[Web of Science][Medline]
4. Collard CD, Body SC, Shernan SK, Wang S, Mangano DT; Multicenter Study of Perioperative Ischemia (MCSPI) Research Group, Inc; Ischemia Research and Education Foundation (IREF) Investigators. Preoperative statin therapy is associated with reduced cardiac mortality after coronary artery bypass graft surgery. J Thorac Cardiovasc Surg 2006;132:392–400[Abstract/Free Full Text]

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