Invited commentary

Abstract

Assessment of preoperative risk and risk modeling is an integral part of clinical practice. The current retrospective observational study recognizes an independent association between preoperative white cell count (WCC) and postoperative mortality during a 12-month period [1Newall N. Grayson A.D. Aung Y.O. et al.Preoperative white blood cell count is independently associated with higher perioperative cardiac enzyme release and increased 1-year mortality after coronary artery bypass grafting.Ann Thorac Surg. 2006; 81: 583-590Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar]. No causal relationship can be established because it is an observational study. The WCC is readily available, but it is a relatively crude inflammatory marker, and as the authors have stated, they did not measure other more specific inflammatory markers such as C-reactive protein, interleukin-6, and tumour necrosis-factor alpha. White cell count varies and a single sample may not be representative. Subgroup analysis revealed that neutrophil count largely explained the association. The WCC can be elevated in a wide range of comorbid conditions, some of which need to be identified and treated prior to cardiopulmonary bypass (eg, bacterial infection). The key question is the threshold at which these results affect clinical practice. Dacey and colleagues [2Dacey L.J. DeSimone J. Braxton J.H. et al.Northern New England Cardiovascular Disease Study GroupPreoperative white blood cell count and mortality and morbidity after coronary artery bypass grafting.Ann Thorac Surg. 2003; 76: 760-764Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar] showed a modest increase in mortality with preoperative WCCs between 6 and 12 × 109/L with a sharp increase greater than that level. The current article [1Newall N. Grayson A.D. Aung Y.O. et al.Preoperative white blood cell count is independently associated with higher perioperative cardiac enzyme release and increased 1-year mortality after coronary artery bypass grafting.Ann Thorac Surg. 2006; 81: 583-590Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar] suggests that any WCC greater than 10 x 109/L may be clinically important. There may be insufficient time to investigate an underlying cause of the WCC elevation in patients who present acutely. However, in elective circumstances the authors have suggested that even a slight elevation of the WCC should be evaluated carefully because of the strong association with higher morbidity and mortality in the following 12 months. The causes of death not presented in their article might have provided clues to underlying disease processes. Interestingly there was no association between WCC with wound infection or stroke. The interaction of neutrophils, macrophages, and endothelial cells causing the systemic inflammatory response is complex. The authors have raised the question of whether there are long-term benefits in patients with elevated WCCs by reducing the WCC during cardiopulmonary bypass by leuco-depletion. This is a provocative study that raises more questions than it answers. Careful investigation of the cause of any elevated WCC should be considered if time permits. Longitudinal observational studies of patients with elevated WCCs may provide important information about associated disease processes. However, a randomized clinical trial is required to eliminate selection bias. If these findings are reproducible, WCC or other inflammatory markers should be included in the predictive risk models such as the Euroscore [3Nashef S.A. Roques F. Michel P. et al.European system for cardiac operative risk evaluation (EuroSCORE).Eur J Cardiothorac Surg. 1999; 16: 9-13Crossref PubMed Scopus (2709) Google Scholar], the Society of Thoracic Surgeons [4STS Evidence Based Guidelines, 2004. Cardiac Surgery Risk Models. Available at: http://www.sts.org/doc/8868. Updated August 30, 2004. Accessed August 05, 2005.Google Scholar] or the American Heart Association [5Eagle K.A. Guyton R.A. Davidoff R. et al.ACC/AHA guidelines for coronary artery bypass graft surgery A report of the American College of Cardiology/American Heat Association Task Force on Practice Guidelines.Circulation. 1999; 100 (Committee to Revise the 1991 Guidelines for Coronary Artery Bypass Graft Surgery): 1464-1480Crossref PubMed Scopus (346) Google Scholar] models.