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J Thorac Cardiovasc Surg 2007;133:591
© 2007 The American Association for Thoracic Surgery

Letter to the Editor

Reply to the Editor

^a Alfa Institute of Biomedical Sciences (AIBS), Athens, Greece
^b Department of Medicine, Henry Dunant Hospital, Athens, Greece
^d Department of Cardiac Surgery, Henry Dunant Hospital, Athens, Greece
^c Department of Medicine, Tufts University School of Medicine, Boston, Mass

We appreciate the comments of Vandijck and colleagues regarding our study.¹ They raised the issue of the potential mortality attributable to infection in our study group (patients who underwent off-pump coronary artery bypass grafting). They consider that confounding factors, such as age, comorbidity, left ventricular ejection fraction, antimicrobial treatment, and EuroSCORE values, might have led to the observed statistically significant difference in mortality between patients with and without microbiologically documented nosocomial infection.

Our results regarding mortality of patients who underwent coronary artery bypass grafting are in accordance with the results of previous studies (a fact that is mentioned in the discussion section of our article).^2,3 For example, using data from the US Society of Thoracic Surgeons National Cardiac Database, Fowler and associates² showed that patients with major infection had significantly higher mortality (17.3% vs 3.0%, P < .0001) and postoperative length of stay of longer than 14 days (47.0% vs 5.9%, P < .0001) than patients without infection.

However, we agree with Vandijck and colleagues that infections are sometimes the consequence of other postoperative complications or comorbidity that predispose to infections. It should be emphasized that the majority of patients (4/7 [57%]) with sternal wound infection in our cohort had a history of previous sternotomy or postoperative invasive interventions at the surgical site.

We did not collect data to estimate EuroSCORE values for the group of patients who did not have nosocomial infection based on the design of our study, and these data are not readily available now to be analyzed. However, we performed an additional analysis of factors associated with mortality in our cohort of patients. Variables that were statistically associated (P < .05) with mortality in the bivariable analysis were entered in a backward, stepwise, multivariable logistic regression model. This statistical analysis revealed that independent risk factors for death were urgent operation, anemia (hematocrit, <34%), and low left ventricular ejection fraction on admission (P < .001 for all these variables).

We also agree with Vandijck and colleagues that appropriate antimicrobial treatment of postoperative infections is essential to improve patient outcome. It has been shown that inappropriate empirical therapy is associated with increased mortality, especially among patients with infections caused by multidrug-resistant bacteria.⁴ In fact, old antibiotics, such as polymyxins, have been used recently to combat some of these infections.⁵ Two of 21 patients with infection in our cohort (patients 2 and 17 in Table 3 of our article)¹ were infected with multidrug-resistant isolates; these patients did not receive appropriate empirical antimicrobial therapy until the results of the in vitro susceptibility testing of the isolated pathogens became available.

References

1. Falagas ME, Rosmarakis ES, Rellos K, Michalopoulos A, Samonis G, Prapas SN. Microbiologically documented nosocomial infections after coronary artery bypass surgery without cardiopulmonary bypass. J Thorac Cardiovasc Surg 2006;132:481-490.[Abstract/Free Full Text]
   
2. Fowler Jr VG, O’Brien SM, Muhlbaier LH, Corey GR, Ferguson TB, Peterson ED. Clinical predictors of major infections after cardiac surgery. Circulation. 2005;112(suppl):I358-I365.
   
3. Kollef MH, Sharpless L, Vlasnik J, Pasque C, Murphy D, Fraser VJ. The impact of nosocomial infections on patient outcomes following cardiac surgery. Chest 1997;112:666-675.
   
4. Falagas ME, Kasiakou SK, Rafailidis PI, Zouglakis G, Morfou P. Comparison of mortality of patients with Acinetobacter baumannii bacteraemia receiving appropriate and inappropriate empirical therapy. J Antimicrob Chemother 2006;57:1251-1254.[Abstract/Free Full Text]
   
5. Falagas ME, Michalopoulos A. Polymyxins: old antibiotics are back. Lancet 2006;367:633-634.[Medline]
   

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