|
|
||||||||
Eur J Cardiothorac Surg 2003;23:943-949
© 2003 Elsevier Science NL
a Department of Cardiothoracic Surgery, The Cardiothoracic Centre Liverpool, Thomas Drive, Liverpool L14 3PE, UK
b Department of Research and Development, The Cardiothoracic Centre, Liverpool, UK
Received 10 December 2002; received in revised form 15 February 2003; accepted 24 February 2003.
* Corresponding author. Tel.: +44-151-293-2397; fax: +44-151-220-8573
e-mail: brian.fabri{at}ctc.nhs.uk
| Abstract |
|---|
|
|
|---|
Key Words: Sternal wound infection Coronary artery bypass grafting Risk factors Mid term survival
| 1. Introduction |
|---|
|
|
|---|
Many risk factors have been identified as predictive of sternal wound infection following CABG, which include pre-operative (e.g. obesity, diabetes, male sex) [2,4,6,810], operative (e.g. use of bilateral mammary arteries) [2,4,6], and post-operative (e.g. mechanical ventilation) [2] variables.
However, little has been published on the experiences of hospitals in the United Kingdom with regards to the risk factors associated with sternal wound infection after CABG and the impact on mid-term survival.
This study aimed to quantify the incidence of sternal wound infection following CABG at a specialist Cardiothoracic Centre in the North West of England. We also examined the patient and disease characteristics associated with sternal wound infections, and the impact on mid-term survival.
| 2. Methods |
|---|
|
|
|---|
Data was prospectively collected during the patient's admission as part of routine clinical practice on the following variables: age, sex, body mass index (BMI), urgency of operation, prior cardiac surgery, New York Heart Association (NYHA) functional class, Canadian Cardiovascular Society (CCS) angina class, history of myocardial infarction, smoking, diabetes, hypercholesterolaemia, hypertension, peripheral vascular disease, cerebrovascular disease, renal dysfunction and previous cardiological interventions, as well as the extent of coronary disease, and left ventricular ejection fraction. Duration of anaesthesia time and use of cardiopulmonary bypass were also collected, along with the number and type of grafts used during the procedure. Post-operative data collected included the volume of blood loss on the intensive care unit (ICU), the need for re-exploration for bleeding after initial departure from theatre, intra-aortic balloon pump (IABP) support, duration of mechanical ventilation, sternal wound infection and in-hospital mortality, as well as post-operative length of stay. The bacteriology and treatment of the sternal wound infection was noted during the patients hospital admission.
The primary outcome measure for our study was sternal wound infection, prior to discharge, defined in accord with the published evidence-based guidelines by the Centre for Disease Control and Prevention [12]. This included both deep and superficial sternal wound infections. In brief, a sternal wound infection was defined as an infection of the anterior mediastinal space with one of the following criteria: (1) an organism isolated from culture of mediastinal tissue/fluid; (2) evidence of mediastinitis is seen during operation; (3) one of the following: chest pain, sternal instability, fever (>38 °C), and there is either a purulent discharge from the mediastinum or an organism isolated from blood culture or culture of mediastinal area drainage.
2.2. Patient follow-up
Patient records were linked to the National Strategic Tracing Service (NSTS), which records all deaths in the United Kingdom, to establish current vital status (as from the 31 July, 2002). Patients were matched to the NSTS based on patient name, National Health Service number, date of birth, gender, and postcode.
2.3. Statistical analysis
Continuous variables are shown as median with 25th and 75th centiles and categorical variables are shown as a percentage with 95% confidence intervals (CI). Comparisons were made with Wilcoxon rank-sum tests and chi-square tests as appropriate. Standard statistical tests were used to calculate odds ratios (OR) and 95% CI. Multiple logistic regression analyses were undertaken to identify risk factors for sternal wound infection [13]. The C statistic (equivalent to the area under the receiver operating characteristic curve) and the LemeshowHosmer goodness-of-fit statistic were calculated to assess the performance and calibration of the model, respectively [13,14]. A C statistic of greater than 0.7 indicates a reasonable ability to discriminate between patients who developed sternal wound infections and those who did not. For the LemeshowHosmer goodness-of-fit statistic, the predicted risks of individual patients were rank-ordered and divided into deciles. Within each decile of estimated risk, the number of sternal wound infections predicted were accumulated against the number of observed sternal wound infections, a P-value of greater than 0.05 indicates acceptable calibration of the model. Patient survival was described using the product-limit methodology of KaplanMeier [15]. We used Cox proportional hazards analysis to calculate adjusted hazard ratios (HR) and to risk adjust the KaplanMeier survival curve for differences in patient and disease characteristics [16]. In all cases a P-value of less than 0.05 was considered significant. Statistical analysis was performed retrospectively with SAS for Windows version 8.2.
| 3. Results |
|---|
|
|
|---|
3.2. Bacteriology and treatment
Sixty of the 109 patients who developed sternal wound infections had organisms identified from culture. The most common pathogen from wound cultures for gram positive organisms was staphylococcus epidermidis which caused 29 (36.7% of 60) infections, followed by staphylococcus aureus 18 (30% of 60), and methicillin-resistant Staphylococcus aureus nine (15% of 60). There were 23 patients who developed sternal wound infections with gram negative organisms, of which enterococci contributed to seven (30.4% of 23) and Pseudomonas three (13% of 23).
The different treatment methods of patients with sternal wound infections are summarized in Table 1.
|
|
|
Significant multivariate risk factors for deep and superficial wound infections are shown in Tables 4 and 5, respectively, with the C statistic and LemeshowHosmer goodness-of-fit statistic.
|
|
3.5. Mid-term mortality
Three hundred and forty-one (8.1% (95% CI 7.38.9)) deaths occurred during the study period, with a mean follow up of 3.2 (standard deviation 1.3) years and 13 322 total patient years.
Out of the 109 patients who developed sternal wound infection, 20 (18.3%) died during the follow-up period (deep, 10 out of 28 (35.7%); superficial, 10 out of 81 (12.4%)). There were 321 deaths out of 4119 (7.8%) patients with no sternal wound infection.
The crude HR of mid-term mortality for sternal wound infection patients was 2.51 (95% CI 1.593.94; P<0.001). Freedom from death in patients who developed sternal wound infections at 30 days, and 1, 2 and 4 years was 95.4, 84.4, 82.4 and 79.7%, respectively, compared with 97.8, 95.8, 94.2 and 90.9% for patients without sternal wound infections.
After adjustment for differences in patient and disease characteristics identified in the logistic regression analysis (obesity, NYHA class ≥3, use of bilateral internal mammary arteries, number of grafts, re-exploration for bleeding, and prolonged mechanical ventilation), the adjusted HR of mid-term mortality for sternal wound infection patients was 1.64 (95% CI 1.032.61; P=0.037). The adjusted KaplanMeier survival curves are shown in Fig. 1 (y-axis starts at 50%). The adjusted freedom from death for sternal wound infections at 30 days, and 1, 2 and 4 years was 96.8, 93.7, 91.4 and 86.7%, respectively, compared with 98.1, 96.1, 94.7 and 91.7% for patients without sternal wound infections.
|
| 4. Discussion |
|---|
|
|
|---|
With increased scrutiny of cardiac surgery outcomes, it is increasingly important to consider underlying differences in patient case-mix when examining either institutional or even surgeon specific outcomes. This paper identifies a number of risk factors, which need to be considered when risk adjusting sternal wound infection rates.
As with other reports [2,4,6,17], we identified diabetes as a risk factor causing sternal wound infections. Trick et al. found that diabetes with a pre-operative blood glucose level of 200 mg/dl was an independent risk factor for deep sternal wound infection [17].
Several studies have identified obesity as a risk factor for sternal wound infections [2,810,18,19]. This finding concurs with the observations by Kuduvalli [8] and Birkmeyer [9], which have both shown that the risks of sternal wound infection were substantially increased in the obese and severely obese. Moulton et al., in a study of 2299 cardiac surgery patients, found an association with obese patients being 2.3 times more likely to develop superficial sternal wound infections [10]. Ridderstolpe and colleagues, in a more recent study involving over 3000 patients, showed a similar relationship with obese patients being 2.1 times more likely to have sternal wound infections [2]. In our study, obese patients were two times more likely to develop sternal wound infections.
Investigators have also found a relationship between the use of bilateral mammary arteries and sternal wound infections [2,4,6]. Our experience shares the finding of Borger and colleagues [6], in their large study of 12 267 consecutive cardiac surgical patients, with the use of bilateral internal mammary arteries increasing the risk of sternal wound infections by 3.2 times. Stahle et al., in another large study involving 13 285 cardiac surgery patients, also found an association between bilateral internal mammary arteries and sternal wound infections (OR 3.3; P<0.05) [4].
As with other reports, our study has described an increased risk of sternal wound infections when mechanical ventilation is prolonged [2,3]. Re-exploration for bleeding, NYHA class ≥3, and peripheral vascular disease have also been identified previously as associated with sternal wound infections [2,3,5]. Loop and colleagues showed that blood transfusions had a relative risk of causing sternal wound complications of 1.05 per unit [3].
We have shown a significant increase in mid-term mortality after developing sternal wound infections, the risk-adjusted mortality rate at 4 years was 13.3% compared to 8.3% for patients without sternal wound infections (P=0.037). This highlights the importance of identifying those patients at greater risk of developing sternal wound infections prior to coronary artery bypass surgery, with the potential for risk factor modification when possible.
Furnary et al. found that reducing glucose levels in diabetic patients could lower the incidence of wound complications after cardiac surgery [20]. They revealed that elevated blood glucose levels (>200 mg/dl) on the first and second post-operative day was associated with increased sternal wound infection in diabetic patients and that tight control of glucose levels through perioperative intravenous insulin infusion can substantially reduce infectious morbidity.
Milano and colleagues hypothesized that the main cause of sternal wound infection in obese patients may partly be due to perioperative antibiotics not being properly adjusted for the increased volume of distribution in these patients. They also suggest that skin preparation can be difficult and inadequate due to deep skin folds. Thus the appropriate choice and dose of prophylactic antibiotics may help in obese patients [21].
Patients with a high NYHA classification are more likely to require prolonged ventilation [22], further increasing the risk of developing sternal wound infections. These patients may benefit from appropriate use of epidural therapy, which we have observed in our institution can help reduce the duration of intubation. Priestly et al., in a randomized control trial of CABG surgery, showed that patients receiving high (T1T4) thoracic epidural anesthesia were extubated earlier [23].
The avoidance of using bilateral internal mammary arteries in patients who are either diabetic, obese, or even have peripheral vascular disease may also be desirable to help reduce the risk of wound infection in patients already at high-risk. Lemma and colleagues have shown, in a recent publication, that radial arteries can provide a safe alternative and extend the benefits of multiple arterial grafting with good perioperative and short-term outcomes [24]. Unpublished data from our own centre, by Pandey et al., has revealed that the incidence of sternal wound infections can be as high as 8.2% in patients receiving bilateral internal mammary arteries, compared to 2.7% with single mammary arteries and 2.2% for radial arteries (P<0.001).
This report represents a relatively recent population undergoing cardiac surgery with a large sample size, with multivariate analysis to identify risk factors for sternal wound infection and adjusted survival analysis. However, there are some limitations, which may affect the findings drawn from our study. Multivariable analysis is not a substitute for a properly well designed randomized control trial. The retrospective nature of the study cannot account for the unknown variables affecting the outcome that are not measured in this study. On the other hand, retrospective comparisons with multivariable analysis are more versatile and more widely applicable than randomized control trials. In this case, we could never randomize whether a patient would have a sternal wound infection following coronary artery bypass grafting. The low event rate is another limitation, with only 28 (0.7%) deep sternal wound complications recorded, which may not be sufficient for an accurate prediction [25]. This precluded us from sub-analysing the mid-term survival into deep and superficial sternal wound infections. Another limitation is that our study only evaluated those cases of sternal wound infection identified prior to discharge. We have no reason to believe that the risk factors and mortality outcome of these cases is significantly different from cases diagnosed after hospital discharge.
In conclusion, we have identified a number of risk factors for sternal wound infection, which support previously published reports, and can be used to properly assess the differences in infection rates between individual institutions and individual surgical teams for quality improvement purposes. We have also shown that there is a significant increase in mortality in patients with sternal wound infection during a 4-year follow-up period after CABG. Focus on modifiable risk factors is desirable for reducing this severe complication.
| Acknowledgments |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
A. Sachithanandan, P. Nanjaiah, P. Nightingale, I. C. Wilson, T. R. Graham, S. J. Rooney, B. E. Keogh, and D. Pagano Deep sternal wound infection requiring revision surgery: impact on mid-term survival following cardiac surgery Eur. J. Cardiothorac. Surg., April 1, 2008; 33(4): 673 - 678. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Nakano, H. Okabayashi, M. Hanyu, Y. Soga, T. Nomoto, Y. Arai, T. Matsuo, M. Kai, and M. Kawatou Risk factors for wound infection after off-pump coronary artery bypass grafting: Should bilateral internal thoracic arteries be harvested in patients with diabetes? J. Thorac. Cardiovasc. Surg., March 1, 2008; 135(3): 540 - 545. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. J. Poncelet, B. Lengele, B. Delaere, F. Zech, D. Glineur, J.-C. Funken, G. El Khoury, and P. Noirhomme Algorithm for primary closure in sternal wound infection: a single institution 10-year experience Eur. J. Cardiothorac. Surg., February 1, 2008; 33(2): 232 - 238. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Lindstedt, M. Malmsjo, and R. Ingemansson Blood Flow Changes in Normal and Ischemic Myocardium During Topically Applied Negative Pressure Ann. Thorac. Surg., August 1, 2007; 84(2): 568 - 573. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Reiss, U. Schuett, M. Kemper, A. Bairaktaris, and R. Koerfer New Method for Sternal Closure After Vacuum-Assisted Therapy in Deep Sternal Infections After Cardiac Surgery Ann. Thorac. Surg., June 1, 2007; 83(6): 2246 - 2247. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. K. Choong, C. Gerrard, K. A. Goldsmith, H. Dunningham, and A. Vuylsteke Delayed re-exploration for bleeding after coronary artery bypass surgery results in adverse outcomes Eur. J. Cardiothorac. Surg., May 1, 2007; 31(5): 834 - 838. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Petzina, M. Ugander, L. Gustafsson, H. Engblom, J. Sjogren, R. Hetzer, R. Ingemansson, H. Arheden, and M. Malmsjo Hemodynamic effects of vacuum-assisted closure therapy in cardiac surgery: Assessment using magnetic resonance imaging J. Thorac. Cardiovasc. Surg., May 1, 2007; 133(5): 1154 - 1162. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Sjogren, M. Malmsjo, R. Gustafsson, and R. Ingemansson Poststernotomy mediastinitis: a review of conventional surgical treatments, vacuum-assisted closure therapy and presentation of the Lund University Hospital mediastinitis algorithm Eur. J. Cardiothorac. Surg., December 1, 2006; 30(6): 898 - 905. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. M. Eklund, O. Lyytikainen, P. Klemets, K. Huotari, V.-J. Anttila, K. A. Werkkala, and M. Valtonen Mediastinitis After More Than 10,000 Cardiac Surgical Procedures Ann. Thorac. Surg., November 1, 2006; 82(5): 1784 - 1789. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Mills and P. Bryson The role of hyperbaric oxygen therapy in the treatment of sternal wound infection. Eur. J. Cardiothorac. Surg., July 1, 2006; 30(1): 153 - 159. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. V Ghotkar, A. D Grayson, and W. C Dihmis Effect of Prolonged Intensive Care Stay on Survival Following Coronary Surgery Asian Cardiovasc Thorac Ann, December 1, 2005; 13(4): 345 - 350. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Sjogren, J. Nilsson, R. Gustafsson, M. Malmsjo, and R. Ingemansson The Impact of Vacuum-Assisted Closure on Long-Term Survival After Post-Sternotomy Mediastinitis Ann. Thorac. Surg., October 1, 2005; 80(4): 1270 - 1275. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. R. Pai, I. R. Ramnarine, A. D. Grayson, and N. K. Mediratta The effect of chronic steroid therapy on outcomes following cardiac surgery: a propensity-matched analysis Eur. J. Cardiothorac. Surg., July 1, 2005; 28(1): 138 - 142. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Sjogren, R. Gustafsson, J. Nilsson, M. Malmsjo, and R. Ingemansson Clinical Outcome After Poststernotomy Mediastinitis: Vacuum-Assisted Closure Versus Conventional Treatment Ann. Thorac. Surg., June 1, 2005; 79(6): 2049 - 2055. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Kubal, A. K. Srinivasan, A. D. Grayson, B. M. Fabri, and J. A.C. Chalmers Effect of Risk-Adjusted Diabetes on Mortality and Morbidity After Coronary Artery Bypass Surgery Ann. Thorac. Surg., May 1, 2005; 79(5): 1570 - 1576. [Abstract] [Full Text] [PDF] |
||||
![]() |
O. Jarvinen, J. Julkunen, T. Saarinen, J. Laurikka, and M. R. Tarkka Effect of Diabetes on Outcome and Changes in Quality of Life After Coronary Artery Bypass Grafting Ann. Thorac. Surg., March 1, 2005; 79(3): 819 - 824. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. De Paulis, S. de Notaris, R. Scaffa, S. Nardella, J. Zeitani, C. Del Giudice, A. Penta De Peppo, F. Tomai, and L. Chiariello The effect of bilateral internal thoracic artery harvesting on superficial and deep sternal infection: The role of skeletonization J. Thorac. Cardiovasc. Surg., March 1, 2005; 129(3): 536 - 543. [Abstract] [Full Text] [PDF] |
||||
![]() |
I. K. Toumpoulis, C. E. Anagnostopoulos, J. J. DeRose Jr, and D. G. Swistel The Impact of Deep Sternal Wound Infection on Long-term Survival After Coronary Artery Bypass Grafting Chest, February 1, 2005; 127(2): 464 - 471. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Pandey, A. D. Grayson, D. M. Pullan, B. M. Fabri, and W. C. Dihmis Total arterial revascularisation: effect of avoiding cardiopulmonary bypass on in-hospital mortality and morbidity in a propensity-matched cohort Eur. J. Cardiothorac. Surg., January 1, 2005; 27(1): 94 - 98. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. K. Srinivasan, A. D. Grayson, and B. M. Fabri On-Pump Versus Off-Pump Coronary Artery Bypass Grafting in Diabetic Patients: A Propensity Score Analysis Ann. Thorac. Surg., November 1, 2004; 78(5): 1604 - 1609. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. H. Lindhout, C. W. Wouters, and L. Noyez Influence of obesity on in-hospital and early mortality and morbidity after myocardial revascularization Eur. J. Cardiothorac. Surg., September 1, 2004; 26(3): 535 - 541. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Karthik, A. D. Grayson, E. E. McCarron, D. M. Pullan, and M. J. Desmond Reexploration for bleeding after coronary artery bypass surgery: risk factors, outcomes, and the effect of time delay Ann. Thorac. Surg., August 1, 2004; 78(2): 527 - 534. [Abstract] [Full Text] [PDF] |
||||
![]() |
U. O. von Oppell and K. S. Rammohan Risk factors for sternal wound infection following coronary artery bypass graft surgery Eur. J. Cardiothorac. Surg., January 1, 2004; 25(1): 142 - 142. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN |