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Interact CardioVasc Thorac Surg 2007;6:167-171. doi:10.1510/icvts.2006.132191
© 2007 European Association of Cardio-Thoracic Surgery
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Work in progress report - Cardiac general

Factors associated with deep sternal wound infection and haemorrhage following cardiac surgery in Victoria{star}

Penelope J. Robinsona, Baki Billaha, Karin Ledera, Christopher M. Reida,b,* and on behalf of the ASCTS Database Committee

a NHMRC Centre of Clinical Research Excellence in Therapeutics, Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Commercial Road, Melbourne, VIC 3004, Australia
b Baker Heart Research Institute, Melbourne, Australia

Received 6 March 2006; received in revised form 14 November 2006; accepted 16 November 2006

{star} Presented at the Australasian Society of Cardiac and Thoracic Society Annual Scientific Meeting, Noosa Heads, Queensland, Australia, October 28–30, 2005.

*Corresponding author. Tel.: +61 3 9903 0752; fax: +61 3 9903 0556.

E-mail address: chris.reid{at}med.monash.edu.au (C.M. Reid).


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusions
 Acknowledgements
 References
 
Serious non-fatal complications of cardiac surgery include deep sternal wound infection (DSWI) and haemorrhage. Understanding the factors associated with these complications (both pre-operatively and intra-operatively) may aid in the prevention and avoidance of such complications. The aim of the current report is to identify factors associated with DSWI and haemorrhage for all patients undergoing cardiac surgical procedures in Victorian public hospitals from July 2001 to June 2005. Multiple logistic regression analysis incorporating preoperative and intraoperative variables was used to identify risk factors for DSWI and haemorrhage. There were 153 cases of DSWI (1.3%) and 413 cases of haemorrhage (3.5%) in 11,848 patients. The risk factors differ between DSWI and haemorrhage, with pre-operative factors being more commonly associated with DSWI and intra-operative factors associated with haemorrhage. Strategies directed towards minimising modifiable pre-operative risk factors (diabetes, preoperative dialysis, respiratory disease, being overweight and angina CCS Class 3 or 4) may reduce the incidence of DSWI. Improvements in operative factors (perfusion time, ventricular assist device, intraaortic balloon pump and aortic dissection) and surgical technique, may impact on reducing the incidence of haemorrhage.

Key Words: Cardiac surgery; Deep sternal wound infection; Haemorrhage; Risk factors


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 5. Conclusions
 Acknowledgements
 References
 
In Australia approximately 23,000 cardiac surgical procedures are conducted each year, however, until recently there has been no standardised system to identify complications and risk factors associated with their occurrence [1]. Internationally, several large standardised databases exist including the Society of Thoracic Surgeons (STS) National database [2], and the European System for Cardiac Operative Risk Evaluation (EuroSCORE) [3], allowing monitoring of complications, benchmarking and comparison of outcomes between hospitals. A new initiative in Australia through the Australasian Society of Cardiac and Thoracic Surgeons (ASCTS) database will enable outcomes from this region to be included in comparisons [1].

Surgical complications include death, deep sternal wound infection (DSWI), haemorrhage, stroke, peri-operative myocardial infarction, gastrointestinal complications, renal failure and respiratory failure [4]. DSWI and haemorrhage are both reasonably common complications associated with a high mortality rate. Risk factors for these complications have not previously been studied using Australian data.

The aim of this study is to identify factors that are associated with postoperative DSWI and haemorrhage at the individual patient level for those subjects included in the ASCTS Database, and to identify any such risk factors that may be modifiable.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 5. Conclusions
 Acknowledgements
 References
 
All adult patients undergoing cardiac surgery between 1 July 2001 and 30 June 2005 in Victorian public hospitals are included in the ASCTS database for analysis. DSWI was defined as one or more of the following: (1) Deep Sternal Infection, which ‘Involves muscle and bone, with or without mediastinal involvement, as demonstrated by surgical exploration, with wound debridement and positive culture, or treatment with antibiotics’, or (2) Readmission within 30 days of surgery for DSWI. Haemorrhage was defined by ‘operative re-intervention was required for bleeding/tamponade’.

The type of procedure was classified into: isolated CABG only, valve(s) surgery only, valve(s) and CABG only, and ‘other’ — which included all other cardiac surgery. The minimum data set for each procedure in the ASCTS database includes 240 preoperative, intraoperative and postoperative fields which have been described elsewhere [1]. All subjects are followed up 30 days post procedure to confirm vital status and post discharge complications.

2.1. Statistical analysis

Descriptive statistics and multivariate binary logistic regression analyses were used to describe and establish risk factors for DSWI and haemorrhage. Odds ratios (OR) and 95% confidence intervals (CI) are presented and a P-value of 0.05 was regarded as significant. Patient age and gender, urgency of operation and type of procedure were included in analyses regardless of their significance. Analyses were conducted using SPSS Version 12.0.1 (SPSS Inc., Chicago, 2003) and Stata Version 9.2 (Stata Corp, College Station Texas, 2006).


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 5. Conclusions
 Acknowledgements
 References
 
All 11,848 cardiac procedures conducted during the period were included in the analysis and the majority of patients were male (72.1%), and almost half (43.0%) were admitted on the day of surgery. Most (67.9%) were aged between 50 and 75 years, with 21.6% aged over 75 years. The characteristics of the patient population are shown in Table 1. The prevalence of important risk factors in the population as a whole, as well as in patients who developed DSWI or haemorrhage, is shown in Table 2.


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  		Table 1 Patient characteristics in the ASCTS database, July 2001–June 2005, n=11,848

 

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  		Table 2 Prevalence of patient characteristics in database — as a whole and by DSWI/Haemorrhage status (n=11,848)

 
3.1. DSWI (deep sternal wound infection)

Overall, there were 153 cases (1.3%) of DSWI reported from the 11,848 cardiac surgical procedures. 78 cases (51%) required readmission for DSWI after the initial discharge, 70 of which had not been diagnosed during the first admission. The 30-day mortality rate from DSWI was 2.6% (4/153), and the overall mortality rate was 6.5% (10/153), which represented 2.2% of deaths.

Significant preoperative risk factors associated with DSWI included diabetes (OR 2.5; CI 1.79–3.47), preoperative dialysis (OR 2.31; CI 1.04–5.12), respiratory disease (OR 1.72; CI 1.10–2.68), body mass index >25 kg/m2 (OR 1.72; CI 1.10–2.68) and angina CCS Class 3 or 4 (OR 1.52; CI 1.05–2.21), see Table 3. The intra-operative factors were use of a ventricular assist device (VAD) (OR 3.30; CI 1.19–9.17), cardiac transplantation (OR 4.0; CI 1.09–14.83) and a procedure involving the use of both internal thoracic arteries (ITAs) (OR 2.40; CI 1.53–3.76). In comparison to isolated CABG, valve procedures carried a higher risk of DSWI (OR 1.98; CI 1.14–3.43)


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  		Table 3 Risk factors for DSWI and haemorrhage

 
For those with DSWI, the most common risk factors were diabetes (49.67% of DSWI patients), being overweight (83.01% of patients) and both ITAs used (17.65% of patients), see Table 2.

3.2. Haemorrhage (re-operation for bleeding)

Overall, there were 413 cases (3.5%) of haemorrhage (requiring re-exploration) reported from the 11,848 cardiac surgical procedures. The 30-day mortality rate from haemorrhage was 12.6% (52/413), and the overall mortality rate was 13.8% (57/413), which represented 12.6% of deaths.

The preoperative risk factors for haemorrhage were: creatinine level >0.133 mmol/l (OR 1.36; CI 1.03–1.80), respiratory disease (OR 0.73; CI 0.54–0.99), and cerebrovascular disease (OR 1.40; CI 1.06–1.86), see Table 3. Intra-operative risk factors included increased perfusion time (each 30 min) (OR 1.09; CI 1.04–1.15), the use of an intra aortic balloon pump (IABP) (OR 1.77; CI 1.27–2.46) or VAD (OR 4.35; CI 2.61–7.26), and an aortic dissection procedure (OR 2.16; CI 1.13–4.11).

Postoperative haemorrhage was more frequent in patients undergoing ‘other’ types of cardiac surgery (28.9% – non-CABG or valve surgery), emergency or salvage procedure (16.46% of patients) and where an IABP (16.71% of patients) or VAD (8.30% of patients) was used.


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
5. Conclusions
 Acknowledgements
 References
 
This is the first study from Australia to report the major risk factors associated with DSWI and return to theatre for haemorrhage. The rates of DSWI (1.3%) and haemorrhage (3.5%) were similar to other reports in the literature [5].

We showed that diabetes, preoperative dialysis, angina CCS class ≥3, respiratory disease, being overweight, use of VAD, cardiac transplantation and use of both ITAs were risk factors for DSWI. Diabetes [6–8], being overweight or obese [6,7], and use of both ITAs [8,9] are all well established risk factors in the literature. In particular, Furnary's group showed that continuous insulin infusion reduces the risk of DSWI in diabetics [7]. These are all important risk factors for DSWI, as they are very common risk factors in the cardiac surgery population, in particular for those who develop DSWI.

Despite being a rare condition, preoperative dialysis was a risk factor for DSWI, as previous studies suggested [5,9]. Respiratory disease has also been identified previously [6]. No previous studies have identified angina CCS score as a risk factor. We also noted that more complicated procedures involving the use of VAD, IABP or cardiac transplantation were associated with higher risk of DSWI.

Cardiac transplantation is a less common operation, and several early studies in the literature only focused on CABG procedures, so that may explain why it has not previously been identified.

We found that elevated creatinine level, respiratory disease, cerebrovascular disease, perfusion time, IABP, VAD and aortic dissection were risk factors for haemorrhage. As in previous studies we found non-elective surgery (emergency/salvage only) [10,12] to be associated with increasing risk. Males were at greater risk for haemorrhage than females. In addition, valve or ‘other’ (non-CABG or valve) surgery had increased risk, in particular aortic dissection — confirming that operations of increasing complexity [13] or non-CABG procedures [14] are risk factors for haemorrhage.

An elevated creatinine level, indicative of poor renal function, was also associated with an increased risk of haemorrhage, supporting the observed relationship between poorer renal function and haemorrhage [12]. It is unclear why patients with cerebrovascular disease were more likely to haemorrhage, except that these patients may have been more likely to be on thrombolytic medications which increase the risk of bleeding [10,11,13,14].

We showed that an increasing perfusion time (as a continuous variable in 30-min increments) increased the risk of haemorrhage. Previous studies [10] have been inconclusive regarding the risk of CPB vs. off-pump surgery. In our univariate analysis, off-pump surgery (1.2%) had a lower rate of haemorrhage than CPB and cardioplegia (3.6%) or CPB only (10%), but this lost significance in the multivariate analysis and thus was not a risk factor for haemorrhage.

The presence of an IABP or VAD, both indicative of poor patient condition, was also associated with an increased risk of haemorrhage. The presence of IABP or VAD were common risk factors in patients who haemorrhaged. However, these are risk factors that cannot be changed. It is also unclear why having respiratory disease is protective against haemorrhage.

Two recent studies have shown that being underweight is a risk factor for haemorrhage [6,15], but it was only significant in our univariate analysis. This is probably due to the small number of patients who were underweight (342, 2.9% of patients) compared to the large proportion of patients who were overweight or obese. A previous study suggested that cardiogenic shock or use of inotropes were risk factors for haemorrhage [11], but they failed to reach significance in the current analysis.

One might expect that the risk factors for DSWI and haemorrhage would be the same, but this was not the case. Respiratory disease (protective for haemorrhage) and use of VAD were the only risk factors relevant to both DSWI and haemorrhage.

In the DSWI model, more (5/8) of the risk factors were preoperative, whereas for haemorrhage more (4/7) of the risk factors were intra-operative. This indicates that intra-operative factors are particularly important for haemorrhage, including the possibility of surgical technique and thrombolytic medication which we could not measure, and perfusion time which is unknown until after surgery. Advances in surgical technique and prophylactic treatment may be key factors in reducing the rates of DSWI and postoperative haemorrhage. Monitoring of performance indicators in these areas will identify ‘centres of excellence’ where complication rates are lower than expected.

Some of the factors in the models (e.g. diabetes) are reasonably prevalent in the database, whereas others (e.g. preoperative dialysis, IABP, and VAD) are reasonably rare — despite being associated with high risk. Risk modification focusing on the most common risk factors may have more impact on the incidence of DSWI and haemorrhage than the rarer conditions.


   5. Conclusions
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusions
Acknowledgements
 References
 
In conclusion, we have shown that the risk factors differ between DSWI and haemorrhage. Common risk factors are poor renal function and angina CCS class ≥3. Of the risk factors identified, risk modification targeted towards common risk factors (such as diabetes control by continuous insulin infusion for diabetics as Furnary showed, and weight loss for overweight patients having elective surgery) are likely to have the greatest impact on reducing the incidence of these complications, as most intraoperative/procedure-related factors cannot be changed. Advances in surgical technique and prophylactic treatment may be key factors in reducing the rates of DSWI and postoperative haemorrhage.

Further development of the ASCTS database on a National level will determine whether these factors are consistent across and allow further investigation into the risk factors and preventative strategies to minimize the costs and human impact of these complications.


   Acknowledgements
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusions
 Acknowledgements
References
 
The ASCTS Database Committee includes G. Shardey, P. Skillington, J. Smith, M. Yii, A. Pick, S. Seevanayagam and M. Mohajeri M. We would like to thank the site data managers and surgeons of the hospitals that contributed to the data, and data managers Diem Dinh, Claudia Retegan and Anne Nadonza from the Baker Heart Research Institute, and all patients contributing to the registry. The ASCTS Database Project is supported by the Department of Human Services, Victoria.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusions
 Acknowledgements
 References
 

  1. Reid CM, Rockell M, Skillington PD, Shardey GC, Smith JA, Yii M, Seevanayagam S, Mohajeri M, Rowland M. Initial Twelve Months Experience and Analysis for 2001–2002 from the Australasian Society of Cardiac and Thoracic Surgeons—Victorian Database Project. Heart Lung Circ 2004; 13:291–297.
  2. Grover FL. The Society of Thoracic Surgeons National Database: current status and future directions. Ann Thorac Surg 1999; 68:367–373. discussion 374–376.[Abstract/Free Full Text]
  3. Nashef SA, Roques F, Michel P, Gauducheau E, Lemeshow S, Salamon R. European system for cardiac operative risk evaluation (EuroSCORE). [see comment]. Eur J Cardiothorac Surg 1999; 16:9–13.[Medline]
  4. Toumpoulis IK, Anagnostopoulos CE, Swistel DG, DeRose JJ Jr. Does EuroSCORE predict length of stay and specific postoperative complications after cardiac surgery? Eur J Cardiothorac Surg 2005; 27:128–133.[Abstract/Free Full Text]
  5. Hollenbeak CS, Murphy DM, Koenig S, Woodward RS, Dunagan WC, Fraser VJ. The clinical and economic impact of deep chest surgical site infections following coronary artery bypass graft surgery. Chest 2000; 118:397–402.
  6. Birkmeyer NJO, Charlesworth DC, Hernandez F, Leavitt BJ, Marrin CAS, Morton JR, Olmstead EM, O'Connor GT. Obesity and risk of adverse outcomes associated with coronary artery bypass surgery. Circulation 1998; 97:1689–1694.
  7. Furnary AP, Zerr KJ, Grunkemeier GL, Starr A. Continuous intravenous insulin infusion reduces the incidence of deep sternal wound infection in diabetic patients after cardiac surgical procedures. [see comment]. Ann Thorac Surg 1999; 67:352–360. discussion 360–362.[Abstract/Free Full Text]
  8. Stahle E, Tammelin A, Bergstrom R, Hambreus A, Nystrom SO, Hansson HE. Sternal wound complications – incidence, microbiology and risk factors. Eur J Cardiothorac Surg 1997; 11:1146–1153.[Abstract]
  9. Toumpoulis IK, Anagnostopoulos CE, Derose JJ Jr, Swistel DG. The impact of deep sternal wound infection on long-term survival after coronary artery bypass grafting. Chest 2005; 127:464–471.
  10. Karthik S, Grayson AD, McCarron EE, Pullan DM, Desmond MJ. Reexploration for bleeding after coronary artery bypass surgery: risk factors, outcomes, and the effect of time delay. Ann Thorac Surg 2004; 78:527–534.[Abstract/Free Full Text]
  11. Frankel TL, Stamou SC, Lowery RC, Kapetanakis EI, Hill PC, Haile E, Corso PJ. Risk factors for hemorrhage-related reexploration and blood transfusion after conventional versus coronary revascularization without cardiopulmonary bypass. Eur J Cardiothorac Surg 2005; 27:494–500.[Abstract/Free Full Text]
  12. Winkelmayer WC, Levin R, Avorn J. Chronic kidney disease as a risk factor for bleeding complications after coronary artery bypass surgery. Am J Kidney Dis 2003; 41:84–89.[CrossRef][Medline]
  13. Dacey LJ, Munoz JJ, Baribeau YR, Johnson ER, Lahey SJ, Leavitt BJ, Quinn RD, Nugent WC, Birkmeyer JD, O'Connor GT. Reexploration for hemorrhage following coronary artery bypass grafting: incidence and risk factors. Northern New England Cardiovascular Disease Study Group. Arch Surg 1998; 133:442–447.[Abstract/Free Full Text]
  14. Moulton MJ, Creswell LL, Mackey ME, Cox JL, Rosenbloom M. Reexploration for bleeding is a risk factor for adverse outcomes after cardiac operations. J Thorac Cardiovasc Surg 1996; 111:1037–1046.[Abstract/Free Full Text]
  15. Kim J, Hammar N, Jakobsson K, Luepker RV, McGovern PG, Ivert T. Obesity and the risk of early and late mortality after coronary artery bypass graft surgery. [see comment]. Am Heart J 2003; 146:555–560.[CrossRef][Medline]

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