ARTICLE IN PRESS doi:10.1510/icvts.2006.132191
Interactive CardioVascular and Thoracic Surgery 6 (2007) 167–171 www.icvts.org
Work in progress report - Cardiac general
Factors associated with deep sternal wound infection and haemorrhage following cardiac surgery in Victoria夞 Penelope J. Robinsona, Baki Billaha, Karin Ledera, Christopher M. Reida,b,*, on behalf of the ASCTS Database Committee 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
a
Received 6 March 2006; received in revised form 14 November 2006; accepted 16 November 2006
Abstract 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. 䊚 2007 Published by European Association for Cardio-Thoracic Surgery. All rights reserved. Keywords: Cardiac surgery; Deep sternal wound infection; Haemorrhage; Risk factors
1. Introduction 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 w1x. Internationally, several large standardised databases exist including the Society of Thoracic Surgeons (STS) National database w2x, and the European System for Cardiac Operative Risk Evaluation (EuroSCORE) w3x, 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 w1x. Surgical complications include death, deep sternal wound infection (DSWI), haemorrhage, stroke, peri-operative myocardial infarction, gastrointestinal complications, renal failure and respiratory failure w4x. 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. 夞 Presented at the Australasian Society of Cardiac and Thoracic Society Annual Scientific Meeting, Noosa Heads, Queensland, Australia, October 28– 30, 2005. *Corresponding author. Tel.: q61 3 9903 0752; fax: q61 3 9903 0556. E-mail address:
[email protected] (C.M. Reid). 䊚 2007 Published by European Association for Cardio-Thoracic Surgery
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 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 bleedingy 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 w1x. All subjects are followed up 30 days post procedure to confirm vital status and post discharge complications.
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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 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. 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% (4y153), and the overall mortality rate was 6.5% (10y153), which represented 2.2% of deaths. Significant preoperative risk factors associated with DSWI included diabetes (OR 2.5; CI 1.79–3.47), preoperative Table 1 Patient characteristics in the ASCTS database, July 2001–June 2005, ns11,848 Mean Patient characteristics Age EuroSCORE Body mass index Height (cm) Weight (kg) Last pre-op. creatinine level (mmolyl) Intra-operative characteristics Cross-clamp time (min) Perfusion time (min) Post-operative economic variables Ventilation time (h) ICU stay (h) Length of stay (days) Post-procedure length of stay (days) Post-procedure complications of interest Overall mortality DSWI Haemorrhage (return to theatre)
S.D.
Median
65.2 6.0 27.9 168.3 79.2 0.11
12.1 4.0 4.8 9.7 15.9 0.09
67.3 5 27.4 169 78 0.09
79.8 110.5
45.3 60.2
76 103
23.5 50.5 12.6 9.8 n
82.5 112.4 15.7 12.4 (%)
9 23 8 7
427 153 413
3.6% 1.3% 3.5%
EuroSCORE, European System for Cardiac Operative Risk Evaluation; ICU, Intensive Care Unit; CCS, Canadian Cardiovascular Society; CABG, Coronary Artery Bypass Graft; IABP, Intra Aortic Balloon Pump; VAD, Ventricular Assist Device; ITAs, Internal Thoracic Artery; DSWI, Deep Sternal Wound Infection.
dialysis (OR 2.31; CI 1.04–5.12), respiratory disease (OR 1.72; CI 1.10–2.68), body mass index )25 kgym2 (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) 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% (52y413), and the overall mortality rate was 13.8% (57y413), which represented 12.6% of deaths. The preoperative risk factors for haemorrhage were: creatinine level )0.133 mmolyl (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% – nonCABG 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 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 w5x. We showed that diabetes, preoperative dialysis, angina CCS class G3, respiratory disease, being overweight, use of VAD, cardiac transplantation and use of both ITAs were risk factors for DSWI. Diabetes w6–8x, being overweight or obese w6,7x, and use of both ITAs w8,9x 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 w7x. 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 w5,9x. Respiratory disease has also been identified previously w6x. 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.
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Table 2 Prevalence of patient characteristics in database — as a whole and by DSWIyHaemorrhage status (ns11,848) Total
Preoperative risk factors Male Diabetic Healthy weight (BMI 20–25) Underweight (BMI-20) Overweight (BMI)25) Preoperative dialysis Creatinine level )0.133 mmolyl Respiratory disease Cerebrovascular disease Previous myocardial Infarction Angina CCS Class 3 or 4 Cardiogenic shock Resuscitation -1 h preop. Medications: anticoagulants Medications: aspirin Redo CABG surgery Redo valve surgery Redo other surgery Any redo surgery Intraoperative factors Isolated CABG Valve(s) only Valve(s)qCABG Other Elective surgery Urgent surgery EmergencyySalvage surgery Direct transfer from catheter lab Cardiac transplant Aortic dissection IABP VAD Both ITAs used
DSWI (ns153)
Haemorrhage (ns413)
n
(%)
n
(%)
8545 3333 2969 342 8503 198 1288 1832 1393 5139 5236 382 162 2355 4447 365 154 168 964
72.1 28.1 25.1 2.9 72.0 1.7 10.9 15.5 11.8 43.4 44.2 3.2 1.4 19.9 42.1 3.1 1.3 1.4 8.1
105 76 24 2 127 7 20 36 20 68 83 6 2 28 57 6 1 4 15
68.6 49.7 15.7 1.3 83.0 4.6 13.1 23.5 13.1 44.4 54.3 3.9 1.3 18.3 40.7 3.9 0.7 2.6 9.8
7712 1414 1119 1603 7291 3786 771 154 97 157 780 137 1237
65.1 11.9 9.4 13.5 61.5 32.0 6.5 1.3 0.8 1.3 6.6 1.2 10.4
99 20 16 18 87 53 13 1 3 2 9 5 27
64.7 13.1 10.5 11.8 56.9 34.6 8.5 0.7 2.0 1.3 5.9 3.3 17.7
* * * * * *
*
* * * * * * * *
* *
n
(%)
313 91 116 20 277 5 77 51 67 154 140 45 17 92 149 8 11 22 56
75.8 22.0 28.1 4.8 67.1 1.2 18.7 12.4 16.2 37.4 33.9 10.9 4.1 22.3 41.7 1.9 2.7 5.3 13.6
176 74 47 116 216 129 68 8 9 22 69 34 41
42.6 17.9 11.4 28.1 52.3 31.2 16.5 1.9 2.2 5.3 16.7 8.3 9.9
噛 噛 噛 噛 * * * 噛 噛 噛 噛
噛 噛 噛 * * * * * * * 噛 * * *
* – in final risk factors, 噛 – univariate P-value-0.05 (so significant), but not in final risk factors. BMI – Body Mass Index, CCS – Canadian Cardiovascular Society, CABG – coronary artery bypass graft, IABP – Intraaortic balloon pump, VAD – ventricular assist device, ITA – Internal thoracic artery.
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 (emergencyysalvage only) w10,12x 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 w13x or non-CABG procedures w14x 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 w12x. 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 w10,11,13,14x.
We showed that an increasing perfusion time (as a continuous variable in 30-min increments) increased the risk of haemorrhage. Previous studies w10x 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 w6,15x, 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
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Table 3 Risk factors for DSWI and haemorrhage DSWI
Male Gender 10 year increase in age Type of operation Valve(s) only (cf isolated CABG) Valve(s)qCABG (cf isolated CABG) Other (cf isolated CABG) Urgency of operation Urgent (cf elective surgery) Emergencyysalvage (cf elective surgery) Diabetes Preoperative dialysis Preop creatinine )0.133 mmolyl Cerebrovascular disease Respiratory disease Body Mass Index Underweight (BMI-20) wcf BMI 20–25x Overweight (BMI)25) wcf BMI 20–25x Angina CCS Class 3 or 4 Each 30 min perfusion time Intra aortic balloon pump Ventricular assist device Cardiac transplant Aortic dissection Both ITAs
Haemorrhage
OR
P-value
95% CI
OR
P-value
95% CI
0.86 1.11
0.390 0.201 0.090 0.015 0.334 0.967 0.698 0.914 0.436 0.000 0.039
0.60–1.22 0.95–1.30
1.42 1.06
1.11–1.82 0.97–1.16
1.14–3.43 0.76–2.28 0.55–1.88
2.46 1.38 1.92
1.83–3.31 0.96–1.98 1.40–2.62
0.68–1.42 0.68–2.46 1.79–3.47 1.04–5.12
1.13 1.45
0.005 0.180 0.000 0.000 0.080 0.000 0.153 0.322 0.058
1.36 1.40 0.73
0.032 0.020 0.042
1.03–1.80 1.06–1.86 0.54–0.99
1.09 1.77 4.35
0.000 0.001 0.000
1.04–1.15 1.27–2.46 2.61–7.26
2.16
0.020
1.13–4.11
1.98 1.31 1.01 0.98 1.29 2.50 2.31
1.68 0.74 1.72 1.52
0.008 0.034 0.682 0.017 0.027
1.14–2.46
0.89–1.43 0.99–2.13
0.17–3.16 1.10–2.68 1.05–2.21
3.30 4.00
0.022 0.036
1.19–9.17 1.09–14.63
2.40
0.000
1.53–3.76
CABG, Coronary Artery Bypass Graft; CCS, Canadian Cardiovascular Society; ITA, Internal Thoracic Artery; BMI, Body Mass Index; IABP, Intra Aortic Balloon Pump; VAD, Ventricular Assist Device.
risk factors for haemorrhage w11x, 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 (5y8) of the risk factors were preoperative, whereas for haemorrhage more (4y7) of the risk factors were intra-operative. This indicates that intraoperative 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.
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 intraoperativeyprocedurerelated 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 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.
5. Conclusions 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 G3. Of the risk
References w1x Reid CM, Rockell M, Skillington PD, Shardey GC, Smith JA, Yii M, Seevanayagam S, Mohajeri M, Rowland M. Initial Twelve Months Expe-
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ICVTS on-line discussion A Title: Definitions of sternal wound complications Author: Mohamad Fouad Ismail, Mansoura University, Mansoura 35511, Egypt doi:10.1510/icvts.2006.132191A eComment: I read with interest the article w1x and I am astonished by your effort to collect these data. However, I do have some comments. I) Definitions of sternal wound complications are as follows:- (1) Mediastinal dehiscence: median sternotomy wound breakdown in the absence of clinical or microbiologic evidence of infection. (2) Mediastinal wound infection: clinical or microbiologic evidence of infected presternal tissue and sternal osteomyelitis, with or without mediastinal sepsis and with or without unstable sternum. Subtypes include: (A) superficial wound infection: wound infection confined to the subcutaneous tissue; and (B) deep wound infection (mediastinitis): wound infection associated with sternal osteomyelitis with or without infected retrosternal space w2x. Deep sternal wound infections, or mediastinitis, is classified into four subtypes based on the time of the first presentation, the presence or absence of risk factors, and whether previous attempts at treating the condition have failed w3x. Type I: Mediastinitis presenting within 2 weeks after operation in the absence of risk factors. Risk factors identified in three or more major studies. Currently accepted incremental risk factors for mediastinitis are diabetes, obesity, and the requirement of immunosuppressive agents. Type II: Mediastinitis presenting at 2 to 6 weeks after operation in the absence of risk factors. Type IlIA: Mediastinitis type I in the presence of one or more risk factors. Type IIIB: Mediastinitis type II in the presence of one or more risk factors. Type IVA: Mediastinitis type I, II, or III after one failed therapeutic trial. Failed therapeutic trial includes any surgical intervention with intent to treat mediastinitis. Type IVB: Mediastinitis type I, II, or III after more than one failed therapeutic trial. Type V: Mediastinitis presenting for the first time more than 6 weeks after operation. II) I think that the collection of DSWI and haemorrhage following cardiac surgery in one article is not satisfactory as every one of them in regard to the risk factors should be titled as a separate one. III) I am not convinced of the results as regard to the case of urgent operations which was found not significant either with haemorrhage or DSWI. I think that urgent operations made it possible for both of them to happen. References w1x Robinson PJ, Billah B, Leder K, Reid CM. Factors associated with deep sternal wound infection and haemorrhage following cardiac surgery in Victoria. Interact CardioVasc Thorac Surg 2007;6;167–171. w2x Loop FD, Lytle BW, Cosgrove DM, Mahfood S, McHenry MC, Goormastic M, Stewart RW, Golding LA, Taylor PC. Sternal wound complications after isolated coronary artery bypass grafting: early and late mortality, morbidity and cost of care. Ann Thorac Surg 1990;49:179–186.
