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Eur J Cardiothorac Surg 2003;23:170-174
© 2003 Elsevier Science NL

Off-pump coronary artery bypass surgery does not reduce gastrointestinal complications

^a Department of Cardiothoracic Surgery, Manchester Royal Infirmary, Oxford Road, Manchester, M13 9WL, UK
^b Department of Cardiothoracic Surgery, The Cardiothoracic Centre–Liverpool, Thomas Drive, Liverpool, L14 3PE, UK
^c Department of Research and Development, The Cardiothoracic Centre–Liverpool, Thomas Drive, Liverpool, L14 3PE, UK

Received 4 June 2002; received in revised form 13 August 2002; accepted 14 November 2002.

* Corresponding author. Tel.: +44-161-276-1234; fax: +44-161-276-8522
e-mail: r.hasan{at}man.ac.uk

	Abstract

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

 
Objectives: Gastrointestinal (GI) complications following on-pump coronary artery bypass grafting (CABG) are rare, but carry a high mortality rate. Prolonged cardiopulmonary bypass (CPB) has been associated with a higher incidence of such complications. Little is known about the effect of avoiding CPB on GI complications. Our hypothesis was that off-pump CABG might reduce such complications. Methods: A total of 2327 consecutive cases undergoing isolated CABG between April 1997 and May 2001 were identified from four consultants' practice at the two cardiothoracic centres involved in this study. We performed a multivariable logistic regression analysis to identify the risk factors for development of post-operative GI complications. Potential risk factors considered in the logistic model were age, sex, angina, ejection fraction, peripheral vascular disease, renal dysfunction, redo operations, previous GI complications, priority of surgery and the use of CPB. Results: A total of 1210 cases were performed on CPB, compared to 1117 off-pump. The incidence of GI complications was 1.2% (n=14) in the on-pump group and 1.6% (n=18) in the off-pump group (P=0.347). The incidence of in-hospital mortality, in the patients who had a GI complication, was 28.6% (n=4) and 22.2% (n=4), respectively (P=0.681). The results of the logistic regression analysis showed that renal dysfunction, advancing age and previous history of GI surgery are significant risk factors for GI complications after coronary bypass surgery whether CPB is used or not. Conclusions: Our study suggests that off-pump and on-pump techniques are similar in the rates of GI complications. We suggest that a properly designed randomized control trial is needed to verify our findings.

Key Words: Off-pump • Coronary bypass • Gastrointestinal • Complications

	1. Introduction

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

 
Although the incidence of gastrointestinal (GI) complications following cardiac surgery is relatively low (0.8–3.7%), the associated mortality is high (13.9–86.9%) [1–9]. Several studies have suggested prolonged use of cardiopulmonary bypass (CPB) as a risk factor for the development of GI complications [1–3,5,7,8,10–12]. Off-pump coronary artery bypass grafting (CABG) is increasingly being used as an alternative to conventional coronary revascularization with CPB and has been shown to have better outcomes [13–15]. However, little is known about the effects of avoiding CPB on GI complications. In this study, we investigate whether avoiding CPB during CABG reduces the incidence GI complications.

	2. Methods

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

 
2.1. Patient population
A total of 2327 consecutive patients undergoing CABG surgery between 1st April 1997 and 31st May 2001 were identified from the cardiac surgery database of the two participating institutions (The Cardiothoracic Centre in Liverpool and Manchester Royal Infirmary in Manchester). Patients undergoing CABG that was incidental to valve repair or replacement, resection of a ventricular aneurysm or another surgical procedure were not included. These patients represented the entire coronary revascularization practice of four surgeons (two surgeons from each institution, D.K., R.H., D.M.P. and B.M.F.).

All data were collected prospectively during the patient admission and entered onto a cardiac surgery database as part of routine clinical practice. Methods of data collection and definitions have been previously published [16]. Data were collected on the following variables: age, sex, body mass index, urgency of operation, prior cardiac surgery, angina class, history of myocardial infarction, smoking, diabetes, hypercholesterolaemia, hypertension, peripheral vascular disease, cerebrovascular disease, respiratory disease, renal dysfunction, previous gastric ulcer, previous GI surgery as well as the extent of coronary disease and left ventricular ejection fraction. Data on the duration of CPB, aortic cross-clamp, and mechanical ventilation, plus the need for intra-aortic balloon pump support were also collected.

The main outcome measure for our study was GI complications, which included GI bleeding, pancreatitis, ischaemic bowel and perforation. Definitions for GI complications were in line with the definitions of The Society of Cardiothoracic Surgeons of Great Britain and Ireland minimum dataset [17]. Data on in-hospital mortality (defined as death within the same hospital admission regardless of cause) were also collected. All patients transferred from the base hospital to another hospital were followed up to confirm their status at discharge.

2.2. Statistical methods
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. The European System for Cardiac Operative Risk Evaluation (EuroSCORE) was derived to assess differences in patient case mix between off-pump and on-pump patients [18]. To control for confounding variables, we used multivariable logistic regression to examine the effect of CPB on post-operative GI complications [19]. Forward stepwise selection was used to identify significant risk factors. Potential confounding factors offered to the logistic model included patient age, sex, unstable angina, left ventricular ejection fraction, history of peripheral vascular disease, renal dysfunction, prior CABG, previous gastric ulcer and/or GI surgery. Also offered to the multivariable logistic regression analyses were any significant or closely associated (P<0.1) univariate risk factors for post-operative GI complications from our own experience, along with the surgical technique. The C statistic and the Lemeshow–Hosmer goodness of fit statistic were calculated to assess the performance and calibration of the model, respectively [19]. In all cases a P value of <0.05 was considered significant. All statistical analysis was performed retrospectively with SAS for Windows Version 8.

	3. Results

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

 
A total of 1210 cases were performed on CPB compared to 1117 off-pump. Table 1 lists patient and disease characteristics for the two groups. There were no differences between off-pump and on-pump patients according to age, sex, angina class, previous myocardial infarction, history of diabetes, peripheral vascular disease, renal dysfunction, respiratory disease, cerebrovascular disease, prior cardiac surgery and left ventricular ejection fraction. Off-pump patients compared to on-pump patients, however, were less likely to undergo emergency surgery (0.9% (95% CI: 0.5–1.7) versus 3.1% (95% CI: 2.3–4.3); P<0.001) and had a lower number of diseased coronary vessels (62.1% three vessel disease (95% CI: 59.2–64.9) versus 79.1% three vessel disease (95% CI: 76.7–81.3); P<0.001). Additionally, off-pump patients were more likely to be current smokers (24.9% (95% CI: 22.5–27.6) versus 14.7% (95% CI: 12.8–16.9); P<0.001), hypertensive (48.8% (95% CI: 45.8–51.8) versus 40.3% (95% CI: 37.6–43.2); P<0.001), hypercholesterolaemic (80.6% (95% CI: 77.9–83.1) versus 73.3% (95% CI: 70.7–75.8); P<0.001), had previous gastric ulcer (9.1% (95% CI: 7.5–11.1) versus 6.8% (95% CI: 5.4–8.0); P<0.001), had previous GI surgery (9.8% (95% CI: 8.2–11.8) versus 3.8% (95% CI: 2.8–5.1); P<0.001) and had a higher body mass index (28 kg/m² (25th and 75th centiles: 25–31) versus 27 kg/m² (25th and 75th centiles: 25–30; P=0.008). The overall risk score (EuroSCORE) was similar between the groups, indicating a similar case mix.

A total of 3.8% (95% CI: 2.8–5.1) of on-pump patients required mechanical ventilation over 24 h compared to 3.7% (95% CI: 2.7–5.1) in the off-pump group (P=0.96). Intra-aortic balloon pumps were used in 1.6% (95% CI: 1.0–2.5) of on-pump patients compared to 1.4% (95% CI: 0.8–2.4) of off-pump patients (P=0.78).

The median post-operative length of stay was 7 days (25th and 75th centiles: 6–8) for on-pump patients, compared to 6 days (25th and 75th centiles: 5–7) for off-pump patients (P<0.001).

Overall, 32 patients developed post-operative GI complications, giving a prevalence of 1.4%. The incidence of GI complications was 1.6% (95% CI: 0.9–2.6) in the off-pump group, and 1.2% (95% CI: 0.7–1.9) in the on-pump group (P=0.35). Table 2 displays the distribution of GI complications encountered in both groups. The crude odds ratio for GI complications (off-pump versus on-pump) was 1.39 (95% CI: 0.69–2.82; P=0.35). The incidence of in-hospital mortality in the patients who had a GI complication was 22.2% (95% CI: 7.4–48.1) and 28.6% (95% CI: 9.6–57.9), respectively (P=0.68).

Pre-operative risk factors for the development of post-operative GI complications found by univariate analysis are shown in Table 3. These were added to the logistic model along with surgical technique and other known risk factors.

The results of the multivariable logistic regression analysis are shown in Table 4. Significant risk factors for GI complications were history of renal dysfunction, advancing age and previous GI surgery. The use of CPB was not a risk factor for the development of post-operative GI complications.

	4. Discussion

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

 
CPB has long been recognized as one of the major causes of the systemic inflammatory response, which may contribute to post-operative complications and multiple organ dysfunction [20]. Avoidance of CPB during CABG is believed to be associated with lower morbidity [13–15,21].

Although GI complications after cardiac operations are infrequent, they are associated with high mortality [1–9]. Successful outcome depends on prompt diagnosis and intervention. In this study we sought to investigate whether CPB is a significant risk factor for the occurrence of GI complications seen after CABG.

The reported incidence of GI complications after cardiac operations using CPB varies between 0.8% and 3.7% with a resultant mortality of 13.9–86.9% [1–9]. In this study, the overall prevalence of GI complications for both groups (off-pump and on-pump) was 1.4% (32 patients out of 2327). There was no difference in the crude rate of GI complications between off-pump and on-pump patients. The in-hospital mortality among those who developed GI complications was also similar between the two surgical techniques.

This study shows, through multivariable logistic regression analysis, that CPB is not an independent risk factor for the development of post-operative GI complications. As with other reports [5,6,8,11,12,22] we found that advanced age was an independent risk factor for the development of post-operative GI complications. We also identified pre-operative renal dysfunction as an independent risk factor for GI complications. Fitzgerald et al. found that patients who had GI complications were more likely to have end-stage renal disease [2]. This study also identifies previous GI surgery as an independent predictor, while Yilmaz et al. showed previous history of peptic ulcer as an independent risk factor [5].

Yilmaz and his group [5] demonstrated that, along with advancing age (65 years or older) and previous history of ulcer disease, low cardiac output syndrome, re-exploration of chest, sternal infection, prolonged mechanical ventilation and prolonged CPB time are important risk factors for GI complications. A study involving just CABG with CPB patients by Christensen and colleagues showed hypertension, NYHA class III or IV, poor left ventricular ejection fraction, priory cardiac surgery, urgent operations, and age greater than 70 years as independent risk factors [6]. These studies highlight that the cause of GI complications after coronary bypass operations is multifactorial.

The major contributing factor for GI complications after cardiac surgery is likely to be a low flow state with subsequent hypoperfusion of end organs [22]. Peri-operative hypotension, hypovolaemia, prolonged CPB, use of vasoconstrictors, post-operative arrhythmias, haemorrhage and pre-existing vascular disease play an important role in reducing mucosal injury and organ damage [8,11,22–24].

This report represents a recent population undergoing coronary artery bypass graft surgery, with a relatively large sample size and multiple institutions. A limitation of this study was the fact that it was not randomized and therefore carries with it many confounding factors and possible selection bias. However, the case mix of the off-pump and on-pump groups was comparable given the fact they have identical risk profiles according to the EuroSCORE (Table 1) [18]. Another limitation is the low event rate, and with only 32 GI complications recorded there may not be sufficient power to conclusively demonstrate that the two techniques are equivalent [25]. This is confirmed by the confidence limits around the adjusted odds ratio for GI complications (off-pump versus on-pump) which were relatively wide, 0.57–2.41. However, the C statistic (equivalent to the area under the receiver operating characteristic curve) was 0.76, indicating a good ability to discriminate between patients who developed GI complications and those who did not [19]. Our results may be affected by factors such as previous cardiac surgery and emergent procedures, which may blur our findings, even though neither were associated with GI complications. An alternative method for analysis may be to exclude these patients, however, we have not done this due to concerns over further reducing the sample size of our studies.

In summary, our study suggests that off-pump surgery does not protect against GI complications following CABG. However, we would suggest a properly designed randomized control trial to verify our findings. These complications do occur with similar frequency and carry similar mortality in off-pump patients as with CPB patients. Advancing age, renal dysfunction and a previous history of GI surgery were shown to be significant risk factors for GI complications after coronary bypass surgery in our experience.

	Acknowledgments

 
We would like to thank Suzanne Chaisty and Janet Deane who maintain the quality and ensure completeness of data collected in our Cardiac Surgery Registry.

	Footnotes

 
Presented at the 2002 Annual Meeting of the Society of Cardiothoracic Surgeons of Great Britain and Ireland, Bournemouth, UK, March 18, 2002.

	References

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

 

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