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Eur J Cardiothorac Surg 2001;19:662-666
© 2001 Elsevier Science NL

Severe obesity does not adversely affect perioperative mortality and morbidity in coronary artery bypass surgery

Department of Cardiovascular Surgery, University Hospital Kiel, Arnold-Heller-Strasse 7, 24105 Kiel, Germany

Received 7 October 2000; received in revised form 26 January 2001; accepted 24 February 2001.

Corresponding author. Tel.: +49-431-597-4401; fax: +49-431-597-4402
e-mail: mbrandt{at}kielheart.uni-kiel.de

	Abstract

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Objective: Obese patients are usually thought to have an increased risk for complications in coronary artery bypass surgery. Methods: Therefore, the data of 500 consecutive patients undergoing coronary artery bypass grafting at our department in 1998 by use of cardiopulmonary bypass were analyzed. Severe obesity was defined as body mass index (BMI) 30.0 kg/m². Obese patients (n=100; group O) were compared to the remaining 400 patients (group C). Both groups were comparable with respect to sex, history of prior myocardial infarction, chronic obstructive pulmonary disease, previous stroke, duration of cardiopulmonary bypass, aortic cross-clamp time and number of distal anastomoses performed. Obese patients were slightly younger and diabetes and hypertension were more common in these patients. Results: Survival and potential complications including perioperative myocardial infarction, sternal wound infection, wound infection at the leg, renal failure, stroke, prolonged mechanical ventilation, pneumonia, reexploration for bleeding, and atrial arrhythmias were analyzed. No significant differences between obese and non-obese patients were detected. Conclusion: Severe obesity does not necessarily adversely affect perioperative mortality and morbidity in patients undergoing coronary artery bypass grafting in this study.

Key Words: Coronary artery bypass surgery • Obesity • Body mass index

	1. Introduction

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Body weight is influenced by genetics and habits [1,2]. Today nearly half of the adult German population is overweight (body mass index 25 kg/m²) [2,3]. Obesity is well known to be a risk factor for the development of diabetes mellitus, hypertension and coronary artery disease [4,5]. It is often assumed that obesity is predisposing to major complications following coronary artery bypass grafting and other major surgical procedures. Technical difficulties during the surgical procedure and major impacts in postoperative care of obese patients as well as factors increasing the severity of the coronary artery disease like hypertension and diabetes contribute to this opinion. In as much severe obesity even represents a strict contraindication for any kind of cardiac procedures remains controversially discussed. However, we hypothesized that obese patients would not necessarily have a higher mortality and morbidity after coronary artery bypass grafting.

	2. Material and methods

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Five hundred consecutive patients following coronary artery bypass surgery with aid of cardiopulmonary bypass within 1998 in our department were retrospectively analyzed.

Demographic data regarding each patient were obtained from the patient's chart. Preoperative variables including age, sex, weight, height, urgency of the operation, history of previous cardiac surgery, myocardial infarction, NYHA functional class, diabetes, chronic obstructive pulmonary disease, and renal insufficiency as well as procedural details including cardiopulmonary bypass time, aortic cross-clamp time, number and type of distal anastomoses were recorded. The postoperative data of interest were reexploration for bleeding, operative mortality, arrhythmias, renal failure, duration of mechanical ventilation, pneumonia, stroke, superficial and deep sternal wound infection, sternal dehiscence, wound infection at the vein harvest site, length of intensive care unit and hospital stay. All data were entered in a computer database (Excel 97, Microsoft).

The body mass index (BMI) is defined as the weight in kilograms divided by the height in meters squared. Patients with a body mass index 30 kg/m² were defined as severe obese for this study (group O; n=100). The remaining 400 patients served as control group (group C). Preoperative demographic data of both groups are presented in Table 1.

	3. Results

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Twenty percent of the patients included in this study had a body mass index 30 kg/m² and were accordingly defined as severely obese (group O). The distribution of the body mass index of all patients in the study is shown in Fig. 1. The mean body mass index was 32.6±2.6 kg/m² in group O compared with 25.5±2.7 in group C (P<0.001).

View larger version (18K): [in this window] [in a new window]   Fig. 1. Distribution of the body mass index for the whole study group

3.2. Operative variables (Table 2)
Again no differences were obtained for cardiopulmonary bypass time, aortic cross-clamp time and the use of unilateral or bilateral internal thoracic artery (ITA) as bypass graft. The total number of distal anastomoses was also similar in both groups. Overall operation time was increased in obese patients (group O: 231±53 min; group C: 204±56 min; P<0.01). The percentage of redo procedures and combined procedures was similar in both groups.

3.3. Postoperative variables (Table 3)
No significant differences between obese and non-obese patients could be detected according to in-hospital mortality (group O: 4%; group C: 3.6%; not significant (n.s.)), length of hospital stay and intensive care unit stay, duration of mechanical ventilation, incidence of myocardial infarction, reexploration for bleeding, atrial arrhythmias (group O: 31%; group C: 39%; n.s.), renal failure, stroke, pneumonia and sternal dehiscence (group O: 3%; group C: 3.0%; n.s.). The incidence of leg wound infections (group O: 9%; group C: 7.8%; n.s.) as well as superficial (group O: 9%; group C: 6.8%; n.s.) and deep sternal wound infections (group O: 3%; group C: 2.0%; n.s.) were similar in both groups.

	4. Discussion

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

However, severe obesity was not associated with a increased risk for in-hospital mortality or major complications in patients undergoing coronary artery bypass grafting at our center. This is in part concordant with previous studies of other groups and is also true for cerebrovascular accidents [7]. In contrast to results published by the groups of Birkmeyer, Fasol and Prasad (see Table 4), we did not observe an increased incidence of different degrees of wound infections [7–9]. The relative high incidence of wound infection up to 9% in our study seems to be a result of a wide definition, as all kinds of non-primary healing wounds, even wound secretion, were regarded as wound infection.

Prasad et al. detected an increased incidence of respiratory problems, arrhythmias, sternal dehiscence and postoperative myocardial infarction [8]. Similar findings were reported by Fasol et al., who observed that obese patients had a greater risk of perioperative myocardial infarction, arrhythmias, pulmonary infection, leg wound infection, and sternal dehiscence [9], which is evidently different from our results. Conversely, we could confirm the study by Koshal et al. showing no increase in pulmonary complications and a similar length of hospital stay [10].

In accordance with our results, Moulton et al. found no increase in the rate of pulmonary complications or deep sternal wound infections, but in contrast reported that superficial sternal wound infections, leg infections and atrial dysrhythmias were significantly higher in obese patients [11].

Regarding malnutrition, not only obesity may impair the outcome after open heart surgery but also a low body mass index and hypoalbuminemia may predict increased morbidity and mortality, as published by Engelmann et al. [12].

There are several potential limitations that should be considered when interpreting the results of this study. There is some error measuring obesity by the body mass index like in this study because a substantial variation occurs in lean body mass among people of the same height [13]. However, the body mass index was chosen as basic parameter for group definition as body mass index correlates least with height and most with more direct measures of percent body fat [13]. Another limitation is that postoperative complications are only encountered when occurring during the primarily hospital stay. But complications leading to ambulatory care or admission to other hospitals are not included. However, in case of major complications readmission to the center, where cardiac surgery was initially performed, can usually be assumed. No patients were excluded from surgery for obesity. However, it can not be excluded that some severely obese patients were not referred from the cardiologists to the cardiac surgeon.

In summary, obese patients may safely undergo coronary artery bypass grafting. Our data and previous studies do not support the statement that obese patients face a higher mortality risk. Also, respiratory complications and even wound infections were not increased in our study. However, the long-term course of the obese patient should be further evaluated because the unfavorable risk profile combined with a younger age may predispose to an inferior long-term perspective.

	Footnotes

 
Presented at the 14th Annual Meeting of the European Association for Cardio-thoracic Surgery, Frankfurt, Germany, October 7–11, 2000.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Dr P. Sergeant (Leuven, Belgium): I am interested in your title. You have pointed out severe obesity does not adversely affect perioperative mortality. That can have a lot of legal consequences. A few times we have been confronted as experts in cases where very obese patients have been treated and have died through the procedure. Are you really convinced that the wording ‘severe obesity’ is correct in this setting, because most of us who are familiar in the Western countries where food is abundant that 15, 20 kilos overweight or a body mass of 30 kg/m², as you are saying, is very frequent and are not really the patients that are giving us problems. The actual problem patients are females of 155 cm and 120 kilos, 50 kilos overweight. If you would restrict your analysis – of course I understand you would have less patients, but are you convinced that the statement ‘severe obesity’ is correct here in this setting?

Dr Brandt: As I said, severe obesity in this study is defined as a body mass index greater than 30, because everything greater than 25 we can perhaps call overweight. You are right, if you define severe obesity as a body mass index greater than 40 or something like this; the results may be obvious, but we cannot conclude this from our data.

Dr A.P. Kappetein (Leiden, The Netherlands): Don't you think that there is a very big chance that you made a so-called Type II error in your analysis. The incidence of, for example, deep sternal wound infection is so low, it is about a half a percent, that with 100 patients in the obese group you will certainly make a Type II error if your group is not larger. So I think that you can't make the statement until you have a larger group. It is not a case control study but it is an observational study that you did.

Dr Brandt: You may be right that this is a limitation of the study.

Dr M. Emara (Cairo, Egypt): It is not our policy ever to use the bilateral mammary in obese and diabetic patients. I think you are very brave. Would you tell me the way you are using your bilateral mammary, the way of dissection, is it skeletonized or something, and can you tell me the secret of not having such a dehiscence sternum, only three cases in such a big group?

Dr Brandt: There were not three cases, it was 3%, a percentage figure, and we don't exclude any patients according to obesity or diabetes for bilateral internal thoracic artery grafting. We don't use this as a contraindication.

Dr Emara: Do you skeletonize them or do you take them pedicle?

Dr Brandt: We use a pedicle.

Dr M. Brais (Ottawa, Canada): In your introduction you define obesity as a body mass index more than 25 and severe obesity as a body mass index of more than 30. Then you compare your obese patients with patients in a control group, and if I am not wrong, the average weight in your control group is 25.5 body mass index. Have you compared the obese with the non-obese, meaning those that have an average weight of less than 25?

Dr Brandt: Yes, we have done this, but the results are the same.

Dr A. Manche (Gwaradamangia, Malta): My comments are very much like Dr Sergeant's in that your definition of severe obesity is not in conformation with, say, the modified Parsonnet score, which only weighs a body mass index over 35. Our experience in Malta is that we have no added morbidity up to 35 but significant problems with wound healing over a body mass index of 35. And I would also comment on your operative bleeding rate, in that the very obese patients bleed less. Do you have a trend there already?

Dr Brandt: No, we have no trend of less bleeding in obese patients.

Dr Manche: Do you have any figures on the 33 patients of body mass index over 35 with regard to your complications?

Dr Brandt: I have no figures on this, but we have analyzed this and there was no difference.

Dr C. Yankah (Berlin, Germany): We do actually operate up to 140, 150 kg in such patients, and electively we don't actually refuse any patient for such an operation. My question is, we also stabilize the sternum, because that is very important for postoperative sternal dehiscence and so forth, and also the wound infection, which is also a very important issue. In a patient who is diabetic, which is also a very important factor for the wound infection after surgery, may I know what kind of sternal closure technique you use, and also, which patient would you refuse for surgery?

Dr Brandt: We haven't refused anyone for obesity, and we use steel wires for closure of the sternum.

Mr T. Treasure (London, UK): I have two questions for you which relate to statistical analysis. One is a simple one. When you give the time on the ventilator, the time in hospital and you give it a mean and a standard deviation, you lose all the detail, unfortunately, because in actuality 80 or 90% of the patients might clear the ICU in a day but another 5% or a few staying 2 or 3 months skew it. It is a well-known thing in statistics and it comes out; we can see it from the size of the standard deviations.

Have you got available for us information, I think you should have it in your manuscript in due course, telling us what proportion of the obese patients are a long time in the ICU as opposed to averaging the whole lot?

Dr Brandt: I don't have the number at the moment.

Mr Treasure: You could do it, though?

Dr Brandt: Yes.

Mr Treasure: There is another thing which worries me a little bit. You said you didn't turn anybody down because of obesity, but in selection, for example, you can produce, and I have wonderful tables showing that it is better off if you are a smoker for coronary surgery, and it is because the people who come to surgery, who, for instance, are smokers, come younger, they have lower lipids, there are fewer diabetics, and therefore by selecting one factor in this way you can skew it. Would it be possible that the people who come to surgery in your institution, even though they are obese, are actually in other ways favorable cases, or do you just take them as they come?

Dr Brandt: We take them as they come, but I cannot tell you if the cardiologists made any decisions.

Mr Treasure: Yes, of course, that's right, there is that too. Anyway, I mean, it doesn't devalue the observation but it just gives caution to its generalization to other situations.

	References

Top Abstract 1. Introduction 2. Material and methods 3. Results 4. Discussion Appendix A. Conference... References

 

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2. Heseker H., Hartmann S., Kubler W., Schneider S. An epidemiologic study of food consumption habits in Germany. Metabolism 1995;44(Suppl 2):10-13.[Medline]
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