ARTICLE IN PRESS doi:10.1510/icvts.2005.121996
Interactive CardioVascular and Thoracic Surgery 5 (2006) 282–284 www.icvts.org
Institutional report - Cardiac general
Does body mass index (BMI) affect cost in cardiac surgery? ‘A pound (£) for pound (lb) analysis’" Andrew J. Drain*, Caroline Gerrard, Jonathan I. Ferguson, Fay Cafferty, Roy Gurprashad, Alain Vuylsteke Papworth Hospital, Cambridge, CB3 8RE, UK Received 29 September 2005; received in revised form 6 February 2006; accepted 7 February 2006
Abstract The effect of BMI on cost of intensive care unit (ICU) stay and ward stay in cardiac surgery is currently unknown. To assess these data on BMI, ICU stay and EuroSCORE were prospectively collected for 6100 patients undergoing cardiac surgery between 2000 and 2004. Patients were categorised according to BMI and comparisons were conducted, using non-parametric tests (Kruskal-Wallis and Mann-Whitney U-tests). One day in ICU was costed at £1,300 and one ward-day £300yday by this hospital’s finance department. Despite similar median (due to a distribution skewed to a short ICU stay), a significant difference is observed between all 6 groups (Kruskal-Wallis; P-0.001) for ICU stay and ward stay. Underweight and morbidly obese patients had longer ICU stays compared with the ideal weight patients (Ps0.010 and Ps0.004, respectively); while overweight and obese patients had shorter ICU stays (P-0.001 and Ps0.007, respectively). Underweight patients had a longer ward stay than ideal weight patients (Ps0.005) but there was no difference between ideal and morbidly obese patients (Ps0.789). These results demonstrate that BMI has a significant impact on ICU and ward stay with ‘ideal weight’ not always being ideal for patients undergoing cardiac surgery. This cost appears to be independent of EuroSCORE. ! 2006 Published by European Association for Cardio-Thoracic Surgery. All rights reserved. Keywords: Body mass index; Cost; Length of stay; Intensive care; Cardiac surgery
1. Introduction Historically surgeons have assumed obesity and cachexia have adversely affected outcome following surgery. In cardiac surgery, potential adverse outcomes generally considered to be associated with abnormal body mass index (BMI) include operative mortality, deep sternal wound infection, superficial sternal wound infection, infection at the saphenous vein harvest site, stroke, renal failure, adult respiratory distress syndrome, prolonged mechanical ventilation, pneumonia, sepsis, atrial arrhythmias, pulmonary embolism, need for early reexploration for bleeding, and ventricular arrhythmias w1–7x. The consequence of such adverse outcomes is generally assumed to result in increased hospital and ICU stay. This study explores the impact of BMI on the cost of ICU and ward stay. 2. Methods Data on BMI, ICU stay, ward stay, and risk status (EuroSCORE) were prospectively collected for 6100 consecutive patients undergoing elective adult cardiac surgery between 2000 and 2004. Patients were categorised into 6 groups according to BMI; underweight -18.5, ideal 18.5–24.9, " Presented at the joint 19th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 13th Annual Meeting of the European Society of Thoracic Surgeons, Barcelona, Spain, September 25–28, 2005. *Corresponding author. Tel.: q44-1480-830541; fax: q44-1480-834648. E-mail address:
[email protected] (A.J. Drain). ! 2006 Published by European Association for Cardio-Thoracic Surgery
overweight 25.0–29.9, obese 30.0–34.9, very obese 35.0– 39.9 and morbidly obese 39.9 kgym2 w8x. Comparisons were conducted, using non-parametric tests (Kruskal-Wallis and Mann-Whitney U-tests) and multivariate regression analysis. Since ICU stay (and cost) is highly positively skewed, analysis using median (IQR) rather than mean (S.D.) was used. One day in ICU was costed at £1,300 and one ward-day £300yday by this hospital’s finance department. 3. Results Despite similar median (due to a distribution skewed to a short ICU stay), a significant difference is observed between all 6 groups (Kruskal-Wallis; P-0.001) for ICU stay and ward stay (see Table 1 and Fig. 1). Underweight and morbidly obese patients had longer ICU stays compared with the ideal weight patients (Ps0.010 and Ps0.004, respectively); while overweight and obese patients had shorter ICU stays (P-0.001 and Ps0.007, respectively). Underweight patients had longer ward stay than ideal weight patients (Ps0.005) but there was no difference between ideal and morbidly obese patients (Ps0.789). Also, blood costs were significantly higher for underweight patients than ideal weight patients (P-0.005). When first time coronary surgery was assessed in isolation having excluded valve, major aortic and redo surgery, which may have a direct effect on patient weight, the correlation between BMI and ICU length of stay remained (see Fig. 2).
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Table 1 Median ICU stay, ward stay, blood product usage and cost by BMI grouping. IQR: inter-quartile range, FyPyC: fresh frozen plasma, platelets, cryoprecipitate BMI
n
Median days (ICU)
Median days (IQR)
Cost (ICU) (£)
Total cost
Underweight Ideal Overweight Obese Very obese Morbidly obese
90 1758 2760 1168 268 56
3.2 2.7 2.1 2.3 2.7 3.6
1 1 1 1 1 2
4160 3510 2730 2990 3510 4680
8333 6511 5477 5550 6265 7790
(1.2) (1.2) (1.1) (1.2) (1.1) (1.3)
In order to adjust for the effect of EuroSCORE we also used multivariate analysis (using EuroSCORE and BMI grouping) for predicting whether or not patients would remain on ICU for longer than a day (see Fig. 3). Results showed a similar result to the variation seen with cost in relation to BMI. Overall 25.9% of cases stayed in ICU for more than 1 day. There was significant variation between the groups in the proportion, with 45.6% of underweight patients and 51.8% of morbidly obese patients having prolonged stay compared with 31.1% of ideal weight patients, 20.9% of overweight patients and 26.1% of obese patients (P-0.001). 4. Discussion The effect of cardiac disease on BMI has been recognised for decades but only studied in depth recently w9x. These results have demonstrated that there was a longer ICU stay in the morbidly obese and underweight compared to ideal weight. When all six groups were compared, overweight and obese patients had shorter stays compared to ideal weight patients (P-0.001, Ps0.007, respectively). The data also showed that the EuroSCORE was higher in the underweight patient group and reflected a longer ICU stay. The morbidly obese group by contrast tended to have a lower EuroSCORE yet were four times as likely to remain in ICU for greater than one day compared to a patient with ideal weight and same EuroSCORE. This shows that EuroSCORE cannot be used as a predictor of ICU stay and remains independent with no statistically significant relationship to BMI. This study also shows that overweight and obese patients had shorter stays in ICU compared to ideal weight patients. In fact ideal weight was not shown to predict the shortest
Fig. 1. Graphical representation of BMI affect on hospital stay.
Fig. 2. Graphical representation of BMI affect on hospital stay for first time CABG.
ICU stay. We accept that while this study has used the most commonly used criteria for BMI w8x other ranges do exist w10x. The observation that ‘ideal’ body weight patients were more complicated than moderately overweight ones may be due to the fact that there was no body composition assessment, and the group of ideal weight may include some severely malnourished cardiac patients with a pseudonormal weight due to oedema. While these results only demonstrate correlation and not causation between BMI and length of ICU stay it is clear that extremes of BMI are likely to lengthen ICU stay and overall cost in patients undergoing cardiac surgery. Preoperative estimation of BMI may allow patients to be listed more appropriately to maximise ICU resources. For example, underweight and morbidly obese patients may be considered pre-operatively rather than reactively, to need a longer ICU stay. Organisational approaches may then be tailored accordingly. Recent studies have emphasised that an enhanced rate of recovery can be achieved by a multi-modal approach focused on modulating the metabolic status of the patient before (e.g. carbohydrate and fluid loading), during (e.g. epidural anaesthesia) and after (e.g. early oral feeding) surgery w11x. If we assume that lengthened ICU stay is a surrogate marker for morbidity, then these data may even support further study into the benefit of pre-operative feeding of cachectic patients in cardiac surgery. As is current practice in many centres we recommend that morbidly obese patients with stable cardiac disease should also be referred for pre-operative dietetic advice.
Fig. 3. Graphical representation of proportion of patients staying on ICU for 1 day.
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References w1x Mokdad AH, Ford ES, Bowman BA, Dietz WH, Vinicor F, Bales BS, Marks JS. Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. J Am Med Assoc 2003 Jan 1;289:76–79. w2x Mokdad AH, Serdula MK, Dietz WH, Bowman BA, Marks JS, Koplan JP. The spread of the obesity epidemic in the United States, 1991–1998. J Am Med Assoc 1999 Oct 27;282:1519–1522. w3x Edwards FH, Carey JS, Grover FL, Bero JW, Hartz RS. Impact of gender on coronary bypass operative mortality. Ann Thorac Surg 1998 Jul; 66:125–131. w4x Birkmeyer NJO, Charlesworth DC, Hernandez F, Leavitt BJ, Marrin CJ, Morton JR, Olmestead EM, O’Connor GT. Obesity and risk of adverse outcomes associated with coronary artery bypass surgery. Northern New England Cardiovascular Disease Study Group. Circulation 1998 May 5;97:1689–1694. w5x Prabhakar G, Haan CK, Peterson ED, Coombs LP, Cruzzavala JL, Murray GF. The risks of moderate and extreme obesity for coronary artery bypass grafting outcomes: a study from the Society of Thoracic Surgeons’ database. Ann Thorac Surg 2002 Oct;74:1125–1130. w6x Moulton MJ, Creswell LL, Mackey ME, Cox JL, Rosenbloom M. Obesity is not a risk factor for significant adverse outcomes after cardiac surgery. Circulation 1996 Nov 1;94:II87–92. w7x Schwann TA, Habib RH, Zacharias A, Parenteau GL, Riordan CJ, Durham SJ, Engorren M. Effects of body size on operative, intermediate, and long-term outcomes after coronary artery bypass operation. Ann Thorac Surg 2001 Feb;71:521–530. w8x Garrow JS. Body mass index. Am J Clin Nutr 1981 Mar;47:553. w9x Anker SD, Sharma R. The syndrome of cardiac cachexia. Int J Cardiol 2002;85:51–66. w10x Renquist K. Obesity classification. Obesity Surgery 1998;8:480. w11x Fearon KC, Luff R. The nutritional management of surgical patients: enhanced recovery after surgery. Proc Nutr Soc 2003 Nov;62:807–811. Review.
Appendix. Conference discussion Dr D. Wong (Halifax, Canada): I have just a quick question. Did you happen to look at any other anthropomorphic indices, like waist-to-hip ratio or anything like that? Dr Gurprashad: Sorry? Dr Wong: Did you look at any other indices besides BMI, such as waist-tohip ratio? There are other measures that people have suggested besides BMI to measure; truncal obesity, for example. Dr Gurprashad: No, no. We actually based it entirely on BMI, but there is an ongoing, although larger project, in which we’re looking at other ways of making the measurements, and also the relationship with BMI, other ways of measuring weight and also blood loss and return to theater, et cetera. So it’s an ongoing, evolving project. Dr R. Lorusso (Brescia, Italy): I feel a little bit more reassured about many things. I knew that, but now I have the proof, so thank you. I would like to know the extremes. Did they perform differently, I mean the kind of complications which determined an increased length of stay in the intensive care unit? Of course, they should be different, but could you elaborate a little bit on that? Dr Gurprashad: If you are asking for the reasons that may be underlying, no, we haven’t actually looked at that directly. It’s just raw weight or BMI in relation to ICU stay and cost. But I agree, yes. The overweight with maybe a sternal wound dehiscence or wound complications or pneumonic processes or in the low cachectic patients, dilution or hemoglobin, yes, I think these are things that are going to be considered, but we haven’t looked at that directly as the actual underlying reasons for the length of stay, just as raw data that they have stayed longer. Dr J. Pirk (Prague, Czech Republic): Did you check if the female or male gender makes some difference? Dr Gurprashad: We have that available to us, but, no, we haven’t broken it down, and I think, yes, that’s something that we will look at, because I do know that it’s suggested in some of the literature that the underweight tend to be the women and tend to do a lot worse, and there’s lots of evidence for that, and whether it’s because we’re operating on the elderly, small lady or the young population, it’s very difficult to say, but, yes, it’s something that we are going to look at as well.
