WTC Report 2014: Should we set limits on an acceptable BMI for transplantation?

By William Bernal, King’s College Hospital, London, UK.  Body mass index (BMI; weight in kilograms divided by height in metres squared) is an important measurement for assessing perioperative risk in patients undergoing surgery; however, although BMI is a significant marker of co-morbidity in the general population, its relationship with surgical outcomes is complex, particularly in the context of chronic liver disease. In a featured symposium on risk evaluation and outcomes, Dr William Bernal from King’s College Hospital in London stressed that BMI should be applied with judgement to guide rather than hinder clinical decision-making. Anthropometric assessments such as analytic morphomics and morphometric age are currently in development and may enable multidimensional assessments of individual patient risk in the near future.

BMI is a basic measure of nutritional status: a patient with a BMI of less than 18.5 kg/m² is classified as underweight, a BMI of 18.5 to 25 is regarded as normal, and BMI between 25 and 30 represents overweight. Patients with BMI over 30 are classified as obese (Class 1; BMI 30-35 kg/m²), severely obese (Class 2; BMI 35-40 kg/m²) or very severely obese (Class 3; BMI >40 kg/m²). In the transplantation setting, BMI has been shown to be associated with pre-transplant morbidity – a recent single-study showed that obese patients were significantly more likely to have diabetes and hypertension pre-transplantation [1]. In terms of post-transplant outcome, obese patients are significantly more likely to develop wound complications such as wound infections, hernias and pulmonary complications [2,3].

However, the link between obesity and adverse outcomes is a lot less clear when it comes to mortality. Whilst overweight and obesity (as well as underweight) have been shown to be associated with increased all-cause mortality in the general population [3], this does not seem to apply to critically ill patients – the so-called obesity paradox [4,5]. Study data in transplant patients does indeed indicate decreased first-year and longer-term mortality in overweight and moderately obese patients [6,7]. Data from the United Network for Organ Sharing (UNOS) in the United States has shown that amongst patients on the waiting list for liver transplantation, underweight patients have a significantly higher hazard of death whilst at the same time there is a trend for patients with moderate obesity to have a lower risk compared with patients with normal BMI. The survival benefit of transplantation over remaining on the waiting list was highly significant in all BMI groups, including underweight and Class 3 obese patients [8]. Underweight patients have also been shown to have significantly longer hospital stay and poorer long-term survival following liver transplantation compared with Class 3 obese patients [7].

The data presented by Dr Bernal was substantiated by a report by Dr Sherilyn Gordon Burroughs and colleagues from Houston Methodist Hospital in Texas, USA, on a study which found no statistically significant difference in one-, three-, or five-year survival after liver transplantation between obese patients (group III) and patients in the normal (group I) and overweight (group II) BMI range. Nor were any significant differences seen in the 30-day sepsis rate or length or hospital stay (Table 1) and Dr Gordon Burroughs and colleagues concluded that pre-transplant bariatric surgery cannot be justified.

Dr Bernal concluded his presentation with a brief overview of anthropometry as a novel means of assessing transplant patients. Published data using hand-grip strength or analytic morphomics suggest that, not surprisingly, malnourished patients and patients with signs of clinically significant muscle wasting have significantly higher mortality and morbidity in chronic liver disease [9-11] and post-transplantation [12,13]. Combining anthropometric variables to determine the morphometric age has been shown to be a better predictor of survival than the chronologic age of the patient [14]. Frailty indices may be used for bedside assessment [15]. Dr Bernal closed by stressing the importance of interpreting BMI and anthropometric parameters in their proper context so as to not become barriers to care, and reminded the audience not to underestimate the impact of under- as well as over nutrition.

Table 1. Post-transplant mortality and complications by BMI group.

BMI Group	1-yr Survival (%)	3-yr Survival (%)	5-yr Survival (%)
I	89	77	70
II	97	85	76
III	95	87	81

BMI Group	30-day Sepsis rate(%)	Mean Post-op LOS (days)
I	1.4	16.7
II	1.5	13.6
III	1.5	15.05

References

1.         LaMattina, J.C., et al., Complications associated with liver transplantation in the obese recipient. Clin Transplant, 2012. 26(6): p. 910-8.

2.         Schaeffer, D.F., et al., Surgical morbidity in severely obese liver transplant recipients – a single Canadian Centre Experience. Ann Hepatol, 2009. 8(1): p. 38-40.

3.         Berrington de Gonzalez, A., et al., Body-mass index and mortality among 1.46 million white adults. N Engl J Med, 2010. 363(23): p. 2211-9.

4.         O’Brien, J.M., Jr., et al., Body mass index is independently associated with hospital mortality in mechanically ventilated adults with acute lung injury. Crit Care Med, 2006. 34(3): p. 738-44.

5.         Mullen, J.T., D.W. Moorman, and D.L. Davenport, The obesity paradox: body mass index and outcomes in patients undergoing nonbariatric general surgery. Ann Surg, 2009. 250(1): p. 166-72.

6.         Rustgi, V.K., et al., Impact of body mass index on graft failure and overall survival following liver transplant. Clin Transplant, 2004. 18(6): p. 634-7.

7.         Dick, A.A., et al., Liver transplantation at the extremes of the body mass index. Liver Transpl, 2009.15(8): p. 968-77.

8.         Pelletier, S.J., et al., Effect of body mass index on the survival benefit of liver transplantation. Liver Transpl, 2007. 13(12): p. 1678-83.

9.         Huisman, E.J., et al., Protein energy malnutrition predicts complications in liver cirrhosis. Eur J Gastroenterol Hepatol, 2011. 23(11): p. 982-9.

10.       Montano-Loza, A.J., et al., Muscle wasting is associated with mortality in patients with cirrhosis. Clin Gastroenterol Hepatol, 2012. 10(2): p. 166-73, 173 e1.

11.       Tandon, P., et al., Severe muscle depletion in patients on the liver transplant wait list: its prevalence and independent prognostic value. Liver Transpl, 2012.18(10): p. 1209-16.

12.       Englesbe, M.J., et al., Sarcopenia and mortality after liver transplantation. J Am Coll Surg, 2010. 211(2): p. 271-8.

13.       Krell, R.W., et al., Association between sarcopenia and the risk of serious infection among adults undergoing liver transplantation. Liver Transpl, 2013. 19(12): p. 1396-402.

14.       Waits, S.A., et al., Morphometric age and mortality after liver transplant. JAMA Surg, 2014. 149(4): p. 335-40.

15.       Sonnenday, C.J. and M.J. Englesbe, Frailty Score Predicts Outcomes Among Liver Transplant Candidates and Recipients. Presented at AASLD 2013, 2013.