Is Obesity Associated with Better Liver Transplant Outcomes? A Retrospective Study of Hospital Length of Stay and Mortality Following Liver Transplantation. Anesthesia and Analgesia. 2022.
Background: The rise in obesity in the United States, along with improvements in antiviral therapies, has led to an increase in the number of obese patients receiving liver transplants. Currently, obesity is a relative contraindication for liver transplant, although exact body mass index (BMI) limits continue to be debated. Studies conflict regarding outcomes in obese patients, while some argue that BMI should not be used as an exclusion criterion at all. Therefore, this retrospective study-utilizing a large national database-seeks to elucidate the association between recipient BMI and hospital length of stay and mortality following liver transplant.
Methods: A retrospective study was conducted using the United Network for Organ Sharing Standard Transplant Analysis and Research database. Fine-Gray competing risk regressions were used to explore the association between BMI and rate of discharge, which varies inversely with length of stay. In our model, subdistribution hazard ratio (SHR) represented the relative change in discharge rate compared to normal BMI, with in-hospital death was considered as a competing event for live discharge. Cox proportional hazard models were built to assess the association of BMI category on all-cause mortality after liver transplantation. Cluster-robust standard errors were used in all analyses to construct confidence intervals.
Results: Within the final sample (n = 47,038), overweight (≥25 and <30 kg/m2) patients comprised the largest BMI group (34.7%). The competing risk regression model showed an association for increased length of stay among underweight (SHR = 0.82, 95% confidence interval [CI], 0.77-0.89; P < .001) and class 3 obesity patients (SHR = 0.88, 95% CI, 0.83-0.94; P < .001), while overweight (SHR = 1.05, 95% CI, 1.03-1.08; P < .001) and class 1 obesity (SHR = 1.04, 95% CI, 1.01-1.07; P = .01) were associated with decreased length of stay. When the sample excluded patients with low pretransplant functional status, however, length of stay was not significantly shorter for overweight and obesity class 1 patients. Cox proportional hazard models demonstrated increased survival among overweight, class 1 and class 2 obesity patients and decreased survival among underweight patients.
Conclusions: Our results provide evidence that overweight and obesity class 1 are associated with decreased length of stay and mortality following liver transplant, while underweight and obesity class 3 are associated with prolonged length of stay. Pretransplant functional status may contribute to outcomes for overweight and class 1 obese patients, which necessitates continued investigation of the isolated impact of BMI in those who have had a liver transplant.
Comments made by Cale Kassel M.D., FASA
In this retrospective study1 examining obesity in liver transplant patients, the authors utilized data from the Scientific Registry of Transplant Recipients (SRTR) to compare obesity class and hospital length of stay (LOS) and mortality. With nonalcoholic steatohepatitis (NASH) set to become the leading indication for LT, providers must consider the risks of transplantation in obese patients. With conflicting data on the risk of obesity in LT, this is usually a center-specific guideline on listing patients with elevated BMI. A total of 47,038 patients were reviewed and divided into 6 groups (underweight, normal, overweight, obese I, obese II, and obese III).
Compared to normal weight patients, hospital LOS was lower in the overweight and class I obesity group while it was longer in the obese III and underweight groups. Further risk analysis that excluded patients with hospitalization prior to transplant, functional status < 50%, mechanical ventilation still demonstrated longer LOS with underweight and obese III groups.
At 90 days, survival was lowest in the underweight and class III obesity group of patients (95.5%, 94.1% respectively). Survival at 1 year and 10 years were lowest in the underweight group of all groups studied. Interestingly, the class I obesity group had the best 1-year and overall survival by the unadjusted Kaplan-Meier model.
The retrospective nature of the study and the presence of ascites are both limitations interpreting the data. Factoring in ascites in the body weight calculation can be challenging and may have led to overrepresentation of obese patients in this study.
Ultimately, the authors found shorter LOS in overweight and class I obesity. Both underweight and class III obesity had longer LOS. Further research into this topic is needed to evaluate the role of functional status in obesity and outcomes. For programs looking to identify specific cutoffs, the authors suggest, based on their findings, that many centers may benefit from a BMI cutoff of > 40 kg/m2. It should be noted that both the AASLD and AST consider class III obesity as a contraindication for LT. The EASL suggests careful evaluation of patients with a BMI > 35 kg/m2.
- Du AL, Danforth DJ, Waterman RS, Gabriel RA. Is Obesity Associated with Better Liver Transplant Outcomes? A Retrospective Study of Hospital Length of Stay and Mortality Following Liver Transplantation. Anesthesia and Analgesia. 2022.