The clinical and demographic characteristics of 3,960 patients in the study cohort are listed by BMI classification in . 2.5% were underweight (n=98), 32.4% had a normal body mass index (n=1,284), 33.4% were overweight (n=1,323), and 31.7% were obese (n=1,255). Overweight patients were the oldest of the cohort, but the average age of each group ranged from 55 to 60 years. Of the total cohort, 33.5% was male (n=1,329). The underweight group had the largest proportion of female individuals. The underweight classification also had a significantly greater proportion of non-white patients at 23.2%. The types of operations differed significantly by BMI classification. Obese patients accounted for 2.7-6.2% more segmental resections than other patients. More than 14% of underweight patients underwent trisegmentectomy compared to approximately 8-10% of the patients in the other groups. Only 1.5% (n=56) of patients were coded as having liver tumor ablation (radiofrequency, chemical, or cryo-ablation) prior to liver resection. Obese patients had a slightly higher rate of ablation compared to the other groups, but this was not significant. With regards to co-morbidities, statistically significant differences among the four BMI classifications were observed with regards to hypertension, diabetes, active smoking, dialysis dependence, recent weight loss, and ASA class. Obese patients were more likely to be hypertensive and diabetic, but significantly less likely to be active smokers in the last year compared to normal and underweight patients. The underweight patients had a greater propensity toward dialysis dependence, and moribund ASA class. Notably, there were no significant differences between the groups with regards to the various metrics that could be attributed to preexisting liver disease, specifically ascites and varices.
Preoperative Characteristics of 3,960 Patients who underwent Hepatectomy by Obesity Classification
The overall rate of complications was 23.3%, and the overall mortality rate was 2.5%. Cumulatively, obese patients had the highest unadjusted complication rate (p= 0.0051; ). Obese patients had 34% higher odds of having a complication in an unadjusted model (OR 1.34, 95% CI 1.12-1.61), while underweight and overweight patients, respectively, did not have significantly different odds of complications compared to normal BMI patients. The obese group had the highest proportion of patients who had three or more complications (obese 6.1% vs. overweight 4.1% vs. normal 3.7% vs. underweight 5.1%). Obese patients also had greater unadjusted odds of having multiple complications (≥3 complications: OR 1.69, 95% CI 1.17-2.46). While the mortality rate across the BMI distribution was highest in the underweight group, underweight patients did not have significantly higher odds of mortality in the unadjusted regression model (OR 1.34, 95% CI 0.84-2.14), likely related to the small sample size of this group. Only obese patients had significantly higher odds of death following hepatectomy in this model (OR 1.79, 95% CI 1.05-3.05). These models suggest that the baseline morbidity and mortality risk for obese patients was substantial.
Fig. 1 Unadjusted complication and 30-day mortality rates following hepatectomy by obesity classification. By obesity classification, the frequency of having a complication and mortality follow a U-shaped distribution, respectively. Underweight and obese patients (more ...)
With regards to specific complications, on unadjusted analysis, obese patients had significantly higher rates of several complications (). Superficial surgical site infection and progressive renal insufficiency were greater than two-fold more common among the obese compared to the normal BMI patients, respectively. Underweight patients had a ten-fold higher risk of stroke compared to normal BMI patients (p=0.014). A greater proportion of obese patients required mechanical ventilation for greater than 48 hours after operation, which approached statistical significance (p=0.051). Underweight patients had a greater proportion of pneumonia, unplanned intubations, acute renal failure, organ space infections, and septic shock than other patients, but these findings did not reach statistical significance.
Unadjusted Complication Rates Following Hepatectomy By Obesity Classification
After adjusting for the clinical co-morbidities in , the effect of obesity on complication rates was attenuated (). Obese patients had 24% higher risk-adjusted odds of having a complication following hepatectomy compared to normal BMI patients (OR 1.24, 95% CI 1.01-1.55). Underweight patients also trended toward higher complication rates compared to normal BMI patients, but this was not significant (OR 1.17, 95% CI 0.67-2.06). Obese and normal patients had similar odds of having multiple complications as well (≥3 complications, obese vs. normal, OR 1.49, 95% CI 0.97-2.28). With regards to risk-adjusted mortality, as BMI increased, the risk of dying after hepatectomy appeared to increase in a stepwise fashion, but this did not reach statistical significance. Notably, obese patients trended toward an 80% higher risk of postoperative death compared to normal BMI patients (OR 1.83, 95% CI 0.98-3.46, p=0.059), but this risk was abrogated by covariate-adjustment.
Fig. 2 Risk-adjusted odds of complications and perioperative mortality following hepatectomy by obesity classification. The risk-adjusted odds of complications and mortality are displayed in these Forest plots. Following risk-adjustment, obese patients had significantly (more ...)
We subsequently analyzed the effect of obesity on complications and mortality using the subset of hepatic surgery patients who underwent major resections (n= 1,626). In both the unadjusted and risk-adjusted models, obesity was neither associated with significantly increased complication rates nor mortality rates ().
Complication and Mortality Risk Following Major Hepatic Resection by Obesity Classification