Extreme BMIs elevate cause-specific mortality risks after lung transplantation
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Key takeaways:
- Risk for death due to acute respiratory failure and chronic lung allograft dysfunction was high among those with BMIs of 16 kg/m2 and 36 kg/m2.
- Obesity elevated the risk for death from primary graft dysfunction.
Lung transplant recipients with extreme low or high BMIs had heightened risks for death due to acute respiratory failure and chronic lung allograft dysfunction, according to results published in Annals of the American Thoracic Society.
“Our study shows that obesity is a risk factor for acute lung injury,” Michaela R. Anderson, MD, MS, assistant professor of medicine at the Hospital of the University of Pennsylvania, told Healio. “We learn repeatedly in medical school about the effects of obesity on the development of cardiovascular disease. Our study further highlights the effects of obesity on outcomes in acute lung injury, even in this highly selected patient population of lung transplant recipients. I would urge clinicians to add this to the list of reasons why we need to help our patients manage their weight.
“[Additionally,] for pulmonologists who diagnose these patients with lung disease and manage them long before they require lung transplantation, we need to emphasize the importance of actively managing obesity and malnutrition,” Anderson added. “I would encourage pulmonologists to work with local obesity medicine specialists, primary care doctors, transplant pulmonologists and dieticians to begin to address these issues long before the patient requires transplantation.”
In a retrospective analysis, Anderson and colleagues assessed 26,319 adults (median age, 60 years; 60% men; 81% white) in the U.S. who received a lung transplant between May 4, 2005, and Dec. 2, 2020, to find links between extreme low/high BMIs and causes of death following the procedure.
Of the total cohort, 1,734 individuals (mean age, 39 years; 39% men; 33% ever smokers) had a BMI less than 18.5 kg/m2 at transplantation and 1,815 (mean age, 60 years; 65% men; 66% ever smokers) had a BMI greater than 32 kg/m2, with the remaining recipients falling between these.
The most common diagnosis among transplant recipients in the low BMI group was cystic fibrosis (50%), whereas the most common diagnosis in the high BMI group was restrictive lung disease (81%).
During median follow-up of 2.8 years, 11,468 of the lung recipients died.
The risk for death did not differ among those with a BMI between 28 kg/m2 and 32 kg/m2 but was heightened among individuals with low or high BMIs, showing a U-shaped association.
Researchers found especially strong associations linked to increased mortality risk for low BMI (16 kg/m2) among those with cystic fibrosis (HR = 1.77; 95% CI, 1.39-2.26) and high BMI (36 kg/m2) for individuals with a restrictive or obstructive lung disease who were aged younger than 65 years (HR = 1.45; 95% CI, 1.23-1.71).
Researchers then grouped the 76 reported causes of deaths into 16 distinct categories and found several additional U-shaped associations between BMI and some of these categories.
For instance, researchers found that having a low BMI vs. a BMI of 24 kg/m2 at transplantation heightened the risks for death due to chronic lung allograft dysfunction (HR = 1.82; 95% CI, 1.34-2.46) and acute respiratory failure (HR = 1.38; 95% CI, 0.99-1.9). Meanwhile, those with a high BMI also faced a greater risk for death of acute respiratory failure (HR = 1.44; 95% CI, 0.97-2.12) and chronic lung allograft dysfunction (HR = 1.42; 95% CI, 0.93-2.15) compared with an individual with a BMI of 24 kg/m2.
However, only those with low BMI showed increased mortality risk due to infection (HR = 1.62; 95% CI, 1.18-2.22).
Researchers also observed an elevated mortality risk due to primary graft dysfunction among individuals with an elevated BMI (HR = 2.85; 95% CI, 1.28-6.33).
“We saw an association between high BMI and two forms of lung injury after transplant: primary graft dysfunction and acute respiratory failure,” Anderson told Healio. “This is consistent with a growing body of literature identifying obesity as a risk factor for acute lung injury in the general population.”
Notably, Anderson said the association between high BMI and death from chronic lung allograft dysfunction was surprising because it has not been described in the past.
“[This association] is a focus of our ongoing work,” she told Healio.
“Future studies will need to focus on (1) how to help our lung transplant candidates optimize their body composition prior to undergoing lung transplantation, (2) mechanisms linking body composition to these causes of death and (3) to better understand how changes in body composition and weight after transplantation affect overall and cause-specific survival,” Anderson added.