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BMI Not Associated With Meaningful Differences in COVID-19 Critical Illness Outcomes

Key findings

  • This observational cohort study compared intensive care unit (ICU) outcomes in adult patients, with and without obesity, admitted to the Massachusetts General Hospital ICU with laboratory-confirmed COVID-19
  • At the point of ICU admission, there were no significant differences in respiratory physiology or inflammatory markers between patients with obesity and patients without obesity
  • At 60-day follow-up, there were no significant differences in mortality or other clinical outcomes between patients with and without obesity
  • While obesity may be a risk factor for developing severe COVID-19, this study suggests there are no differences in outcomes between patients with and without obesity when managed with standard ICU therapies

Obesity is associated with increased incidence of chronic medical conditions, and in the context of COVID-19, the Centers for Disease Control and Prevention has listed class 3 obesity (defined as a body mass index (BMI)of >40 kg/m2) as a risk factor for developing severe COVID-19. Cohort studies have identified obesity as a risk factor for ventilatory support and overall mortality in COVID-19, however the relationship between obesity and critical illness remains complex.

"Recent literature has found an association between obesity and development of critical illness in COVID-19. What we didn't know is, once patients are critically ill and admitted tothe intensive care unit (ICU), does having obesity continue to increase risk," says Molly Wolf, MD, pediatric specialist and fellow at Massachusetts General Hospital.

Dr. Wolf, along with Jehan Alladina, MD, physician-scientist, and their colleagues in the Division of Pulmonary and Critical Care Medicine at Mass General, and University of California San Diego, performed a retrospective cohort study to examine the association of BMI with measures of critical illness in COVID-19. They found no significant differences in respiratory physiology, inflammatory profile or clinical outcomes. The study was published in Obesity.

Study Methods

The researchers reviewed the electronic medical record for 277 adult patients admitted to an ICU unit at Mass General with laboratory-confirmed SARS-CoV-2 infection from March 14 to May 3, 2020, to collect demographic and clinical information. Patients were divided into 4 groups based on BMI class:

  • No obesity (BMI ≤29.9kg/m2)
  • Class 1 obesity (BMI 30-34.9 kg/m2)
  • Class 2 obesity (BMI 35-39.9 kg/m2)
  • Class 3 obesity (BMI ≥40 kg/m2)

Detailed ICU parameters were collected for the first six days of ICU admission, and initial laboratory values were collected within the first 72 hours of ICU admission.

The Cohort at ICU Admission

Compared with patients without obesity, this cohort of patients with obesity were younger (median age 56 vs 66, P<0.05) and had a lower prevalence of pre-existing heart failure (9% vs 13%, P<0.05). Both groups had a high prevalence of diabetes and hypertension, but otherwise did not vary significantly with regards to sex, ethnicity, race or smoking history.

At ICU admission, patients with obesity had higher plateau pressures (22.5 cmH2O vs 20.0 cmH2O, P<0.05), initial applied PEEP (IQR 10.0-12.0 vs. IQR 8.0-12.0 in patients without obesity, P<0.05), and initial central venous pressure (CVP; 9.0 cmH2O vs 7.0 cmH2O, P=0.04) compared to patients without obesity. Additionally, ferritin (788 ug/L vs 1012 ug/L, P<0.05) and D-dimer levels (1202 ng/mL vs 1329 ng/mL, P=0.05) were lower in patients with obesity compared to patients without obesity. All other laboratory tests and ICU admission characteristics, including measures of respiratory physiology, both within 72 hours of ICU admission and on day 6 of ICU admission, showed no significant differences between groups.

Clinical Outcomes

There were no significant differences in ICU interventions during the first 6 days of ICU admission. There were no differences in measured clinical outcomes at 60 days, in terms of survival, days in the ICU, days on mechanical ventilation, need for reintubation or tracheostomy.


"While many studies have shown obesity to increase the risk for critical illness due to COVID-19, this study is unique in that it shows that—once critically ill—patients have similar outcomes across the body mass index spectrum," says Dr. Alladina.

"Future work should examine outcomes of larger cohorts of patients with and without obesity once they are admitted to the ICU. It would also be helpful to get more detailed physiologic measurements, such as esophageal balloon pressures," says Dr. Wolf. "We hope this work will encourage the equal application of standard and advanced critical care therapies for patients suffering from COVID-19 illness."

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