Use of Compromised Lung Volume in Monitoring Usage of Steroid Therapy on Severe COVID-19

As there was no consensus on the use of steroids in the early stage of the COVID-19 pandemic, all steroid therapies were initiated at the time of admission at the discretion of attending physicians on the basis of clinical symptoms and CT images. According to our previous experience, intravenous methylprednisolone at a dose of 1.0-1.5 mg/kg every 12 h was initiated for 5 days or until oxygen saturation improved, followed by gradual tapering by 0.5 mg/kg every 3-5 days.

Standard care such as the use of antibiotics, ventilation, laboratory testing, and hemodynamic management were performed following the sixth edition of the Guidelines on the Diagnosis and Treatment of COVID-19 published by the National Health Commission of China.

According to different Hounsfield unit (HU) intervals in the quantitative chest CT scan, we divided each lung into nonaerated lung volume (%NNL, 100 to -100 HU), poorly aerated lung volume (%PAL, -101 to -500 HU), normally aerated lung volume (%NAL, -501 to -900 HU), and hyperinflated lung volume (%HI, -901 to -1000 HU) regions. The additional "compromised lung" volume (%CL) was considered as the sum of %PAL and %NNL (-500 to 100 HU).

To monitor COVID-19 progression during the treatment process, we chose changes in the percentage of compromised lung volume (Δ%CL) at different stages (Δ%CL = %CL at different stages-baseline %CL) as the primary outcome. The negative value of Δ%CL thus reflected clinical improvement.