Early follow-up of COVID-19 patients identified a primary restrictive defect with reduced diffusing capacity that resembled defects previously observed in patients with acute respiratory distress syndrome. The long-term pulmonary consequences of COVID-19, particularly in severe cases requiring ICU admission, are not known. The objective of the current study is to prospectively follow the pulmonary function of COVID-19 survivors who required ICU admission and compare outcomes amongst patients who needed high-flow oxygen (HFO), mechanical ventilation (MV) and extracorporeal life support (ECLS) for 1-year post-recovery. Osc is particularly sensitive to peripheral lung dysfunction and has been shown to identify lung disease earlier than conventional PFT. Thus, we will also compare Osc with conventional PFT in detecting respiratory dysfunction amongst the three groups.
COVID-19 patients who survived ICU admission and were followed at the TGH post-recovery outpatient clinic are prospectively enrolled for quarterly Osc and conventional PFT. Demographic and clinical information are extracted from patients’ electronic medical records.
From August 20-November 26, 2020, we enrolled 15 patients (12 M/3 F; mean age 53±15 years) who were 5.6±1.1 months post-infection. Conventional PFT showed restrictive defects only in the MV [%predicted total lung capacity (%TLC) =77±16, %predicted forced vital capacity (%FVC) =79±16, n=6] and ECLS (%TLC=71±14, %FVC=74±12, n=5) groups. Diffusing capacity and 6-minute walk distance were normal in all patient groups. In contrast, Osc was abnormal in all groups, particularly in the indices of peripheral airway obstruction and ventilatory inhomogeneity: R5-19 (difference in respiratory resistance between 5 and 19 Hz) and AX (area of reactance). The respective median (IQR) values for the HFO, MV and ECLS groups are as follows: R5-19 =1.47 (0.92-1.49), 1.02 (0.62-1.31), 1.29 (0.61-1.48) cmH2O.s/L (normal median range=0.11-0.66 cmH2O.s/L) and AX=12.65 (7.67-15.62), 10.83 (9.15-15.82), 14.32 (12.22-22.63) cmH2O/L (normal median range=2.11-5.79 cmH2O/L).
Early findings in a cross-section of severe COVID-19 survivors revealed restrictive defects in the MV and ECLS groups when assessed by conventional PFT. However, abnormalities in respiratory mechanics were detectable by Osc in all patients suggesting that Osc may provide an early biomarker of subsequent lung function impairment.