**12. Lung involvement, ARDS and Multiorgan dysfunction**

COVID-19 infection may start with influenza like illness with mild symptoms which can progress to severe acute respiratory distress in around 5.6–13.2% patients; a pooled estimate being around 9.4% [86–92]. A systematic review and metaanalysis reported risks of severity and mortality estimated from 18.0 and 3.2%, respectively. If we extrapolate the data of this meta-analysis, additional around 9% will have risk of severe disease other than ARDS [86]. ABG analysis data of critically ill COVID-19 patients showed mixed ABG picture, suggesting multi-organ involvement [87]. If only lung involvement was the cause of severe disease and/ or death, ABG picture should have been of respiratory acidosis or in patients with hyperventilation and CO2 washout of respiratory alkalosis which was not the case in this study [87]. Accompanied metabolic acidosis in a mixed ABG pattern can be because of sepsis, AKI, lactic acidosis ketoacidosis which is reported in COVID-19 patients and in sepsis [87–89].

In lungs, diffuse alveolar damage (DAD), a pathological hallmark of ARDS, has been observed in direct viral invasion of cells and lytic effects [90]. In a systemic review by Bao et al. of 2700 patients of COVID-19, most common abnormalities found on HRCT Chest were ground glass opacifications (83%), ground glass opacification with mixed consolidation (58%) and adjacent pleural thickening (52%) followed by interlobular septal thickening (48%) and air bronchograms (46%) [91]. ARDS can be related to inflammatory markers and also to glycaemic variability, and thus ARDS can be one of the spectrums of MODS and may result in a vicious circle of metabolic derangements [92].
