COVID-19 Does Not Lead to a “Typical” Acute Respiratory Distress Syndrome

ventilation strategy was applied to the first four patients to increase pulmonary efficiency to eliminate CO2, and this was used in the next four patients. Gas exchange consists of oxygenation and ventilation. Oxygenation is quantified by the PaO2/FIO2 ratio, and this method has gained wide acceptance, particularly since publication of the Berlin definition of ARDS (7). However, the Berlin definition does not include additional pathophysiological information about ARDS, such as alveolar ventilation, as measured by pulmonary dead space, which is an important predictor of outcome (8). Increased pulmonary dead space reflects the inefficiency of the lungs to eliminate CO2, which may lead to hypercapnia. In our patients with ARDS with COVID-19, hypercapnia was common at ICU admission with low VT ventilation. Assuming the anatomic portion of dead space is constant, increasing VT with constant respiratory rate would effectively increase alveolar ventilation. Any such increase in VT would decrease PaCO2, which would be captured by VR (6). VR, a novel method to monitor ventilatory adequacy at the bedside (4–6), was very high in our patients, reflecting increased pulmonary dead space and inadequacy of ventilation. With an acceptable plateau pressure and driving pressure, titration of VT was performed. PaCO2 and VR were significantly decreased when an intermediate VT (7–8 ml/kg PBW) was applied. We suggest that intermediate VT (7–8 ml/kg PBW) is recommended for such patients. Therefore, low VT may not be the best approach for all patients with ARDS, particularly those with a less severe decrease in respiratory system compliance and inadequacy of ventilation. In summary, we found that hypercapnia was common in patients with COVID-19–associated ARDS while using low VT ventilation. VR was increased in these patients, which reflected increased pulmonary dead space and inadequacy of ventilation. An intermediate VT was used to correct hypercapnia efficiently, while not excessively increasing driving pressure. Clinicians must have a high index of suspicion for increased pulmonary dead space when patients with COVID19–related ARDS present with hypercapnia. n