Transpulmonary bubble transit in patients hospitalised with COVID-19 pneumonia

Background We previously demonstrated a high prevalence of transpulmonary bubble transit (TPBT) using transcranial Doppler (TCD) in patients with COVID-19 pneumonia, but these observations require confirmation. Methods Patients at two academic medical centres, hospitalised with COVID-19 pneumonia and requiring any form of respiratory support, were studied. The first TCD study was performed at the time of enrolment and repeated approximately 7 and 14 days later if participants remained hospitalised. Results 91 participants were enrolled. At the first TCD, 14 participants (15%) were receiving oxygen by nasal cannula, 41 participants (45%) were receiving oxygen by high flow nasal cannula, 8 participants (9%) were receiving non-invasive positive pressure, 28 participants (31%) were receiving mechanical ventilation and 2 participants (2%) were receiving extracorporeal membrane oxygenation. 33 participants (36%) demonstrated TPBT at the first TCD. There was evidence that the presence of TPBT and increased heart rate together was associated with in-hospital death (p=0.02). For every one-unit increase in heart rate, the odds of death increased 11% (OR 1.11, 95% CI 1.02 to 1.20, p=0.01) for those with TPBT; however, there was no evidence of this increase for those without TPBT (OR 1.01, 95% CI 0.97 to 1.05, p=0.76). For participants with subsequent TCD assessments, 55% demonstrated TPBT during the second TCD assessment, and 85% demonstrated TPBT at the third TCD assessment. Conclusions The prevalence of TPBT in hospitalised patients with COVID-19 pneumonia is higher than expected and the presence of TPBT increases over time in those that remained alive and hospitalised. In patients with TPBT, increased heart rate, a marker of hyperdynamic circulation, is associated with increased mortality.