Isabella Canavero, MD
COVID-19 has been reported to increase the risk of ischemic stroke, especially from large vessel disease, probably due to a combination of hypercoagulability and vascular inflammation. To explore the pathophysiology of COVID-19–related neurological and especially cerebrovascular diseases, Ziai et al. analyzed TCD findings in patients with and without COVID-19 infection, some of which also suffered from acute ischemic stroke. Indeed, differently from other radiological techniques, specific practical advantages make TCD easy to perform in the critical care setting. In cerebrovascular patients, TCD allows the identification of useful information such as detection of circulating microemboli and the assessment of cerebral blood flow velocity (CBV).
In the study, twenty-six patients with confirmed or suspected COVID-19 infection were enrolled: 16 confirmed COVID-19 pneumonia and 10 patients with a negative RT-PCR; 2 of the COVID-19–negative cases suffered from severe acute respiratory distress syndrome (ARDS). All the COVID-19–negative cases but only 2 COVID-19 patients also suffered from ischemic stroke; however, all the enrolled cases underwent TCD evaluation because of encephalopathic signs. TCD was performed in all patients at median 4 days after admission. Besides demographics, patient clinical evaluation included routine laboratory tests and transthoracic echocardiography to explore their relationship with TCD findings. Of note, microembolic signals were not detected in any patient, although their potential occurrence cannot be excluded if considering the limited duration of TCD monitoring (15 minutes). However, other works are suggesting that high-intensity transient signals could not be the expected hallmark for COVID-19–associated abnormal hemostasis, which seems to result from localized rather than disseminated or sepsis-induced thrombotic processes. Relatively low CBVs in COVID-19 patients were observed, despite low hematocrit. Mean CBFVs in the M1 division of the MCA were significantly correlated with arterial oxygen content (CaO2) and C-reactive protein. Surprisingly, the correlation between CaO2 and MCA CBV was positive; Although cerebral autoregulation was not specifically addressed, the finding could be explained by its disease-induced impairment. The low CBVs observed found no correlation with left ventricular ejection fraction, failing to identify a cardiogenic mechanism. Of note, 75% of COVID-19 patients received mechanical ventilation, in contrast to about one third of the COVID-19–negative subjects.
This study demonstrates another modality, to monitor critically ill patients with severe respiratory disease and thrombotic events like acute ischemic stroke in the COVID-19 pandemic era. The implication of TCD CBV findings and microemboli detection is unknown. TCD is a pragmatic tool to use in the ICU, and its utility in monitoring for neurologic complications needs further investigation.