The co and principal investigator, due to limited resources and timing, have decided to withdrawal the study and close.

Assessment of common carotid artery flow is more easily done and can be taught more broadly than transthoracic echocardiography, providing a greater number of clinicians a tool to assess volume responsiveness. These assessments are of great importance to patients with COVID-19, who often present with hypotension requiring fluids, which must be balanced against limiting fluid administration to minimize pulmonary edema.

Optimizing volume status for patients in shock is of critical importance to their outcomes, both in the provision of helpful, and avoidance of harmful fluid volumes. As such, much work has been done to develop and assess measures of volume responsiveness; that is, tests that indicate whether additional fluid administration will increase cardiac output by at least 10%. The passive leg raise (PLR) providing a reversible "auto-bolus" has been demonstrated to be the most predictive assessment of fluid responsiveness.

Recent studies of changes in carotid artery blood flow suggest it can be used as a surrogate for changes in cardiac output with moderate reliability. This has been assessed in several populations with anticipated changes in volume status (e.g. before/after blood donation), and more recently assessed by Sidor et al. against several preload augmenting maneuvers. Interestingly, while decreasing preload resulted in a decrease in cardiac output and systolic carotid blood flow, it did not result in a decrease in corrected carotid flow time, although a PLR produced an expected increase in all measures.

In our study we seek to validate these results, questioning if there is a lower limit of corrected carotid flow time that de-couples the relationship between carotid systolic flow and corrected carotid flow time.

Inclusion Criteria:

• Adult patient admitted to hospital with diagnosed COVID-19, on up to 6L oxygen, and able to undergo leg compression testing and passive leg raise.

Exclusion Criteria:

• known cardiac disease, carotid atherosclerosis, prior right-sided neck surgery, chest wall deformity, or deep-venous thrombosis identified on admission

20 adult (age 18-80) patients admitted to the hospital with COVID-19 requiring supplemental oxygen, up to 6L, willing to undergo transthoracic and right carotid ultrasonography.