This data lends weight to the advice of moderate exertion during a trek to HA and suggests that reducing perceived exertion may reduce AMS.

Background: Acute kidney injury (AKI) is a common complication of COVID-19 critical illness but the pathophysiology is uncertain. Some evidence has indicated that a vascular aetiology may be implicated. We used contrastenhanced ultrasound (CEUS) and echocardiography to study renal perfusion and global blood flow and compared our findings with measurements taken in a group of septic shock patients and healthy volunteers. Methods: Prospective casecontrol study. Renal perfusion variables were assessed with CEUS; macrovascular blood flow was assessed using Doppler analysis of large renal vessels; echocardiography was used to assess right and left heart function and cardiac output. Results: CEUS-derived parameters were reduced in COVID-19 associated AKI compared with healthy controls (perfusion index 3,415 vs. 548 a.u., P ¼ 0Á001; renal blood volume 7,794 vs. 3,338 a.u., P ¼ 0Á04). Renal arterial flow quantified using time averaged peak velocity was also reduced compared with healthy controls (36Á6 cm/s vs. 20Á9 cm/s, P ¼ 0.004) despite cardiac index being similar between groups (2.8 L/min/m 2 vs. 3.7 L/min/m 2 , P ¼ 0.07). There were no differences in CEUSderived or cardiac parameters between COVID-19 and septic shock patients but patients with septic shock had more heterogeneous perfusion variables. Conclusion: Both large and small vessel blood flow is reduced in patients with COVID-19 associated AKI compared with healthy controls, which does not appear to be a consequence of right or left heart dysfunction. A reno-vascular pathogenesis of COVID-19 AKI seems likely.

Background Reduced renal perfusion has been implicated in the development of septic AKI. However, the relative contributions of macro- and microcirculatory blood flow and the extent to which impaired perfusion is an intrinsic renal phenomenon or part of a wider systemic shock state remains unclear. Methods Single-centre prospective longitudinal observational study was carried out. Assessments were made at Day 0, 1, 2 and 4 after ICU admission of renal cortical perfusion in 50 patients with septic shock and ten healthy volunteers using contrast-enhanced ultrasound (CEUS). Contemporaneous measurements were made using transthoracic echocardiography of cardiac output. Renal artery blood flow was calculated using velocity time integral and vessel diameter. Assessment of the sublingual microcirculation was made using handheld video microscopy. Patients were classified based on the degree of AKI: severe = KDIGO 3 v non-severe = KDIGO 0–2. Results At study enrolment, patients with severe AKI (37/50) had prolonged CEUS mean transit time (mTT) (10.2 vs. 5.5 s, p < 0.05), and reduced wash-in rate (WiR) (409 vs. 1203 au, p < 0.05) and perfusion index (PI) (485 vs. 1758 au, p < 0.05); differences persisted throughout the entire study. Conversely, there were no differences in either cardiac index, renal blood flow or renal resistive index. Sublingual microcirculatory variables were not significantly different between groups at study enrolment or at any subsequent time point. Although lactate was higher in the severe AKI group at study enrolment, these differences did not persist, and there were no differences in either ScvO2 or ScvCO2-SaCO2 between groups. Patients with severe AKI received higher doses of noradrenaline (0.34 vs. 0.21mcg/kg/min, p < 0.05). Linear regression analysis showed no correlation between mTT and cardiac index (R-0.18) or microcirculatory flow index (R-0.16). Conclusion Renal cortical hypoperfusion is a persistent feature in critically ill septic patients who develop AKI and does not appear to be caused by reductions in macrovascular renal blood flow or cardiac output. Cortical hypoperfusion appears not be associated with changes in the sublingual microcirculation, raising the possibility of a specific renal pathogenesis that may be amenable to therapeutic intervention. Trial Registration Clinical Trials.gov NCT03713307, 19 Oct 2018.