Effects of extracorporeal membrane oxygenation pump flow, backflow cannulae, mean arterial blood pressure, and pulse pressure on Doppler-derived flow velocities of the lower limbs in patients on peripheral veno-arterial extracorporeal membrane oxygenation: A pilot study

Abstract

BackgroundReported rates of limb ischaemia on peripheral veno-arterial extracorporeal membrane oxygenation (pVA ECMO) vary from 1–52%. ObjectivesPrimary: To explore (i) the feasibility for appropriately trained intensive care unit staff to measure Doppler derived flow velocities of the lower limbs for patients on pVA ECMO; and (ii) whether these measurements are clinically useful. Secondary: explore the relationship between ECMO pump flow, backflow cannulae (BFC) properties, mean arterial blood pressure (MAP), and pulse pressure on flow velocities. MethodInclusion criteria: age>18 years, on pVA ECMO >24 hours. Exclusion criteria: any guardianship limitations and patients without a BFC.Serial patients receiving pVA-ECMO over a 10 month period had Doppler derived flow velocities of the lower limbs sampled. Simultaneously, other pertinent parameters were recorded. 80% inclusion was considered clinically feasible. Study personnel were asked for feedback regarding the ease and usefulness of studies. Results15 of 17 patients were included: 88% inclusion. Mean peak systolic velocity (PSV) in the cannulated limb was 31 ± 29 cm/s in the dorsalis pedis (DP) and 27 ± 18 cm/s posterior tibial (PT). Similar flows were recorded in the non-cannulated limbs (DP 34 ± 29 cm/s, PT 44 ± 36 cm/s; P > 0.05). PSV was positively correlated with pulse pressure in cannulated and non-cannulated limbs respectively (r=0.63, P < 0.05; r=0.67 and P < 0.05). There was no significant correlation between PSV and MAP. ECMO pump flow and BFC were negatively correlated with PSV (r=−0.51, P < 0.05; r=−0.43, P < 0.05). ConclusionIt is generally feasible for ICU staff to measure flow velocities of the lower limbs for patients on pVA ECMO. It remains unclear how clinically useful these measurements are. Doppler derived flow velocities of arteries of the lower limbs of patients on pVA ECMO appear different to non-ECMO patients. PSV in the lower limbs of patients on pVA ECMO seems to be more related to pulse pressure than to other haemodynamic parameters.