Extracorporeal Membrane Oxygenation Blood Flow and Blood Recirculation Compromise Thermodilution-Based Measurements of Cardiac Output

Abstract

The contribution of veno-venous (VV) extracorporeal membrane oxygenation (ECMO) to systemic oxygen delivery is determined by the ratio of total extracorporeal blood flow (trueQ˙EC) to cardiac output (trueQ˙). Thermodilution-based measurements of trueQ˙ may be compromised by blood recirculating through the ECMO (recirculation fraction; Rf). We measured the effects of trueQ˙EC and Rf on classic thermodilution-based measurements of trueQ˙ in six anesthetized pigs. An ultrasound flow probe measured total aortic blood flow (trueQ˙A0) at the aortic root. Rf was quantified with the ultrasound dilution technique. trueQ˙EC was set to 0–125% of trueQ˙A0 and trueQ˙ was measured using a pulmonary artery catheter (PAC) in healthy and lung injured animals. PAC overestimated trueQ˙ (trueQ˙Pa) at all trueQ˙EC settings compared to trueQ˙A0. The mean bias between both methods was 2.1 L/min in healthy animals and 2.7 L/min after lung injury. The difference between trueQ˙Pa and trueQ˙A0 increased with an trueQ˙EC of 75–125%/trueQ˙A0 compared to QEC <50%/trueQ˙A0. Overestimation of trueQ˙Pa was highest when trueQ˙EC resulted in a high Rf. Thus, thermodilution-based measurements can overestimate cardiac output during VV ECMO. The degree of overestimation of trueQ˙Pa depends on the trueQ˙EC/trueQ˙A0 ratio and the recirculation fraction.

Prone positioning in ARDS patients supported with VV ECMO, what we should explore?

“…In contrast, Gattinoni et al suggested that decrease in partial pressure of carbon dioxide (PaCO 2 ) (decreased physiologic dead space ratio) with PP is predictive of improved outcome in ARDS [18]. Recently, a study used PaCO 2 instead of oxygenation as a key marker to identify the effects of PP on ARDS patients receiving VV ECMO; they exhibited a significant decrease in PaCO 2 from 39 (34)(35)(36)(37)(38)(39)(40)(41) mmHg to 31 (29)(30)(31)(32)(33)(34)(35)(36)(37) mmHg after a PP session (P = 0.03) without any variation in sweep gas flow [19]. Overall, the exact effect of PP on gas exchange in ARDS patients supported on VV ECMO remains uncertain; rather than oxygenation, PaCO 2 might be an alternative parameter to assess the effect of PP.…”

“…These effects of PP on hemodynamics during ECMO are hardly predictable, suggesting that careful hemodynamic monitoring is needed. Notably, in patients on VV ECMO, conventional methods such as pulmonary artery thermodilution and transpulmonary thermodilution are known to be inaccurate for cardiac output measurement due to indicator loss into the extracorporeal circuit [29][30][31][32]. Transthoracic echocardiography, a bedside noninvasive technique, will play an important role in monitoring cardiac function, and transesophageal echocardiography has been shown to be safe in ARDS patients on VV ECMO despite systemic anticoagulation [33][34][35].…”

Blood flow but not cannula positioning influences the efficacy of Veno-Venous ECMO therapy

“…Other methods measure recirculation via thermodilution or ultrasound dilution techniques 11 , 12 . Those findings are limited in their clinical use because they are based on animal data, fixed cannulation strategies or dual lumen cannulae.…”

Swans in Swine: Cardiac Output Monitoring in Pigs Supported on Venovenous Extracorporeal Membrane Oxygenation

“…We have read, with great interest, the article by Russ et al . 1 regarding their findings that thermodilution based measurements can overestimate cardiac output during veno-venous extracorporeal membrane oxygenation (ECMO) and that the degree of overestimation correlates with recirculation fraction and the ECMO blood flow (Q EC )/aortic blood flow (Q AO ). Conducting this study in actual lung-injured pigs keeps true to significant confounding factors in patients with acute respiratory distress syndrome.…”

“…Overall, Russ et al . 1 has provided a very well-conducted study seeking to quantify the inaccuracies of thermodilution based measurements of cardiac output, adding to the original body of evidence. A more comprehensive, and ideally minimally invasive, method is needed to capture true cardiac output.…”