Background: Recirculation is a major contributor to refractory hypoxemia during veno-venous ECMO (V-V ECMO), yet it remains difficult to measure at the bedside. In an animal study, we applied the trans-ECMO thermodilution (TET) to quantify the phenomenon, identify its determinants and estimate the mixed venous oxygenation non-invasively. Methods: Eight pigs (65±3 kg) were anesthetized and cannulated for femoral-jugular V-V ECMO. Acute respiratory distress syndrome (ARDS) was induced using oleic (n=4) or hydrochloric acid (n=4) targeting a PaO 2 /FiO 2 of 150 mmHg. The experiment lasted 24 hours, with serial measurements of blood gases, hemodynamics and respiratory mechanics. TET was performed by injecting a bolus of cold saline downstream the membrane lung and by recording the resulting temperature changes in the drainage and return cannulas. Recirculation was calculated as the ratio of the areas under the temperature-time curves (AUCs). The determinants of the recirculation were analyzed with mixed linear models, including a random intercept. The measured recirculation was incorporated in a series of mass-transfer equations to estimate the mixed venous oxygen content and saturation. Results: Median recirculation was 7.4% IQR [1.1-22.0] and presented large inter-subject variability. In 55% of measurements, recirculation was <10% (minimal recirculation, MR). In the remaining measurements, the recirculation measured 27.4 [15.0- 43.5] (significant recirculation, SR). The ratio of extracorporeal blood flow to cardiac output (ECS F ) measured 0.63 [0.55-0.72] and was the only physiological factor correlated with recirculation (overall Pearson correlation coefficient r=0.67, in the SR r =0.81). The distance between the tip of the cannulas was, in our setup, non-significantly associated to the recirculation (p=0.74). An increased recirculation was modestly associated with a decreased mixed venous PO 2 (r=-0.37). The non-invasive estimation of the mixed venous oxygenation was highly accurate (r=0.98, bias +0.48 ml/100 ml for the oxygen content, r=0.98, bias +4% for saturation). Conclusions: TET is a promising technique to measure the recirculation during V-V ECMO. Increasing the blood flow does not always lead to an improvement in oxygenation given the tight relationship between ECS F and recirculation. The proposed numerical method allows the non-invasive estimation of the mixed venous oxygenation without the need of a pulmonary artery catheter.
Recirculation quantified by Trans-ECMO thermodilution to predict mixed venous oxygenation during V-V ECMO: an in vivo porcine study
Gattarello, Simone;
2026
Abstract
Background: Recirculation is a major contributor to refractory hypoxemia during veno-venous ECMO (V-V ECMO), yet it remains difficult to measure at the bedside. In an animal study, we applied the trans-ECMO thermodilution (TET) to quantify the phenomenon, identify its determinants and estimate the mixed venous oxygenation non-invasively. Methods: Eight pigs (65±3 kg) were anesthetized and cannulated for femoral-jugular V-V ECMO. Acute respiratory distress syndrome (ARDS) was induced using oleic (n=4) or hydrochloric acid (n=4) targeting a PaO 2 /FiO 2 of 150 mmHg. The experiment lasted 24 hours, with serial measurements of blood gases, hemodynamics and respiratory mechanics. TET was performed by injecting a bolus of cold saline downstream the membrane lung and by recording the resulting temperature changes in the drainage and return cannulas. Recirculation was calculated as the ratio of the areas under the temperature-time curves (AUCs). The determinants of the recirculation were analyzed with mixed linear models, including a random intercept. The measured recirculation was incorporated in a series of mass-transfer equations to estimate the mixed venous oxygen content and saturation. Results: Median recirculation was 7.4% IQR [1.1-22.0] and presented large inter-subject variability. In 55% of measurements, recirculation was <10% (minimal recirculation, MR). In the remaining measurements, the recirculation measured 27.4 [15.0- 43.5] (significant recirculation, SR). The ratio of extracorporeal blood flow to cardiac output (ECS F ) measured 0.63 [0.55-0.72] and was the only physiological factor correlated with recirculation (overall Pearson correlation coefficient r=0.67, in the SR r =0.81). The distance between the tip of the cannulas was, in our setup, non-significantly associated to the recirculation (p=0.74). An increased recirculation was modestly associated with a decreased mixed venous PO 2 (r=-0.37). The non-invasive estimation of the mixed venous oxygenation was highly accurate (r=0.98, bias +0.48 ml/100 ml for the oxygen content, r=0.98, bias +4% for saturation). Conclusions: TET is a promising technique to measure the recirculation during V-V ECMO. Increasing the blood flow does not always lead to an improvement in oxygenation given the tight relationship between ECS F and recirculation. The proposed numerical method allows the non-invasive estimation of the mixed venous oxygenation without the need of a pulmonary artery catheter.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
