Agreement between cardiac output measurements by pulse wave analysis using the Pressure Recording Analytical Method and transthoracic echocardiography in patients with veno-venous extracorporeal membrane oxygenation therapy: An observational method comparison

BACKGROUND

Measuring cardiac output (CO) is important in patients treated with veno-venous extracorporeal membrane oxygenation (vvECMO) because vvECMO flow and CO need to be balanced. Uncalibrated pulse wave analysis with the Pressure Recording Analytical Method (PRAM) may be suitable to measure CO in patients with vvECMO therapy.

OBJECTIVE

To assess the agreement between CO measured by PRAM (PRAM-CO; test method) and CO measured by transthoracic echocardiography (TTE-CO; reference method).

DESIGN

A prospective observational method comparison study.

SETTING

The ICU of a German university hospital between March and December 2021.

PATIENTS

Thirty one adult patients with respiratory failure requiring vvECMO therapy: 29 of the 31 patients (94%) were treated for COVID-19 related respiratory failure.

MAIN OUTCOME MEASURES

PRAM-CO and TTE-CO were measured simultaneously at two time points in each patient with at least 20 min between measurements. A radial or femoral arterial catheter-derived blood pressure waveform was used for PRAM-CO measurements. TTE-CO measurements were conducted using the pulsed wave Doppler-derived velocity time integral of the left ventricular outflow tract (LVOT) and the corresponding LVOT diameter. PRAM-CO and TTE-CO were compared using Bland-Altman analysis and the percentage error (PE). We defined a PE of <30% as clinically acceptable.

RESULTS

Mean ± SD PRAM-CO was 6.86 ± 1.49 l min -1 and mean TTE-CO was 6.94 ± 1.58 l min -1 . The mean of the differences between PRAM-CO and TTE-CO was 0.09 ± 0.73 l min -1 with a lower 95% limit of agreement of -1.34 l min -1 and an upper 95% limit of agreement of 1.51 l min -1 . The PE was 21%.

CONCLUSIONS

The agreement between PRAM-CO and TTE-CO is clinically acceptable in adult patients with vvECMO therapy.

The Impact of Recirculation on Extracorporeal Gas Exchange and Patient Oxygenation during Veno-Venous Extracorporeal Membrane Oxygenation-Results of an Observational Clinical Trial

Background: Recirculation during veno-venous extracorporeal membrane oxygenation reduces extracorporeal oxygen exchange and patient oxygenation. To minimize recirculation and maximize oxygen delivery (DO2) the interaction of cannulation, ECMO flow and cardiac output requires careful consideration. We investigated this interaction in an observational trial. Methods: In 19 patients with acute respiratory distress syndrome and ECMO, we measured recirculation with the ultrasound dilution technique and calculated extracorporeal oxygen transfer (VO2), extracorporeal oxygen delivery (DO2) and patient oxygenation. To assess the impact of cardiac output (CO), we included CO measurement through pulse contour analysis. Results: In all patients, there was a median recirculation rate of approximately 14−16%, with a maximum rate of 58%. Recirculation rates >35% occurred in 13−14% of all cases. In contrast to decreasing extracorporeal gas exchange with increasing ECMO flow and recirculation, patient oxygenation increased with greater ECMO flows. High CO diminished recirculation by between 5−20%. Conclusions: Extracorporeal gas exchange masks the importance of DO2 and its effects on patients. We assume that increasing DO2 is more important than reduced VO2. A negative correlation of recirculation to CO adds to the complexity of this phenomenon. Patient oxygenation may be optimized with the direct measurement of recirculation.

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

Despite being vital in treating intensive-care patients with lung failure, especially COVID-19 patients, Veno-Venous Extra-Corporeal Membrane Oxygenation does not exploit its full potential, leaving ample room for improvement. The objective of this study is to determine the effect of cannula positioning and blood flow on the efficacy of Veno-Venous Extra-Corporeal Membrane Oxygenation, in particular in relationship with blood recirculation. We performed 98 computer simulations of blood flow and oxygen diffusion in a computerized-tomography-segmented right atrium and venae cavae for different positions of the returning and draining cannulae and ECMO flows of 3 L/min and [Formula: see text]. For each configuration we measured how effective Veno-Venous Extra-Corporeal Membrane Oxygenation is at delivering oxygen to the right ventricle and thus to the systemic circulation. The main finding is that VV-ECMO efficacy is largely affected by the ECMO flow (global peak blood saturation: [Formula: see text]; average inter-group saturation gain: 9 percentage points) but only scarcely by the positioning of the cannulae (mean saturation ± standard deviation for the 3 L/min case: [Formula: see text]; for the [Formula: see text] case: [Formula: see text]). An important secondary outcome is that recirculation, more intense with a higher ECMO flow, is less detrimental to the procedure than previously thought. The efficacy of current ECMO procedures is intrinsically limited and fine-tuning the positions of the cannulae, risking infections, offers very little gain. Setting a higher ECMO flow offers the biggest benefit despite mildly increasing blood recirculation.