Hemodynamic Monitoring and Fluid Responsiveness in Venovenous Extracorporeal Membrane Oxygenation (VV ECMO) - "HemodynamECMOnitoring-VV Study"

Transthoracic echocardiography (TTE) is used for intermittent non-invasive stroke volume (SV) measurements. It is calculated by multiplication of left ventricular out flow tract (LVOT) and LVOT velocity time integral (VTI), obtained in a parasternal long axis view and apical five chamber view, respectively.

Pulse Contour Analysis allows an automated and continuous measurement of stroke volume (SV). Its underlying principle is that the integral of the systolic arterial pressure curve directly correlates with stroke volume.

Transpulmonary thermodilution (TPTD) involves the administration of a cold saline bolus into a central venous catheter. A special thermistor catheter placed in the femoral or brachial artery detects the successive changes in blood temperature. The resulting heat dissipation curve is analyzed to estimate stroke volume, cardiac output and other hemodynamic variables such as intrathoracic thermal volume (ITTV), pulmonary thermal volume (PTV), global end-diastolic volume (GEDV), intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). Intermittent TPTD-derived cardiac output measurements (typically performed 1-3x/d) are used to calibrate pulse contour analysis.

In esophageal Doppler, a thin ultrasound probe, coated with aqueous ultrasound gel, is orally or nasally inserted into the esophagus and orientated towards the aorta. By emission and detection of continuous wave Doppler signals, real time spectral waveforms of red blood cell velocity in the aorta are obtained, from which cardiac indices can be derived.

Bioreactance is a noninvasive hemodynamic monitoring technique, in which four double electrode sensors are placed on the skin of the chest. A high frequency sine wave is transmitted across the thorax. Pulsatile flow in the aorta causes phase shifts and amplitude changes of this signal, which are measured across the different electrodes and used to compute cardiac output.

Passive Leg Raising (PLR) is a maneuver that mimics a fluid challenge by shifting about 300 ml of venous blood from the lower body to the heart. Thereby, it can help to predict fluid responsiveness without actual fluid infusion. To start with, the patient is placed in a semi-recumbent position. Then, the bed is adjusted so that the patient's torso is moved to a horizontal position and the lower limbs are raised to an angle of 45°. Hemodynamic effects occur and can be measured within one minute.

Inferior Vena Cava (IVC) Ultrasound has become a popular technique for assessing volume status. IVC diameter is measured in a subcostal long-axis IVC view 1-2 cm from the junction with the right atrium. The magnitude of distensibility during mechanical ventilation cycles or collapsibility during spontaneous breathing has been proposed to correlate with fluid responsiveness

In preload-dependent patients, mechanical ventilation induces periodic changes in cardiac output. Standardized maneuvers of end-expiratory or end-inspiratory interruption over 15 seconds may increase or decrease stroke volume, respectively, which is a valid predictor of fluid responsiveness

To verify fluid responsiveness, 500 ml of balanced crystalloids will be infused over a time of 15-20 min (25-33.33 ml/min) after completion of passive leg raising and restoration of baseline patient positioning.