Shunting of Oxygenated Blood to the Venous System in the Avalon® Cannula on Venovenous Extracorporeal Membrane Oxygenation with High-frequency Oscillatory Ventilation

High-frequency oscillatory ventilation (HFOV) may assist in the prevention of volutrauma for high-risk patients with acute respiratory distress syndrome (ARDS) during venovenous extracorporeal membrane oxygenation (VV ECMO). In combined VV ECMO and HFOV, we noted that increased intrathoracic pressure contributed to shunt formation in the dual-lumen Avalon® cannula (Maquet, Rastatt, Germany). A 51-year-old female with ARDS secondary to aspiration pneumonia was placed on VV ECMO using a single Avalon cannula. By ECMO Day 16, she became unable to ventilate due to elevated peak airway pressures, even with low tidal volume ventilation and an otherwise stable VV ECMO course. HFOV was introduced to minimize ventilator-induced lung injury. Shortly after HFOV started, the patient desaturated, and consequently, the fraction of inspired oxygen (FiO2) was increased to 100%. We noted that a flash of bright red, oxygenated blood was flowing retrograde in the Avalon cannula at the same rate as the beat of the oscillator, while the patient's ECMO flow rate, arterial blood gas, and blood pressure all remained stable. The ECMO flow was increased above 5.5 L/min and the resolution of the retrograde shunt through the Avalon cannula was immediately observed.  Concurrent use of HFOV with VV ECMO using an Avalon cannula may result in a shunt that becomes visible with arterial O2 saturations nearing 100%. Due to pressure differences between the venous and arterial lumens of the Avalon cannula, increasing the ECMO flow rate appeared to decrease this shunting effect caused by elevated intrathoracic pressure.