Open or closed left atrium during EVLP
A distinctive feature of the Toronto EVLP protocol is use of a closed left atrium at a pressure of ca 3-5 mmHg whereas the left atrium is open in the Lund protocol.
Recently Linacre et al, 2014(8), published a comparative study on pig lungs to evaluate the relative effects of open or closed left atrium. They reported a significant advantage for the closed atrium alternative (see figures below) when EVLP exceeded 4 – 5 hours. The study protocol involved 4 hours of cold ischemic time followed by 12 hours of warm EVLP. The full 12 hours of EVLP could not be completed in 4 of 5 open atrium cases due to pulmonary edema (after 7 hours EVLP these lungs showed increases in PVR, peak inspiratory pressure and decreases in lung compliance and oxygenation – see figs below). All lungs with closed atrium completed 12 hours EVLP.
Others however have suggested that in clinical practice there may be little true difference in de facto pressures since the open atrium alternative is usually associated with use of red cells in the STEEN Solution™ perfusate which increases its viscosity and flow resistance. In addition, cardiac output is generally twice that used in the Toronto protocol. Both of these variables may well increase left atrial pressure even if the atrium is “open”. This controversy thus still seems unresolved.