Physiologic assessment of the ex vivo donor lung for transplantation

Background The evaluation of donor lungs by normothermic ex vivo acellular perfusion has improved the safety of organ utilization. However, this strategy requires a critical re-evaluation of the parameters used to assess lungs during ex vivo perfusion compared with those traditionally used to evaluate the donor lung in vivo. Using a porcine model, we studied the physiology of acellular lung perfusion with the aim of improving the accuracy of clinical ex vivo evaluation. Methods Porcine lungs after 10 hours of brain death and 24 hours of cold ischemia and uninjured control lungs were perfused for 12 hours and then transplanted. PaO2 , compliance, airway pressure and pulmonary vascular resistance were measured. Ventilation with 100% nitrogen and addition of red blood cells to the perfusate were used to clarify the physiologic disparities between in vivo blood perfusion and ex vivo acellular perfusion. Results During 12 hours of ex vivo perfusion, injured lungs developed edema with decreased compliance and increased airway pressure, but ex vivo PO2 remained stable. After transplantation, injured lungs demonstrated high vascular resistance and poor PaO2 . A reduced effect of shunt on ex vivo lung perfusion PO2 was found to be attributable to the linearization of the relationship between oxygen content and PO2 , which occurs with acellular perfusate. Conclusions Ex vivo PO2 may not be the first indication of lung injury and, taken alone, may be misleading in assessing the ex vivo lung. Thus, evaluation of other physiologic parameters takes on greater importance.