Q: What is the most likely cause of primary graft dysfunction (PGD) in new lung transplant patients? 

Answer:  Ischemia-reperfusion injury

About 10-15 percent of patients develop PGD after lung transplantation. It has been classified into four grades which determines increased 90 days mortality.

• Grade 0 – P/F ratio more than 300 with normal chest x-ray 
• Grade 1 – P/F ratio more than 300  but with diffuse allograft infiltrates on chest x-ray 
• Grade 2 – P/F ratio 200 to 300 
• Grade 3 – P/F ratio less than 200

Reference: 

Christie JD, Carby M, Bag R, et al. Report of the ISHLT Working Group on Primary Lung Graft Dysfunction part II: definition. A consensus statement of the International Society for Heart and Lung Transplantation. J Heart Lung Transplant 2005; 24:1454.