Variability in Pressure of Arterial Oxygen to Fractional Inspired Oxygen Concentration Ratio During Cellular Ex Vivo Lung Perfusion: Implication for Decision Making.

BACKGROUND: The pressure of arterial oxygen to fractional inspired oxygen concentration (PaO2/FiO2, P/F) ratio has been the gold standard in the assessment of transplant suitability in ex vivo lung perfusion (EVLP) with red blood cells. However, several reports using mathematical models and clinical data analysis suggest that the P/F ratio fluctuates at different FiO2. The purpose of this study was to examine the variations in P/F ratio at different FiO2 during EVLP and develop a practicable decision making algorithm in the EVLP.

METHODS: Porcine lungs (n = 16) were perfused in cellular EVLP for 2 hours after a combination of warm ischemia (20-420 min) and cold ischemia (120-600 min). The P/F ratio, vascular/airway parameters, shunt fraction, alveolar-arterial gradient and oxygenation index were measured at FiO2 of 0.21, 0.4 and 1.0 at 1 hour. All 16 cases were divided into two groups according to the relationship between P/F0.21 and P/F1.0; P/F0.21 < P/F1.0, P/F0.21 > P/F1.0.

RESULTS: The P/F ratio was not constant at different FiO2. The pattern of P/F0.21 < P/F1.0 was significantly associated with higher P/F ratio, higher pulmonary compliance, lower shunt fraction, lower alveoli-arterial gradient and lower oxygenation index compared to the pattern of P/F0.21 > P/F1.0 in porcine lungs (P < 0.05, each). In nonsuitable group, pulmonary vascular resistance was increased at FiO2 of 0.21 compared to FiO2 of 1.0.

CONCLUSIONS: The P/F ratio must be considered in combination with the FiO2. The relationship between P/F0.21 and P/F1.0 might be a complementary indicator of lung function in cellular EVLP.