Abnormal oxygenation is a common finding in patients suffering from cirrhosis, ranging from asymptomatic increase in the alveolar to arterial oxygen gradient, (A-a)O2, to a severe respiratory failure. Diffusion limitation, VA/Q disequilibrium and intrapulmonary shunt, as determinants of hypoxemia, however don’t appear to have same relevance.
In order to give more evidence to lung diffusion scenario in explaining abnormal oxygenation, the transfer factor for CO (TLCO), its components, namely capillary blood volume (Vc) and membrane diffusion capacity (DM), its ratio with alveolar volume (TLCO/VA), all as percent of predicted value, and the DM/Vc ratio (normal value 0.78) have been measured in 65 candidates for liver transplant classified according to the Child-Pugh classes A, B, C.
Progressively reduced values of TLCO (94.6±14.4 vs 79.1±17.4, A vs C, p=.0161) and TLCO/VA (83.02±15.2 vs 71.8±10.5, A vs C, p=.0141) with the severity of the disease were mainly found. At the same time, DM (57.07±14.8 vs 44.77±14.4 A vs C, p=.0102) and Vc (124.13±36.08 vs 163.39±45.9, A vs B, p=.0129) values resulted significantly decreased and increased among different classes of severity of liver disease, respectively, their ratio being always lower than normal in the whole group of patients and however significantly reduced in C than A classes of patients (0.36±0.144 vs 0.25±0.163, A vs C, p=.0154). The most severe patients showed abnormal values of oxygenation and their A-a O2 correlated significantly with TLCO (p=.0003, r=.465) and DM (p=.0001; r=.457), but not with Vc, though its values resulted increased.CONCLUSIONS: These findings suggest that more than 50% of the abnormal oxygenation could be explained by the hypothesis that in patients with liver cirrhosis the lung diffusion limitation is apparently due to morphologic changes in the alveolar-capillary membrane whereas the increase of blood volume capillary fails to counteract the gas exchange impairment.
Components of lung diffusion should be measured when patients with liver cirrhosis, being evaluated for the liver transplant, show reduced TLCO.
R. Prediletto, National Research Council of Italy, Grant monies.