Ascites imposes a restrictive load on the thoracic cage indirectly by the additional weight caused by abdominal swelling from intraperitoneal fluid. This additional load impedes movement of the diaphragm when these patients are in the supine position. The condition creates a type of restrictive lung disease characterized by decreased lung compliance due to extrinsic compression from increased intra-abdominal pressure. As a result, all lung volumes are reduced. Thus, both FEV1 and FVC are reduced but the FEV1/FVC ratio is preserved. The decreased FRC produces low lung compliance and also results in arterial hypoxemia because of V/Q mismatching. These patients usually breathe rapidly and shallowly and tolerate apnea poorly. Despite preoxygenation with an FiO2 of 1.0, arterial hypoxemia and desaturation can occur quickly.
Huffmyer JL, Nemergut EC. Respiratory dysfunction and pulmonary disease in cirrhosis and other hepatic disorders. Respir Care: 2007, 52(8);1030-6