REVERSE VENTILATION-PERFUSION MISMATCH IN LUNG-CANCER SUGGESTS INTRAPULMONARY FUNCTIONAL SHUNTING

We report on a patient with squamous cell cancer of the left lung who was first considered ineligible for surgery because of severe hypoxemi a. A ventilation-perfusion scan showed ''reverse'' ventilation-perfusi on mismatch, with 20% of the total lung perfusion going to the left lu ng, which showed no ventilation with radioactive aerosols. This patter n suggested that the hypoxemia was due to intrapulmonary functional sh unting and could therefore be improved by surgical resection of the tu mor. Balloon occlusion of the left pulmonary artery resulted in an imm ediate rise in PaO2, indicating a right-to-left intrapulmonary shunt. After left pneumonectomy, PaO2 levels were normal. This patient provid es an example of dysregulation of the pulmonary hypoxic vasoconstricti on response in a non-small cell lung cancer. Lung cancer patients with severe hypoxemia should undergo ventilation-perfusion scanning to loo k for reverse ventilation-perfusion mismatch suggestive of intrapulmon ary functional shunting.