Pulmonary microvascular cytology. A new diagnostic application of the pulmonary artery catheter

When pulmonary disorders involve primarily the microvasculature, definitive diagnosis is difficult and, in some cases, is not possible until autopsy. In patients with amniotic fluid embolism, fat embolism, and lymphangitic carcinomatosis, terminal pulmonary arterioles and capillaries contain abundant diagnostic material. We hypothesized that withdrawal of blood from a pulmonary artery catheter, particularly in the wedge position, should recover diagnostic cells and debris in patients with these disorders. We describe the technique of pulmonary microvascular cytology and show examples of the recovery of fetal squames in amniotic fluid embolism, fat globules in fat embolism, and malignant cells in lymphangitic carcinomatosis. Megakaryocytes, normal inhabitants of the pulmonary capillary bed, are readily seen in wedged blood and confirm the microvascular origin of a blood sample.