OedemaEdema may be defined as expansion of the extracellular volume leading to palpable swelling (Stern, Pathophysiology and etiology of edema in adults. UpToDate.com . Topic last updated: Jan 29, 2020. Last accessed: Oct 8, 2020). Cor pulmonaleCor pulmonale is the commonest cause of pedal (peripheral) oedema in long-standing or severe respiratory disease. In general, pedal oedema that is bilateral usually has a systemic cause (varicose veins are a notable exception), whereas pedal oedema that is unilateral has a localised cause. Generalised oedema will usually become clinically apparent only after the interstitial volume has expanded by ~2.5–3 L (Stern, Pathophysiology and etiology of edema in adults. UpToDate.com . Topic last updated: Jan 29, 2020. Last accessed: Oct 8, 2020). This chapter discusses the pathophysiology of peripheral oedema in lung disease and the differential diagnosis of unilateral and bilateral leg oedema in the context of pulmonary and extrapulmonary disease. Cor pulmonaleCor pulmonale has been discussed in Chap. 60 .