Oedema, the mechanisms, the red flags and the plan.

Oedema is the build-up of interstitial fluid in the tissues that produces visible swelling. It can be peripheral, most often in the legs, or generalised (anasarca), and it can also affect the lungs, brain, retina or airway. The underlying mechanism is always an imbalance between fluid entering the tissues and lymphatic drainage removing it.

Prolonged standing or sitting, hot weather, pregnancy and simple venous insufficiency all raise hydrostatic pressure in the legs and produce bilateral pitting oedema that eases overnight. A single tender swollen leg, or oedema with breathlessness, is different and needs same-day medical review.

Pitting oedema leaves an indentation when a finger is pressed into the swollen area for a few seconds. It usually reflects raised hydrostatic pressure (heart failure, venous disease) or low oncotic pressure (low albumin). Non-pitting oedema is firm and rebounds quickly and suggests lymphoedema or myxoedema in severe hypothyroidism.

Yes. Amlodipine and other calcium channel blockers are the classic culprits, followed by gabapentin and pregabalin, NSAIDs, oral steroids and glitazones. A careful medication review is often as valuable as adding a diuretic and should always come first.

Sudden swelling in one leg, swelling with breathlessness, chest pain, sudden facial or lip swelling, or oedema with confusion, fever or heavy protein in the urine all need urgent review. Chronic, symmetrical, gradually developing swelling is rarely an emergency but still deserves a proper cause-hunt.

A specialist lymphoedema service combines manual lymphatic drainage, compression bandaging or garments, structured skin care, exercise and, in selected cases, intermittent pneumatic compression or reconstructive surgery such as lymphaticovenous anastomosis. Diuretics alone are not effective for pure lymphoedema.