Oedematous legs (the normal look for elephants), normal gazelle legs (Beth Shortt)
Oedema can be local or general. Generalised oedema presents commonly in the ankles in adults, but may also be evident as ascites, pleural effusion, or as facial swelling. Diagnosis is from history and examination of the cardiovascular and gastrointestinal systems, and urine test for protein and blood for serum albumin. Generalised oedema implies expanded extracellular fluid volume and sodium retention.
Increased extracellular fluid
Total extracellular fluid volume may be increased in a number of conditions. Sodium retention by the kidney is usually the major cause. Here are some examples
- Heart failure
- Renal failure
- Low albumin conditions –
- Nephrotic syndrome
- Liver failure
- Administration of too much salt in hospital – e.g. too much saline infusion. Usually in combination with one of the above causes of reduced excretion.
Increased Hydrostatic Pressure
Increased hydrostatic pressure in the veins or lymphatics reduces fluid return to the circulation. This is commonly local (e.g. after a venous occlusion by thrombus or lymphatic occlusion by tumour), but may be general (e.g. in heart failure).
- Generalised: Venous pressure is generally high in heart failure or in volume (or sodium) overload.
- Local: venous pressure will be raised by DVT or venous insufficiency, or by extrinsic obstruction such as pregnancy or tumour. Lymphatic obstruction may cause a non-pitting, localised oedema (known as lymphoedema when chronic). This occurs with some infections (e.g. filariasis), malignancy, radiation injury, or as a congenital abnormality.
Increased Capillary Permeability
Proteins leak into the interstitium, thus reducing the osmotic pressure gradient that draws fluid into the blood and lymphatics.
- Locally with infection or inflammation
- Systemically in severe sepsis
Lowered Oncotic Pressure of Blood
There is low serum albumin due to reduced synthesis or increased loss. Associated with avid sodium retention by the kidney – the problem is probably never purely a problem with oncotic pressure.
- Liver failure (prominent ascites); reduced synthesis of albumin
- Nephrotic syndrome (heavy proteinuria); increased loss of serum proteins
- Malnutrition/malabsorption; reduced synthesis
All cause generalised oedema which tends to be worse in dependent regions. In children, and those with liver disease, ascites tend to occur early.
Management of generalised oedema is by use of diuretics, along with salt (and fluid) restriction. However if the cause is local, this will lead to hypovolaemia.
Compression devices (e.g. stockings) are used for local relief.
- Oedema with hyponatraemia – whole body sodium is increased, treatment with saline is not usually appropriate.
- Ankle oedema may not be due to a generalised problem. Check JVP if you suspect heart failure. Diuretics in the absence of generalised fluid retention causes dehydration (desalination, really).
- Excessive sodium administration – where is it coming from? Look out for hidden and unexpected sources such as high salt snacks, effervescent drug preparations.
Cases to test your knowledge
- (Malawi) A 2 year old girl with generalised oedema (long virtual patient)
- (Malawi) A 16 year old girl with oedema (Short case)