Physiology
Cardiovascular
The tendency for oedema to occur will be increased by which of the following:
Answer:
Oedema occurs when more fluid is filtered out of the capillaries than can be returned to the circulation by the lymphatics. Filtration is increased by changes that increase capillary hydrostatic pressure or decrease plasma oncotic pressure. Arteriolar constriction will reduce hydrostatic capillary pressure and transiently increase absorption of fluid. Dehydration would increase plasma protein concentration and therefore increase plasma oncotic pressure and absorption. Increased venous pressure would increase capillary hydrostatic pressure and filtration.Oedema
Physiology / Cardiovascular / Peripheral Vascular System
Last Updated: 28th February 2019
Oedema is swelling of the tissues due to excess fluid in the interstitial space.
This may be caused by increased filtration, resulting in fluid overwhelming the lymphatic system, or due to obstruction or dysfunction of the lymphatic system itself.
A reduction in plasma protein (e.g. starvation), or a loss of endothelium integrity with diffusion of protein into the interstitial space (e.g. inflammation, ischaemia), will reduce the oncotic pressure gradient, leading to enhanced filtration and loss of fluid into the tissues.
Reduced venous drainage (increased venous pressure) will increase capillary hydrostatic pressure with a similar effect. Standing without moving the legs prevents the operation of the muscle pump leading to local venous pressure rises and leg oedema. In congestive heart failure, reduced cardiac function results in increased pulmonary and central venous pressures, leading to pulmonary oedema and peripheral oedema respectively.
| Mechanism of Oedema | Causes |
|---|---|
| Increased capillary hydrostatic pressure | Caused by increased venous pressures e.g. by gravitational forces, volume expanded states, in heart failure or with venous obstruction |
| Decreased plasma oncotic pressure | Caused by decreased protein concentration in blood e.g. nephrotic syndrome, protein malnutrition, liver failure |
| Increased capillary permeability (leading to reduced oncotic pressure gradient) | Caused by proinflammatory mediators or by damage to the structural integrity of capillaries so that they become more 'leaky' e.g. in tissue trauma, burns and severe inflammation |
| Lymphatic obstruction | Caused by, for example, filariasis or following lymph node dissection, surgery or radiation therapy |
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
