For each case of fluid balance disturbance A–E, select the most appropriate option from the following list

 A. Option 2 Decreased total body water. In the absence of any water intake, a person loses a minimum of around 1500 ml per day (500 ml insensible loss from the lungs, 500 ml insensible loss from the skin and 500 ml as the minimum amount of water which can dissolve excreted solid waste products in the urine). A urine volume of 100 ml in five hours confirms this condition. After several days there will be a water deficit of around four to five litres or 10 per cent of total body water, so the osmolality has risen by about 10 per cent. The water deficit is distributed between intracellular and extracellular fluid and oral water would correct the deficit.

B. Option 4 Decreased extracellular fluid. The patient has lost a considerable volume of intestinal secretions. This fluid is isotonic and rich in sodium and chloride, the main extracellular ions. His main depletion is of extracellular fluid and this is confirmed by signs of severe peripheral circulatory failure evidenced by a low arterial blood pressure despite vasoconstriction (cold peripheries) and a rapid heart rate. He urgently needs replenishment of his extracellular fluid by intravenous infusion of isotonic (normal) saline. Although Option 8 accounts for the peripheral circulatory failure, Option 4 is more appropriate as it includes the underlying mechanism and points to the appropriate treatment.

C. Option l Increased total body water. Inappropriately raised secretion of antidiuretic hormone causes excessive reabsorption of water as fluid passes through the collecting ducts. This dilutes all body fluids as indicated by the low sodium level (osmolality would be correspondingly reduced). The waterlogging of the body cells impairs function and this effect in the brain is manifested by confusion. Restricted water intake would improve the condition.

D. Option 7 Increased blood volume. Replacement of blood loss is urgent in the elderly, but over-transfusion can increase the blood volume above normal. In the elderly there is an increased risk of heart failure and increasing the blood volume can precipitate this so that the heart cannot adequately clear the venous return. The filling pressure of the two sides of the heart increases, causing pulmonary oedema and breathlessness plus increased systemic venous pressure. Diuretic therapy would reduce blood volume by causing excretion of salt and water, thereby lowering extracellular fluid volume.

E. Option 10 Decreased plasma volume. By damaging capillaries, burns cause increased loss of fluid and proteins from the circulation. In addition large amounts of interstitial fluid are lost through the damaged skin. Both effects lower plasma volume, raising the haematocrit. Low blood volume can lead to peripheral circulatory failure. The standard treatment is to infuse large quantities of normal saline, in proportion to the area of seriously burnt skin.