For each of the intravenous fluids A–E, select the most appropriate option from the following list of infusions.
1. 50 per cent glucose.
2. 1.8 per cent saline.
3. 5 per cent glucose (dextrose).
4. Normal (0.9 per cent) saline (sodium
5. 8.4 per cent sodium bicarbonate. 4. chloride).
- An isotonic solution which expands mainly the extracellular fluid volume.
- An isotonic solution which expands both intra- and extracellular fluid volumes.
- A major nutrient used in intravenous nutrition.
- A hypertonic fluid with about twice the osmolality of plasma.
- A fluid occasionally used to treat severe acidosis.
Medicine
A. Option 4 Normal saline. Normal saline has the same tonicity (osmolality) as plasma and extracellular fluid. Sodium doesn’t enter intracellular fluid appreciably. The chloride and water remain with the sodium in the extracellular space.
B. Option 3 5 per cent glucose. 5 per cent glucose (dextrose) is also isotonic. It has the same number of particles as 0.9 per cent saline. Saline dissociates so the average particle molecular weight is about 30. Dextrose has a molecular weight of 180 and does not dissociate so about six times the mass of dextrose is required for isotonicity.
C. Option 1 50 per cent glucose. A litre of 50 per cent glucose contains 500 grams of glucose, yielding about 2000 kilocalories (about 9 megajoules, MJ), around the resting daily requirement of an adult.
D. Option 2 1.8 per cent saline. This is twice the osmolality of normal saline – around 600 as compared with around 300 mosmoles per kg.
E. Option 5 8.4 per cent sodium bicarbonate. This concentrated bicarbonate solution has a high buffering capacity for hydrogen ions. However correcting acid–base balance is a complex procedure rarely benefiting from such drastic measures.
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