CV - Sodium chloride: sodium chloride 0.9%, sodium chloride 0.45%

Question 1

Sodium chloride: sodium chloride 0.9%, sodium chloride 0.45%

Common indications

Answer 1

• Sodium chloride 0.9% and 0.45% are used to provide sodium and water intravenously in patients unable to take enough orally.
• Sodium chloride 0.9% is used to expand circulating volume in states of circulatory compromise (including shock). Compound sodium lactate and colloids are alternatives.
• Sodium chloride 0.9% is used for reconstitution and dilution of drugs intended for administration by injection or infusion. Glucose solutions and sterile water are alternatives.

Question 2

Sodium chloride: sodium chloride 0.9%, sodium chloride 0.45%

Mechanisms of action

Answer 2

• (ECF) comprises intravascular and interstitial fluid. Extracellular sodium concentrations are maintained at around 140 mmol/L by Na+/K+-ATPase, which pumps sodium out of cells in exchange for potassium.
• As the main cation in extracellular fluid, sodium is the principal determinant of its osmolality.
• As the body seeks to keep osmolality constant, an increase in body sodium results in an increase in extracellular water volume.
• Administration of sodium chloride therefore expands ECF volume (until the excess sodium is excreted).
• The amount by which it expands depends on the sodium concentration of the fluid relative to the ECF.
• Sodium chloride 0.9% contains 154 mmol/L sodium and is therefore roughly isotonic with ECF.
• This means that ECF expands by approximately the same amount as the volume of sodium chloride 0.9% administered.
• About 20% of this remains in the intravascular space to expand circulating volume.
• Sodium chloride 0.9% and 0.45% are also used to provide sodium and water intravenously. The normal sodium requirement for adults is about 1 mmol/kg/day.
• This may be increased in disease states, for example due to diarrhoea.

Question 3

Sodium chloride: sodium chloride 0.9%, sodium chloride 0.45%

Important adverse effects

Answer 3

• Excessive administration of sodium chloride can cause a fall in cardiac output and precipitate heart failure by increasing left ventricular filling beyond the point of maximal contractility on the Starling curve
• Oedema may be caused by providing sodium more rapidly than the patient can excrete it.
• This is especially relevant in patients who have received large amounts of fluid for circulatory compromise, since about 80% of the administered volume will have been ‘lost’ into interstitial fluid
• Also, sodium chloride 0.9% contains 154 mmol/L of chloride, compared with about 100 mmol/L in ECF
• The hyperchloraemia that may result from large-volume infusion can generate acidosis, due to increased urinary losses of bicarbonate.