Na – Sodium (Salt)

Sodium (Salt)

Plays vital role in regulation of fluid balance and blood pressure, as the major anion of extracellular fluid. Restriction is essential for compliance in fluid restricted patients.

Guidelines for general population = max 6g (100 mmol*) NaCl per day – but this is much more than is essential. An estimated 75% of salt intake comes from processed foods. All renal patients advised on a ‘No Added Salt’ (NAS) diet: 80-100mmols/day.

  • Avoid adding salt at the table
  • Use small amount in cooking or none at all
  • Reduce intake of salty foods (e.g. cheese, smoked food, savoury snacks)
  • Limit intake of packet, processed & convenience foods
  • But avoid salt replacements (e.g. Lo Salt) because of their potassium content
  • Encourage use of pepper, herbs and spices as alternative flavourings

* Sodium, salt and millimoles

  • Atomic weight of Na = 23
  • Atomic weight of Cl = 35.5
  • Therefore mol weight of NaCl = 58.5.  1 mol = 1000 mmol = 58.5g in weight.
  • 1g of NaCl = 1000/58.5 mmol = 17 mmol.
  • Na makes up 39% of NaCl by weight. So if you see ‘sodium content’ of food quoted in grams, you need to multiply by 2.5 to work out the equivalent salt content.
  • ‘Normal saline’ (higher in sodium and chloride than ECF, but osmotically similar) = 0.9%, i.e. 9g per 1000ml. That’s 150 mmol per litre (9×17 = 153)

See, all that Chemistry was useful.  Recommended: the Royal Society of Chemistry’s interactive periodic table (also as a free phone app)

Extracellular fluid and sodium

It might be useful to go back to our fluid therapy tutorial (EdRen textbook)
The perils of salt (history of nephrology; optional further reading)