The Magic Numbers: The Soldier’s 5 of Arterial Blood Results (Lesson 1)

So you want to interpret your patient’s arterial blood results but it seems a lot to learn and you’re not sure where to start?

Here’s the Soldier’s 5 version:


  1. 35 and 45 are the two ‘Magic’ numbers to remember
  2. pH should be 7.35 to 7.45. Lower than 7.35 is acidotic, greater than 7.45 is alkalotic (determining a respiratory or metabolic cause is a bit more complicated – see point 2)
  3. pCO2 should be 35 mmHg to 45 mmHg. Lower than 35 mmHg can drive a respiratory alkalosis, higher than 45 mmHg can drive respiratory acidosis (if pCO2 is normal then a deranged pH has a metabolic cause or is compensated)
  4. Sodium (Na) should be 135 mmol/L to 145 mmol/L. Lower than 135 is hyponatraemia, higher than 145 is hypernatraemia
  5. Potassium (K) should be 3.5 mmol/L to 4.5 mmol/L.(*) Lower than 3.5 is hypokalaemia, higher than 4.5 is hyperkalaemia.



Interpreting blood results isn’t something that nurses should be afraid of. Don’t be afraid to have a go – talk to the staff you’re working with and ask them to help. Practice makes perfect.


If you think you’ve found something abnormal on your patient’s blood work, report it. In the worse case, it’s a great learning opportunity.



(*) some texts suggest a potassium of 5.2 mmol/L is the upper end of normal.


The values listed for Sodium and Potassium are the blood values – intracellular (or cytosol) values are almost perfectly reversed. This prevents osmosis of water into the cell.




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