Soldier’s 5

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.




A Soldier’s 5 is good for Clinicians, too

I spent some 6 years as an Army reservist in the Australian Army. Several aspects of my time (and training) have helped me in my career in both Anaesthetic and Intensive Care nursing. I’ll address some of these in future posts.


Perhaps the most relevant of these is the concept of the “Soldier’s 5”. It is a choice of 5 seconds, 5 minutes or 5 points that a soldier needs to know NOW.

An example might be using a new weapon:

  1. the pointy end (towards the bad guy)
  2. the safety (how not to hurt yourself)
  3. the trigger (how to actually fire the thing)
  4. The aiming reticle (how to aim it)
  5. Where the ammunition goes and how to re-attach magazines (how to keep the thing going)

Of course in the real world, a soldier would ideally have lessons on new equipment before heading into battle.


Much like healthcare.


The benefit of the “Soldier’s 5” is that the method can be used from simple points with new practitioners through to more complex tasks with experienced practitioners.


A clinical example might be:


  1. Synchronous Intermittent Mandatory Ventilation (SIMV) is a form of positive pressure ventilation
  2. SIMV requires the patient breathe through an ETT
  3. It can be volume or pressure controlled (set volume OR pressure)
  4. SIMV allows a set number of breaths/minute but will “Synchronise” with spontaneous breaths
  5. SIMV generally allows PEEP and Pressure Support adjustment


It works with auditory and kinetic learners, and the short points can be recorded by visual learners.


The “Soldiers 5” is generally highly repeatable: once used, the learner can rapidly become the teacher.


Of course, there is no scope for in depth understanding or for learner questioning, so a thorough follow up session relating theory to practice with an educator is recommended.