slideshow widget

Tuesday, February 21, 2012

Blood Gases: 4-5-6, 7,8,9 Rule

Technically speaking, so long as you have an accurate pulse oximetry reading, you shouldn't have to draw an ABG to determine how well a person is oxygenating.  This is because the oxyhemoglobin dissociation curve allows you to estimate one by knowing the other.  

For instance, all you have to do use the following formula:

  • Estimated PO2 = SpO2 minus 30
This can also be drawn out as the  4-5-6-7-8-9 Rule.  It goes like this.
  • 4...................7
  • 5...................8
  • 6...................9
or...
  • 40 PO2 = 70 SpO2
  • 50 PO2 = 80 SpO2
  • 60 PO2 = 90 SpO2
Essentially, SpO2 can be used to estimate PO2 and level of hypoxemia. 


90% SpO2
60 PO2
Mild Hypoxemia
No oxygen needed
80% SpO2
50 PO2
Moderate Hypoxemia
Oxygen needed
70% SpO2
40 PO2
severe Hypoxemia
Oxygen needed
Further reading:

No comments: