A study in AJEM compares arterial and capillary blood gases obtained from 187 patients. The authors conclude with how it ‘appears to exist a strong correlation between samples collected from the finger tip capillaries with arterial blood samples’. Who would have thought?
The study
Arterial and capillary blood gases from 187 ED patients were collected and compared. Indications for gas analysis were reduced LOC, sepsis, COPD, trauma and DKA
Results
Results are in the table below. C = capillary A = Arterial. Because of capillary gas exchange, PaO2 and SaO2 will always be lower in the capillaries.
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We in Pediatrics have known this for a long time. Make sure the digit is warmed and the sample flows freely.
This is not ground breaking news, but what is more important is how to interpret the arterial blood gas when the sample is taken. What is normal in the artery is not what is normal in the capillary!
The trick is knowing the difference, let alone knowing how to take a successful capillary blood gas!