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How to take an arterial blood gas (ABG) sample


Role of an arterial blood gas (ABG) sample

  • To interpret oxygenation levels
  • To assess for potential respiratory derangements
  • To assess for potential metabolic derangements
  • To monitor acid-base status
  • To assess carboxyhaemoglobin in CO poisoning
  • To assess lactate
  • To gain preliminary results for electrolytes and Haemoglobin
  • Can be conducted as a one off sample or repeated sampling to determine response to interventions

Equipment required for ABG sampling

  • Gloves
  • Sharps bin
  • Cleaning swab
  • Gauze
  • Tape
  • ABG syringe

 Contraindications to ABG sampling

  • Local infection
  • Distorted anatomy
  • Presence of arterio-venous fistulas
  • Peripheral vascular disease of the limb to be sampled
  • Severe coagulopathy or recent thrombolysis

Procedure for arterial blood gas (ABG) sampling

  • Consent the patient verbally after explaining the procedure
  • Set up a tray with a sharps bin
  • Expel excess heparin from ABG syringe
  • Palpate for radial pulse
  • Transfix artery between forefinger and middle finger
  • Insert ABG syringe into palpated artery
  • Depending on the syringe it may self fill or you may need to withdraw the plunger carefully
  • Remove needle and syringe after sample gained (only 1-2ml required)


Click here for a New England Journal of Medicine video on ABGs

 Post procedure care

  • Apply pressure to area with gauze and tape. Advise patient to continue giving pressure for 5-10 minutes
  • Take sample to the analyser as soon as possible
  • Ensure the result is labelled with the patients details and documented in the notes (not just stuck)
  • Ensure inspired oxygen concentration is clearly documented
  • Ensure adequate pressure on sampled area to prevent a haematoma

In the event of failure

  • Call for senior help

 Top tips for arterial blood gas (ABG) sampling

  • Most contraindications are relative and rarely encountered.  Decide whether to proceed with the test if a contraindication is present on the basis of how urgent the sample is. Remember there is always the other arm where the test could be performed.
  • Ensure you avoid inserting the ABG needle through superficial veins as this will lead to a mixed sample.
  • Before performing the test ensure you know where the nearest working blood gas analyser is because prompt testing ensures accurate results. It may be necessary to place the ABG sample on ice if interpretation is going to be delayed.
  • If you do not gain the sample on first attempt, you may not need to completely withdraw the needle but it may be possible to re-angle the needle provided you are happy you are in the correct place.


Click here for medical student OSCE and PACES questions about arterial blood gas (ABG) sampling

Common ABG questions for medical students, finals, OSCEs and MRCP PACES

Click here to download free teaching notes on arterial blood gas (ABG) sampling: Procedures – ABG

Perfect revision for medical students, finals, OSCEs and MRCP PACES