The equipment for radial artery puncture includes:
- Alcohol wipes
- Sterile gloves, protective glasses, and apron
- Cotton wool or gauze
- Pre-heparinised 3mL arterial blood gas syringe, a rubber block, and cap
- 23 gauge needle.
Absolute contraindications include:
- Absence of a palpable pulse in an otherwise conscious patient
- Prosthetic arterial bypass graft or stent at intended site of puncture
- Arteriovenous fistula
- Aneurysmal artery
- Negative Allen’s test indicating insufficient ulnar artery supply to the hand
- Cellulitis or other infections in the tissues overlying the radial artery (particularly as other sites are likely to be available).
Relative contraindications include:
- Coagulopathy or bleeding tendency
- A pulse that is weakly palpable.
Arterial blood gas sampling is used together with clinical assessment, venous blood samples, imaging, and physiological tests to help with diagnosis, treatment, and monitoring the response to treatment in a variety of clinical settings. When radial puncture is not possible, the femoral artery provides an alternative – for example, in the peri-arrest situation, or when the patient has a contraindication to radial puncture.
Several parameters of arterial blood are measured from the sample, including:
- Oxygen level
- Carbon dioxide level
- Bicarbonate level
- pH, base excess, and acid-base balance
- Carbon monoxide level.
- Bleeding, bruising, and haematoma formation
- Local infection or cellulitis
- Nerve injury
- Formation of a false aneurysm
- Vasospasm, thrombosis, or embolus, causing transient or significant ischaemia to the distal extremity (this is rare)
- Needle stick injury if insufficient care is taken when pushing the needle into the rubber block before disposal.
Maintain pressure over the arterial puncture site for several minutes. This action can be delegated to an assistant, while the person who performed the procedure carefully disposes of the sharps, labels the specimen, and organises for it to be analysed.
Check the patient several minutes after the procedure to make sure that the perfusion of the extremity is adequate and the arterial puncture site is not haemorrhaging or forming a haematoma.
Send the sample for analysis immediately, labelling and documenting the inspired oxygen concentration clearly.
Normal values for arterial blood vary slightly in each laboratory and machine, and these values should be cross-referenced when interpreting the results of arterial blood gas analysis. Some blood gas analysers also need the patient’s temperature.
An unexpected or very abnormal result may indicate serious pathology or indicate that a venous sample was taken.