Arterial Blood Gases (ABG)
An arterial blood gas (ABG) is a blood test that is performed taking blood from an artery, rather than a vein. It is performed so that an accurate measurement of oxygen and carbon dioxide levels can be obtained, which then allows the patients oxygen to be delivered appropriately. It is performed on patients in respiratory distress e.g. asthma attack. This skill is one you should be familiar with and can be extended to involve the interpretation of blood gas results.
Wash your hands, introduce yourself to the patient and clarify their identity. Explain what you would like to do and obtain consent. This is a slightly uncomfortable procedure so you should let the patient know this.
Gather the necessary following equipment:
- a blue (23 G) needle
- 2ml syringe with heparin
- a cap for the syringe
- a plastic bung
- local anaesthetic (plus needle and syringe for giving)
- alcohol gel
- a sharps bin
Usually, the syringe, needle, cap and bung are all provided in one pack.
Position the patient’s arm with the wrist extended.
Locate the radial artery with your index and middle fingers. Perform Allen’s test where you compress both the radial and ulnar arteries at the same time. The hand should become white, release the ulnar artery and the colour should return to the hand. This ensures that there will still be a blood supply to the hand should the ABG cause a blockage in the radial artery.
Put on your gloves and attach the needle to the heparinised syringe.
Also prepare your local anaesthetic and give a small amount over the palpable radial artery.
Take the cap off the needle, flush the heparin through the syringe and again locate the radial artery using your non-dominant hand.
Let the patient know you are about to proceed and to expect a sharp scratch.
Insert the needle at 30 degrees to the skin at the point of maximum pulsation of the radial artery. Advance the needle until arterial blood flushes into the syringe. The arterial pressure will cause the blood to fill the syringe.
Remove the needle/syringe placing the needle into the bung. Press firmly over the puncture site with the gauze to halt the bleeding. Remain pressed for 5 minutes.
Remove the needle and discard safely in the sharps bin.
Cap the syringe, push out any air within it, and send immediately for analysis ensuring that the sample is packed in ice. Remove your gloves and dispose them in the clinical waste bin. Wash your hands and thank the patient.
An extension to this station could be Blood gas interpretation. Before attempting to interpret the results you should know whether the patient was on room air or on oxygen when the sample was taken, and if on oxygen, what concentration.
It is also useful to know whether the patient has a temperature or not, and this should be clearly written on the sample.
The information below shows the changes in pH, CO2 and bicarbonate concentrations in different situations: