An Arterial Blood Gas (ABG) is a blood sample taken from an artery, usually from the radial artery. An ABG sample will often be processed quickly and give a clinician an idea of the oxygen, carbon dioxide and pH levels in the blood. This is often very important in the treatment if an acutely unwell patient. It is also a blood test that is important for monitoring if a treatment is working for a patient for example those that come in with Chronic Obstructive Pulmonary Disease (COPD) or Asthama.
Performing an ABG gives the clinician key information about:
It is usual to get an ABG sample from the radial artery. If the patient is peripherally shut‐down and acutely unwell it can also be taken from the femoral artery.
Wash your hands using the Ayliffe technique
Introduce yourself and give your name and grade
“Hi, my name is John Smith and I am a 4th year medical student”
Clarify patients identity by confirming their name and asking for their DOB
Explain what examination you are performing and what this involves
“Today I will be taking some blood from one of the arteries in your wrist. This may be slightly more painful than other blood tests you may have had, but it’s really important that we get this blood sample as it will help guide your treatment”
“Would this be okay with you?”
Consider also a local anaesthetic if the patient is not acutely unwell.
Gloves + Apron
2% chlorhexidine wipe
Needle (blue for radial and green for femoral)
Sharps disposal container
Modified Allen’s test (not commonly done in practice but may be required in your OSCE - check before hand with clinical skills staff)
Let the patient know you have finished examining them and thank them for their time.
“That’s the end of the procedure. Thank you for your time.”
Ensure that you have taken with you the patient’s details, often a sticky lable from the notes shall suffice. Also ensure that you note down how much oxygen the patient is on.
Ensure that this is done promptly and ensure syringe is placed in ice if there is a delay
Hold syringe like a pen
To steady your hand try anchoring it against patient’s hand
It’s in the bag when you see pulsating, bright red blood filling the syringe quickly
Compare blood oxygen saturations with sats prob to ensure it is an arterial sample
Don’t expect immediate changes on an ABG after changing a patient’s oxygen level.
Try on the other side, as multiple attempts on the same side may provoke arterial spasm which reduces the chance of a further success.
Get help! If a patient is unwell they may be peripherally shut down so it may be difficult to get a sample, always best to get help rather than waste too much time.
Femoral arterial sample if struggling – if experienced in the procedure.
Femoral arterial sample
Equipment – same as above, this time green needle (21G).
As above. Important differences include:
Lying the patient flat
Identify femoral pulse, which lies at the midpoint between the anterior superior iliac spine and the pubic symphysis
Inserting the needle at 90 degree angle at the point of pulsation
Apply lots of firm pressure for 5 minutes or until bleeding stops, don’t just put tape over gauze and leave.