Arterial Blood Gas Sampling - Brief Description Of The Procedure

Arterial Blood Gas Sampling is done to measure the oxygen and carbon dioxide tensions and acid–base status of arterial blood.

Indications: Arterial blood gas sampling was a research procedure until the mid-1960s but is now widely performed,either by direct arterial puncture or from indwelling arterial lines.
Indications include:
• respiratory failure (type I or II);
• renal failure;
• hepatic failure;
• cardiac failure;
• drug intoxication (aspirin and narcotics);
• endogenous acid overproduction (ketoacidosis or lactic acidosis);
• severe illness, cause unknown.

Contraindications: Care should be taken in the presence of bleeding disorders. Renal physicians will be appropriately unimpressed if an arterial blood gas sample is taken from an arteriovenous fistula.

What The Patients Should Know Before The Procedure: The procedure should be explained to the patient. The possibility of requiring more than one attempt should be mentioned.

A Brief Description Of The Practical Procedure:
1.Before investigation: The patient should be lying or sitting comfortably and an appropriate site is selected. The radial artery of the non-dominant arm is most commonly used, but the brachial or femoral arteries can be used. Make sure you have enough sterile gauze to apply immediate pressure after the procedure.

2. The investigation: 

• Clean the skin over the wrist with antiseptic solution. Palpate the artery between the tips of the forefinger and the middle finger of one hand.
• Holding it between your fingers,introduce the needle (with heparinised syringe attached) at an angle of 45° and slowly advance the needle along the line of the artery. On puncturing the artery, a small spurt of blood will be seen entering the syringe.
• Withdraw 3–4 mL of blood and press a sterile dressing over the site of puncture.
• Expel any air bubbles and cap the syringe. The syringe should be labelled and sent to the laboratory immediately on ice if a blood gas machine is not available at the bedside.
• The role of local anaesthesia remains controversial. Although used by some, especially in paediatric practice, skilled operators maintain that it adds unnecessary complexity to the procedure.

3. After investigation: It would be best if an assistant or the patient could apply direct pressure for the required minimum 5 minutes.

Complications: In practice, complications are rare:
• haematoma;
• arterial spasm leading to distal ischaemia;
• femoral nerve lies lateral to the femoral artery and can be injured if femoral artery is the chosen site;
• median nerve lies medial to the brachial artery and can be injured.