• Moderate or severe respiratory failure
• Patients with severe respiratory or cardiac disease scheduled for major abdominal or thoracic surgery
• Suspected acid-base disturbance
• Suspected carbon monoxide poisoning
• Emergency blood sampling when venepuncture impossible

• Consider risks and benefits in patients with bleeding diathesis

Radial Artery

Position of patient

• Arm extended and supported on pillow with wrist extended 20°

Angle of needle to skin

• 30°. See Figure 1

Puncture site

• Proximal to proximal transverse crease on radial aspect of wrist

Advantages

• Easily accessible
• Easily compressible, therefore useful if there is known bleeding tendency

Contraindications

• Buerger's disease
• Raynaud's disease
• Arteriovenous dialysis shunt present or imminent
• Absent ulnar collateral circulation - relative contraindication, consider Allen's test

Brachial artery

Position of patient

• Arm extended and supported on pillow

Angle of needle to skin

• 30°

Puncture site

• Medial to biceps tendon in antecubital fossa
• CARE: Median nerve medial

Advantages

• Easily accessible

Disadvantages

• Risk of ischaemia

Contraindications

• Arteriovenous fistula in arm
• Elbow fractures

Femoral artery

Position of patient

• Supine

Angle of needle to skin

• 60°

Puncture site

• Mid-inguinal point 2 cm below inguinal ligament
• CARE: Femoral nerve lateral and femoral vein medial 

Advantages

• May be only quickly accessible artery in shocked patient

Disadvantages

• Risk of infection and ischaemia
• Venous sample more likely than at other sites

Contraindications

• Severe peripheral vascular disease
• Aortofemoral bypass surgery 

• Non-sterile disposable gloves
• Alcohol wipes or other antiseptic solution
• Lidocaine 1% plain 2 mL, 25 or 27 G needle and/or ice pack
• Blood gas syringe with 23 G needle
• smaller needles have shown longer draw times, and no pain benefit
• Plastic syringe cap
• Cotton wool balls or similar to press over site after arterial puncture
• Sharps' Bin

• If not competent in procedure, organise supervision by a clinician experienced in the procedure

Consent

• Explain procedure and reassure patient
• Obtain and record consent
• Positive Patient Identification (PPID) confirmed

Preparation

• If blood gas analysis not going to be performed within a few minutes, have an ice bag ready to cool sample
• Consider using ice (in a plastic bag) on skin for up to 3 min or cryogesic spray for additional/alternative analgesia to lidocaine
• Check concentration of oxygen patient is breathing at time arterial sample is taken
• if time permits, check it remains constant for 15 min before sampling
• note it on request form, in patient notes and on results printout
• Note patient's temperature on request form

Aseptic technique and position of patient

• Select site of puncture and position patient. See Which artery
• Wear gloves, cleanse patient's skin

Local anaesthetic

• Palpate artery and infiltrate skin with lidocaine plain 1% 0.5-1 mL
• always aspirate before injection of local anaesthetic to prevent injection of lidocaine into the artery

Sampling

• Hold blood gas syringe with 23 G needle, bevel up; for radial (Figure 1) and brachial arteries at about 30° to skin surface; for femoral artery at 60°
• Advance needle towards artery
• with some blood gas syringes, blood pulsates into syringe; others will need to be drawn
• if shooting pain felt, nerve may have been entered. Remove needle and redirect
• if no blood obtained, withdraw needle slowly, observing for pulsation at base of needle; arterial blood often enters during withdrawal
• if necessary, try once more. If unsuccessful, seek help
• Obtain 1.5-2 mL blood
• a smaller volume may suffice for immediate analysis
• Withdraw needle
• Apply pressure to site for 5 min, or if site bleeds, longer
• Dispose of needle in sharps bin
• Remove bubbles in syringe by holding hub upwards and gently tapping side and depressing plunger
• Immediately cap syringe and gently mix for 30 sec
• Attach patient ID label to sample and record FiO₂ (%), patient temperature and time sample taken
• If source of blood (arterial/venous) uncertain, take heparinised venous sample for comparison

• Take sample to nearest blood gas analyser for analysis
• ensure all data fields displayed on screen are accurately completed
• Try to ensure sample is analysed within 15 min of drawing
• Clotting increases as sample ages, therefore ensure syringe is continuously and gently mixed to reduce risk of clotting
• Do not analyse aged samples (taken >20 min before)
• Ensure printed record displays all inputted details