Indications
- • Suspected respiratory failure
- • Acid–base disturbance
- • Critical illness / shock
- • Carbon monoxide / methaemoglobin
Contraindications
- ⚠ Inadequate collateral circulation (modified Allen's)
- ⚠ Local infection / AV fistula limb
- ⚠ Severe coagulopathy (relative)
Equipment
- • Pre-heparinised 2–3 mL syringe with 23G needle
- • Alcohol swab
- • Gauze + tape
- • Local anaesthetic 1% lidocaine (optional)
- • Ice slurry if delay to analyser
Technique
- • Perform modified Allen's test if radial
- • Position wrist extended over rolled towel
- • Clean site, optional 0.1–0.2 mL lidocaine SC
- • Palpate pulse, insert needle at 45° towards pulse
- • Allow syringe to fill passively (1–2 mL)
- • Withdraw, apply firm pressure ≥5 min (longer if on anticoag)
- • Expel air bubbles, cap, label, analyse within 10 min
Complications
- ⚠ Pain, haematoma, arterial spasm
- ⚠ Distal ischaemia (very rare)
- ⚠ Infection
- ⚠ Nerve injury (median nerve at wrist)
Aftercare
- • Document FiO₂ at time of sample
- • Pressure ≥5 min then check distal perfusion
- • Pair with VBG / serum lactate if relevant
Clinical pearls
- • Femoral useful in arrest / shock
- • Bubbles falsely raise PaO₂ + lower PaCO₂
- • Delay to analyser overestimates lactate / underestimates pH
Perform under supervision until competent. Follow local SOPs and consent policy.
