There are two methods, one with the use of guide-wire and the other with a plastic cannula over a needle. Both are described.
Allen’s test is performed to ensure radial and ulnar patency. This is done by first occluding the radial and ulnar pulses and asking the patient to open and close their first to drain blood from the hand. The pallor observed in the palm should turn pink with the release of the ulnar pulse. Note that the dominant artery to the hand is the ulnar artery.
The wrist is extended and supinated. A soft support is placed (and may be fixed with tape to the palm) under it to exaggerate wrist extension. This lifts the radial artery superficially as the radial styloid moves anteriorly.
The whole upper limb is positioned such that the direction of the cannulation is from the dominant side of the operator to the non-dominant side. The operator’s dominant hand holding the cannula may be placed on the palm of the patient and the non-dominant on the radial pulse.
Use alcohol/chlorhexidine to prep the skin and infiltrate a small amount <1-2ml of fast-acting local anaesthetic (lidocaine 3mg/kg) without adrenaline in the dermis. Avoid deeper infiltration to prevent arterial injection and distortion of the pulse.
Scrub up (wash hands, wear sterile gown, cap, mask and gloves) and prep the wrist and hand with chlorhexidine.
Apply a sterile drape with the fenestration bordering the distal wrist crease and an adequate segment of the radial pulse.
Wait for the cleaning solution to dry before starting.
Check the cannula by flushing it with sterile heparinised saline. Ensure it slides freely over the needle. The cap is removed.
Check the integrity of the guide-wire and allow it to pass freely through the needle, which is also flushed with heparinised saline.
The cannula is held at an angle of 45 degrees in a precision grip with the needle bevel up. A swab is placed just distally to catch any blood trickling out of the cannula. (Alternately, a 2ml syringe with the piston removed may be attached to the needle; this will catch all the blood and simultaneously allow guide-wire introduction.) If using the guide-wire, ensure it is placed within easy reach.
The needle is advanced through the skin and slowly into the artery. If using the cannula, ensure the plastic cannula does not scrunch up when advancing through the skin.
As a guide, the shallower the angle of entry, the greater the distance the needle has to travel subcutaneously before reaching the underlying radial artery. E.g. if the radial artery is 0.5cm deep and using an angle of 30 degrees, the needle tip has to travel 1cm before reaching the radial artery. If the angle is 45 degrees, then 0.7cm; for an angle of 60 degrees, 0.6cm.
Once flashback is obtained, hold it steady and advance the needle 1mm further at the same angle. The flashback should turn into a pulsating spurt from the needle.
At this point, make the angle of the needle shallower before advancing it another 1mm.
If the flashback is lost, the needle tip has either penetrated the back wall of the artery, or it had not entered the artery directly above it and has come out of the side.
If using the cannula, slide the cannula into the artery over the needle. Do not withdraw the needle until the cannula slides freely into the artery.
If using the guide-wire, thread it using the dominant hand into the needle which is held steady with the non-dominant hand. Ensure at least 4-5cm is inside the artery. The needle is withdrawn as the guide-wire is held in either hand. The plastic cannula is then advanced over the guide-wire.
Connect the cannula to a flushed line. (Ask the assistant to zero the trace.)
Ensure correct placement by check for arterial waveform, withdrawal of blood and blood gas readings.
Secure the cannula using adhesive dressings and a suture leaving a long tie for easy removal.
Observe the hand for any complications such as vascular phenomena.