Step 1: Allen test
- Put
on clean, but not necessarily sterile gloves.
- Have
patient hold wrist in supine position.
- Perform Allen test for collateral flow.
Allen test:
The most common site for arterial puncture is the radial artery at the
wrist. Because of the potential for formation of an obstructing
thrombus in the artery after puncture it is recommended that the
operator demonstrate the presence of good collateral flow through the
ulnar artery prior to proceeding. The Allen test is performed by having
the patient clench their fist several times while the operator occludes
the radial and ulnar artery at the wrist. The patient then extends their fingers, palm up,
which should show a "blanched" hand. The operator then releases the
pressure on the ulnar artery and the hand is observed for "blushing".
If the color of the hand does not return in 5-10 seconds the Allen test
is considered positive and arterial puncture should not be attempted at
that site. It should be noted that the risks of hand ischemia after
arterial puncture are very low and in fact many clinicians do not
routinely perform an Allen test. Having said this it is a simple and
quick test to perform and it is our recommendation that students do an
Allen test prior to attempting arterial puncture at the wrist.