Which test requires a pulse oximeter with waveform visualization?

• A. Modified Allen's Test
• B. Allen's Test
• C. Oximetric Allen's Test
• D. Doppler ultrasonography

Answer: (C)

Assessing collateral circulation to the hand before radial artery access. The oximetric Allen's test uses a pulse oximeter on a finger and visualizes the waveform to confirm that arterial perfusion returns through the palmar arches when the radial artery is occluded. If the waveform reappears promptly after releasing the ulnar artery, collateral flow is sufficient; if not, there is a risk of ischemia with radial cannulation.

The traditional Allen's tests rely on visual blanching and capillary refill, which are more subjective. Doppler ultrasonography uses Doppler flow signals rather than pulse oximeter waveform, so it doesn’t fit the requirement of waveform visualization.