In the oximetric Allen's test, which result indicates no access to the radial artery?

• A. Type A: no change in waveform
• B. Type B: dampened but distinct waveform
• C. Type C: loss of waveform
• D. Type D: irregular waveform

Answer: (C)

This test uses the finger’s pulse oximeter waveform to judge whether the hand will stay well perfused if the radial artery is cannulated. After temporarily occluding both the radial and ulnar arteries, you release the artery you plan to use and watch the waveform. If the waveform reappears, there is some arterial inflow to the hand from that vessel or via collateral circulation, suggesting radial access could be safe. If the waveform is lost, there is no adequate inflow from that artery or from collateral supply, meaning there would be no reliable perfusion if the radial artery were cannulated. So a loss of waveform signals no access to the radial artery for safe cannulation.