what is Allen's Test ?

A strong recommendation for the radial procedure is the performance of the Allen's test. The Allen's test assesses the adequacy of the palmar arch and ulnar flow. It is performed as follows: The patient makes a fist pushing blood from the hand. The radial and ulnar arteries are compressed and simultaneously occluded. When the hand is opened, the palm appears blanched. Release of the ulnar artery should result in return of pink hand color within 8 to 10 seconds.

 Another and more objective measurement of satisfactory ulnar flow can be documented by pulse oximetry. Using the pulse oximeter, the pulse wave is displayed with both arteries open . The radial artery is then compressed and the pulse wave of ulnar flow observed .A reverse Allen's test can also be performed by occluding the ulnar artery. It is recommended for patients with a history of previously accessed radial arteries either for catheterization or arterial blood gases. The results of the oximetric Allen's test are divided into four grades of waveforms: type A, no change in pulse wave; type B, damping of waveform that returns to normal within 2 minutes; type C, loss of phasic pulse waveform that returns within 2 minutes; type D, loss of pulse waveform without recovery within 2 minutes. Although use of the Allen's test and grading of the results for patient selection safety concerns may not be well supported by data, in some areas, this may be considered standard of community practice. In such cases, radial artery cannulation is recommended with types A or B results, can be considered with type C results, and contraindicated with type D results.