We report the use of a simple bedside test for identifying ulnar collateral flow that can be done before placement of arterial monitoring lines or removal of arterial blood from the radial artery. This procedure is recommended as a replacement of the Allen test or Doppler identification of ulnar flow, both of which often present results that are difficult to interpret in hypotensive patients. We have successfully applied this technique in hypotensive and normotensive patients and have occasionally noted asymmetrical collateral flow between two extremities in a single patient.

The procedure involves placement of a bedside oximeter on a digit of the hand being considered for a radial line. After an adequate reading of oxygen saturation on the monitor is obtained, the radial and ulnar arteries should be occluded with digital pressure until no reading can be obtained on the oximeter. As in the Allen test, the ulnar artery occlusion should be released first. Returning flow to the nailbed will restore the oximetry readout as a result of ulnar arterial flow with an adequately perfused deep palmar arch and collateral flow. Obtaining the same oximetric reading while continuing occlusion of the radial artery gives an objective assessment of this collateral flow. If the result is positive, the radial artery is then safe for puncture or line placement. If the oximeter does not detect a pulse to the nailbed upon release of the ulnar artery pressure, the radial artery occlusion is released. Return flow after release of the radial artery pressure confirms that ulnar collateral flow alone is inadequate to allow safe arterial puncture or line placement. Arterial puncture is not advised with this negative result. If flow to the nailbed cannot be initially identified by oximetry, radial arterial puncture or monitoring should never be considered. In such cases, an alternative site for arterial study, such as the femoral artery, must be used.

We would like to call the technique the Sullivan test, in recognition of the resident who serendipitously identified this helpful and accurate method of identifying collateral flow.