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Ann Thorac Surg 1999;67:536-537
© 1999 The Society of Thoracic Surgeons
a 171 E Gunhill Rd, Bronx, NY 10467, USA
Invited commentary
Fox and associates must be commended for sounding a cautionary note regarding the possibility for hand ischemia when the radial artery is used as a conduit for coronary artery bypass grafting. They note the importance of cardiac output in the maintenance of a borderline collateral circulation to the hand. The implications for testing are obvious. Safe radial artery harvest requires appropriate assessment of the adequacy of forearm collateral flow and palmar arch continuity. The occurrence of ischemia may in part be due to the lack of standards for testing adequacy of collateral circulation prior to radial artery harvest and to methodological and protocol issues not addressed in their report.
A few comments about testing methods are appropriate. The modified Allen test is a well-known screening tool, but it is a subjective test, and requires patient cooperation and the capacity of the hand to develop visible rubor. The test has a low false-negative predictive accuracy, particularly if the observer uses almost instantaneous return of palmar and thenar eminence rubor. There is a tendency to accept an Allen test as negative for radial artery harvest if rubor returns at 5 and even 10 seconds after release of ulnar artery compression. If the result is inconclusive, it is better not to harvest if one is relying solely on the Allen test. The positive predictive accuracy of Allen’s test is low. If one is willing to accept a not infrequently false-positive test result and to exclude these patients for radial artery harvest, then the Allen test is a satisfactory, though not ideal, gross screening tool.
The issues are whether to use some other more objective test of collateral circulation and palmar arch continuity sometimes or all the time, what test, and what testing protocol. Plethysmography and Doppler echo techniques may prove useful. In regard to pulse oximetry, it should be pointed out that a drop in oxygen saturation lags the onset of ischemic perfusion and is therefore not a useful indicator. Use of objective testing modalities minimizes the likelihood of encountering hand ischemia after radial artery harvest, though clearly these tests currently are not foolproof. As no test has proved to be predictive of the occurrence of hand ischemia and as it may be difficult if not impossible to prove, in the United States, the Health Care Financing Administration will not reimburse for preoperative testing.
Whatever objective testing method is developed, the equipment should not be unwieldy and expensive, and testing should not be time-consuming or difficult to perform. The challenge is to identify the test and the testing protocol, its sensitivity, specificity, and positive and negative predictive accuracy.
Related Article
Ann. Thorac. Surg. 1999 67: 535-536.
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