The StenTec™ Gauge provides a method to determine the static intra-access pressure ratio (PIa Ratio) within a fistula or graft. The StenTec Gauge estimates the peak systolic pressure within the fistula or graft by measurement of the distance that the blood–air interface progresses into the tubing of the fistula needle, after the needle is inserted “dry” into the fistula or graft and before the cap is removed from the tubing. The peak systolic pressure is graphically compared with the systolic arterial blood pressure of the patient, to determine PIa Ratio. For best accuracy, the StenTec Gauge should be chosen that best matches the internal volume of the fistula needle tubing (2.3–2.6 ml for 12-inch tubing and 3.6 ml for 16-inch tubing) and the approximate elevation of the city in which it is used (0–1000, 1000–3000, and 3000–6000 feet above sea level). In this article, we explain the rationale for this method of surveillance, evidence for accuracy of the StenTec Gauge, and the correlation of changes in the PIa Ratio to the development of stenosis in a fistula or graft.