We determined how often and for how long usable pressure waveforms were unavailable from a radial intraarterial pressure cannula during anesthesia and surgery in 41 patients. During cardiac surgery with a continuous flush system, usable arterial pressure was unavailable 8.7% of the time. It was unavailable 9.1% of the time during noncardiac surgical procedures with a continuous flush system, and 14.7% of the time in system without continuous flush. Thus, the use of a continuous flush device improves intraarterial pressure availability. Artifact is the principal contributor to unavailability, followed by flushing and blood sampling. With rare exceptions the use of a Riva-Rocci cuff for occasional return-to-flow maneuvers on the same arm as the intraarterial cannula reduces intraarterial pressure availability only slightly, certainly not enough to detract from its usefulness in providing an estimation of systolic pressure during intraarterial pressure monitoring.