Perioperative monitoring of blood flow in femoroinfragenicular vein grafts with Doppler ultrasonography: a preliminary report. A system for monitoring blood flow in femorodistal vein grafts with Doppler ultrasonography in the immediate postoperative period has been developed. Twenty-three grafts have been monitored for periods of up to 72 hours. Seventeen grafts have remained patent at minimum follow-up of 6 months, and six grafts occluded in the immediate postoperative period. Successful Doppler recordings were obtained in 16 successful and all failed grafts. Fast Fourier transform analysis of the Doppler signals was performed, and pulsatility index and time-averaged mean velocity were derived from the spectral information. Successful grafts displayed hyperemic flow with pulsatility index less than 2 and time-averaged mean velocity greater than 10 cm/sec. Failed grafts could be classified in two groups: those that occluded less than 24 hours after operation and those that occluded after 24 hours after operation. Short-term failure was categorized by highly pulsatile flow, with pulsatility index rising rapidly and time-averaged mean velocity falling correspondingly before actual cessation of flow. Delayed failure was less well defined but was suggested by failure to develop, or early deviation from, the hyperemic flow seen in successful grafts. Occlusion was heralded by development of the pulsatile pattern seen in the short-term failure group. 