Implantable venous Doppler microvascular monitoring: laboratory investigation and clinical results

The purpose of this study was to compare the sensitivity of a 20-mHz ultrasonic Doppler device to detect microvascular thrombosis placed on the vein with that placed on the artery. A feasibility study in animals preceded a comparative clinical study in patients. Six rabbits were used to develop a bilateral hind limb perfusion model. The femoral artery and vein were isolated, and Doppler probes were affixed to each. Clamping of the artery and vein separately was followed by simultaneous measurements in both vascular probes using audio signals and strip-chart recordings. A total of 48 measurements were obtained. Probes placed on the artery immediately detected an arterial occlusion but continued to record pulsation for 220 +/- 40 minutes following venous occlusion. Mean arterial waveform amplitudes diminished by 50 percent of initial values 1 hour following venous occlusion but showed little change thereafter when followed for 6 hours. By contrast, probes placed on the vein detected venous occlusion immediately and arterial occlusion at 6 +/- 2.4 minutes (p < 0.001). Over a 4-year period, 133 patients had free-tissue transfers monitored by implantable 20-mHz ultrasonic Doppler devices: 30 arterial and 103 venous. The arterial monitors detected vascular thromboses in 4 of 6 patients, with 3 flaps salvaged. Venous Doppler monitors detected 16 of 16 thromboses, with 12 flaps salvaged. Six patients had probe/machine malfunctions during their postoperative course and were monitored by clinical means thereafter without thrombosis. There were two late extrusions of the probe cuffs implanted in subcutaneous locations. No adverse effects on the flap vessels were noted in the study. The 20-mHz ultrasonic Doppler device is an effective monitor of blood flow in microvascular anastomoses. When it is placed on the vein, a greater degree of sensitivity is demonstrated, particularly to venous obstruction, compared with probes monitoring arterial flow. The device has been reliable in a variety of institutions and nursing units without need for intensive care monitoring and has resulted in an increased salvage rate for flaps experiencing vascular thrombosis.