|Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.|
| Ultrasound Doppler devices convert sound waves reflected by columns of moving blood cells into an audible signal or wave form pulse tracings.5,6 The Doppler probes may be intermittently or permanently placed on the tissue's surface3 or implanted on or around vessels.7-9 Intermittent Doppler examinations can be misleading when they pick up signals from adjacent or underlying vessels. Permanent probe placement can be complicated by dislodgement with loss of signal. Perivascular probes may cause arterial compression or, when removed, pedicle injury. 7,8
Electromagnetic flowmetry permits direct, continuous monitoring of pedicle blood flow. The technique requires that a flow probe containing an electromagnetic field be placed around a vessel. The system then measures the electrical potential generated by a column of blood passing through the magnetic field.10 The strength of this potential is proportional to the volume of blood flow. Requirements for successful preparation and placement of the probe as well as calibration and maintenance of the flowmeter are complicated and may render this device impractical for clinical use.
PULSE VOLUME RECORDER (PVR)
PVR measures air displacement changes that occur when a cuff is inflated to a known pressure (40 mm Hg) around a digit containing a pulsatile vessel.11 The pulsations are recorded by a sensitive plethysmograph. PVR provides reliable information, but cuffs may not be practical for multiple digit replants or short replanted parts.
Thermocouple probes detect heat conduction generated by a moving column of blood in a vessel.12 Comparison of temperatures proximal and distal to an anastomosis provides a means of detecting blood vessel obstruction. A stagnant column of blood dissipates heat rapidly, whereas active blood flow maintains a uniform temperature. This technique requires placing the probes around pedicle vessels. Vascular compression, erroneous readings secondary to probe malposition, and vascular trauma during removal of the probe are potential complications.
These techniques permit measurement or inference of the general perfusion of the monitored tissue.
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