| |
From the time of injury to the time of elective reconstruction, significant vascular alterations may occur in and around the defect. In such cases, a preoperative arteriogram of the site is almost always indicated. Arteriography permits assessment of the quality of the vessel that will receive the donor vessel, determines the exact location of the recipient vessel, precisely outlines the vessel's anatomy, and usually demonstrates its collateral circulation. If a major vessel is to be ligated at the time of the operation, an arteriogram should always be done preoperatively to make sure there is adequate blood supply to the extremity through other vessels. In the traumatic situation, the vascular injury may extend more proximal than the apparent zone of injury. Therefore, proximal intimal damage may be missed at the time of the operation, which may lead to flap failure. In such cases, arteriography can predict problems.11 Long vein grafts must be used to bypass the traumatized area and reach normal recipient vessels. If an arteriogram is performed on both the donor and recipient sites, one can also anticipate any vessel size discrepancy that may make end-to-end anastomosis difficult.
Preoperative arteriography also provides comprehensive information about the location and quality of the venous drainage. This information is helpful postoperatively if a flap appears to be undergoing venous compromise. If the preoperative arteriogram shows good flow in the recipient vein, the problem is either at the venous anastomosis or an intrinsic venous problem within the flap.
|
|
DOPPLER
In 1842, Christian Doppler noted that the pitch of a sound, when emitted or reflected from a moving object, varies with velocity and direction of the object. The range of audible sound waves is 10 to 20,000 H2 per second; ultrasound begins at 700,000 H2 per second and diathermy between 650,000 to 800,000 H2 per second. Sound waves transmitted from most continous-wave Doppler machines are between 2 and 10 mH2. Tissue penetration is inversely related to frequency; therefore, the lower the frequency, the more penetrating the Doppler transmission. Most Doppler probes have a transmitter and a receiver and work on a continuous-wave mode. The transmitted sound is altered by the flowing movement of particles. Through the receiver, these altered sounds can then be heard with a stethoscope or a loudspeaker, or can be permanently recorded by a tracing machine. The ultrasonic Doppler can differentiate between arterial flow (a pulsatile flow), and venous flow (a continuous low-frequency flow that varies only slightly). Venous Doppler sounds can be compared with the sound of wind blowing through a dense forest.12 The quality of the sound can be augmented by pressing on the vascular bed distal to the sensing probe.
next page... |
