Doppler velocimetry can be used before below the knee amputation to predict if the operative wound will heal. Moving red blood cells in blood vessels cause a doppler shift of incident light, which correlates with the velocity of blood flow.
Procedure: Laser doppler velocimeter is used to measure cutaneous blood flow in the study region. This is continuous and noninvasive.
Sites tested:
(1) anterior calf
(2) posterior calf
(3) upper arm
critical calf reading in mV =
= minimum (anterior calf reading in mV, posterior calf reading in mV)
calf-to-brachial index =
= (critical calf reading in mV) / (upper arm reading in mV)
Interpretation:
• If both the anterior or posterior calf reading is >= 20 mV, then the wound will heal in most (96%) patients.
• If either the anterior or posterior calf reading is < 20 mV, then the wound will probably not heal.
• The calf-to-brachial index does not offer more accuracy than the critical calf reading, but wounds that failed to heal show a lower index.
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