The presence of palpable pedal pulses in a warm, pink limb is a reliable indicator that arterial flow is adequate to support healing of a below-knee amputation. Conversely, an absent ipsilateral femoral pulse is associated with an 80% chance of failure of a primary below-transtibial amputation. The presence of a palpable pulse in the major artery immediately above the amputation site indicates a high probability of amputation primary healing, and absence of a palpable pulse in these locations significantly reduces the likelihood of amputation healing.
Measurement of Blood Pressure
Measurement of blood pressure in the thigh and ankle with a Doppler ultrasound device and pneumatic cuffs is a useful for determining the level of amputation. Readings are not accurate enough, however, to be the sole basis for decision making. Segmental blood pressures are fallible, and blood pressure in the ankle is an unreliable guide to healing in the foot if the tibial vessels are calcified and cannot be compressed by the cuff, a condition reported in at least 20–25% of diabetics. In addition, significant lower extremity edema hinders accurate measurements. The notion that above-knee amputation is mandatory if the blood pressure in the ankle is below 60 mm Hg is unwarranted. This technique does not adequately demonstrate collateral circulation, and healing is common even when ankle pressures are extremely low or undetectable. Absence of an arterial flow signal in the popliteal space, however, reliably predicts that transtibial amputation will fail to heal.
Oxygen Tension Measurements
Transcutaneous measurement of oxygen tension is another guide to healing. A transcutaneous PaO2 of zero indicates a high probability that healing will be unsatisfactory at that site, whereas a PaO2 above 40 mm Hg indicates that good healing is likely. Transcutaneous PaO2 measurement is noninvasive and very reproducible. Disadvantages of the technique are the expense of the equipment and the time required for examination (about 30 minutes per site). It is important to heat the skin to 44 °C, which causes a temperature-dependent microstructural change in the lipid phase of the stratum corneum from solid to liquid.
Other Measures of Skin Perfusion
Multiple techniques are available to assess the skin perfusion for determination of the optimal amputation level. Most of these methods have not gained widespread use in clinical practice. Problems with these techniques include impracticality, expense, and technical difficulty—and inconsistent confirmatory studies.
Laser Doppler Studies
Laser Doppler is a noninvasive technique to determine the velocity of blood flow. This method is popular but has not been extensively used in North America. Absence of flow reliably predicts nonhealing, but specific flow velocities have not been differentiated.
Intravenous injection of fluorescein dye followed by measurements of skin fluorescence with a fluorometer have been reported to predict healing with 80% accuracy. Fluorometers are commercially available, but this technique has not gained widespread application.
Infrared thermography has been correlated with skin blood flow. A single report demonstrated a 94% positive predictive value but only an 11% negative predictive value.
Arteriography provides anatomic, not physiologic, information. It assesses feasibility of vascular reconstructions but is of little value in selecting the amputation site because findings do not correlate with circulation to the skin. Arteriography provides anatomic information, not physiologic data.