Arterial diagnostics is technically rather easy with a high degree of certainty in interpretation. The Doppler stethoscope is the first-line diagnostic tool to be used in primary care for the detection of ischaemia in the lower extremities.
A reduced (< 0.9) or increased (> 1.3) ankle-brachial index (ABI) found in even one artery of the ankle suggests an increased risk of arterial disease.
Diagnostics of venous insufficiency is relatively easy.
acute pain in the lower extremity (suspected embolism or thrombosis)
distal ulcers in lower extremity
coldness in the feet
fear of gangrene.
Patients to be referred to a vascular surgeon can be selected reliably through examination with a Doppler stethoscope.
Examination procedure
The patient is in a supine position.
Perform the measurements after at least 5 minutes of rest.
Palpate the pulses and the temperature of the limb. Detection of peripheral pulses or a weak pulse does not rule out mild arterial occlusive (ASO) disease, and their absence is insufficient for a diagnosis of vascular obstruction. The detection of a temperature boundary is significant in the diagnosis of embolism.
With the Doppler stethoscope (picture 1), find the pulse sounds of the posterior tibial artery behind the medial malleolus, and the dorsal artery on top of the foot. The sound is best located by moving the sensor of the Doppler stethoscope slowly across the direction of the artery. Occasionally, instead of the dorsal artery it is easier to hear the lateral tarsal artery, which is more laterally situated. The quality of the sound itself will point to a possible occlusion.
Normally, the sound is as sharp as a whipslash and has at least two phases (first a rapid forward flow, then a short backflow caused by the elasticity of the artery; video Normal Pulse Sounds at Pen Doppler Examination). Often a third phase is also heard, in which the blood flows slowly forward during the diastole.
If the obstruction is severe, the sound can be found only by searching carefully for it, and sometimes only with earphones.
Place a sphygmomanometer cuff around the ankle. Increase the cuff pressure rapidly at first until the sound becomes weaker, and then very slowly until the sound disappears (video Normal Pulse Sounds at Pen Doppler Examination). When the pressure is slowly lowered, the sound becomes audible again. The latter pressure reading is the most exact measure of the systolic pressure. However, if the sound is very weak, the reappearance of the sound may be difficult to hear: in such cases the point where the sound disappears when the pressure is increased should be recorded as the systolic pressure. Auscultate both the posterior tibial artery (ATP) and the dorsal foot artery (ADP), and record the readings for both.
If the pressures in ADP and ATP differ, use the higher pressure reading for the assessment of circulation in the lower extremity. When assessing the patient's overall risk of general arterial disease, use the lower reading.
Measure the upper extremity pressure from both upper arms. Record the higher pressure reading. Auscultate the wrist for the pulse sound preferably with a Doppler stethoscope (measurement with an ordinary stethoscope is valid too).
Calculating the index is required in order to determine the extent of the obstruction and to monitor the condition (the ankle pressure will vary from one measurement to another, as will the blood pressure measured from the upper extremity).
If the aim of the diagnostics is merely to confirm or rule out an arterial obstruction and to determine its extent, the ankle and ABI measurement is sufficient. Segmental pressure measurement may be performed later within specialized care.
Interpretation
If the ankle pressure is lower than the upper limb pressure (ABI < 0.9), there is a high likelihood of an arterial obstruction.
Ankle pressure below 50 mmHg and an ulcer in the foot or pain at rest are signs of critical ischaemia, which requires urgent care.
Segmental pressure readings taken above the ankle are usually higher than those at the ankle because of the dampening effect of thicker tissues on the cuff pressure (thigh/ankle = 1.2, equal pressure in the upper arm and thigh usually suggests a proximal obstruction at the iliac level or in the femoral artery). It is important to note bilateral differences.
In about one third of diabetics, the inelasticity of vessel walls may cause too high readings in ankle pressure (ABI >1.3).
The absence of a two-phase pulse sound suggest an obstruction.
In such a case, the ankle pressure can be estimated by elevating the leg and simultaneously observing the moment when the flow sound disappears (the pole test). A height difference of one centimetre from the level of the heart is equivalent to 0.75 mmHg in ankle pressure.
If symptoms suggesting an occlusive arterial disease, a one-phased pulse sound or ABI < 0.9 are found in a diabetic patient with a foot ulcer, he/she should be referred to specialized care for vascular surgical evaluation.
ABI <0.9 or > 1.3 suggests an increase in the overall cardiovascular risk and is an indication to check the patient's risk factors for arterial diseases, to lifestyle counselling and, if needed, to start medication to prevent clinical arterial disease.
Normal valves prevent the backflow of blood in the deep veins. In the Doppler stethoscope, the blood flow in the posterior tibial vein, behind the medial malleolus, sounds like a howling wind. The sound is interrupted for a moment if the calf is pressed by hand, and becomes stronger as soon as the grip is released and the flow increases.
In deep venous insufficiency, as the calf is pressed, a clear hiss caused by the backflow can be heard. The severity of the venous insufficiency can be determined if the thigh is also pressed and the backflow then heard again (video Superficial Venous Insufficiency (Pen Doppler Examination)). This examination also serves as a concrete demonstration to the patient of the cause of the swelling.
Defective segments of a superficial vein may be detected by auscultating the vein and simultaneously compressing the vein repeatedly at different heights proximally to the site of auscultation. Sometimes backflow is detected all the way from the thigh to the ankle (video Superficial Venous Insufficiency (Pen Doppler Examination)).
Colour doppler duplex ultrasound scan is the primary examination in the diagnostics, and invasive treatment must always be based on ultrasonography.
Measuring the ankle pressure with a Doppler stethoscope does not usually frighten a child, and the measurement can be taken while the child is calm. The child may sit on the parent's lap. Blood pressure in the upper extremity is also worth measuring while auscultating the wrist with a Doppler stethoscope.
Interpretation
Normally, a pressure reading taken from the ankle of a sitting child is at least 10 mmHg higher than the pressure from the upper extremity.
If the readings are equal, the measurement should be repeated later.
If the upper extremity pressure is higher than the lower extremity pressure, the child should generally be referred to a specialist for ruling out coarctation.
Measuring blood pressure in a patient in shock
Doppler stethoscopy may be used to measure systolic blood pressure even in a situation where measurement with an ordinary stethoscope or automatic blood pressure meter is unsuccessful. If the Doppler stethoscope includes earphones, they are worth using.