Commonly used in patients with diabetes and peripheral arterial disease, a toe brachial pressure index (TBPI) is a noninvasive way of determining arterial perfusion in feet and toes. A Doppler device and a sphygmomanometer are used to measure systolic pressure in the arm and the great toe. The TBPI is a ratio of these two readings. (See Calculating Toe Brachial Pressure Index.)
What are the pros and cons of TBPI compared with traditional techniques?
Calcification, which commonly occurs in people with diabetes or renal disease, can lead to incompressible arteries in the ankle, which makes ankle pressures difficult to measure accurately by traditional techniques. Because calcification occurs less commonly in digital arteries, a TBPI is a more reliable indicator of peripheral arterial disease than an ankle brachial index.
A disadvantage of TBPI is that it may not reveal an arterial occlusion in the tip of the toe because the sphygmomanometer cuff is placed at the base of the toe. And because TBPI is an indirect assessment of perfusion, it can’t pinpoint the location of arterial occlusion.
What preparation is needed to measure TBPI?
First, ensure the patient has avoided tobacco and caffeine for 30 minutes before the procedure; both can increase blood pressure. Next, gather the equipment: a handheld, battery-operated Doppler ultrasound device with a probe; a sphygmomanometer with an arm cuff 5 inches (12.5 cm) wide and 9 inches (22.5 cm) long, and a toe cuff 1 inch (2.5 cm) wide and 5 inches long; room-temperature ultrasound transmission gel; and gauze. (Note: Some toe cuffs contain latex.)
Place the patient supine with the toes level with the heart. Cover the patient with a blanket if the room is cool. While the patient rests for 10 minutes, explain the procedure. Then, follow the steps shown in these photographs.
Brooks B, Dean R, Patel S, Wu B, Molyneaux L, Yue DK. TBI or not TBI: that is the question. Is it better to measure toe pressure than ankle pressure in diabetic patients? Diabet Med 2001; 18:528–32.
Leskinen Y, Salenius JP, Lehtimaki T, Huhtala H, Saha H. The prevalence of peripheral arterial disease and medial arterial calcification in patients with chronic renal failure: requirements for diagnostics. Am J Kidney Dis 2002; 40( 3):472–9.
Calculating toe brachial pressure index
Divide the toe’s systolic pressure by the brachial systolic pressure in the arm with the higher pressure. A toe brachial pressure index (TBPI) less than 0.64 warrants further evaluation and testing.
Toe systolic pressure ÷ brachial systolic pressure = TBPI
For example, if right brachial systolic pressure is 120 mm Hg, left brachial systolic pressure is 110 mm Hg, and toe systolic pressure is 60 mm Hg, the TBPI calculation would be as follows: 60 mm Hg ÷ 120 mm Hg = 0.50