Toe pressure measurements compared to ankle artery pressure measurements

The Trans-Atlantic Inter-Society Consensus (TASC)-recommended absolute toe pressure is < 30-50 mm Hg for definition of chronic critical limb ischemia (CLI). Toe pressures can be measured by different techniques. The authors analyzed the clinical use of the Doppler technique and an automatic device with optical sensors and estimated their value in documentation of chronic critical limb ischemia compared to ankle artery pressures. Three different investigations were performed: (1) In 16 healthy subjects the digital artery pressures were measured by using 3 different optical sensors (transmission, reflection, and microcirculation sensor) and compared to the systolic brachial pressure. (2) In 50 patients with and without peripheral arterial occlusive disease the toe pressures at digits 1 and 2 of both feet were determined by Doppler technique (8 MHz) and by optical sensors (cuff width constant 1.5 cm) and were compared to the ankle artery pressure determined by Doppler technique. (3) In 175 patients the toe pressures were measured at 1 toe and the ankle artery pressures were determined. In this group they estimated the clinical use of the toe pressure in regard to the definition of CLI (toe pressure < 50 mm Hg) compared to the ankle pressure < 70 mm Hg. The digital artery pressures measured with the different optical sensors, and the systolic brachial pressures were not significantly different and the correlation coefficients were around 0.7. In 21 of 50 patients the toe pressure at D1 and D2 could not be measured by Doppler technique because with the applied cuff no Doppler signal could be detected at the tip of the toe, but in 24 of these 29 patients the optical measurement was possible. Mean toe pressures at D1 were 108 +/- 45 mm Hg and D2 102 +/- 45 mm Hg, which were statistically not different. The correlation coefficient for the highest ankle artery pressure and the highest toe pressure determined by the Doppler technique was 0.389; for the highest ankle artery pressure and the toe pressure measured by the optical sensors it was 0.369, and for the toe pressures measured by Doppler technique and the optical sensors it was 0.506. Defining systolic ankle artery pressure < or = 50 to 70 mm Hg as the golden standard for CLI, the sensitivity of optical toe pressure measurement for the detection of CLI was 8%, the specificity was 96%, the positive predictive value 12%, and the negative predictive value was 94%. Independent of technique the absolute systolic toe pressures did not correlate with the absolute systolic ankle pressures. The optical measurement was more suitable for toe pressure measurement because it could be used in 90% of all patients. All in all, toe pressure measurements are more useful to exclude CLI than to prove it.