Falsely elevated ankle pressures in severe leg ischaemia: The pole test—An alternative approach
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Ankle-branchial pressure indices (ABPIs), measured by sphygmomanometer and Doppler probe, are an accepted index of chronic leg ischaemia. However, tibial artery sclerosis or calcification decreases compliance, producing falsely elevated cuff occlusion pressures. Arterial cannulation is invasive and impractical, but by elevating the foot and measuring the height at which the Doppler signal disappears, ankle systolic pressure in mmHg can be derived. Using an 8MHz Doppler apparatus and calibrated pole, ankle systolic pressures measured by sphygmomanometer and elevation were compared in 49 severely ischaemic legs (40 patients). ABPIs were derived by dividing ankle systolic pressure by brachial pressure. Median (interquartile range) ABPI assessed by sphygmomanometry was 0.46 (0.35-0.56). Median ABPI measured by leg elevation was significantly lower at 0.21 (0.14-0.30), p < 0.0001, Wilcoxon. In 20 patients undergoing in situ vein bypass grafting, direct transducer-derived pressure measurements were obtained. Median ABPI for this method was 0.15 (0.11-0.27). No significant difference was found when compared with ABPIs derived by elevation, median 0.2 (0.13-0.31), p = 0.324, however median ABPI measured by sphygmomanometry was significantly higher at 0.37 (0.27-0.6), p = 0.0008. Correlation of elevation with transducer-assessed pressure measurements (r = 0.88) was closer than with cuff-derived measurements (r = 0.69). Pressures derived by leg elevation provide a more accurate index of severe leg ischaemia than sphygmomanometry, although the technique is limited to assessing pressures of less than approximately 60 mmHg. Falsely elevated ABPIs may underestimate the extent of disease in patients assessed for vascular reconstruction.
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