Non-invasive estimation of peripheral resistance using Pulse Generated Runoff before femorodistal bypass

The measurement of peripheral resistance (PR) is a useful technique for predicting the outcome of femorodistal bypass. In an attempt, noninvasively, to predict PR, Pulse Generated Runoff (PGR) was used to assess 35 consecutive patients undergoing femorodistal non-reversed vein bypass for critical ischaemia. The PGR subscores (anterior tibial, posterior tibial, peroneal, pedal arch status were correlated against the measured PR. Using multiple linear regression three resistance values were derived for runoff at different levels: (1) a single calf vessel (R1); (2) distal popliteal artery (R3); (3) irrespective of the level (R0). There was good agreement between the predicted resistances R0, R1 and R3 and the measured PR. In the single calf vessel group (R1) the limits of agreement (-0.41 to +0.39) and 95 per cent confidence interval (-0.16 to +0.14) with the measured PR were better than in the R0 and R3 groups. These levels of agreement are small enough to replace the measured PR with the predicted PR method. Using the appropriate resistance equation in a further prospective series of 14 cases, there was agreement between the predicted and measured PR (limits of agreement -0.67 to +0.41; 95 per cent confidence interval -0.26 to +0.15). These results confirm the value of PGR in the assessment of critically ischaemic limbs particularly with a single calf vessel. Calf vessel continuity with the pedal arch appears to be a major determinant of PR, particularly in the isolated calf vessel group. A non-invasive resistance value can be derived which will predict the intraoperative peripheral resistance and should help predict subsequent graft outcome.