The value of non-invasive techniques for the assessment of critical limb ischaemia

Abstract

The European Consensus Document (ECD) defines critical ischaemia (CI) according to clinical (Fontaine) and blood pressure parameters. However, clinical symptoms may be non-specific and CI may exist without severely reduced blood pressures. This study prospectively investigated the additive value of transcutaneous oxygen tension (pO2) and toe blood pressure measurements to assess the presence of CI. Forty-nine patients with 65 legs clinically classified as Fontaine stages III (n = 23) and IV (n = 26) were studied. Ankle and toe systolic blood pressure and pO2 were measured to assess the presence of CI (cut-off values were 50, 30 and 30 mmHg, respectively). The surgeon was blinded for the toe pressure and pO2 results. The treatment received within 1 month after presentation was recorded as being either conservative or invasive (vascular surgery or PTA). An ankle pressure of < or = 50 mmHg classified only 17% of the legs as having CI. By adding toe pressure and pO2, significantly more legs (63%; p < 0.0001) were classified as CI, of which 68% received invasive therapy. Forty-nine percent of the legs with an ankle pressure > 50 mmHg were treated invasively, whereas only 32% of the legs classified as not having CI by means of toe pressure and pO2 underwent invasive therapy. If the need for invasive treatment is used as the "gold standard" for the presence of CI, 54% of the legs would accurately be classified on the basis of the ankle blood pressure. The combination of toe pressure and pO2 would have yielded 71% and the ECD criteria 72% and accurately classified legs. The odds ratio for invasive therapy given a pO2 or toe pressure above the cut-off value was 14. Ankle blood pressure measurements have limited diagnostic value. Adding toe and/or oxygen pressures enhances the detection of CI requiring invasive therapy.