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

Objective: 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.

Methods: 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 pressures 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).

Results: An ankle pressure of ≤ 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% accurately classified legs. The odds ratio for invasive therapy given a pO₂ or toe pressure above the cut-off value was 14.

Conclusion: Ankle blood pressure measurements have limited diagnostic value. Adding toe and/or oxygen pressures enhanced the detection of CI requiring invasive therapy.