Reference Probe for TcpO(2) at Rest: A Systematic Review

(1) Background: Transcutaneous oxygen pressure (TcpO(2)) is used to determine the severity of lower extremity arterial disease (LEAD). Many authors used a ratio of limb to chest TcpO(2), also called the regional perfusion index (RPI), which should be independent of variations in oxygen delivery and reflective of local limb oxygen supply. The relevance of a reference probe-positioned TcpO(2) electrode is debated. We aimed to review the relevance of the reference probe in previous studies using rest TcpO(2). (2) Methods: We searched Medline and the Cochrane Central Register of Controlled Trials on 22 September 2022 using keywords related to TcpO(2), reference probe and LEAD. (3) Results/Discussion: Fifteen studies were included in the review. Nine studies investigated LEAD severity (n = 9), amputation healing predication (n = 4), surgical outcome prediction (n = 2), therapeutic effect (n = 3) and difference according to diabetic status (n = 1). Four studies investigated more than 1 indication. Among 12 (16.7%) studies using RPI, only two authors found a benefit of using RPI instead of absolute TcpO(2). Using only univariate analysis, one author reported that RPI was significantly related to viability at 1 year, while distal TcpO(2) was not, on 13 limbs. The following year, the same author published a new study including 118 limbs that reported that RPI and absolute TcPO(2) were both prognostic factors for limb viability at 1 year using a multivariate model. (4) Conclusions: Only one study firmly supporting the use of RPI, calculated using a reference probe on the arm, to predict BKA healing. Prospective studies are needed to validate this result; for other indications there is insufficient data supporting the use of a TcpO(2) reference probe at rest.