Lower Extremity Near-infrared Spectroscopy After Popliteal Block For Orthopaedic Foot Surgery

BACKGROUND: Noninvasive measurement of cutaneous tissue oxygenation using near-infrared spectroscopy (NIRS) has become common in peri-operative care. Following institution of peripheral nerve blocks, neurovascular alterations in the blocked region have been described. OBJECTIVE: The primary aim of this study encompassed the assessment of the influence of a popliteal block on changes in regional oxygen saturation (SrO(2)), and the location of most prominent changes. METHOD: We conducted a prospective randomised controlled trial. Hundred twenty patients who received a popliteal block for foot surgery were included. Popliteal block was performed under echographic guidance. The patients were randomized in 3 groups according to the location of the SrO(2) electrodes on the legs. Bilateral SrO(2) measurements were performed simultaneously. SrO(2) in the operated leg and in the control leg was measured at baseline and 1, 5, 10, 15, and 30 minutes after the perineural injection. We quantified the evolution in SrO(2) by calculating over time the differences in SrO(2) values between the operated and control leg (=ΔSrO(2)). RESULTS: At 30 minutes, ΔSrO(2) increased significantly (p<0.05) at the plantar side of the foot (11.3% ± 2.9%), above the ankle (4.9% ± 1.3%) and the popliteal fossa (3.6% ± 1.2%). CONCLUSION: At 30 minutes after institution of the popliteal block, ΔSrO(2) was most prominent at the plantar side of the foot as compared with measurement performed above the ankle or under the knee.