Plasma concentrations of ropivacaine following ultrasound-guided or nerve-stimulator-guided femoral nerve block: A prospective randomised study.

Objective: Our aim was to establish a plasma concentration curve for ropivacaine following femoral nerve blockade and to ascertain whether the resulting plasma concentrations differ significantly depending on whether neurostimulation (NS) or ultrasound (US) guidance was used.

Methods: Sixteen male and female subjects aged 18 to 80 who were scheduled to undergo unilateral total knee replacement or anterior cruciate ligament reconstruction under general or spinal anaesthesia, and for whom a femoral nerve block was indicated for postoperative analgesia, were enrolled in this prospective, randomised study. Patients were randomised to undergo either US or NS-guidance femoral nerve blocks.