The posterior lumbar plexus (psoas compartment) block and the three-in-one femoral nerve block provide similar postoperative analgesia after total knee replacement.

PURPOSE: To compare the efficacy of a continuous posterior lumbar plexus (PSOAS) block to a continuous three-in-one femoral nerve (FEM) block in patients undergoing primary total knee replacement (TKR). METHODS: Sixty patients were randomly allocated to receive iv patient-controlled morphine analgesia (PCA), PCA plus a continuous FEM block with 30 mL ropivacaine 0.5% and epinephrine 1:200,000 bolus followed by an infusion of ropivacaine 0.2% at 12 mL.hr(-1) for 48 hr, or PCA plus a continuous PSOAS block with the same bolus and infusion regimen as the FEM group. Postoperative morphine consumption, verbal analogue scale pain scores at rest and during physiotherapy, and evidence of sensory and motor blockades were noted. RESULTS: Both regional techniques significantly reduced 48 hr morphine consumption (FEM 37.3 +/- 34.7 mg, P = 0.0002; PSOAS 36.1 +/- 25.8 mg, P < 0.0001) compared to PCA (72.2 +/- 26.6 mg). Pain scores at rest, six and 24 hr after TKR were lower in the FEM and PSOAS groups compared to the PCA group (P < 0.0001). Although sensory and motor blockades of the obturator nerve were achieved more often in the PSOAS group than in the FEM group (P < 0.0001), morphine consumption and pain scores did not differ between the two groups. CONCLUSION: Both continuous PSOAS block and continuous three-in-one FEM block provided better analgesia than PCA but no differences were seen between the two regional techniques.

Ropivacaine plasma concentrations are similar during continuous lumbar plexus blockade using the anterior three-in-one and the posterior psoas compartment techniques.

PURPOSE: To compare ropivacaine blood concentrations obtained after a continuous lumbar plexus block performed either by the anterior three-in-one femoral (FEM) technique or the posterior (psoas compartment; PSOAS) technique. METHODS: As a substudy of a larger clinical trial, 24 patients were randomly allocated to receive a bolus of 30 mL of ropivacaine 0.5% plus epinephrine 1:200,000 followed by an infusion of ropivacaine 0.2% at 12 mL.hr(-1) for 48 hr via one of the two continuous lumbar plexus block techniques. Plasma ropivacaine concentrations, up to 48 hr, were measured by high performance liquid chromatography. RESULTS: Mean plasma ropivacaine concentrations were higher in the PSOAS group at 15, 30, and 60 min (two-way analysis of variance, P < 0.0001) but areas under the curve were similar for both groups (FEM 452.4 +/- 253.6 mg.hr(-1).L(-1), PSOAS 433.4 +/- 99.0 mg.hr(-1).L(-1)). Mean maximal plasma concentrations were observed at 48 hr and were comparable for the two techniques (FEM 2630.9 +/- 1470.3 ng.L(-1), PSOAS 2325.1 +/- 604.2 ng.mL(-1)). There was no correlation between blood concentrations at 48 hr and body weight (r2 = 0.085, P = 0.21). One patient in the FEM group achieved a concentration of 6201 ng.mL(-1) at 48 hr. CONCLUSIONS: Although the posterior PSOAS block results in higher early plasma concentrations of local anesthetic than the anterior three-in-one FEM block, both techniques are equivalent with regards to their potential toxicity when a continuous infusion is administered. Local anesthetic accumulation occurs with an infusion of ropivacaine 0.2% at 12 mL.hr(-1) and can lead to potentially dangerous concentrations at 48 hr.