The efficacy of automated intermittent boluses for continuous femoral nerve block: a prospective, randomized comparison to continuous infusions.

STUDY OBJECTIVE: To determine whether an automated intermittent bolus technique provides enhanced analgesia compared with a continuous infusion for femoral nerve block.

DESIGN: Prospective, single-blinded, randomized controlled trial (ClinicalTrials.gov Identifier: NCT01226927).

SETTING: Perioperative areas and orthopedic surgical ward of a university hospital.

PATIENTS: 45 ASA physical status 1, 2, and 3 patients undergoing unilateral primary total knee arthroplasty.

INTERVENTIONS: All patients received single-injection sciatic and femoral nerve blocks plus femoral nerve catheter placement for postoperative analgesia. Patients were randomly assigned to an automated intermittent bolus (5 mL every 30 min with 0.1 mL/hr basal rate) or a continuous infusion (10.1 mL/hr) delivery method of 0.2% ropivacaine.

MEASUREMENTS: Consumption of intravenous patient-controlled analgesia (IV-PCA) and visual analog scale (VAS) pain scores were assessed postoperatively at set intervals until the morning of postoperative day (POD) 2.

MAIN RESULTS: The mean (SEM) cumulative IV-PCA dose (mg of hydromorphone) for the 36-hour postoperative interval measured was 12.9 ± 2.32 in the continuous infusion rate group (n = 20) and 7.8 ± 1.02 in the intermittent bolus group [n = 21, t(39) = 2.04, P = 0.048; a 39 ± 14% difference in total usage]. Pain scores were statistically significantly lower in the intermittent bolus group in the afternoon of POD 1 (t(39) = 2.47, P = 0.018), but were otherwise similar.

CONCLUSIONS: An automated intermittent bolus infusion technique for femoral nerve catheters is associated with clinically and statistically significantly less IV-PCA use (ie, an opioid-sparing effect) than a continuous infusion technique.