Interscalene perineural ropivacaine infusion:a comparison of two dosing regimens for postoperative analgesia

BACKGROUND AND OBJECTIVS: A continuous interscalene nerve block with a perineural infusion of ropivacaine 0.2% at 8 mL/h has been shown to provide potent analgesia following moderately painful shoulder surgery. However, this high basal rate limits infusion duration for ambulatory patients who must carry the local anesthetic reservoir. We undertook this investigation to determine if the basal rate of an interscalene perineural ropivacaine infusion could be decreased by 50% with a concurrent 200% increase in patient-controlled bolus dose without compromising infusion benefits in ambulatory patients undergoing moderately painful orthopedic shoulder surgery.

Preoperatively, patients (n = 24) received an interscalene perineural catheter and nerve block. Intraoperatively, patients received a standardized general anesthetic. Postoperatively, patients were discharged home with a portable infusion pump delivering ropivacaine 0.2% (500 mL reservoir) with a basal rate of 8 mL/h and a 2 mL patient-controlled bolus available each hour ("8/2" group, n = 12) or a 4 mL/h basal rate and 6 mL bolus dose ("4/6" group, n = 12), delivered in a randomized, double-blinded manner.

Patients in the 4/6 group had higher baseline pain scores only on postoperative day (POD) 2 (P =.011). However, these patients also experienced an increase in breakthrough pain incidence (5.8 boluses/d v 3.2, P =.035) and intensity ("worst" pain = 8/10 v 4/10, P <.05), sleep disturbances (2.0 v 0.0, P <.001), and a decrease in analgesia satisfaction (8 v 10, P =.003). Patients in the 8/2 group exhausted their local anesthetic reservoirs after a median of 61 hours, while the 4/6 group had a median of 131 mL remaining at infusion discontinuation after a median of 75 hours (P <.001).

Following moderately painful ambulatory shoulder surgery, decreasing an interscalene perineural ropivacaine 0.2% basal rate from 8 to 4 mL/h provides similar baseline analgesia and lengthens infusion duration, but compromises other infusion benefits.