Patient-initiated mandatory boluses for ambulatory continuous interscalene analgesia: an effective strategy for optimizing analgesia and minimizing side-effects.

BACKGROUND This prospective, randomized study tested the hypothesis that a reduced dose continuous interscalene regimen incorporating a low background infusion with mandatory boluses would provide similar shoulder surgery analgesia compared with a dose regimen incorporating a conventional higher background infusion. METHODS After rotator cuff surgery, patients received via an interscalene catheter, one of two elastomeric pumps, each having a 5 ml per 60 min bolus function and a 2 ml h⁻¹ (n=38) or 5 ml h⁻¹ (n=43) ropivacaine 2 mg ml⁻¹ infusion. Boluses commenced from the onset of pain and continued for >48 h as required (pro re nata, PRN) up to every hour for a numerical rating pain score (NRPS, 0-10) >2. Group 2 ml h⁻¹ received mandatory 6 hourly boluses irrespective of the NRPS. Rescue tramadol was available. Patients were questioned on postoperative days 1 and 2 for treatment effectiveness and side-effects. RESULTS Postoperative pain was similar between the groups [Group 2 ml h⁻¹ day 2 median (IQR) (95% confidence interval of the mean) worst movement pain=4 (1-5) (2.8-4.7) vs 4 (2-5) (3.1-4.6), P=0.99], as were night awakenings and tramadol consumption. Numerically rated numbness and weakness were similar between the groups; however, nine patients (21%) in the 5 ml h⁻¹ group vs one (3%) in the 2 ml h⁻¹ group required a temporary infusion cessation due to side-effects (predominantly hand numbness) (P=0.02). CONCLUSIONS Continuous interscalene ropivacaine 0.2% 2 ml h⁻¹ with mandatory 6 hourly (and PRN) boluses provides similar analgesia after rotator cuff repair but with reduced side-effects compared with 5 ml h⁻¹ with PRN only boluses.