Adding clonidine to the induction bolus and postoperative infusion during continuous femoral nerve block delays recovery of motor function after total knee arthroplasty

We evaluated the effects of adding clonidine for continuous peripheral nerve infusions. Sixty patients undergoing total knee arthroplasty under combined single-injection sciatic block and continuous femoral infusion were randomly allocated to three groups: block induction with 0.75% ropivacaine followed by 0.2% ropivacame (group control; n +/- 20); block induction with 0.75% ropivacaine and 1 mug/kg clonidine followed by 0.2% ropivacaine (group cloni-bolus; n = 20), and block induction with 0.75% ropivacaine and 1 mug/kg clonidine followed by 0.2% ropivacaine with 1 ug/mL clonidine (group cloni-infusion; n = 20). After surgery, continuous femoral infusion was provided with a patient-controlled infusion pump (basal infusion rate, 6 mL/h; incremental dose, 2 mL; lockout time, 15 min). The median (range) onset time of surgical block was 15 min (5-30 min) in group control, 10 min (5-35 min) in group cloni-bolus, and 10 min (5-30 min) in group cloni-infusion (P = 0.07). No differences were reported among groups in the degree of pain measured with the visual analog scale. The total consumption of local anesthetic solution after a 24-h infusion was 170 mL (144220 mL) in group control, 169 ml, (144-260 mL) in group cloni-bolus, and 164 mL (144-248 mL) in group cloni-infusion (P = 0.51); after the second day of infusion, total consumption was 168 mL (144-200 mL) in group control, 156 mL (144-288 mL) in group clonibolus, and 150 mL (144-210 mL) in group cloni-infusion (P = 0.48). Hemodynamic profiles and sedation were similar in the three groups. Motor function impairment after 48 h of infusion was observed in 27% of cloni-infusion patients but in only 6% of both the control and cloni-bolus groups (P = 0.05). We conclude that adding clonidine 1 mug/mL to local anesthetic for continuous femoral nerve block does not improve the quality of pain relief but has the potential for delaying recovery of motor function.