Small dose of clonidine mixed with low-dose ropivacaine and fentanyl for epidural analgesia after total knee arthroplasty

Background. We studied whether a small dose of clonidine added to a ropivacaine-fentanyl mixture improves epidural analgesia without provoking side effects typically related to larger amounts of epidural clonidine. Methods. In this randomized, double-blinded study, patients (less than or equal to85 yr, ASA I-III) underwent total knee arthroplasty (TKA) performed under spinal anaesthesia. After the operation, patients received an epidural infusion consisting of ropivacaine 2 mg ml(-1) and fentanyl 5 mug ml(-1) either without (Group RF, n=33) or with clonidine 2 mug ml(-1) (Group RFC, n=36). The infusion rate was adjusted within the range 3-7 ml h(-1). Results. Average rate of infusion was slightly smaller in Group RFC than in Group RF (mean (sd) 4.7 (0.72) vs 5.2 (0.8) ml h(-1), P=0.004). Compared with the RF group, patients in the RFC group required significantly less rescue pain medication, that is i.m. oxycodone (median (25th, 75th percentile) 0 (0, 7) vs 7 (0, 12) mg, P=0.027). Arterial pressure and heart rate were slightly lower in Group RFC throughout the study period (mean difference between the groups 5 mm Hg (P<0.002) and 3 min(-1) (P=0.12), respectively). The groups did not differ statistically with respect to nausea, motor block, and sedation. Conclusions. The small amount of clonidine added to the low-dose ropivacaine-fentanyl mixture reduced the need for opioid rescue pain medication after TKA. Clonidine slightly decreased arterial pressure and heart rate without jeopardizing haemodynamics. Otherwise, the side effect profiles were comparable in both groups.