Can the Association of Dexamethasone and Local Anaesthetic in a Single-shot Femoral and Sciatic Nerve Block Improve Analgesia Postoperatively in Patients Submitted to Total Knee Arthroplasty

All blocks are performed using nerve stimulation technique. For the SSFNB, the paravascular approach will be used to identify the femoral nerve.15 A positive location is considered when quadriceps contraction (patellar elevation) is elicited with a current of 0.4 mA or less, and 30mL of ropivacaine 0.375%, with or without 4mg of dexamethasone are injected, according to the randomization.

For the SSSNB the anterior approach will be chosen.16 The common peroneal or the tibial nerves are identified, respectively by dorsiflexion or plantar flexion of the foot, with a current of 0.4 mA or less. Depending on the allocated group, 20mL of ropivacaine 0.2%, with or without 4mg of dexamethasone are then injected. Blocks success should be assessed by the absence of thermal sensitivity on the anterior region of the thigh and the dorsum of the foot 10 minutes after the block.

The participating anaesthesiologists may use the ultrasound for visual guidance but should also use the nerve stimulator in order to maintain the homogeneity of the procedure.

Patients will then have an intravenous induction to general anesthesia, being the maintenance assured with either Desflurane or Sevoflurane. Thirty minutes before the end of the procedure all patients are given paracetamol 1000mg and ketorolac 30mg. Total doses of intraoperative analgesics are recorded.

Before surgery all patients will be explained how to use the PCA, which is connected after arrival to the post-anesthesia unit (PACU). The PCA is programmed for 1mg bolus as required by the patient, with a lockout period of 7 minutes. In what concerns the remaining post-operative analgesia, both groups are prescribed paracetamol 1000mg q8h, diclofenac 50mg q12h, and as rescue strategy, tramadol 100mg q6h.