Concentration Effect of Local Anesthetics on Femoral Nerve Block Efficiency

Concentration-Volume Relationship of Bupivacaine in Femoral Nerve Block Efficiency for Postoperative Analgesia in Primary Total Knee Arthroplasty: A Randomized Controlled Double Blind Clinical Trial

US-guided femoral nerve block is used effectively in post-operative pain management in the surgical treatment of the lower extremity. However, the volume and concentration of the local anesthetic drug to be administered remains controversial. In this prospective, randomized, double-blinded study, patients who underwent unilateral primary total knee arthroplasty and successfully performed spinal anesthesia with standard method and dosage, will be selected for US-guided femoral nerve block after the operation. Patients will be divided into three groups with simple randomization. The First group will be determined as the control group (GCont) and only dressing will be applied to the patients. For second group(G125), 0,125% 20 ml local anesthetic and for the third group (G25), 0,25% 10 ml local anesthetic will be administered to the femoral nerve without changing the drug dose (25 mg bupivacaine). Whether there is a difference between post-op analgesia durations, motor block formation, mobilization time and 90° flexion time between the groups will be investigated.

All patients scheduled for total knee arthroplasty will be evaluated before the operation. Eligible patients will be informed about the study and "Numeric Rating Scale" for pain evaluation. Then, patients will be asked for informed consent. After approval from the local research ethics committee, first patient will be recruited for study and patient's group will be determined by dice roll(1,4: GCont - 2,5: G125 - 3,6: G25). Patients who are scheduled for primary total knee arthroplasty under spinal anesthesia with a planned sensory block level between T4 and T7 dermatomes, will be recruited and assigned to a group. After successfully completed surgery, patients will be administered femoral nerve block or only dressing according to the relevant group. Before femoral nerve block is performed, patients will be re-informed about Numeric Rating Scale(NRS) and will be asked to rate their pain at the moment.

• Control Group(GCont) patients will only be applied sterile dressing for the purpose of blinding the patient and the follow-up physician.
• 0.125% Bupivacaine Group(G125) patients will be administered femoral block with 20 ml 0.125% Bupivacaine by an experienced anesthesiologist.
• 0.25% Bupivacaine Group(G25) patients 10ml will be administered femoral block with 0.25% Bupivacaine by an experienced anesthesiologist.

The procedures will be performed in the operating room under both US and nerve stimulator guidance. Patients will be followed-up in post-anesthesia care unit and in the ward for 48 hours. Scheduled and on-demand(Tramadol) medication for analgesia will be ordered and nurses will be informed about the study. Patients' pain scores and ambulation times will be followed-up by another anesthesiologist and on-demand medication will be recorded and monitored from hospital's computer based hospital management program online. Patients will be followed-up for six months after the surgery in order to explore potential long term benefits and complications.

Inclusion Criteria:

• Patients who are scheduled for primary unilateral total knee arthroplasty under spinal anesthesia
• Patients who has informed consent for study

Exclusion Criteria:

• Patient's refusal to participate
• Patients under 18 years of age
• Patients who are undergoing surgery with an anesthesia technique other than spinal anesthesia for any reason (general anesthesia, laryngeal mask application, etc.)
• Patients with known local anesthetic allergy
• Patients with Body mass index > 35
• Patients diagnosed sepsis and bacteriemia,
• Skin infection at the injection site,
• History of coagulopathy or anticoagulant therapy
• Patients with uncontrolled diabetes ,
• Uncoordinated patients,
• Psychological and emotional lability,
• Surgical intervention longer than 3 hours.
• Patients with pre-operative limitation of movement