Single Shot vs 24hr vs 48hr Continuous Adductor Canal Block After TKA

If the patient is willing to participate and signs the consent, he/she will be randomized to one of the three treatment groups:

1. Single shot block
2. 24 hour catheter
3. 48 hour catheter

The choice of anesthetic technique will be at the discretion of the anesthesiologist. In our institution we usually advocate for spinal anesthesia for total knee arthroplasty. All patients will receive their multimodal perioperative pain protocol (MP3) medication as per protocol in the patient receiving area (400 mg of gabapentin, 200 mg of Celecoxib, and 1gm of acetaminophen).

Patients will be monitored during block performance with standard ASA monitors. All patients will be receiving 2 L of oxygen via a nasal cannula. Sedatives will be titrated to effect. Midazolam 1-2 mg, and fentanyl 50-100 mcg will be used for sedation.

Block time out will be preformed according to standard operating procedure. All blocks will be done under ultrasound guidance. Sonosite S nerve machine will be used with a high frequency linear (HFL) US probe with 6-13 MHZ frequency. Both single shot and continuous adductor canal block will be performed according to the standard operating practices in our department 4. Ultrasound survey at the medial part of the thigh will take place, halfway between the superior anterior iliac spine and the patella. In a short axis view, the femoral artery will be identified underneath the sartorius muscle, with the vein just inferior and the saphenous nerve just lateral to the artery. The needle will be introduced in-plane and 2 to 3 mL of local anesthesia bolus will be used to verify correct placement of the needle in the vicinity of the saphenous nerve in the adductor canal.

For single shot blocks: A bolus of total volume of 20 ml of ropivicaine 0.5% will be injected through the needle.

For the continuous block: The catheter will be introduced and advanced 2-3 cm beyond the tip of the needle under ultrasound visualization. The needle was withdrawn over the catheter. Injection of a bolus of 5 ml of ropivacaine 0.5% will take place through the catheter while observing the spread of local anesthetic under ultrasound. The catheter hub will be affixed to the upper lateral thigh with sterile occlusive dressings and an anchoring device.

Block success will be defined as a change in cutaneous sensation to touch with an alcohol pad in the saphenous nerve distribution over the medial leg within 30min after injection. Subjects with successful catheter placement per protocol and nerve block onset were retained in the study. Subjects with a failed catheter insertion or misplaced catheter indicated by a lack of sensory changes had their catheter replaced or were withdrawn from the study.

At the conclusion of surgery, the catheters will be connected to a pump that will infuse local anesthetic. Ropivicaine 0.2% at 8 ml/hour. In the postoperative anesthesia care unit, intermittent boluses of hydromorphone will be used as needed. Postoperative analgesia will follow the MP3 protocol. Drugs that are used for the multimodal analgesia protocol include acetaminophen (1 gm every 8 hours for 72 hours), celecoxib (200 mg every 8 hours for 72 hours), Gabapentin (300 mg every 8 hours for one week if the patient is opioid naïve and for two weeks if patients are opioid tolerant), and oxycodone (5-10-15 mg oral as needed every 4 hours for pain based on patient reported pain score).

All patients will receive prophylaxis for postoperative nausea and vomiting (PONV) during surgery. The protocol for prophylaxis against PONV include administration of 4 mg of dexamethasone after induction of anesthesia and 4 mg of ondansetron 20 minutes before recovery from anesthesia. Dexamethasone is withheld if the patient has poorly controlled diabetes mellitus (DM). Uncontrolled DM will be defined as random blood glucose above 250 mg/dl.