Effects of Catheter Location Relative to Femoral Artery on Postoperative Analgesia for Continuous Adductor Canal Blocks

This will be a single-center, randomized, controlled investigation. Consenting adults undergoing unilateral total knee arthroplasty with a planned adductor canal perineural catheter will be offered enrollment. Study inclusion will be proposed to eligible patients prior to surgery. If a patient desires study participation, written, informed consent will be obtained using a current UCSD IRB-approved ICF. Selection for inclusion will not be based on gender, race, or socioeconomic status.

Following written, informed consent, we will record baseline anthropomorphic information. All subjects will have a peripheral intravenous (IV) catheter inserted, standard noninvasive monitors applied, supplemental oxygen administered via a nasal cannula or face mask, and positioned supine. Midazolam and fentanyl will be titrated for patient comfort, while ensuring that patients remain responsive to verbal cues. The ultrasound will be placed to visualize the short axis (cross-section) of the adductor canal. If both sites (above femoral artery versus between femoral artery and vein) are acceptable for catheter insertion, the subject will be randomized using a computer-generated list (blocks of 8) to one of two treatment groups in a 1:1 ratio using sealed, opaque, consecutively numbered envelopes: (1) above femoral artery vs (2) between femoral artery and vein.

Catheter insertion will adhere to current UCSD standard-of-care. The only difference for subjects participating in the study will be that the specific catheter insertion location will be determined randomly, instead of the physician simply choosing him/herself. All catheters will be placed by a regional anesthesia fellow under the direct supervision and guidance of a regional anesthesia attending. All catheters will be placed using standard UCSD perineural catheter techniques.

The area of insertion will be cleaned with chlorhexidine gluconate and isopropyl alcohol, and a clear, sterile, fenestrated drape applied. The ultrasound probe will be placed to visualize the short-axis (cross-section) of the target nerve(s). A 17-gauge needle (FlexTip, Teleflex Medical, Triangle Research Park, NC, USA) will be used to place all perineural catheters. The catheter-placement needle will be inserted through the skin wheal, advanced in-plane beneath the US transducer and directed to the target nerve as described below:

"Above-the-artery": The needle will be directed below the nerve to about five o'clock of the artery. The needle will then be advanced to twelve o'clock of the artery while opening the adductor canal space with saline until adequate opening of the canal is realized. At that point, the catheter is placed above the artery.