P030: IMPACT OF INJECTION PRESSURE ON THE SPREAD OF LOCAL ANESTHETIC DURING ADDUCTOR CANAL NERVE BLOCK
Jonathan D Lin, MD1, Andres Missair, MD1, Yiliam Rodriguez, MD1, Isabel Jaraba, MD1, Lee Kaplan, MD2, Michael Baraga, MD2, Ralf Gebhard, MD1; 1Jackson Memorial Hospital, 2University of Miami Hospital
This is a prospective, randomized, double-blinded human clinical trial that will examine how injection pressure influences the spread of a given volume of injectate in the adductor canal, during adductor canal nerve block. Our study population will be patients undergoing elective anterior cruciate ligament repair in the distal lower extremity and receiving preoperative adductor canal nerve blocks for postoperative analgesia. They will be randomized into two groups of 25 patients each. We speculate that high injection pressures (>20 psi) will lead to greater spread of local anesthetic than low injection pressures (<15 psi) during mid-thigh adductor canal nerve blocks. Our primary endpoint is the spread of injectate, defined as the distance between the uppermost and lowermost limits of spread of local anesthetic as assessed by ultrasound. Our secondary endpoints are the incidence of femoral nerve blocks 30 minutes after block placement, amount of IV opioid administered intraoperatively and postoperatively, preoperative and postoperative pain (Numeric Rating Scale, 0-10), and postoperative physical therapy milestone achievement / quality of life measures.
The adductor canal block of the saphenous nerve is a well-established regional anesthetic technique for knee surgery, and it is recognized for its excellent analgesia with a notable absence of motor involvement, even with continuous perineural local anesthetic infusions. The adductor canal block is known for a high success rate because the adductor canal can be easily visualized with ultrasound at the mid-thigh.1 While the anatomy of the adductor canal has been elucidated by several imaging and cadaveric studies, factors influencing the spread of local anesthetic during adductor canal nerve block are less well understood. Different volumes of local anesthetic injected through myriad anatomic approaches produce variable spread.2 Injectate spread has been shown to span from the femoral triangle to the adductor canal hiatus in a cadaver model with 15 mL of aqueous volume.2 One case report notes motor block of the quadriceps muscle with a mid-thigh approach to the adductor canal block.3 Furthermore, one study reports a staggering 67% incidence of motor weakness associated with a bolus of 15 mL of local anesthetic through an adductor canal catheter placed in the midthigh.4 Additionally, injection pressure has been shown to dramatically influence the spread of lumbar plexus block.5 Sustained injection pressures > 20 psi during intermittent injection of local anesthetic into the lumbar plexus have been associated with a 60% incidence of bilateral femoral nerve block and a 50% incidence of neuraxial block to the level of T11 or above, compared to no spread in the low injection pressure group (< 15 psi).5 Injection pressure has not been studied in adductor canal nerve blocks in human clinical trials. We hypothesize that, for a given injectate volume, the pressure during injection will affect local anesthetic spread towards the femoral triangle (cranially) and the adductor canal hiatus (caudally). We speculate that high injection pressures will lead to greater spread of local anesthetic during mid-thigh adductor canal nerve blocks.