4. Discussion
In this study, we investigated the effectiveness of ACB in patients undergoing arthroscopic knee surgery. We determined that ACBs administered with two different concentrations of bupivacaine showed similar postoperative analgesic effects. And it was shown that both concentration groups had lower use of analgesics compared to the control group.
In arthroscopic knee surgeries, femoral nerve blocks and sometimes as well as obturator nerves and lateral femoral cutaneous nerve blocks were used for postoperative analgesia (14). Nowadays, femoral nerve blockage has been abandoned due to complications such as quadriceps weakness that increase the duration of hospital stay, and distal blocks defined as adductor canal block, saphenous nerve block or subsartorial block have been started to be performed by seeking a more distal block that will provide adequate sensorial blockage and do not cause motor block (7,9,15,16). In this study, we will not discuss the efficiency of ACB, but will compare different concentrations in terms of postoperative analgesia efficiency. This study is not a superiority or non-inferiority study.
In most of the studies investigating the efficacy of ACB, we found that bupivacaine at a concentration of 0.5% was used (17–20), and a concentration of 0.25% was used in a very few (11,12,15,21–23).
Differently, in clinical studies conducted by Leung and Balaban, it was reported that a continuous infusion was performed with a 0.125% concentration of bupivacaine after a 0.25% bupivacaine bolus (24,25).
In our study, we compared 0.25% bupivacaine with 0.16% concentrations. Moura et al.(26) in their work; evaluated the effects of femoral nerve block with bupivacaine in different concentrations in arthroscopic meniscectomy surgery patients, and they reported EC50, which is the concentration that creates analgesic effect in 50% of the patients, and EC90, the concentration that creates analgesic effect in 90% of the patients, as 0.16% and 0.27%, respectively. While determining the methodology of our study, we determined our groups as ACB groups using bupivacaine at 0.16% and 0.25% concentrations, taking into account the findings of this study mentioned. While obtaining these concentrations, we obtained concentrations of 0.25% and 0.16% by diluting 0.5% commercial form of bupivacaine with saline. We determined the fixed volume we apply in ACB as 15 mL in line with anatomical studies (27–30). It should be kept in mind that in ACB performed with higher volumes, the local anesthetic agent may progress in the proximal direction as an overflow and cause quadriceps weakness.As a result of our study, we determined that 0.16% bupivacaine in ACB provides similar efficiency to 0.25% bupivacaine, but we do not recommend it because there is no data to support the use of concentrations less than 0.16% in single shot or as an initial bolus in continue technique (26).
Our study has some limitations. More homogenized randomized controlled trials that address patients undergoing a single arthroscopic knee surgery would be more appropriate. In addition, it is preferable to design a sham group instead of the control group. Although there is no postoperative motor weakness in the patients; we did not routinely perform knee joint motor examination of all patients.