The Correlation Between the Diffusion Length of Local Anesthetics in the Subparaneural Space and Duration of Analgesia for Patients Receiving Sciatic Block

Introduction Below-knee surgeries are a common injury of foot, ankle and shin accompanied by severe and difficult-to-treat pain. For patients with Below-knee fractures, surgery is generally the mainstay of treatment to relieve pain and correct foot dysfunction. However, the surgical treatment can result in significant postoperative pain for at least 24 h. In addition, severe pain often leads to physical inactivity, potentially leading to hematoma, incision dehiscence or infection, thereby increasing the difficulty of postoperative nursing and the workload of medical staff. Therefore, effective postoperative analgesia is of great significance to relieve patients' pain and promote postoperative recovery.

Due to various advantages, ultrasound-guided peripheral nerve blocks have gained increasing popularity among anesthesiologists and patients. Popliteal sciatic nerve block is a widely practiced regional anesthesia technique to provide anesthesia or analgesia for below-knee surgeries because it is located superficially and is relatively easy to identify when the popliteal artery is used as an anatomical landmark. The analgesic effect of popliteal approach sciatic nerve block can just last approximately 15 hours after operation even when long-acting local anesthetics are used. But the below-knee surgeries treatment can result in significant postoperative pain for at least 24 hours. Anesthesiologists needs new ways to prolong duration times and decrease the incidence of complications.

One study named the space between paraneural sheath and epimysium of sciatic nerve as the subparaneural space. It has been reported that injection into the subparaneural space has several advantages (improved the quality of the sensory block and resulted in a longer block duration) over conventional perineural injection because paraneral sheath act as conduits for local anesthetic spread during a sciatic nerve block. However, few data are currently available in the literature evaluating analgesic effect and the diffusion length of local anesthetics in the subparaneural space for patients receiving sciatic block. To obtain more information on this topic, the investigators conducted this prospective randomized study to test the hypothesis that, during ultrasound-guided single popliteal sciatic nerve block, diffusion length of local anesthetics in the subparaneural space could predict anesthetic effect and duration of analgesia. The results of this study will develop a novel indicator to facilitate personalized medicine for patients receiving sciatic block.

Methods Subjects After obtaining approval by the Ethics Committees of the General Hospital of Ningxia Medical University (No. KYLL-2022-4940) and written informed patient consent, consecutive patients scheduled for below-knee surgery under general anesthesia combined with peripheral nerve block were enrolled in this study.

One hundred patients aged 19 to 70 years and scheduled for elective below-knee surgery under general anesthesia combined with peripheral nerve block were included. Their physical status was rated I to II by the criteria of the American Society of Anesthesiologists (ASA). Exclusion criteria were clinically significant coagulopathy, infection at the injection site, allergy to the local anesthetics, severe cardiopulmonary disease (NYHA ≥III), a body mass index > 35kg/m2, diabetic or other neuropathy, prior surgery in the popliteal region, or receiving opioids for chronic analgesic therapy. All the patients in this study received nerve block in a separate "block room" furnished with monitoring devices, drugs, and an emergency kit. These procedures were performed 30 minutes early, with the consent of patients and surgeon, because of the long preparation time and the prolonged onset time. All procedures were performed under ultrasonographic guidance (EDGE II, FUJIFILM Sonosite, USA). Eighteen-gauge intravenous access was established in the forearm in the general ward. After arrival in the block room, the investigators applied supplemental oxygen by facial mask at 5 L/min and standard monitoring (noninvasive arterial blood pressure, electrocardiography, and pulse oximetry) throughout anesthesia. Patients were premedicated with intravenous midazolam (0.02 mg/kg) and sufentanil (0.1 ug/kg). All blocks were conducted by one anesthesiologist who had substantial expertise in ultrasound-guided nerve block. The sciatic nerve block of this study was performed using a subparaneural space injection technique. When the surgical procedure involved the medial aspect of the calf and ankle, an additional ultrasound-guided femoral nerve block was performed.