Methods
obesity, loss of pinprick sensation, muscle weakness, mellitus diabetes, swelling, neurological disorder, paralysis, pain, sensory disability, coagulopathy
OBESITY, MUSCLE WEAKNESS, NEUROLOGICAL DISORDER, BLIND, COAGULOPATHY, COMPLICATIONS
The protocol utilized in this study was granted approval by the ethics committee at Cixi People’s Hospital on July 24, 2022, and subsequently reviewed and registered at the Chinese Clinical Trials Registry (ChiCTR-TRC-0000054) on October 3, 2022. This study was conducted from October 2022 to February 2023 at Cixi People’s Hospital.Fifty-four adult patients (18 to 70 yr), classified as American Society of Anesthesiologists (ASA) Physical Status Class I to II, who underwent distal lower extremity surgery, were estimated for eligibility to enter this study. Patients with obesity (BMI ≥ 35), mellitus diabetes, or a history of coagulopathy or neurological disorder were excluded from the study. Following the acquisition of signed informed consent forms, all patients were randomly allocated into warming group (group W, The solutions of ropivacaine 0.5% were prepared with a 1:1 mixture of ropivacaine 1% (Qilu Pharmaceutical, Jinan, China) and normal saline (China Otsuka Pharmaceutical Co.,Ltd., Tianjin, China). For group R, the extension tubes and 20-ml syringes with ropivacaine 0.5% were stored in the operating room set at 23°C before initiating the block. For group W, the extension tubes and 20-ml syringes with ropivacaine 0.5% were stored in an incubator (DHG9011A, Jinghong Laboratory Instrument Co.,Ltd., shanghai, China) set at 30°C for at least 2 h before initiating the block. The solutions were all prepared by a nurse who was not involved in the performance of the intraoperative management, or data collection and analysis.All patients were routinely prohibited from drinking for 6 h and fasted for 8 h. They were monitored by standard noninvasive monitors (MX500, Philips, Boeblingen, Germany) with blood pressure (BP), heart rate (HR), electrocardiograph (ECG) and blood oxygen saturation (SpOPatients were positioned laterally with the affected limb elevated and flexed at the hip and knee. A ultrasound device (MP80, Mindray, Shenzheng, China) with a low-frequency (5–2 MHz), curved-array ultrasound transducer (C5-1S) was used. The ultrasound transducer was performed on the skin in the subgluteal region, oriented parallel to a line between the ischial tubercle and greater trochanteric for sciatic nerve imaging. On this level, the sciatic nerve could be visualized on sonography as an oval or flattened hyperechoic nodule in a transverse plane. Subsequently, the longitudinal section image of the sciatic nerve could be obtained by rotating the transducer 90 degrees from its original position. The position of the sciatic nerve was confirmed by a combination of longitudinal and transverse scanning. The width, thickness and depth of the sciatic nerve were measured on ultrasonography.A 80-mm, 22-gauge needle (TWLB, Kindly Medical Devices Co., Ltd., Zhejiang, China) was carefully advanced in parallel with the ultrasound beam towards the sciatic nerve until the needle tip was positioned adjacent to the nerve tissues on ultrasound imaging. Subsequently, 2–3 ml of saline solution was injected to confirm the correct placement of needle tip by observing a spread around the sciatic nerve. After confirmation of negative aspiration, 30 ml of ropivacaine 0.5% (23℃ or 30℃) was incrementally injected to spread along the dorsal aspect of the nerve tissue without changing the initial position of the needle tip, within less than 20 s. In order to avoid intraneural injection, all injections were administered using 20-mL syringes in incremental doses. Meanwhile, the ultrasound video recorded the injection process around the sciatic nerve for subsequent assessment of the occurrence of intraneural injection. All nerve blocks were performed by a single anesthesiologist proficient in ultrasound regional anesthetic techniques, who remained blinded to group assignment.The sensory and motor blockade was evaluated every 2 min for 30 min after injection. The pinprick (22G) was used on three regions of the lower limb for the assessment of sensory blockade, including the dorsal aspect of the foot (common peroneal nerve, CPN), the plantar aspect of the foot (tibial nerve, TN) and the lateral cutaneous side of the lower leg (sural nerve, SN). Sensation to pinprick was classified as follows: 0 = normal sensation (no block); 1 = blunted sensation (analgesia); 2 = absence of sensation (anesthesia). It was considered complete when patients received complete loss of pinprick sensation (score = 2). The onset time of sensory blockade was defined as the time from the end of injection to complete blockade in three dermatomes. The degree of dorsal and plantar flexion in the foot and toes was assessed as an evaluation index for motor blockade. It was classified as follows: 0 = normal movement; 1 = decreased movement; 2 = absence of movement (complete motor block). It was considered complete if the patient showed paralysis with dorsal and plantar flexion of the foot and toes (score = 2). The onset time of motor blockade was defined as the time from the end of injection to completion of motor block. Block failure was defined that the completion of sensory and motor block was not achieved whithin 30 min after injection and these patients were excluded from analysis. The time for resolution of motor blockade and the first request for pain medication were documented on the first day after surgery. Additionally, the neural complications for patients such as sensory disability and/or muscle weakness in the lower limbs were assessed on the second day after surgery. All data was collected by an investigator blinded to randomization. A comprehensive review of all videos was conducted by another investigator who was blind to all the information and data of patients, including the group assignment.Intraneural injection was defined that any segment of the nerve showed significant swelling in a transverse plane on ultrasonography during administration of local anesthetics [After achieving successful sensory and motor blockade, LMA general anesthesia was induced using propofol at a dosage of 2–3 mg/kg, followed by maintenance with sevoflurane (2.0%-2.5%) while ensuring spontaneous breathing of the patient. During the surgery, sufentanil citrate was administered intermittently with dosage adjustments based on the patient’s noninvasive blood pressure, respiratory rate, and heart rate.