Patients' Positions on Analgesic Efficacy of ESPB

After signed the informed consent form, 200 patients scheduled for elective thoracoscopic surgery were randomly divided into four groups: supine position group (group S, n = 50), prone position group (group P, n = 50), lateral position group (group L, n = 50) and paravertebral block group (group C, n = 50). After ESPB block, the corresponding position was maintained for 30 minutes.

Ultrasound-guided ESPB was performed 30min before general anesthesia. Ultrasound-guided ESPB methods: The ultrasonic high-frequency linear array probe (5-13 MHZ, Sonosite, USA) was placed parallel to the spine on the surface of the transverse process tip of the seventh thoracic vertebra. Under ultrasound, the transverse process and the surface of the erector spinae were clearly exposed. Then a long beved-plane needle was used, and the needle was inserted from the head side. 2ml of normal saline was injected using the water separation technique to confirm the position of the needle tip, and then 30ml 0.375% ropivacaine was injected.

After completion of the block, patients in group S were kept in the supine position for 30min, patients in group L were kept in the upper lateral position for 30min, and patients in group P were kept in the prone position for 30min. After 30 minutes of observation, an anesthesiologist who was unaware of the grouping used an ice cube to determine the extent of sensory block. General anesthesia was then performed.

General anesthesia was performed as follows: routine ECG monitoring was performed after the patient was admitted to the operating room, and invasive arterial blood pressure was monitored by radial artery puncture and catheterization. General anesthesia was induced with dexamethasone 10mg, midazolam 0.05mg.kg-1, propofol 1.5-2.0 mg.kg-1, sufentanil 0.2 ug.kg-1, cisatracurium 0.2 mg.kg-1, and then a double-luminal bronchial tube was inserted under a video laryngoscope and mechanically ventilated (tidal volume: 6-10ml.kg-1,PEEP: 3-5 cm H2O). Anesthesia was maintained with propofol (2-4 mg.kg-1.h-1), remifentanil (0.12-0.3 ug.kg-1.min-1) and Micuronium (0.6mg.kg-1.h-1). Intraoperative hemodynamics was maintained within 20% of baseline. Flurbiprofen axetil 50mg was given intravenously for analgesia and tropisetron 4mg was given to prevent nausea and vomiting when there were no contraindications during the operation. Oxycodone 3mg was administered intravenously 30min before the end of the procedure. At the end of the operation, the patient was transferred to PACU with an endotracheal tube. After neuromuscular blocking antagonism, the tracheal tube was extubated.

NRS was used to evaluate the pain scores at rest and during movement at 1, 3, 6, 12 and 24h ，48h after operation by a nurse who was unaware of the grouping. Oxycodone 30mg diluted to 150ml was used for patient-controlled intravenous analgesia after operation. The parameters of analgesia pump were set as background dose 0.5 ml.h-1, bolus 5ml, lockout time 8min. If NRS≥4 at rest after surgery, patient-controlled analgesia (PCA) was performed by pressing the PCA pump. When NRS≥4 at rest was still ≥4 after two times of PCA, oxycodone 1mg was given once as rescue analgesia, and the patients were reevaluated until NRS≤3.