Patients and study design
This prospective randomized controlled study was approved by the ethics committee of Beijing Chaoyang Hospital (2017-ke-81) and registered with the Clinical Trial Registry of China (ChiCTR-INR-17011499). The study took place at the Department of Anesthesiology, Beijing Chaoyang Hospital, Capital Medical University, Beijing, from Jun 1, 2017, to May 30, 2018. All patients provided written informed consent before being enrolled into the study.
Patients suffering from lung cancer were eligible for enrollment in this study if they were between 20 and 70 years of age, were scheduled to undergo video-assisted thoracoscopic lobectomy for a single lobe and systematic lymphadenectomy, and had an American Society of Anesthesiologists (ASA) class of I or II. Patients with local infection, coagulopathy, allergy to local anesthetics, obesity (body mass index > 30 kg/m2), decreased pulmonary reserve, major cardiac disorders, liver and renal dysfunction, pre-existing neurological deficits, or psychiatric illness were excluded.
Randomization and blinding
The patients were randomized using sequential sealed envelopes prepared by an independent statistician using a computer-generated random number table. Patients were randomly allocated to an ESPB group, a TPVB group, and a control group using computer-generated random numbers. Patients in the control group did not receive any regional block, and patients in ESPB and TPVB groups received the corresponding blocks. The postoperative assessors were blinded to grouping.
Both ESPB and TPVB were performed at level T5 with patients in lateral position, with affected side upward, under ultrasound guidance with a Navi Series ultrasound device (Wisonic Medical Technology Co. Ltd., Shenzhen, China) equipped with a linear ultrasound transducer (4–15 MHz). A 22G 90-mm needle (TuoRen Medical Instrument Finty Company, Zhengzhou, China) with a 18°sharp tip was choosen for both blocks.
In the ESPB group, the transducer was placed 2-3 cm from the midline in a sagittal orientation. After the T5 transverse processes and the erector spinae muscle had been identified, the needle was inserted laterally to medically with out-plane technique until close contact was made with the transverse processe, without air or blood aspiration, 0.5 mL/kg (but no more than 40 ml) of 0.5% ropivacaine was administered. And we could see the liquid spreading between the transverse process and the erector spinae muscle.
In the TPVB group, the transducer was placed 2–3 cm lateral to the midline in a vertical orientation. Once the T5 transverse process, internal intercostal membrane and parietal pleura had been identified, the needle was inserted laterally to medically with in–plane technique until the tip lay in the thoracic paravertebral space beyond the internal intercostal membrane. 2ml normal saline was injected to confirm the pressing of the parietal pleura, 0.3 mL/kg of 0.5% ropivacaine was administered for the block.
Starting from 30 min after block administration, pinprick sensation in the T1–T12 dermatomal distribution was monitored every 5 min by an independent observer who was blinded to the study group. After confirming sensory loss, general anesthesia was induced with midazolam 0.02 mg/kg, sufentanyl 0.3–0.4 μg/kg, and propofol 1.5–2 mg/kg. Rocuronium bromide 0.8 mg/kg was administered to facilitate tracheal intubation. The trochal ports were made at the 7th and 8th intercostal levels along the midaxillary line. Anesthesia was maintained with propofol and remifentanil, and the dosage was adjusted according to the hemodynamic parameters and bispectral index. Additional boluses of intravenous rocuronium bromide were given as required. A chest drain to be placed for at least 48 hours after surgery was inserted before the skin closure at the 7th and 8th intercostal levels. During the 10 min before the end of the operation, only tramadol 100 mg was used for analgesia. The intraoperative remifentanil dosages were recorded. Non-steroidal anti-inflammatory drugs were not used during the operation.
Postoperative analgesia via a patient-controlled intravenous analgesia (PCIA) device was initiated immediately after the surgery and continued until 48 h after the surgery. The PCIA device contained 100 μg sufentanyl and 10 mg tropisetron diluted with normal saline to a volume of 100 mL. The device was set up to administer a background dose of 1 mL/h and a bolus dose of 2 mL with a 15-min lockout interval. Before the operation, patients were taught how to use the PCIA device to manage their pain and the visual analog scale (VAS) to score their pain. If the PCIA device could not meet a patient’s analgesic demand, and the VAS score at rest was 4 or more, 50 mg flurbiprofen axetil was intravenously administered as rescue analgesia.
An investigator blinded to the group allocation recorded the VAS scores at rest and during coughing at 1, 6, 18, 24, and 48 h after the operation. The number of doses administered via the PCIA device, the total volume of analgesic drugs administered via the PCIA device, the doses of flurbiprofen axetil administered, and the incidence of pneumothorax, local anesthetic intoxation, postoperative nausea and vomiting after the surgery were noted.
Sample size calculation
As the primary outcome of this study was the the VAS scores postoperatively, we took the VAS scores at rest 18h post-surgery for example. According to the preliminary study (n=10, unpublished data), the mean VAS scores after ESPB and TPVB was 2.1 and 3.6, respectively, and the SD of the VAS scores was 1.6. We defined an acceptable superiority margin as 1, according to the previous study. A sample size of 7 in each group was required to provide a power of 0.8 and a one-sided α of 0.05, given the possibility of missed follow-up rate 10%.
Statistical analysis was performed using GraphPad Prism 7 software. Numerical data were expressed as mean and standard deviation or median and range, as appropriate. Qualitative data were expressed as frequency and percentage. Qualitative parameters were analyzed using the chi-square test or Fisher exact test. One-way analysis of variance (ANOVA), followed by Holm-Sidak’s multiple comparisons, was used to compare the quantitative parameters between groups. P<0.05 was considered statistically significant.