This is a prospective, randomized, parallel-group, trial performed in one hospital. The research approach was approved by the internal Ethics Committee (ID 2982, 6 February 2020) and registered on clinicaltrial.gov (10/10/2019, registration number NCT04123106).
Adult patients planned to receive surgical treatment of elective open lumbar arthrodesis at department of vertebral surgery of IRCCS Policlinico A. Gemelli Foundation of Rome, from May 2020 to September 2020 were enrolled in the study. Inclusion criteria: 1) age of 18-75 years old, no gender preference; 2) patients suffering from intractable lumbar pain, with or without lower limbs radiation, walking limitation (neurogenic claudication) and a different degree of daily life activity limitation, due to degenerative or isthmic spondylolisthesis, lumbar stenosis and/or spinal deformities; 3) surgical treatment of vertebral arthrodesis and decompression of neurologic structures (when required). Exclusion criteria: 1) opioid tolerance (preoperative treatment with opioids for more than 30 days and/or a morphine dosage >15 mg, or morphine equivalent, in the three months before surgery); 2) documented sleep apnoea or home oxygen therapy; 3) history of alcohol or drug abuse; 4) allergy or hypersensitivity to opioids or LA; refusal of the patient. Written informed consent was conventionally signed by all patients the day before surgery.
The patients were randomized to receive erector spine plane block (ESPB group) or wound infiltration (Control group) using a computer-generated randomization table. Patients were blinded to the treatment assignment.
Anesthetic procedure and interventions
All the patients enrolled were managed with open lumbar vertebral arthrodesis with decompression of neurologic structures (when required) through a standard posterior midline approach.
General anesthesia was induced with propofol plus sufentanil, and rocuronium was administered to facilitate tracheal intubation. Anesthesia was maintained using propofol and sufentanil titrated to achieve hemodynamic stability and adequate anesthetic depth, with a Bispectral Index (BISTM, Covidien/Medtronic, Minneapolis, USA) values between 40 and 60. Once placed in the prone position, in the ESPB group, with aseptic technique, a low-frequency ultrasound probe (M-turbo, Sonosite, Fujifilm, Japan) in a sterile sleeve was used to identify the desired vertebral lamina by paramedian sagittal scan starting from the sacral regions. Then the probe was moved 2–3 cm lateral to the midline to identify the tip of the corresponding transverse process. After LA infiltration, a 21-gauge 100 mm needle (Ultraplex 360, B Braun, Melsungen, Germany) was inserted in-plane from cranial to caudal direction until it contacted the corresponding transverse process. After verifying the placement of the needle tip by hydrodissection of the interfascial plane with 2 mL normal saline, 20 mL 0.375% ropivacaine was injected. The same procedure was repeated on the contralateral side.
In the control group, wound infiltration with ropivacaine 0.375% 40 mL was performed by surgeons at the surgical site at the end of surgery.
Motor-evoked potentials and freerunning electromyography were performed during surgery.
After the surgery all patients received an around-the-clock regimen of ketoprofen and acetaminophen and self-administered sufentanil tablets [SSTs (Zalviso®, Grunenthal, Germany)] as needed [19].
Outcome evaluation
The primary measure was pain intensity at Recovery Room (RR) arrival (time zero), assessed through a 11-point Numerical Rating Scale (NRS 0: no pain, 10: the worst pain imaginable). Patients had to be cooperative, oriented and tranquil (Ramsay Sedation Scale Score =2) at the time of assessment. The evaluations were made by an anaesthesiologist blinded to the group allocation of the patient.
Secondary outcomes were: 1) difference in pain intensity between pre-intervention and defined timepoints (RR arrival, at 15 minutes, 30 minutes, 60 minutes, 2, 6, 12, 24, 48 hours); 2) total amount of SSTs requested at the same timepoints; 3) number of any adverse event (sickness, vomiting, itching, numbness, respiratory side effects, procedure-related complications); 4) the length of hospital stay (LOS) after surgery.
Statistical Analysis
Statistical analysis was performed by using the Statistical Package for Social Science (SPSS), release 23.0. Continuous variables were expressed as mean ± standard deviation [SD (range)], categorical variables displayed as frequencies and the Mann-Whitney and Kruskal-Wallis ANOVA nonparametric tests were used to compare different groups at different timings and timing differences within subjects, respectively. Categorical variables were compared using the chi square test. For sample size calculation we used data from a pilot study on 3 controls and patients; a reduction of NRS score at RR timing of at least 2 points in the ESPB in respect to control subgroup was defined as the primary endpoint. A sample size of 12 subjects in each group was estimated for 90% power and alfa of 0.05. A p value of less than 0.05 was considered statistically significant.