Study design

This study was conducted in accordance with the regulations and guidelines of Helsinki. It was approved by our university's Institutional Review Board (IRB#9790, 4–10-2022) and registered at Clinicaltrials.gov (NCT05577559, 13–10-2022). The first patient was enrolled on November 1st. Written informed consent was obtained from all patients.

This randomized prospective clinical study was conducted on 58 patients scheduled for anterior cervical spine surgery under general anesthesia from November 1st, 2022, to December 2023. Patients of both sexes, aged 21 to 60 years old, with American Society of Anesthesiologist Physical Status (ASA PS) I and II, and a body mass index (BMI) from 25 to 35 kg/m2 were included in the study. However, patients with a local infection at the puncture site, altered mental status, a history of allergy to study drugs (bupivacaine, fentanyl), hematological disorders including coagulation abnormalities, severe hepatic or kidney impairment, or chronic pain, were excluded from the study.

The patient has the right to withdraw from the study at any time without any negative consequences for their medical or surgical treatment plan.

The primary outcome was to record the time to the first call for rescue analgesia (nalbuphine), and the secondary outcomes were to measure the performance time, the onset of the sensory block, the intraoperative fentanyl consumption, postoperative pain intensity using VAS, the postoperative total nalbuphine consumption, and postoperative complications such as nausea, vomiting, hypotension, and bradycardia.

After a routine pre-operative evaluation, surgery was performed under general anesthesia. For all patients, an intravenous (IV) line was inserted and IV fluid was started. Monitors were attached to the patients to record basal vital data, including respiratory rate, oxygen saturation, heart rate, and blood pressure. Before the induction of general anesthesia, the patients were divided into two groups using computer-generated randomization table:

IC group (n = 29): Patients received a bilateral ultrasound-guided intermediate cervical plexus block using 15 ml of bupivacaine 0.25% for each side.

ES group (n = 29): Patients received a bilateral ultrasound-guided cervical erector spinae plane block using 15 ml of bupivacaine 0.25% for each side at the level of C6.

Block technique

All blocks were conducted under sterile conditions in the operating room with sedation “midazolam 0.03–0.05 mg/kg as needed”.

Materials

Ultrasound Machine: a portable ultrasound system (MTurbo; FUJIFILM Sonosite Inc., Bothwell, Washington, USA)

Probe: A linear array transducer (6–13 MHz frequency).

Needle: 22-gauge spinal needle, length (70 mm in superficial cervical block and 88 mm in cervical erector spinae block).

Ultrasound guided intermediate cervical plexus block [11]

The patient was positioned supine with a slight elevation of the head and the head turned away from the blocked side. After sterilizing the skin, the ultrasound probe was placed over the middle of the posterior border of the sternocleidomastoid muscle (Fig. 1A and B). The needle was inserted in-plane while keeping the probe in a transverse position. The needle tip was placed under the sternocleidomastoid muscle and below the superficial fascia, and then 15 ml of 0.25% bupivacaine was injected (Fig. 1C). The spread of the local anesthetic was visualized using ultrasound guidance. The same steps were repeated on the other side.

Fig. 1

A Site of ultrasound probe. B Sono-anatomy of Superficial cervical block. C Local anesthetic injection

Ultrasound guided bilateral cervical Erector spinae block [12]

The patient was positioned laterally, with a pillow under their head. Transverse ultrasound scanning of the lower cervical area was done. Starting from the supraclavicular brachial plexus, the transducer was slid in a cephalic direction to show the transverse process of the C7 vertebra. Then, it was moved further cephalic to display the transverse process of C6, along with its characteristic anterior and posterior tubercles. The transducer was then slid posteriorly to show the posterior tubercle of C6, along with the posterior neck muscles above it (trapezius, levator scapula, and erector spinae) (Fig. 2A and B). After prepping and draping the patient using aseptic technique, the needle was inserted (in plane technique from posterior) until it reached the posterior tubercle of C6. Then, 15 ml of bupivacaine 0.25% was injected. The same steps were repeated on the opposite side (Fig. 2C). The patient's ability to detect pinprick sensation was assessed every 5 min for 30 min following the block.

Fig. 2

A Site of ultrasound probe insertion. B Sono-anatomy of cervical erector spinae block (TM = Trapezius muscle, LSM = Levator scapula muscle, ESM = erector spinae muscle and TP = transverse process). C Local anesthetic injection

General anesthesia was induced 30 min after the block using fentanyl (1.5 ug/kg iv), propofol (2 mg/kg iv) and atracurium (0.5 mg/kg iv), and maintained after orotracheal intubation as balanced anesthesia using isoflurane ( 1 MAC). Fentanyl 0.5 ug/kg was administered based on the heart rate and mean arterial blood pressure of patients, if it increased by more than 20% from the baseline measurement after excluding other causes. Mechanical ventilation was adjusted to maintain ETCO2 (end tidal CO2) at 35 to 40 mmHg.

At the end of the surgery, the inhalational anesthetic was turned off and the muscle relaxant was reversed using a combination of neostigmine 0.05 mg/kg and atropine 0.01 mg/kg. The patient was then extubated and transferred to a recovery room.

The outcome assessor, who was an anesthesiologist not involved in the study, evaluated the outcomes.

Data to be collected

1- Time of performance of the technique: the time from probe insertion until the visualization of local anesthetic spread

2. Time of onset of sensory block: the time between the injection of the drugs and the loss of pin prick sensation which was assessed every 5 min for 30 min following the block

3. Total intraoperative fentanyl consumption, excluding the induction dose, measured in micrograms

4. Pain intensity was assessed using Visual Analogue Scale (VAS) scores [13]. A commonly used visual analog scale is a 10-cm line labeled with "worst pain imaginable" on the right border and "no pain" on the left border. The patient was instructed to mark along the line to represent the intensity of pain currently being experienced. VAS scores were assessed at 30 min, 2 h, 4 h, 6 h, 12 h, and 24 h postoperatively. An intravenous increment of 15 mg nalbuphine (rescue analgesic) was given if VAS ≥ 4. 1 g of intravenous paracetamol was given every 6 h as a postoperative pain relief regimen, not exceeding 4 g in 24 h

5. The time to the first call for rescue analgesia (nalbuphine), which is the time between the end of surgery and the first report of postoperative pain, was recorded

6. The total amount of nalbuphine given to each patient during the first 24 h of the postoperative period was recorded

7. Any postoperative complications, such as nausea and vomiting, hypotension, bradycardia, phrenic nerve paresis, or any other complication, were noted

Sample size

The primary outcome of the present study was the time to the first call for rescue analgesia (nalbuphine). We conducted a pilot study on seven patients from each group to estimate the sample size. The mean ± SD of the first time to call for rescue analgesia in the SC group was 9.28 ± 1.25 h, and 10.14 ± 1.07 h in the ES group, with 80% study power, α error of 0.05, and Beta error of 0.2. The number of patients in each group was 29. The soft online Open Epi program (https://www.openepi.com/SampleSize/SSCohort.htm) was used to calculate the sample.

size.

Statistical analysis

IBM SPSS Statistics for Windows, Armonk, Version 23.0, NY: IBM Corp. 2015, was utilized for data collection and analysis. Quantitative data were presented as means and standard deviations (SD), or medians and ranges. Qualitative data were presented as numbers and percentages [N (%)]. A t-test was used to compare between the two groups of quantitative variables or Mann–Whitney if appropriate. The percentage of categorical variables was compared using the Chi-square test or Fisher exact test. All tests were two-sided. A p-value < 0.05 was considered statistically significant.