The inter-semispinal plane (ISP) block is a novel ultrasound-guided technique that involves local anesthetic injection into the fascial plane between the semispinalis cervicis and semispinalis capitis muscles with subsequent block of the dorsal rami of the cervical spinal nerves and hence can get adequate postoperative analgesia.

The authors hypothesized that ISP block can reduce the postoperative analgesic consumption in patients undergoing posterior cervical spine surgeries.

The aim of this study is to evaluate the analgesic efficacy of ISP block in patients undergoing posterior cervical spine surgery.

This study will be performed in the in the Fayoum University hospital after the local Institutional Ethics Committee and local institutional review board approval. The study design will be double-blind randomized controlled study . A detailed informed consent will be signed by the eligible patients before recruitment and randomization.

Patients were randomly allocated into two groups using computer generated sequence and concealed in sealed opaque envelopes.

Control group (C): patients received general anesthesia only. Inter-semispinal plane (ISP) block group: patients received bilateral ultrasound guided ISP block at the level of C5.

All patients will be assessed Preoperative VAS score then premedicated orally with midazolam 0.5 mg/kg 30 min prior to surgery. All patients were monitored by 5 lead ECG, pulse oximetry, non-invasive blood pressure and capnography and an intravenous (IV) access will be established.

The technique of general anesthesia will be standardized for all patients. General anesthesia will be induced by intravenous (IV) 2 mg/kg propofol and 1 μg/kg fentanyl induction. After IV atracurium 0.5 mg/kg, orotracheal intubation was performed. Anesthesia will be maintained with isoflurane (1.2%-1.5%) in oxygen-air mixture (50%-50%). Muscle relaxation will be maintained during the procedure with atracurium in increments.

After induction of general anesthesia, ISP blocks will be performed in the allocated group with the patient in the prone position. In both groups, the treating anesthesiologist left the operating room while another anesthesiologist experienced in ultrasound guided nerve block techniques; with no subsequent role in the study; either performed the ISP blocks in the ISP group, or just prepared the skin and scanned the site of the block using the ultrasound probe in the control group. Fifteen minutes will be awaited in all patients before the surgical procedure was allowed to start.

fentanyl 0.5 μg/kg IV will be administered in case of inadequate analgesia as indicated by >20% increase in heart rate or mean arterial blood pressure. Total intraoperative fentanyl consumption will be recorded.

All anesthetics will be discontinued at the end of the surgical procedure. Extubation will be performed when spontaneous breathing was adequate and following prompt reversal using 0.05 mg/kg of neostigmine and 0.02 mg/kg of atropine. At the end of surgery, paracetamol 1 g will be administered IV to be repeated every 6 h postoperatively. Patients will be transferred to the PACU where HR, respiratory rate, SpO2 and systolic, diastolic and mean arterial blood pressure were monitored.

Sample size was calculated using G* Power 3.1.7.9 software program. Calculation of the sample size was based on the VAS value measured at different time points. Based on the results of a study by Mostafa et al, the authors calculated the sample size to be able to detect a difference in VAS score of 10 points with an effect size of 0.8. Using the previous data, at least 23 patients in each group were required to detect a significance difference in the postoperative pethidine consumption at α value of 0.05 and study power of 90%. The authors decided to recruit 25 patients in each group to compensate for any possible withdrawals. The sample size calculation was based on a 2-sample independent t-test (2-sided)

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status I-II undergoing elective posterior cervical spine surgery

Exclusion Criteria:

• Patient refusal
• Patients with any contraindication to regional anesthesia (e.g. local infection, coagulation abnormality)
• Known allergy to local anesthetics
• Previous cervical disc surgery or fixation
• Mental disorders
• Drug or alcohol abuse.