Intertransverse Process Block Versus Erector Spinae Plane Block for Pain Relief in Lumbar Spine Surgery

Background and rationale

Lumbar spine surgery is associated with moderate to severe postoperative pain, and opioid-based analgesia is limited by side effects such as nausea, vomiting, sedation and respiratory depression. The erector spinae plane block (ESPB) is an established component of multimodal analgesia for spine surgery. The intertransverse process block (ITPB) is a more recently described paraspinal technique in which local anesthetic is injected into the tissue between adjacent transverse processes, closer to the paravertebral space. Direct comparisons of the two techniques in lumbar spine surgery are scarce.

Block procedures

Both blocks are performed bilaterally before induction of general anesthesia, with the patient prone, under ultrasound guidance using a low-frequency curvilinear probe and an in-plane approach with a 10-cm block needle.

ESPB: the needle tip is placed between the deep surface of the erector spinae muscle and the posterior surface of the L3 transverse process.

ITPB: the needle tip is placed in the intertransverse space between the L2 and L3 transverse processes, anterior to the erector spinae muscle and posterior to the intertransverse ligament-muscle complex, without advancing further anteriorly.

Needle position is confirmed by hydrodissection with 2 mL of 0.9% saline after negative aspiration. Ropivacaine 0.375% (prepared from ropivacaine 0.5% and 0.9% saline in a 3:1 ratio) is administered at 2.5 mg/kg (maximum 150 mg), divided equally between the two sides. Sensory block is assessed by pinprick 20 minutes after injection using the Hollmén scale, and the cranial and caudal extent of the block is measured in centimetres from the injection level. A block is considered failed if no sensory change is detected 30 minutes after injection.

In the control group, after induction of anesthesia, the surgeon infiltrates 20 mL of 1% lidocaine with epinephrine 1:200,000 into the skin and subcutaneous tissue along both sides of the planned incision before skin incision.

Anesthesia protocol (all groups)

Anesthesia is induced with fentanyl 2 µg/kg, propofol 2-3 mg/kg and rocuronium 0.6 mg/kg, and maintained with sevoflurane at 1-1.5 MAC. Nociceptive response is assessed using the PRST score (blood pressure, heart rate, sweating, tearing). If PRST is ≥ 4, fentanyl 50 µg is given intravenously and may be repeated after 5 minutes. Paracetamol 1 g IV is given approximately 30 minutes before the end of surgery.

Postoperative analgesia

Once patients are awake in the recovery room and able to rate pain and use the device, intravenous morphine patient-controlled analgesia (PCA) is started: morphine 1 mg/mL, bolus 1 mg, lockout interval 8 minutes, no background infusion, maximum 15 mg per 4 hours. Patients are instructed to press the PCA button when pain is VAS ≥ 4. H0 is defined as the time the patient is awake in the recovery room and able to self-report pain and use PCA.

Sample size

Sample size was calculated for comparison of 24-hour morphine consumption between a block group and the control group, assuming a standard deviation of 6.54 mg (from a previous Vietnamese study of ESPB in lumbar spine surgery) and a minimum clinically important difference of 5 mg, with two-sided α = 0.05 and 80% power. This gave 27 patients per group; allowing for about 10% dropout, 30 patients per group (90 in total) were enrolled.

Randomization and statistical analysis

Eligible patients are randomly allocated in a 1:1:1 ratio to the three groups by drawing lots. Continuous variables are compared using one-way ANOVA or the Kruskal-Wallis test, as appropriate, and categorical variables using the chi-square or Fisher's exact test. Pairwise comparisons are adjusted with the Bonferroni method. Two-sided p < 0.05 is considered statistically significant. Analyses are performed with SPSS version 20.0.