Retrolaminar block: analgesic efficacy and safety evaluation

Retrolaminar block (RLB) is a thoracic truncal block that can produce analgesia for the thoracic and abdominal wall. However, the characteristics of RLB are not well known. The aim of this study was to determine analgesic efficacy by measuring postoperative consume of patient-controlled analgesia (PCA), additional nonsteroidal antiinflammatory drug (NSAID) rescue, and opioid rescue. Our secondary analysis included assessment of the chronological change in arterial levobupivacaine concentrations after the block.

This prospective, randomized, double-blinded study included 30 patients scheduled for modified radical mastectomy under general anesthesia. The patients were randomized to receive either a landmark-guided RLB or paravertebral block (PVB) catheter placement on T4. Continuous infusion with 4 ml/h of 0.25 % levobupivacaine was started for 72 h, after initial injection of 20 ml 0.375 % levobupivacaine before surgery. Postoperative pain was compared using the amount of block PCA (3 ml 0.25 % levobupivacaine with 30-min lockout), NSAID, and opioid rescue. Arterial blood was sampled for 120 min after the initial injection.

The frequency of postoperative block PCA use was significantly high after RLB in 24 h [p = 0.01; 6 (3-12) vs. 2.5 (0.3-3) times, respectively]. There was no PCA use after 24 h in either group. There was no postoperative opioid rescue use throughout the study. After RLB and PVB, there was no significant difference in T _max (p = 0.14; 15 ± 8 vs. 15 ± 8 min, respectively) and C _max (p = 0.2; 0.9 ± 0.2 vs. 0.9 ± 0.3 µg/ml, respectively), and all the concentrations were below the threshold of local anesthetic systemic toxicity.

Continuous RLB was not inferior to PVB except for the first 24 h, and was satisfactory after mastectomy. RLB showed safe, low peak arterial levobupivacaine concentrations.