Subpectoral plexus block to enhance surgical anesthesia produced by a multilevel thoracic paravertebral block for primary breast cancer surgery: a prospective randomized double-blind study

Background and objectives The efficacy of a multilevel thoracic paravertebral block (6m-TPVB at T1-T6), as the sole anesthetic, for primary breast cancer surgery (PBCS) has been questioned. Current literature suggests that a significant number of patients may report pain during various stages of surgery, notably during the detachment of the breast base from the pectoralis major muscle and its fascia. Given that the pectoral muscles are innervated by nerves from the subpectoral plexus (C5-T1), which are not affected by a 6m-TPVB alone, we propose that an additional "subpectoral plexus block" (SPPB) may enhance the surgical anesthesia. Methods 60 patients undergoing PBCS under a 6m-TPVB were randomized to receive an SPPB (Gp-A, n=30) or a sham block (Gp-B, n=30). Midazolam (1-3 mg) and ketamine (10-20 mg) were administered intravenously for sedation and analgesia before the block placement and an infusion of dexmedetomidine (0.1-0.5 mcg/kg/h) was used to maintain conscious sedation during surgery. The 6m-TPVB was ultrasound guided, and 4-5 mL of 0.5% ropivacaine with 1:200 000 epinephrine was injected at each vertebral level (total volume used 25 mL). The SPPB was also ultrasound guided, and 5 mL of 0.25% ropivacaine was injected each near the origin of the thoracoacromial artery in the pectoserratus plane and between the two pectoral muscles (interpectoral plane) in Gp-A, at the level of the third rib. In Gp-B, 3-5 mL of normal saline (sham block) was injected into the pectoralis major muscle. Surgery commenced about 25-30 min after the completion of the SPPB. Ketamine (10-20 mg IV bolus) was used for rescue analgesia (our primary outcome variable) if the patient complained of pain during surgery to an arbitrary maximum of 100 mg, or the anesthesia was deemed inadequate, after which it was converted to general anesthesia. Results The two study groups were comparable with respect to demographic data, total dose of midazolam and dexmedetomidine used, duration of surgery, and overall patient satisfaction. Ketamine, as rescue analgesia, was required to complete surgery in both study groups, but fewer patients in Gp-A (56.7%) required rescue analgesia than in Gp-B (93.3%, p=0.002). Ketamine requirement (median (IQR)) was also significantly lower (p<0.001) in Gp-A (10 (0-40) mg) than in Gp-B (50 (20-70) mg). The surgeons were more (p=0.02) satisfied (mean +/- SD numeric rating scale, 0-100) with surgical conditions in Gp-A (77.29 +/- 10.63) than in Gp-B (65.83 +/- 21.38). Conclusion A SPPB enhances the surgical anesthesia produced by a 6m-TPVB for primary breast cancer surgery. Trial registration number https://www.chictr.org.cn/showprojEN.html?proj=5368, Trial ID No: ChiCTR-TRC-14004200; Date of Registration: 25 January 2014, Study commencement date: 28 February 2014.