Pectoral Nerves Blocks for Chronic Pain (PNBCP)

The purpose of this study is to determine whether pectoral nerves blocks（PECS） would reduce chronic pain at 3 months after modified radical mastectomy（MRM）surgery.

One hundred and forty adult female participants scheduled for elective unilateral modified radical mastectomy under general anesthesia are randomly allocated to receive either general anesthesia plus Pecs block(Pecs group, n=70) or general anesthesia alone (control group, n=70). After arrived in the operating room，the participants in the control group are accepted the general anesthesia.Whereas，after anesthesia induction，the participants in the Pecs group receive an ultrasound-guided Pecs block and a 15 minute observation time prior before the start of the operation. Pecs block technology： A broadband (5-12 hertz) linear array probe of Sonosite Edge portable ultrasound system (Sonosite Inc,Bethel,Washington) is used, with an imaging depth of 4 to 6 cm. After cleaning the infraclavicular and axillary regions with chlorhexidine, the probe is placed below the lateral third of the clavicle, similar to what is done when performing infraclavicular brachial plexus block. After recognition of the appropriate anatomical structures, the skin puncture point is infiltrated with 2% lignocaine, then the block is performed by using a 20-gauge Tuohy needle. The needle is advanced to the tissue plane between the pectoralis major and pectoralis minor muscle at the vicinity of the pectoral branch of the acromiothoracic artery, and 10 mL of 0.35% ropivacaine deposited. In a similar manner, 20 mL is deposited at the level of the third rib below the serratus anterior muscle with the intent of spreading injectate to the axilla.

Ropivacaine hydrochloride injection； Generic name：Naropin； Dosage form：Liquid、Injectable formulation； Dosage：105mg；30ml； Frequency：Once.

Medical Normal saline Generic name：Normal saline； Dosage form：Liquid、Injectable formulation； Dosage：30ml； Frequency：Once.

An anesthesiologist interviews the patients by phone to determine the postoperative pain at 3 months after surgery. Chronic pain is defined as pain in the surgical area or the ipsilateral arm, present at least 4 days a week, with an intensity of 3 or more on the verbal rating scale（0=no pain to 10=worst imaginable pain),described as a typical neuropathic pain consisting of burning pain, shooting pain, pain evoked by pressure, and deep blunt pain.

Inclusion Criteria: Modified radical mastectomy American Society of Anesthesiologists physical status 1-3 BMI 18-35 kg/m2 Exclusion Criteria: Declining to give written informed consent； Uncontrolled hypertension； Allergy to local anesthetics； Pregnancy； Alcohol or drug abuse； Prior breast surgery except for diagnostic biopsies； Contraindication to the use of regional anesthesia； History of chronic pain or psychiatric disorder and pregnant patients； Consumption of NSAID, cyclooxygenase-2 inhibitors or paracetamol within 24 hours before the investigation； Infection at the needle site. Inability to properly describe postoperative pain to investigators (eg, language barrier, neuropsychiatric disorder)

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