Role of dexmedetomidine as an adjuvant in serrates anterior muscle block - A randomised Control Trial

Breast cancer is the most common cancer in women worldwide as per data published by the World Health Organization. The treatment for breast cancer has evolved tremendously over the last decade with early surgical interventions being performed to increase the survival rates of those suffering from it. Modified radical mastectomy (MRM), is widely accepted and performed as a standard surgical procedure for breast carcinoma extensively across the world. Pain after MRM can be moderate to severe in nature and the method of pain alleviation after the procedure is still debatable and not yet clinically defined. Failure to provide adequate post operative analgesia may lead to impaired pulmonary and immune functions with increased risk of ileus, thromboembolism and myocardial infarction.In addition to undesirable effects like post operative nausea and vomiting (PONV), these patients are also at risk of developing chronic pain syndromes like post mastectomy pain syndrome (PMPS).Therefore adequate postoperative analgesia is mandatory after the surgery which not only hastens the recovery but also reduces the risk of development of PMPS as well.

Multimodal analgesia forms the mainstay in provision of adequate postoperative pain relief after MRM, which can be achieved by either regional anesthetic techniques or administering intravenous analgesics or combination of both. Intravenous patient controlled analgesia with opioids provides the benefit of pain relief at the patient’s behest. However, use of opioids is associated with host of deleterious effects like sedation, constipation along with significant PONV. Herein lies the inherent advantage of the regional anesthetic techniques, which reduce the cumulative post operative opioid consumption as well as their side effects. Regional blocks like thoracic epidural, paravertebral, and cervical epidural blocks with local anesthetic agents have been used with varying degrees of success for post operative pain relief. All these blocks may be associated with potentially serious complications when performed using anatomical landmark techniques. With increase in the application of ultrasonography for performance of blocks, interfascial plane blocks have gained popularity due to precise visualization of the anatomy of area concerned and are being extensively employed for providing adequate postoperative analgesia in various surgical procedures.

Serratus anterior muscle block (SAM) has been described recently in MRM and the efficacy of this block is above par due to ultrasound guidance. Described by Blanco, SAM block is an interfascial plane block where the local anesthetic is administered between latissimus dorsi muscle (LDM) and serratus anterior muscle (SAM) using ultrasound. It provides analgesia by virtue of blocking lateral cutaneous branches of the thoracic intercostal nerves (T2-T12). The added advantages associated are decreased vascular injury/hematoma formation, improved sensory blockade, reduced local anesthetic toxicity and decreased opioid consumption. The role of addition of adjuvants to local anesthetics (LA) to prolong the duration of postoperative analgesia is well known in a variety of blocks. Various opioid and non opioid adjuvants like fentanyl, dexamethasone, tramadol, clonidine, dexmedetomidine, epinephrine, adenosine, midazolam, magnesium etc. have all been used in peripheral as well as neuraxial blocks.Search of available literature did not reveal any study evaluating the role of adjuvants with local anaesthetics in SAM block. Based on the hypothesis that addition of an adjuvant would increase the duration of analgesia in the post operative period the present study is being undertaken to compare the efficacy of SAM block with or without the addition of dexmedetomidine as an adjuvant to the local anaesthetic in patients scheduled to undergo elective MRM.