Magnesium Sulphate Versus Ketamine as an Adjuvant to Bupivacaine in Pectoral Nerve Block During Mastectomy

Breast cancer is the most common malignancy in females, and its incidence increases with increase the age of the patients and it is the most expected cause of death in the world .

Surgery is the main treatment of breast cancer and other treatments include chemotherapy, radiotherapy , hormonal therapy and biological therapy or combination treatment and this depends on the type of the cancer and its stage .

Breast surgery is usually associated with significant postoperative pain. Poorly controlled postoperative pain has a negative physiological and psychological impacts as it is associated with an increase in hospital stay , medical care cost, significant postoperative nausea and vomiting , development of chronic pain syndrome and impaired quality of life .

Several methods have been involved in postoperative pain control including multi modal analgesia using multiple medication with different mechanism of action as intravenous and oral opioids , non-steroidal anti-inflammatory drugs and local anesthetic infiltration also has an important role in pain control .

Regional anesthetic procedures have an effective role in acute pain control as thoracic epidural and thoracic paravertebral block are considered the gold standard procedures for postoperative pain management for breast cancer surgery, but not every anesthesiologist is comfortable making these invasive procedures .

Recently, the pectoral nerves blocks (PECS I and PECS II) are recommended for providing intraoperative and postoperative pain control during and after breast surgery. These blocks may be more effective when compared to other regional anesthetic procedures .

Pectoral nerves blocks includes 2 types (PECS I and PECS II). The PECS block type I is a easy and reliable performed by injection an interfacial plane between the pectoralis major and pectoralis minor muscles to block the lateral region of the breast to provide analgesia for breast surgery .

The PECS block type II "modified Pecs's block'' is performed by injection at the interfascial plane between the pectoralis minor muscle and serratus anterior muscle . It aims at blocking the pectoral nerves, the intercostobrachial , intercostals (III, IV, V, and VI), and the long thoracic nerve and these are required to block the axilla also provides analgesia to mammary glands and the skin from the T2-T6 dermatomes extending into the mid-axillary line providing complete analgesia during breast surgery and several types of mastectomies .

Pectoral nerve block is usually performed using an in-line needling technique by ultrasound guidance, which is essential to identify the plane between the pectoralis major, minor muscles, and serratus anterior as well as the anatomical landmarks associated with them .

Hematoma and local anesthetic toxicity and risk of pneumothorax are adverse effects in pectoral nerve block especially PECS II block which may be reduced by using ultrasound guidance and decreasing anesthetic drug concentrations .

Various adjuvants, as fentanyl, morphine, tramadol, epinephrine, α2 agonists, dexamethasone, midazolam, neostigmine and sodium bicarbonate have been added to local anesthetics agents to prolong the time and potency of postoperative analgesia and this is may be associated with adverse effects, and the outcomes have been inadequate.

An understanding of pain mechanisms points to the role of central sensitization and N-methyl-D-aspartate (NMDA) receptor activation by excitatory amino acid transmitters in postsurgical pain .

Magnesium sulfate (MgSO4) is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor in the central and peripheral nervous system, and is found to decrease the intraoperative and postoperative analgesic consumption and also it increases the duration and potency of analgesia when combined with different local anesthetics.

Magnesium augments local anesthetics (LA) action in the peripheral nerves by increasing the firing threshold in both myelinated and unmyelinated axons increasing the transmembrane potential causing hyperpolarization and adding of magnesium to bupivacaine produces an enhancement of nerve blocking .

Ketamine is also a non-competitive antagonist of the N-methyl-D-aspartate NMDA receptor antagonist commonly used for its analgesic and anesthetic effect .

Ketamine decreases the intensity of postoperative pain, reduces 24-hour opioid consumption, and delays the time to first request of analgesic therapy .

Bupivacaine is an amide local anesthetic with a slow onset, long duration of action and high potency. The maximum recommended single bolus dose of bupivacaine is 2.5 mg/Kg, bupivacaine exert its action through impairing sodium influx across the neuronal membrane by blocking the sodium channels .