الفهرس 
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Abstract
Breast cancer is one of the most common causes of cancer death worldwide. Post mastectomy pain is a very common problem after breast cancer surgeries that affects not only the psyche of the patients but also different systems of the body and may lead to PMPS if not adequately treated. Ultrasound guided PVB is a safe method that can be used preferably as a part of multimodal analgesia for perioperative pain management in breast cancer surgeries. The mean duration of surgical analgesia provided by LAs is limited and thus single shot PVB may be not sufficient for post-operative analgesia. The addition of adjunctive analgesics to LAs has been shown to enhance the quality and duration of sensory neural blockade, and decrease the dose of supplemental analgesia.
Bupivacaine is a LA drug that produces its effects through inhibition of the generation and/or dissemination of action potentials at the neuronal membrane and a resulting blockade of afferent nociceptive barrage.
Dexmedetomidine is a potent and highly selective α2-adrenoceptor agonist with a selectivity ratio of 1600:1 (α2:α1). It has a broad range of pharmacological properties, including sedation associated with arousability and orientation without respiratory depression. Additional properties include analgesia, neuroprotection and cardioprotection. It has been used extensively in different doses as adjuvant to LAs in different types of regional blocks to improve the quality of analgesia but studies comparing its usage in different concentrations in PVB are lacking.
The aim of this work was to evaluate the analgesic efficacy of adding different doses of dexmedetomidine to bupivacaine 0.25 % in ultrasound guided TPVB in patients undergoing breast cancer surgery as regards pain intensity as a primary outcome and the characteristics of the block, haemodyanmic stability, sedation and occurrence of complications as a secondary outcome.
After approval of the study by the Research Ethics Committee and obtaining written informed consents from patients, the present study was carried out in the surgical department of the Medical Research Institute Hospital (MRI), Alexandria University on 75 ASA II patients scheduled for breast cancer surgeries with axillary clearance. Refusing patients, patients having reconstructing breast surgery, allergy to LAs or any included medications, those with severe liver, renal or cardiovascular diseases, coagulopathy, infection at the site of injection and those with psychiatric disorder were excluded from the study.
All the patients received ultrasound guided TPVB at T3 and were randomly assigned to one of three groups: group A received 40 ml bupivacaine 0.25% , group B received 40 ml bupivacaine 0.25% including 1 μg /kg dexmedetomidine and group C received 40 ml bupivacaine 0.25% including 1.5 μg /kg dexmedetomidine.
The following parameters were measured:
• Age, weight and duration of surgery.
• Onset of the sensory block identified by decreased sensation to an ice pack applied to T3 every 1 minute for 10 minutes after performing the block.
• Level and degree of the sensory blo