Evaluation of the Effect of Magnesium Sulphate vs. Clonidine as Adjunct to Local Anesthetic during Peribulbar Block

Purpose: This study was designedto compare the effects of magnesium sulphate vs. clonidine co administered peribulbarly as adjunct to local anesthesia. Patients and methods: The study comprised 60 patients undergoing posterior segment eye surgeries. The patients were then divided randomly into three groups (20 patients in each group) according to the medications they received: Group O (control group): local anesthetic + saline 0.9% (1 ml). Group M: local anesthetic + magnesium sulphate 50 mg (in 1 ml 0.9% saline) Group C: local anesthetic + clonidine 30 mcg (1 ml). The onset and duration of lid and globe akinesia were assessed every 1 minute until maximum blockade and then every 15 minutes after surgery until complete recovery of the block. Postoperative analgesia was assessed by using Visual Analogue Score (VAS) every hour up to 6 hours postoperatively. If the VAS was > 5, injection of diclofenac 75mg intramuscular was done. Results: Patients received magnesium sulphate showed significantly rapid onset of lid and globe akinasia than other groups while patients received clonidine showed significantly prolonged duration of lid and globe akinasia than other groups. First analgesic requirement is significantly delayed in group M and group C in comparison with the control group (group C). There were statistically significant differences between the groups as regard the mean VAS in 1,2,3,4 hours, M group and C group have lower median pain score than Control group (control group). Conclusion: The current study establishes magnesium sulphate as a predictable and safe adjunct to local anesthetic in peribulbar block for rapid onset of anesthesia and clonidine for prolonged duration of anesthesia. Introduction: Peri-bulber eye block is a safe and inexpensive technique with the advantage of providing efficient anesthesia with good lid and globeakinesia. It is also an effective treatment of operative pain. It has become a common practice to use polypharmacy approach to enhance the onset and increase the duration of the block, because no drug has yet been identified that specifically inhibits nociception without associated side effects. Research continues concerning different techniques and drugs that could provide better anesthesia and postoperative pain relief [1] Magnesium sulfate has been used for many years on an empirical basis to control convulsions in patients with preeclamptic toxemia. Magnesiumions are essential for many biochemical reactions, and a deficiency may produce clinically important consequences. Many of the pharmacologic properties have only more recently been appreciated. Magnesium is the fourth most prevalent cation in the body and activates approximately 300 enzyme systems, including many involved in energy metabolism. [2] ecause the biological basis for its potential antinociceptive effect is promising. [3] These effects are primarily based on physiological calcium antagonism, that is voltage-dependent regulation of calcium influx into the cell, and noncompe-titive antagonism of N-methyl-D-aspartate (NMDA) receptors. [4] Mag. Sulph. in peribulbar block Abd El-Hamid AM, M.D. 22 Clonidine is a selective partial agonist for α2-adrenoreceptors, with a ratio of approximately 200: 1 (α2 to α1). [5] Clonidine is lipid soluble so, it penetrates the blood-brain barrier to reach the hypothalamus and medulla. Although experience with α2-agonists as sole anesthetics is limited, [6] Data suggest that oral, intravenous, epidural, and intrath-ecal administration of clonidine potentiates the anesthetic action of other anesthetics, volatile or injectable, and reduces general and regional anesthetic requirements with correspondingly fewer side effects. [7] In addition to its use in the operative setting, the addition ofclonidineto local anesthetic increases the duration of analgesia and reduces dose requirements for local and narcotic pain medications. [8] The aim of this study is to compare the effects of magnesium sulphate vs. clonidine co administ-ered peribulbarly as adjunct to local anesthesia. Patients and methods: After obtaining institutional ethical committee approval and written informed consent, 60 patients belonging to ASA physical status I and II, undergoing posterior segment eye surgeries aged 18 to 60 years and axial eye length ranged from 22 to 28 mm. Patients with history of adverse reaction to any study medication, coagulation disorders, and where communication difficu-lties preventing reliable assessment were excluded from this study. After intravenous access, a combination of midazolam (1 mg), fentanyl (30 μg), and propofol (50 mg) are given to provide amnesia and sedation for the placement of the blocks. All patients had peribulbar anesthetic block using10 ml of bupivacaine 0.5% and lidocaine 2% without epinephrine 1: 1 ratio. Hyaluronidase (150 units) is added to speed tissue penetration. The patients were then divided randomly into three groups (20 patients in each group) according to the medications they received: Group O (control group): local anesthetic + saline 0.9% (1 ml). Group M: local anesthetic + magnesium sulphate 50 mg (in 1 ml 0.9% saline) Group C: local anes-thetic + clonidine 30 mcg (1 ml). Light orbital compression for 1 minute then evaluation after 1minute, 3min, 5min, and 10 minutes. The onset and duration of lid and globe akinesia were assessed every 1 minute until maximum blockade and then every 15 minutes after surgery until complete recovery of the block. Motor block evaluation includes lid akinesia (lid closure by orbicularis and lid opening by the levator) and globe akinesia using 3 point scale for every muscle was done using the score system that shown in(Table 1). For assessment of lid akinesia the patients were asked to open their eyelids and then squeeze them together maximally. Orbicularis occuli muscle was assessed separately by using the score in (Table 1). Also levatorpalpebrae muscle for opening eye lid was assessed by the score in (Table 1). Globe akinesia was assessed at 1min., then 3min., 5min., 10min. and 15 minutes. These were scored using the movements of the extra ocular muscles in all 4 main directions on a scale of 0 to 2 as shown in (Table 1). The block was considered satisfactory when loss of at least two movement of the 4 cardinal direction. Ain Shams Journal of Anesthesiology Vol 4-1; Jan 2011 23 Table 1 Scoring system 9 Arterial blood pressure, heart rate and oxygen saturation (SpO2) were checked every 15 minutes during the entire procedure and every 30minutes during the first two postoperative hours. Hypotension and bradycardia were defined as a 20% decrease in blood pressure and heart rate in relation to pre-block value. Postoperative analgesia was assessed by using Visual Analogue Score (VAS) every hour up to 6 hours postoperatively as 0 (no pain) to 10 (maximum pain imaginable). If the VAS was>5, injection of diclofenac 75mg intramuscular was done. Statistical analysis: was done using SPSS version 16, and the tests used are Chisquire and ANOVA. A value of P<5% was considered statistically significant. The results are expressed as mean (SD).