Effect of addition of dexmedetomidine or dexamethasone to bupivacaine for spinal anaesthesia for lower limb surgeries

Abstract

Spinal anaesthesia is a very common technique used in lower limb surgeries. It provides adequate analgesia both intra and post-operative and it also avoids complications associated with general anaesthesia. Spinal block remains the first choice in these types of surgeries due to its rapid onset, superior blockade, low risk of infection as from catheter in situ in cases of epidural, less failure rates and cost effectiveness, but has the disadvantages of limited duration of block and lack of postoperative analgesia so early analgesic intervention is needed in the postoperative period. Various intrathecal adjuvants to local anaesthetics have been found to improve the quality and extend duration of spinal block providing postoperative analgesia such as epinephrine, clonidine, opioids, etc. Dexmedetomidine is a highly selective α2-adrenergic agonist which has been used as pre-medication and as an adjuvant to general anaesthesia. It is found that injection of dexmedetomidine intrathecally prolongs both sensory and motor block and has antinociceptive action for both visceral and somatic pain by depressing the release of nociceptive C fibers transmission and hyperpolarization of post synaptic dorsal horn cells. Also, some studies demonstrate that addition of dexamethasone intrathecally to local anaesthetics is used to prolong duration of sensory block and postoperative analgesia in patients undergoing surgery by reducing inflammation and blocking transmission of nociceptive C-fibers and by suppressing ectopic neural discharge. The aim of this study was to compare the effect of addition of dexmedetomidine or dexamethasone to bupivacaine on the onset time and duration of spinal anaesthesia, quality of block, intraoperative and postoperative complications and postoperative analgesia in patients undergoing lower limb surgeries. Fifty four adult patients of both sexes, aging from 21 to 55 years old, ASA I and II presented to Ain Shams University Hospitals for elective lower limb surgeries were involved in this study after providing written consents and after approval of institutional ethical committee. Those who had contraindications to regional anaesthesia were excluded from the study: patient refusal, ASA III and IV physical status, history of allergy to bupivacaine, history of long-term steroid therapy or α2 agonists, neurologic or psychological disorders, previous spine surgery, alcohol abuse, opium addict or using any drug that modifies pain perception, patients with hypertension or ischemic heart disease using beta blockers, calcium channel blockers, angiotensin converting enzyme inhibitors, patients noted to have dysrhythmias on the electrocardiogram (ECG), chronic liver disease or chronic renal failure, coagulation disorders or receiving anticoagulants or antiplatelets. After obtaining a free flow of cerebrospinal fluid, the appropriate local anaesthetic solution was injected intrathecally. Patients were divided randomly into three equal groups using sealed envelopes. Patients allocated to group A received intrathecal injection of 3ml (15mg) of 0.5% hyperbaric bupivacaine + 2ml of normal saline containing 5μg preservative free dexmedetomidine. Patients allocated to group B received intrathecal injection of 3ml (15mg) of 0.5% hyperbaric bupivacaine + 2ml (8mg) preservative free dexamethasone. Patients allocated to group C received intrathecal injection of 3ml (15mg) of 0.5% hyperbaric bupivacaine + 2ml normal saline. All patients were assessed and monitored for haemodynamics as ECG for heart rate and non-invasive arterial pressure, arterial oxygen saturation. The sensory block level was assessed by ice bag along the midclavicular line bilaterally and the motor block was assessed according to Bromage scale. Sedation was assessed by modified Ramsay sedation score. The pain score was recorded by using numeric rating scale between 0 and 10 (0 = no pain, 10 = most severe pain) every 4 hours for first 24 hours, time of first analgesic dose and the total consumption of rescue analgesia and adverse effects as hypotension, bradycardia, shivering, nausea and vomiting were recorded. . Data were analyzed using SPSS (Statistical Package for Social Science) 21.0 for Windows (SPSS, Chicago, IL, USA). Results of this study showed that the addition of dexmedetomidine or dexamethasone to bupivacaine in spinal anaesthesia significantly prolonged both sensory and motor blockades duration compared with bupivacaine alone. They also prolonged the time of postoperative analgesia as evidenced by significantly longer time to first rescue analgesia and lower NRS scores with minimal adverse effects and haemodynamic stability. Comparing dexmedetomidine with dexamethasone showed that dexmedetomidine caused more prolongation of the spinal block duration and the time of postoperative analgesia than dexamethasone. It also decreased shivering during spinal anaesthesia.