Postoperative analgesia of ultra-low-dose naloxone versus dexmedetomidine with local anesthetic in peribulbar block in cataract surgery

Background and aim Regional anesthesia in eye surgery is a preferred technique and widely used in all eye surgery centers. It is safe, inexpensive, simple, and reliable and provides efficient ocular anesthesia. It is associated with less complications than general anesthesia. Among regional blocks, peribulbar block is safer in comparison with retrobulbar block owing to lesser incidence of complications such as retrobulbar hemorrhage, globe perforation, and brain stem anesthesia, but it has some disadvantages such as incomplete orbital and eyelid akinesia and decrease time of analgesia in which the patient need pain relief postoperatively, so many adjuvant drugs have been added to local anesthetic to overcome these disadvantages. Dexmedetomidine is a central-acting drug, a highly selective α2-agonist, that has been used as an additive to local anesthetic, whereas the mechanism of action of ultra-low-dose naloxone includes inhibition of impulses of the excitatory opioid receptors and release of encephalin. The goal of this study was to assess the effect of ultra-low-dose naloxone and dexmedetomidine as adjuvants for local anesthetic on duration of analgesia as primary outcome and akinesia of the globe and eyelid and occurrence of complications as a secondary outcome. Patients and methods A total of 60 patients were included in this prospective randomized double-blind clinical study scheduled for elective cataract surgery, who were randomly divided into two groups: N group (n=30) received 3.5 ml of lidocaine 2%, 3.5 ml of bupivacaine 0.5% with 15 IU/ml hyaluronidase for both lidocaine and bupivacaine, and 100 ng naloxone in 1 ml normal saline. D group (n=30) received 3.5 ml of lidocaine 2%, 3.5 ml of bupivacaine 0.5% with 15 IU/ml hyaluronidase for both lidocaine and bupivacaine and 25 μg of dexmedetomidine in one-ml normal saline. The assessment includes duration of analgesia (h), which is the time from injection till visual analog scale of more than 4 or request of analgesia by the patient, akinesia of the globe and eyelid assessed every 2 min using a three-point scale, and occurrence of complications (pain during injection, chemosis, diplopia, bradycardia, and hypotension). Results A total of 60 cataract surgery patients were included in the study. Regarding primary outcome (duration of analgesia), we found a highly statistically significant difference in duration of analgesia, with longer duration of analgesia in N group of patients compared with D group (P