Comparative Effects of Intravenous Dexmedetomidine and Ketamine on the Incidence of Shivering During Spinal Anesthesia
Abstract
Background: Shivering complicates a substantial proportion of subarachnoid blocks, raising oxygen consumption, degrading monitoring and dominating patient recollection of surgery. Dexmedetomidine and ketamine lower the shivering threshold by distinct mechanisms, but direct comparisons under spinal anaesthesia are scarce. Objective: To compare prophylactic intravenous dexmedetomidine with ketamine for shivering, sedation and haemodynamic stability in adults having surgery under subarachnoid block. Methods: A prospective, randomised, observer-blinded trial was conducted at Bangladesh Medical College Hospital, Dhaka, from July to December 2024. Sixty ASA I–II adults undergoing elective surgery under subarachnoid block were randomised 1:1 to intravenous dexmedetomidine 25 μg or ketamine 25 mg, administered five minutes after the block. Shivering was assessed using the Crossley–Mahajan scale, with sedation, mean arterial pressure, and adverse events monitored for 120 minutes. Continuous variables were analysed using unpaired t-tests and categorical variables using Pearson’s chi-square or Fisher’s exact test, as appropriate. Results: Groups were comparable at baseline. Shivering was infrequent and never differed between arms, peaking at 1 of 30 (3.3%) with dexmedetomidine versus 2 of 30 (6.7%) with ketamine (P = 1.000). Sedation was far more common with dexmedetomidine from five minutes (83.3% versus 0%; P < 0.001) and remained so at 60 min (93.3% versus 50.0%; P < 0.001). Mean arterial pressure, nausea and vomiting were comparable, and no patient required rescue pethidine. Conclusion: Both dexmedetomidine and ketamine were associated with low shivering rates following subarachnoid block, with no significant difference between groups. Dexmedetomidine produced substantially more sedation, suggesting that ketamine may be preferable when preservation of intraoperative wakefulness is desired.