Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. Low-dose ketamine was effective in reducing the incidence of shivering following spinal anesthesia compared to tramadol.

Evidence Rating Level: 2 (Good)

Following spinal anesthesia in orthopedic patients, post-spinal shivering is a common complication. Shivering that is untreated can lead to increased wound pain, metabolic demand, oxygen consumption, and ultimately, hemostatic dysfunction. Literature investigating prophylactic agents to improve post-spinal shivering is limited. In this prospective cohort study, 516 patients undergoing orthopedic surgery under spinal anesthesia were divided into two groups: patients receiving an intravenous prophylactic dose of Ketamine or Tramadol prior to anesthesia. Ketamine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist which has a role in thermoregulation. Conversely, tramadol is a weak opioid which acts on central monoaminergic pathways and resets the body’s thermoregulatory center. The selected participants were assessed for post-spinal shivering which was graded on a scale of four. The results of this study showed that the incidence of post-spinal shivering was higher in the tramadol group compared to the ketamine group (43.8% vs 28.7%). Low-dose ketamine had a protective effect against developing post-spinal shivering in patients undergoing spinal anesthesia for orthopedic surgery (aOR 0.427, 95%CI 0.28-0.63). Other adverse events such as incidence of nausea and vomiting was significantly higher in the tramadol group. In conclusion, low-dose ketamine as prophylaxis was more effective in reducing incidence of post-spinal shivering compared to tramadol. However, this study still has a few limitations which should be noted. For instance, while post-operative shivering was graded on a scale, this is still a subjective observation. Post-anesthesia shivering may also occur after the allotted observational time of one hour which was not accounted for. Nevertheless, this study does support the use of ketamine as a prophylaxis for post-anesthesia shivering and randomized controlled trials exploring this association in the future could be valuable.

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