The Effect of Intravenous Ketamine After Spinal Anesthesia on the Duration of Postoperative Analgesia and Analgesic Requirement

Objective: To evaluate the impact of ketamine following spinal anesthesia on the duration of postoperative analgesia and the need for analgesics.

Methods: This was a prospective, randomized, double-blinded placebo-controlled study done over a period of two years. A total of 60 participants undergoing elective surgeries under spinal anesthesia were randomized into two groups. After 10 min of spinal anesthesia and achieving the required level of sensory and motor blockade, both groups were given Inj. Midazolam 1 mg intravenously, followed by Inj. Ketamine 0.25 mg/kg, volume made up to 10 mL with normal saline, given intravenously for Group K and Inj. Normal Saline 10 mL was given intravenously for Group N. Hemodynamic monitoring was done intraoperatively, and the postoperative visual analog score (VAS), sedation score, the mean time for the first rescue analgesia, and the total dose of postoperative analgesic required in 24 h were tabulated.

Results: There was no statistical difference between the two groups in terms of age, weight, ASA grade, and duration of surgery. In Group K, the VAS scores were significantly lower and patients were comfortable when compared to Group N (P value <.01). The mean time to first rescue analgesia was longer in Group K (6.4 ± 1.69 h) when compared to Group N (2.9 ± 1.01 h), and the total dose of postoperative analgesia (Tramadol) required in 24 h was also significantly less in Group K (143.33 ± 56.83 mg) when compared to Group N (236 ± 49.01 mg). Changes in hemodynamic parameters (heart rate and mean arterial pressure (MAP)) were statistically and clinically not significant in both the intraoperative and postoperative periods between the groups.

Conclusion: Patients in Group K were more comfortable, had a longer duration of postoperative analgesia, and required less dose of rescue analgesia in the postoperative period. Ketamine is a safe drug that is readily available, and it decreases the use of opioids and opioid-related side effects. Therefore, ketamine can serve effectively as an adjunctive analgesic drug.