Abstract
The analgesic properties of ketamine are associated with its non-competitive antagonism of the N-methyl-D-aspartate receptor; these receptors exhibit an excitatory function on pain transmission and this binding seems to inhibit or reverse the central sensitization of pain. In the literature, the value of this anesthetic for preemptive analgesia in the control of postoperative pain is uncertain. The objective of this study was to ascertain whether preoperative low-dose ketamine reduces postoperative pain and morphine consumption in adults undergoing colon surgery. In a double-blind, randomized trial, 48 patients were studied. Patients in the ketamine group received 0.5 mg/kg intravenous ketamine before surgical incision, while the control group received normal saline. The postoperative analgesia was achieved with a continuous infusion of morphine at 0.015 mg∙kg-¹∙h-¹ with the possibility of 0.02 mg/kg bolus every 10 min. Pain was assessed using the Visual Analog Scale (VAS), morphine consumption, and hemodynamic parameters at 0, 1, 2, 4, 8, 12, 16, and 24 hours postoperatively. We quantified times to rescue analgesic (Paracetamol), adverse effects and patient satisfaction. No significant differences were observed in VAS scores between groups (P>0.05), except at 4 hours postoperatively (P=0.040). There were no differences in cumulative consumption of morphine at any time point (P>0.05). We found no significant differences in incremental postoperative doses of morphine consumption in bolus, except at 12 h (P =0.013) and 24 h (P =0.002). The time to first required rescue analgesia was 70 ± 15.491 min in the ketamine group and 44 ± 19.494 min in the control (P>0.05). There were no differences in hemodynamic parameters or patient satisfaction (P>0.05). Preoperative low-dose-ketamine did not show a preemptive analgesic effect or efficacy as an adjuvant for decreasing opioid requirements for postoperative pain in patients receiving intravenous analgesia with morphine after colon surgery.
Highlights
In spite of the techniques we have at our disposal and the elementary nature of incisional pain, optimal pain management remains a challenge[1]
After activation of C-fibers by noxious stimuli, sensory neurons become more sensitive to peripheral inputs, a process called central sensitization[6,7]
Variables: Sex: 1=male, 2=female; Visual Analog Scale (VAS) score between 0 to 10; Remifent: 1 ml=0.01 mg of remifentanil; Morf: morphine administered at the end of surgery
Summary
In spite of the techniques we have at our disposal and the elementary nature of incisional pain, optimal pain management remains a challenge[1]. These sensitizations produce c-fos expression in sensory neurons[9], and are related to the activation of N-methyl-D-aspartic acid (NMDA)[7,9] and neurokinin receptors[10,11] These genes produce long-lasting changes in the pain-processing system, resulting in hyperexcitation. According to Wall, protection of sensory neurons against central sensitization may provide relief from pain after surgery[12] Based on this assumption, preemptive analgesia has been recommended as an effective aid to control postsurgical pain[4,13,14]. Conclusions: Preoperative low-dose-ketamine did not show a preemptive analgesic effect or efficacy as an adjuvant for decreasing opioid requirements for postoperative pain in patients receiving intravenous analgesia with morphine after colon surgery
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