Ketamine administered intraoperatively in very small doses reduces postoperative opioid consumption. We suggest that this effect is the result of attenuation of acute tolerance to the analgesic effect of opioids. We sought to demonstrate that acute tolerance induced by alfentanil infusion can be attenuated by a dose of ket- amine that is too small to produce a direct antinocicep- tive effect. The experiments were conducted in rats with the use of an infusion algorithm designed to main- tain a constant plasma level of the opioid for 4 h. The degree of acute tolerance was determined on the basis of decline in the level of analgesia measured with a tail compression test. Ketamine (10 mg/kg) did not change. the baseline pain threshold and did not increase the peak of alfentanil-induced analgesia. At the same time, it attenuated the development of acute tolerance to an- algesia during alfentanil infusion and suppressed re- bound hyperalgesia observed the day after the infu- sion. These effects were similar to those observed with dizocilpine (0.1 mg/kg). The development of acute tol- erance to analgesia induced by the infusion of an opioid can be attenuated by ketamine administered in doses that are not large enough to provide a direct antinoci- ceptive effect. Therefore, ketamine has the potential to reduce opioid consumption even in subanalgesic doses.
- Journal Name:
- Anesthesia & Analgesia
- Publication Date:
- December 2000
- PMID:
- 11094005
The Effect of Ketamine on Opioid-Induced Acute Tolerance: Can It Explain Reduction of Opioid Consump
The effect of ketamine on opioid acute tolerance that reveals itself in small subanalgesic doses.