Anesthetic Pharmacology

Jürgen Sandkühler, MD, PhD§ BACKGROUND: Xenon’s (Xe) mechanisms for producing anesthesia and analgesia are not fully understood. We tested the effect of Xe equilibrated in a lipid formulation or normal saline on spinal C-fiber-evoked potentials and on the induction of synaptic long-term potentiation (LTP). METHODS: C-fiber-evoked field potentials were recorded in the superficial lumbar spinal cord in response to supramaximal electrical stimulation of the sciatic nerve. Anesthesia was maintained with isoflurane in one-third O2 and two-thirds N2O. Xe equilibrated at a concentration of 600 L/mL of Lipofundin MCT 20%, (n 5) or solvent alone (n 3), and Xe equilibrated at a concentration of 100 L/mL of normal saline (n 7) or saline alone (n 7) was given IV under apnea. High-frequency stimulation of the sciatic nerve was applied 60 min after the injection of Xe-containing formulations or solvents [to induce LTP]. RESULTS: High-frequency stimulation potentiated C-fiber-evoked potentials to 156% 14% (mean sem) of control. Low-dose Xe in saline 0.9% blocked the induction of LTP. High-dose Xe equilibrated in MC 20% showed no additional effect when compared with the solvent, which blocked the induction of LTP. CONCLUSION: Low-dose Xe in saline 0.9% revealed no antinociceptive, but preventive, action in spinal pain pathways.