Clinical actions of subarachnoid sevoflurane administration in vivo: a study in dogs.

BACKGROUND Halogenated ethers produce clinical effects at spinal sites. Nevertheless, in vitro and in vivo studies have not determined whether the immobilizing effect in the spinal cord is due to inhibition of nociceptive or motor transmission or both. Our goal was to characterize the clinical effects of direct spinal sevoflurane administration. METHODS Five adult beagle dogs completed the study. In a randomized and blinded manner each animal received placebo (saline 0.1 ml kg(-1)) and three concentrations of pure sevoflurane administered intrathecally (0.05, 0.075 and 0.1 ml kg(-1)) by means of a permanent spinal catheter. Sensory and motor block and state of consciousness were determined at baseline and at predetermined regular intervals until at least 2 h after total recovery. RESULTS None of the dogs presented a decrease in consciousness with either 0.05 or 0.075 ml kg(-1) of sevoflurane. Administration of 0.1 ml kg(-1) produced light sedation (2 on a four-point sedation scale) in three of the five dogs. A comparison of the duration of the sensory and motor blocks among the three sevoflurane dosages shows a significant dose-dependent increase that is greater in all cases than that for the saline solution. CONCLUSIONS Spinal administration of pure sevoflurane resulted in a dose-related and totally reversible motor and sensory regional block without any signs of clinical neurotoxicity or significant decrease in consciousness. Therefore the model allows us to comment on the analgesic effects at the spinal level in addition to the direct immobilizing effects of sevoflurane.