Distribution of hypobaric tetracaine within cerebrospinal fluid in a spinal canal model

We studied the distribution of hypobaric tetracaine within cerebrospinal fluid (CSF) using a spinal canal model to examine the spread of a hypobaric anesthetic solution during spinal anesthesia. In our study, 0.2% tetracaine colored with methylene blue was observed to migrate upwards rapidly and spread horizontally in the upper portion of the model placed horizontally and filled with CSF which was collected from several neurosurgical patients. The boundary between the hypobaric solution and CSF could be clearly identified. These results suggest that the hypobaric tetracaine will distribute in the upper portion of the spinal canal during spinal anesthesia. It can be used to produce unilateral spinal blockade in the lateral decubitus position despite a small difference in specific gravity between the hypobaric anesthetic and CSF. In addition, the fact that the hypobaric solution showed a rapid horizontal spread suggests that correct positioning both during and following administration of the anesthetic is important to control the level of anesthesia.