DENSITIES OF DEXTROSE-FREE INTRATHECAL LOCAL-ANESTHETICS, OPIOIDS, AND COMBINATIONS MEASURED AT 37-DEGREES-C

Dextrose-free anesthetic medications are commonly used to provide suba rachnoid anesthesia and analgesia. Hypobaricity has been proposed as a mechanism to explain postural effects on the extent of sensory block produced by these drugs. Densities of dextrose-free solutions of local anesthetics and opioids, and commonly used anesthetic/opioid mixtures were determined at 37.00 degrees C for comparison with the density of human cerebrospinal fluid (CSF). Measurements accurate to 0.00001 g/m L were performed using a mechanical oscillation resonance frequency de nsity meter. All undiluted solutions tested are hypobaric relative to human lumbar CSF with the exception of lidocaine 1.5% and 2.0% with ep inephrine 1:200,000. All mixtures of local anesthetics and opioids tes ted are hypobaric. We observed good agreement between measured densiti es and calculated weighted average densities of anesthetic mixtures. W hile the influence of baricity on the clinical effects of dextrose-fre e intrathecal anesthetics remains controversial, attempts to attribute postural effects to the baricity of these drugs requires establishmen t of accurate density values. These density data may facilitate elucid ation of the mechanisms underlying the behavior of dextrose-free intra thecal anesthetics.