Purpose. This study was performed to determine whether the addition of opioids alters the density and spread of intrathecal anaesthetics in vitro.Methods. InPart 1 the densities of the commercially available local anaesthetics bupivacaine, articaine, ropivacaine, opioids fentanyl, sufentanil, morphine and their mixtures were measured at 24 °C. In Part 2 a model filled with artificial analogue of a cerebrospinal fluid (CSF) warmed to 37 °C was elaborated. Samples from Part 1 coloured with methylene blue at room temperature were injected into the model at controlled rate through spinal needle and extent of their distribution in CSF was measured. Results. Densities of all solutions at 24 °C were higher than the known density of CSF at 37 °C. The spread of isobaric local anaesthetics without or with opioids was symmetrical from the point of injection except of articaine and its mixtures, which had slightly more downward direction (p<0.05). Spread of all hyperbaric anaesthetics or their mixtures had downward direction. Conclusions. We can conclude that admixture of opioids with commercial local anaesthetics does not change their physical characteristics and from this point of view seems to be clinically safe.

        Key words: spinal canal model, intrathecal drugs, local anaesthetics, opioids