title: Assessment of the densities of local anesthetics and their combination with adjuvants: an experimental study.
abstract: OBJECTIVE
  The relative density of a local anesthetic in relation to that of the cerebrospinal fluid (CSF) at 37 degrees C is one of the most important physical properties that affect the level of analgesia obtained after the subarachnoid administration of the drug. The objective of this study was to determine the density of local anesthetic solutions, with and without glucose, and the combination of the local anesthetic with adjuvants at 20 degrees C, 25 degrees C, and 37 degrees C.
  
  
  METHODS
  The density (g.mL(-1)) was determined by using a DMA 450 densimeter with a sensitivity of +/- 0.00001 g.mL(-1). The densities, and variations, according to the temperature were obtained for all local anesthetics and their combination with opioids at 20 degrees C, 25 degrees C, and 37 degrees C. The solution is hyperbaric if its density exceeds 1.00099, hypobaric when its density is lower than 1.00019, and isobaric when its density is greater than 1.00019 and lower than 1.00099.
  
  
  RESULTS
  The densities of both local anesthetics and adjuvants decrease with the increase in temperature. At 37 degrees C, all glucose-containing solutions are hyperbaric. In the absence of glucose, all solutions are hypobaric. At 37 degrees C, morphine, fentanyl, sufentanil, and clonidine are hypobaric.
  
  
  CONCLUSIONS
  The densities of local anesthetics and adjuvants decrease with the increase in temperature and increase when glucose is added. The knowledge of the relative density helps select the most adequate local anesthetic to be administered in the subarachnoid space.
authors.affiliation: Instituto de Anestesia Regional, Hospital de Base, São José do Rio Preto, SP. dr.imbelloni@terra.com.br
authors.forename: Luiz Eduardo
authors.initials: LE
authors.lastname: Imbelloni
authors.forename: Adriano Dias
authors.initials: AD
authors.lastname: Moreira
authors.forename: Flávia Cunha
authors.initials: FC
authors.lastname: Gaspar
authors.forename: Marildo A
authors.initials: MA
authors.lastname: Gouveia
authors.forename: José Antônio
authors.initials: JA
authors.lastname: Cordeiro
mesh_terms: D000759:Adjuvants, Anesthesia / Q000737:chemistry*; D000779:Anesthetics, Local / Q000737:chemistry*; D055598:Chemical Phenomena
chemical_list: D000759:Adjuvants, Anesthesia; D000779:Anesthetics, Local