title: Effect of topical anaesthetics on interstitial colloid osmotic pressure in human subcutaneous tissue sampled by wick technique.
abstract: OBJECTIVE
  To measure colloid osmotic pressure in interstitial fluid (COP(i)) from human subcutaneous tissue with the modified wick technique in order to determine influence of topical application of anaesthetics, dry vs. wet wick and implantation time on COP(i).
  
  
  METHODS
  In 50 healthy volunteers interstitial fluid (IF) was collected by subcutaneous implantation of multi-filamentous nylon wicks. Study subjects were allocated to two groups; one for comparing COP(i) obtained from dry and saline soaked wicks, and one for comparing COP(i) from unanaesthetized skin, and skin after application of a eutectic mixture of local anaesthetic (EMLA®, Astra Zeneca) cream. IF was sampled from the skin of the shoulders, and implantation time was 30, 60, 75, 90 and 120 min. Colloid osmotic pressure was measured with a colloid osmometer. Pain assessment during the procedure was compared for EMLA cream and no topical anaesthesia using a visual analogue scale (VAS) in a subgroup of 10 subjects.
  
  
  RESULTS
  There were no significant differences between COP(i) obtained from dry compared to wet wicks, except that the values after 75 and 90 min. were somewhat higher for the dry wicks. Topical anaesthesia with EMLA cream did not affect COP(i) values. COP(i) decreased from 30 to 75 min. of implantation (23.2 ± 4.4 mmHg to 19.6 ± 2.9 mmHg, p = 0.008) and subsequently tended to increase until 120 min. EMLA cream resulted in significant lower VAS score for the procedure.
  
  
  CONCLUSIONS
  COP(i) from subcutaneous tissue was easily obtained and fluid harvesting was well tolerated when topical anaesthetic was used. The difference in COP(i) assessed by dry and wet wicks between 75 min. and 90 min. of implantation was in accordance with previous reports. The use of topical analgesia did not influence COP(i) and topical analgesia may make the wick technique more acceptable for subjects who dislike technical procedures, including children.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT01044979.
authors.affiliation: Department of Paediatrics, Haukeland University Hospital, Bergen, Norway. hjgu@helse-bergen.no
authors.forename: Hans Jørgen Timm
authors.initials: HJ
authors.lastname: Guthe
authors.forename: Torbjørn
authors.initials: T
authors.lastname: Nedrebø
authors.forename: Olav
authors.initials: O
authors.lastname: Tenstad
authors.forename: Helge
authors.initials: H
authors.lastname: Wiig
authors.forename: Ansgar
authors.initials: A
authors.lastname: Berg
mesh_terms: D000328:Adult; D000779:Anesthetics, Local / Q000494:pharmacology*; D003102:Colloids / Q000737:chemistry*; D019937:Diagnostic Techniques and Procedures; D004487:Edema / Q000188:drug therapy; D045604:Extracellular Fluid / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D008722:Methods; D008875:Middle Aged; D009997:Osmotic Pressure / Q000187:drug effects*; D040521:Subcutaneous Tissue / Q000187:drug effects*
chemical_list: D000779:Anesthetics, Local; D003102:Colloids