Effect of Topical Anaesthetics on Interstitial Colloid Osmotic Pressure in Human Subcutaneous Tissue Sampled by Wick Technique Hans Jørgen Timm Guthe1*, Torbjørn Nedrebø2,3, Olav Tenstad 2 , Helge Wiig2, Ansgar Berg1,4 1 Department of Paediatrics, Haukeland University Hospital, Bergen, Norway, 2 Section of Physiology, Department of Biomedicine, University of Bergen, Bergen, Norway, 3 Hyperbaric Medical Unit, Department of Occupational Medicine, Haukeland University Hospital, Bergen, Norway, 4 Section for Paediatrics, Department of Clinical Medicine, University of Bergen, Bergen, Norway Abstract Objectives: To measure colloid osmotic pressure in interstitial fluid (COPi) 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 COPi. Material and 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 COPi obtained from dry and saline soaked wicks, and one for comparing COPi from unanaesthetized skin, and skin after application of a eutectic mixture of local anaesthetic (EMLAH, 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 COPi 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 COPi values. COPi decreased from 30 to 75 min. of implantation (23.264.4 mmHg to 19.662.9 mmHg, p = 0.008) and subsequently tended to increase until 120 min. EMLA cream resulted in significant lower VAS score for the procedure. Conclusion: COPi from subcutaneous tissue was easily obtained and fluid harvesting was well tolerated when topical anaesthetic was used. The difference in COPi 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 COPi and topical analgesia may make the wick technique more acceptable for subjects who dislike technical procedures, including children. Trial Registration: ClinicalTrials.gov NCT01044979 Citation: Guthe HJT, Nedrebø T, Tenstad O, Wiig H, Berg A (2012) Effect of Topical Anaesthetics on Interstitial Colloid Osmotic Pressure in Human Subcutaneous Tissue Sampled by Wick Technique. PLoS ONE 7(2): e31332. doi:10.1371/journal.pone.0031332 Editor: Rory Edward Morty, University of Giessen Lung Center, Germany Received June 27, 2011; Accepted January 6, 2012; Published February 14, 2012 Copyright: 2012 Guthe et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants from Helse Vest, Haukeland University Hospital, Project number 911441. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: hjgu@helse-bergen.no Introduction Oedema formation is characterized by accumulation of fluid within the interstitial space and is a result of increased transcapillary fluid flux and/or decreased lymphatic drainage as described for more than 100 years ago by Starling [1] and later quantitatively expressed by the equation [2]: Jv~CFC ðPc{PiÞ{s COPp{COPi ~CFCxDP 1 ð Þ Jv denotes net transcapillary filtration and CFC refers to the capillary filtration coefficient, which is defined as the net filtration in 100 g tissue per minute for each mmHg rise in net capillary filtration pressure. Pc and Pi are the hydrostatic pressure in the capillaries and interstitial fluid (IF), respectively. COPp and COPi are the colloid osmotic pressures of plasma and IF, and s is the capillary wall reflection coefficient for plasma proteins. In view of the relations described in the Starling equation, increasing CFC or nP can increase fluid flux across the microvascular wall. The extra vascular forces are smaller than the intravascular pressures, but still important determinants of capillary exchange. Plasma and interstitial colloid osmotic pressure (COP) are therefore essential parameters for understanding fluid exchange during oedema formation and fluid therapy. Sampling of IF by the wick method was first described by Aukland and Fadnes [3] and has been extensively evaluated in animal models [4] [5] [6] [7]. Recently, different groups of patients with fluid disturbances have been studied and have provided important novel data for the PLoS ONE | www.plosone.org 1 February 2012 | Volume 7 | Issue 2 | e31332