Aims: 

To measure colloid osmotic pressure in interstitial fluid (COPi) from human subcutaneous tissue with the modified wick technique in order to determine influence of local application of anaesthetics, pre-implantation condition of the wick and implantation time on COPi .

Methods: 

In 50 healthy volunteers interstitial fluid (IF) was collected by subcutaneous implantation of multi-filamentous nylon wicks. The study subjects were allocated to two groups, one for direct comparison of the use of dry and saline soaked wicks, and one for the elucidation of the possible effects of a eutectic mixture of local anaesthetic (Emla^®, Astra Zeneca, Sweden) cream on the COPi measurements. Implantation time was 30, 60, 75, 90 and 120 min., and IF was sampled in the skin of the shoulders at heart level. Colloid osmotic pressure was measured with a colloid osmometer.

Results: 

COPi estimated in fluid from wet as well as dry wicks declined during the first 75 min. of implantation period. COPi values for both types of pre-treatment increased slightly from 75 min. to 120 min. with no significant difference between 75 min. and 90 min. COPi measurements were not influenced by local anaesthesia and implantation was significant less painful when evaluated by visual analogue score in 10 study subjects.

Conclusion: 

The present study shows that COPi from subcutaneous tissue in humans is easily obtained and fluid harvesting is well tolerated when topical anaesthetic is used. The difference in COPi assessed by wet and dry wicks between 75 min and 90 min. of implantation are in accordance with previous reported values, with the assumption of same optimal wick implantation time. The use of topical analgesia does not influence COPi. Application of topical anaesthetics may establish the wick technique for sampling of IF in more accessible to persons who dislike technical procedures, including children.