Proposal for a Cooling Patch Using the Heat Absorption Reaction of Urea to Reduce Pain During Needle Insertion for Vascular Access in Hemodialysis

Abstract

In order to reduce pain quickly during needle insertion for hemodialysis, we proposed and fabricated a novel disposable cooling patch using the heat absorption reaction of dissolving urea in water. We first examined the effect of amount of urea on temperature drop. We then constructed a prototype of the cooling patch using cotton sheets (30mm in length, 25mm in width) to hold urea particles (less than 2mm in diameter) . The prototype was attached to the forearm skin of a healthy subject. When water was dropped on the patch, time transient waveforms of skin temperature and heat flow through the prototype were measured at sampling frequency of 1Hz. Experimental results showed that skin temperature decreased to 25℃ under the conditions that 2mL of water was dropped on the cotton sheet with 0.9 grams or 0.015mol of urea particles On the other hand, two minutes were required to reach the minimum temperature. The method of dropping water affected the minimum skin temperature. Further study is needed to examine the feasibility of using smaller urea particles, and to find the appropriate method of adding water on the cooling patch in the hospital.