Interstitial fluid colloid osmotic pressure of the subcutaneous tissue in controls and patients before and after open-heart surgery: a comparison between the wick technique and the blister suction technique.

The purpose of this study was to compare the blister suction technique and the wick technique for measuring interstitial colloid osmotic pressure of subcutaneous tissue (COPif). Eight healthy volunteers and 14 patients undergoing aortocoronary bypass using extracorporal circulation (ECC) were included in the investigation. Colloid osmotic pressure was measured in fluid collected either from blisters (COPbl) developed by application of subatmospheric pressure to the chest skin, or from nylon wicks (COPw) implanted subcutaneously on the chest in the same area as the blisters were formed. Colloid osmotic pressure was then recorded on a colloid osmometer made for 5 microliter samples. In the patients, the measurements were performed 12-18 h pre-operatively (mean 15 h) and, on average, 4 h (range 1.5-7 h) following termination of extracorporal circulation. In the control subjects as well as in the patients, COPbl was significantly lower than COPw. However, the two types of measurements were found to change in the same direction, as a highly significant positive correlation exists between the two methods.