Interstitial colloid osmotic and hydrostatic pressures in subcutaneous tissue of human thorax

Abstract

Interstitial colloid osmotic pressure ( π i) of human subcutaneous tissue was measured simultaneously by three different techniques: in fluid collected by implanted nylon wicks or empty wick catheters, and by implantable colloid osmometers. Hydrostatic pressure in interstitial fluid ( P i) was measured by wick catheters and by wick-in-needle technique. The implantations were done at heart level on the side of the thorax in 15 healthy male subjects. They were divided in two groups, one for a direct comparison of the methods and one for a further investigation on the effect of suction in empty wick catheters. In nylon wicks implanted for 60 min, π i averaged about 16 mm Hg in both groups. In fluid sampled with empty wick catheters, a suction pressure of −10 cm H 2O, and 60-min implantation time, the mean π i was 10.5 and 12.9 mm Hg in the first and second group, respectively. Two factors contributed to lowering of π i in empty wick catheters: dilution of the samples by saline contained in the wick catheter before implantation, and a π i-lowering effect of suction. Measurements with implantable colloid osmometers averaged 9.8 mm Hg. Mean implantation time was 30 min. However, the π i value was positively correlated to implantation time and linear extrapolation to 60 min gives π i values similar to implanted nylon wicks. We therefore conclude that the three methods give the same π i in the same area of human subcutaneous tissue provided equal implantation time and little or no suction in empty wick catheters. P i was −0.2 mm Hg with both wick catheter and wick-in-needle technique.