Interstitial hydrostatic pressures in patients undergoing CABG and valve replacement.

Using the Scholander-Hargens wick technique to measure interstitial fluid hydrostatic pressure (IFP) in thigh muscle (MIP) and subcutaneous tissue (SQIP), we have studied 12 patients undergoing cardiopulmonary bypass (CPB). Simultaneous measurements were made of serum total proteins (TP) and colloid osmotic pressure (COP). Bypass was carried out with a nonblood, noncolloid prime. In the postoperative period, colloid and blood were given which raised COP above prebypass levels (see Table II). MIP rises more with hemodilution than does SQIP and is less negative throughout. MIP rises faster when COP drops than does SQIP. These findings suggest that subcutaneous tissue interstitial space is loose and has a high compliance, whereas muscular tissue interstitial space is tight and has a low compliance. The increased pressure represents increase in fluid which is then removed promptly as COP is restored in the postoperative period. Experimental studies in animals show a response similar to MIP in the myocardium.