Transcapillary fluid balance in subcutaneous tissue of patients undergoing aortocoronary bypass with extracorporeal circulation

Abstract

Colloid osmotic pressure in plasma (COP_pl) from a cubital vein and in interstitial fluid (COP_if) in the subcutaneous tissue at heart level, and interstitial fluid pressure (P_if) at the same level, were measured in 18 healthy subjects and in 28 patients requiring aortocoronary bypass. Interstitial fluid was collected via subcutaneously implanted double nylon wicks and P_if was measured with the ‘wick-in-needle’ technique. Measurements were made preoperatively and 1 1/2 to 8 hours (mean 4 hours) after termination of extracorporeal circulation. P_if rose to 2.3 mmHg above the pre-bypass level. COP_pl concomitantly fell from 22.2 to 14.4 and COP_if from 12.4 to 10.1 mmHg. These changes were statistically significant. Although the relatively large COP_pl drop resulted in a net rise of 3.2 mmHg in filtration pressure, the incidence of pulmonary complications was low and no subcutaneous edema was discernible. The fall in COP_if and rise in P_if may be regarded as important edema-preventing mechanisms.

Key Words:

• aortocoronary bypass grafting
• extracorporeal circulation
• interstitial fluid colloid osmotic pressure
• interstitial tissue fluid pressure
• plasma colloid osmotic pressure
• transcapillary forces