Interstitial fluid pressure changes during cardiopulmonary bypass.

The effects of cardiopulmonary bypass using hemodilution on interstitial fluid pressure were measured using the Scholander wick technique. In 10 mongrel dogs, interstitial fluid pressure was measured in subcutaneous tissue, skeletal muscle, stomach, and left ventricle before and during 2 hours of cardiopulmonary bypass. Changes in interstitial fluid pressure were correlated with plasma colloidal osmotic pressure and duration of bypass. In subcutaneous tissue and skeletal muscle, interstitial fluid pressure increased during bypass; it did not change in the stomach. End-diastolic interstitial fluid pressure in the left ventricle increased significantly. These increases in pressure were presumably due to an increase in interstitial water. The rise in interstitial fluid pressure acts to partially neutralize the fall in plasma colloidal osmotic pressure.