Microvascular permeability after cardiopulmonary bypass. An experimental study

Microvascular permeability is presumed to increase during cardiopulmonary bypass, but this has not been directly demonstrated.

Therefore, a controlled experimental study was performed in dogs in which the permeability ratio of the small intestinal microvasculature was determined. Shortly after 120 minutes of cardiopulmonary bypass (experimental group, n = 7) or a sham procedure (control group, n = 7), the superior mesenteric venous pressure was raised in a stepwise fashion until the intestinal lymph/plasma protein concentration stabilized at a minimum value.

Minimal lymph/plasma concentration ratio (permeability ratio) of the total proteins and each of six protein fractions was greater in dogs that had been on bypass than in control dogs (p = 0.01 for total proteins and less than 0.05 for five of the fractions). The variability in this regard was large in both groups, and in some animals subjected to bypass the permeability ratio was more than twice the maximum value for the control group. The increase in permeability ratio was greater for large molecules. Inferences: Cardiopulmonary bypass results in a variable increase in microvascular permeability. This results primarily from an increase in the size of large pores in the microvascular barrier.