Oncotic Pressure (Colloid Osmotic Pressure) Albumin Hypoalbuminemia Explained Oncotic pressure (colloid osmotic pressure) and albumin (hypoalbuminemia) explained in fluid movement: Fluid and electrolytes #shorts review. Oncotic pressure is the pulling effect on water, and it is highly dependent on a protein called albumin, which is a colloid. Albumin hangs out in high amounts within the capillaries, and it is so big that it cannot escape the capillary walls. Because there is a high concentration