7.Two causes of low oncotic pressure are cirrhosis, where the liver makes fewer proteins and nephrotic syndrome, where proteins are lost through the urine.
8.With less protein in the blood the oncotic pressure falls, which lowers the overall osmotic pressure, which drives water out of the blood vessels and into the tissues, called edema.
9.A transudative pleural effusion occurs when too much fluid starts to leave the capillaries either because of increased hydrostatic pressure or decreased oncotic pressure in the blood vessels.
10.Regardless of the cause, low oncotic pressure leads to fluid moving from the capillary and into the interstitial space throughout the body, and in the lungs that results in pulmonary edema.
11.The next factor, though, is oncotic pressure; which is a type of osmotic pressure exerted by cells and proteins that can't cross the capillary membrane and therefore tend to attract fluid.
12.To understand pulmonary edema, let's first talk about the three main factors that determine how fluid moves between the capillaries and interstitial fluid, which are the hydrostatic pressure, oncotic pressure and capillary permeability.