Nutrients and oxygen routinely leave blood vessels to enter the tissues those vessels sustain. When microbes invade, white blood cells and certain proteins leave vessels to attack the germs. But when too much fluid leaves blood vessels, it can accumulate abnormally in spaces between vessels and tissues. In the abdominal region such accumulation is known as ascites, which may be loculated or non-loculated.
Ascites is the accumulation of serous fluid in the peritoneal cavity, according to "Taber's Cyclopedic Medical Dictionary." "Serous" means thin and watery rather than syrupy, states the medical dictionary. The "peritoneal cavity" is the space between the two layers of a double-layered membrane called the peritoneum, observes Gerard Tortora in his book "Principles of Human Anatomy, 9th Ed." Most abdominal organs lie in the peritoneal cavity, Tortora points out.
"Loculated" refers to loculi, plural of loculus, which means space or cavity, states "Taber's Cyclopedic Medical Dictionary." Loculated fluid is fluid trapped in spaces and, consequently, unable to flow freely, suggest Sophia Schiza et al in the journal "Pulmonary Pharmacology and Therapeutics." Hence, "loculated ascites" implies ascitic fluid trapped in spaces within the peritoneal cavity. Non-loculated ascites implies ascitic fluid not pocketed in spaces but able to flow from one part of the peritoneal cavity to another.
A primary cause of ascites is high blood pressure in the veins that lead to the liver (portal hypertension), note Sue Huether and Kathryn McCance in their book "Understanding Pathophysiology, 2nd Ed." This can arise from heart failure impeding the flow of blood from heart to lungs, impediments in the circulatory system between the liver and the heart, or obstructions in the liver itself, observe Huether and McCance.
Additionally, sodium retention and the loss of a protein called albumin can contribute to ascites, states the book "Medical-Surgical Nursing, 6th Ed.," by Joyce Black et al. Sodium retention causes fluid in the circulatory system to increase, adding to portal hypertension. The loss of albumin from blood decreases capillary osmotic pressure--blood's capacity to hold fluid inside vessels. When portal hypertension exceeds osmotic pressure, fluid leaves vessels, enters the peritoneal cavity and, thereby, causes ascites, note Huether and McCance.
Conditions leading to portal hypertension, sodium retention or albumin loss include: cirrhosis of the liver; right-sided heart failure; inflammation of the peritoneum associated with tuberculosis; complications of inflammation of the pancreas; and cancer, observe Black et al. To these may be added: malnutrition; constrictive pericarditis (inflammation of the sac enclosing the heart); and nephrotic syndrome (a kidney condition involving massive loss of proteins in urine), note Huether and McCance.
Ascites causes weight gain and increased abdominal girth, state Huether and McCance. Large volumes of ascitic fluid (10 to 20 litres) will displace the diaphragm (the muscle that regulates breathing), causing laboured breathing and shortness of breath, Huether and McCance indicate. While large accumulations of ascitic fluid are obvious, marked by bulging flanks and a distended abdomen, smaller amounts of fluid may evade detection, suggest Black et al.