Edema, Effusion, and Hemorrhage

Edema and Effusion

• Edema involves the accumulation of fluid in tissues.
• Effusion involves the accumulation of fluid in body cavities.
• Swelling occurs due to the expansion of interstitial fluid volume in tissues or an organ.
• Edema and effusion are seen due to disorders which disturb cardiovascular, renal, or hepatic function.
• Edema is a critical clinical feature for diagnostic medicine.
• Edema presentation can be unilateral, bilateral, localized, or generalized.

Normal Fluid Dynamics

• Vascular hydrostatic pressure tends to push water and salts out of capillaries into the interstitial space.
• Plasma colloid osmotic pressure tends to pull water and salts back into vessels.
• A small net movement of fluid goes into the interstitium, then drains into lymphatic vessels and ultimately returns to the bloodstream.
• Ideally, fluid dynamics result in no edema.

Shifts in Fluid Dynamics

• Elevated hydrostatic pressure or diminished colloid osmotic pressure disrupts fluid balance, resulting in increased fluid movement out of vessels.
• Fluid accumulates if the net rate of fluid movement exceeds the rate of lymphatic drainage.
• Serosal surface involvement leads to fluid accumulation within a body cavity as an effusion.

Characteristics of Edema Fluids

• Edema fluids and effusions can be inflammatory or noninflammatory.
• Inflammation-related edema and effusions are protein-rich exudates.
• Protein-rich exudates accumulate due to increased vascular permeability caused by inflammatory mediators.
• Non-inflammatory edema and effusions are protein-poor fluids called transudates.

Causes of Edema

• Increased hydrostatic pressure is mainly caused by disorders that impair venous return.
• Reduced plasma osmotic pressure happens due to inadequate albumin synthesis or increased loss.
• Increased salt retention causes both increased hydrostatic pressure and diminished vascular colloid osmotic pressure.
• Disruption of lymphatic vessels impairs clearance of interstitial fluid, causing lymphedema, as seen in Filariasis which invovles the obstructive fibrosis of lymphatics and lymph nodes.
• Tissue factors: Increased oncotic pressure of interstitium/Decreased Hydrostatic pressure

Pathophysiologic Categories of Edema

• Increased Hydrostatic Pressure via impaired venous return can be caused by congestive heart failure, constrictive pericarditis, ascites (liver cirrhosis), venous obstruction or compression, thrombosis, external pressure, or lower extremity inactivity with prolonged dependency.
• Increased Hydrostatic Pressure happens from arteriolar dilation can be caused by heat or neurohumoral dysregulation.
• Reduced Plasma Osmotic Pressure (Hypoproteinemia) is the result of protein-losing glomerulopathies (nephrotic syndrome), liver cirrhosis, malnutrition, or protein-losing gastroenteropathy.
• Lymphatic Obstruction from inflammation, neoplasm, postsurgical complications, or postirradiation can cause edema.
• Sodium Retention is caused by excessive salt intake with renal insufficiency, increased tubular reabsorption of sodium, renal hypoperfusion, or increased renin-angiotensin-aldosterone secretion.
• Inflammation in acute, chronic, or angiogenesis settings can contribute to edema.

Mechanism of Systemic Edema

• Systemic edema can be caused by heart failure, renal failure, malnutrition, hepatic failure, and nephrotic syndrome.

Morphology of Edema

• Common Edema Sites: Subcutaneous tissue, lungs, and brain

Microscopic and Macroscopic Features of Edema

• Macroscopic: Edema is recognized easily.
• Microscopic: Clearing and separation of the extracellular matrix (ECM) and cell swelling.
• Diffuse in regions with high hydrostatic pressures
• Distribution is often influenced by gravity, such as dependent edema in the legs when standing, or in the sacrum when recumbent.
• Pitting Edema: Finger pressure over markedly edematous subcutaneous tissue displaces the interstitial fluid.
• Edema in severe renal diseases appears in loose connective tissue, such as periorbital edema.
• Subcutaneous edema is the accumulation of fluid in the subcutaneous tissues.

Pulmonary Edema

• Acute pulmonary edema is a critical form of local edema due to serious functional impairment.
• Fluids accumulate not only in the tissue space but also in the pulmonary alveoli.

Etiology and Pathogenesis of Pulmonary Edema

• Causes: Left heart failure, mitral stenosis, pulmonary vein obstruction, thyrotoxicosis, cardiac surgery, nephrotic syndrome, obstruction to the lymphatic outflow by tumor or inflammation, increased vascular permeability, or high altitude

Pulmonary Edema Features

• Lungs are often two to three times their normal weight.
• Sections show frothy, blood-tinged fluid, which is a mixture of air, edema, and extravasated red cells.
• Alveoli are filled with a smooth to slightly floccular pink material.
• Capillaries in the alveolar walls are congested with many red blood cells.

Cerebral Edema

• Brain edema can be localized or generalized, depending on the nature and extent of the pathologic process or injury.
• Localized cerebral edema is related to abscess or neoplasm.
• Generalized cerebral edema is caused by encephalitis, hypertension, or obstruction to venous outflow.
• Generalized edema leads to flat gyri, narrowed sulci, and compressed ventricular cavities.
• The brain is swollen.

Effusions

• Transudative effusions are typically protein-poor, translucent, and straw-colored.
• Effusions involving the pleural cavity are called hydrothorax.
• Effusions involving the pericardial cavity are called hydropericardium.
• Effusions involving the peritoneal cavity are called hydroperitoneum or ascites.
• Peritoneal effusions due to lymphatic blockage are known as chylous effusion and it appears milky because lipids are present that were absorbed from the gut.
• Exudative effusions are protein-rich and often cloudy due to the presence of white blood cells.
• Anasarca refers to severe and generalized edema which includes swelling of the subcutaneous tissues.

Hemorrhage

• Hemorrhage is simply bleeding.
• Hemorrhage can range from a minor cut to a severely spurting artery, or a ruptured spleen.
• Types: External bleeding (visible) an Internal bleeding.
• Simply means bleeding and is the escape of blood from a blood vessel.
• They may occur externally or internally into serous cavities such as hemothorax, hemoperitoneum, hemopericardium, or into a hollow viscus.

Extravasation Terminology

• Extravasation of blood into the tissues with swelling is known as a hematoma.
• Large extravasations into the skin and mucous membranes are called ecchymoses.
• Purpuras are small areas of hemorrhages (up to 1 cm) into the skin and mucous membrane.
• Petechiae are minute, pinhead-sized hemorrhages.
• A type of haemorrhage in which blood loss may be large and sudden.

Chronic Hemorrhage

• A type of haemorrhage in which small repeated bleeds may occur over a period of time
• Trauma to the vessel wall
• Spontaneous haemorrhage e.g. rupture of an aneurysm, septicaemia, bleeding diathesis (such as purpura), acute leukaemias, pernicious anaemia, scurvy.

Causes of Hemorrhage

• Inflammatory lesions of the vessel wall, such as bleeding of the chronic peptic ulcer.
• Neoplastic invasion, such as haemorrhage following vascular invasion in carcinoma of the tongue.
• Vascular diseases, such as atherosclerosis.
• Elevated pressure within the vessels, such as cerebral and retinal haemorrhage in systemic hypertension.

Effects of Hemorrhage

• Effects of blood loss depend upon 3 main factors: The amount of blood loss, the speed of blood loss and the site of haemorrhage.
• The loss up to 20% of blood volume suddenly or slowly generally, has little clinical effects because of compensatory mechanisms.
• A sudden loss of 33% of blood volume may cause death, while loss of up to 50% of blood volume gradually over a period of 24 hours may not be necessarily fatal.
• However, chronic blood loss generally produces iron deficiency anaemia, whereas acute haemorrhage may lead to serious immediate consequences such as hypovolaemic shock.