Types of Edema

Etiological Classification

Depending on the underlying cause (etiology), the main types of edema include:

• Cardiac edema;
• Renal edema (strictly subdivided into two fundamentally different types: nephrotic and nephritic);
• Cachectic edema (often referred to in clinical practice as "starvation" edema);
• Hepatic edema;
• Angioneurotic edema;
• Allergic edema;
• Toxic edema, among others.

Each type has its specific clinical presentation while obeying the general laws of pathogenesis.

General Mechanisms: Hormones and the Lymphatic System

Systemic hormonal regulation of water and electrolyte balance plays a massive role in the progression of any edema syndrome. The key trigger in this process is hypovolemia—a pathological decrease in the circulating blood volume. It initiates the following neurohumoral cascade:

1. In response to decreased blood volume, the secretion of aldosterone rises sharply. This hormone causes massive sodium retention in the body, leading to hypernatremia.
2. Concurrently, the production of antidiuretic hormone (ADH) increases. The primary function of ADH is water retention, ultimately resulting in hypervolemia.

In addition to hormonal imbalance, dynamic lymphatic insufficiency inevitably develops in the tissues. This mechanism is driven by physical factors: due to the massive efflux of water from blood vessels into the interstitial space, a sharply increased volume of lymph is produced. The lymphatic vessels simply cannot adequately drain such a colossal amount of fluid, worsening the edema.

Cachectic ("Starvation") Edema

This type of edema manifests in stage III of general or protein malnutrition (cachexia). Under conditions of severe nutrient deficiency, the body is forced to use its own structural proteins to meet basic energy demands. Catabolism proceeds sequentially: blood plasma proteins (primarily albumin) are consumed first, followed by tissue proteins, including vital structural proteins of vascular membranes.

Pathogenesis of cachectic edema is complex, mixed, and unfolds in stages:

1. Oncotic factor (leading factor): Develops first. Protein depletion leads to marked hypoproteinemia (blood hypo-oncquia). Plasma oncotic pressure drops, and fluid shifts into the tissues.
2. Osmotic factor: Recruits secondarily. Fluid loss into tissues causes hypovolemia, which immediately activates the aldosterone–ADH system.
3. Membranogenic factor: Occurs due to the breakdown of proteins within the vascular wall itself, critically increasing its permeability to the fluid fraction of blood.
4. Hydrodynamic factor: Joins in terminal states (e.g., during starvation syncope or cachectic coma) when severe cardiovascular failure compounds the overall exhaustion.

Nephritic Edema

Etiologically, nephritic edema is inextricably linked to the early stage of acute diffuse glomerulonephritis—a severe condition based on infectious-allergic injury to the renal glomeruli.

The pathogenesis of nephritic edema follows a completely different sequence of mechanisms:

1. Membranogenic factor: In this case, it serves as the initiating factor. Generalized capillary damage occurs, leading to a sharp increase in microvascular permeability throughout the body.
2. RAAS activation: The inflammatory process in the glomeruli reduces renal blood flow. This immediately activates the renin-angiotensin-aldosterone system, causing pathological retention of Na^+ and H_2O ions.
3. Hypervolemia: A drop in the glomerular filtration rate leads to a sharp reduction in urine output. Consequently, the circulating blood volume pathologically increases.
4. Oncotic factor: Progressive blood hypo-oncquia develops. In nephritic edema, this is caused by three factors simultaneously:
5. Dilution of plasma proteins due to the established hypervolemia;
6. Moderate proteinuria (loss of protein in the urine);
7. Leakage of protein from the vascular bed into tissues through damaged capillary walls.