lesson 98- edema

Presented by: Hector Zerpa, St. George's University School of Veterinary Medicine, Grenada, West Indies

By the end of this session, students will be able to:

Describe edema classification according to cause:
- Inflammatory: Understanding the role of pathogens and immune responses.
- Non-inflammatory: Recognizing conditions leading to edema without a direct inflammatory response.
Recognize the function of lymphatic vessels in the development of edema. These vessels play a crucial role in managing fluid balance and protein transport in the body.
Describe the four basic causes of edema, emphasizing the mechanisms that lead to fluid accumulation.
Describe the development of:
- High-pressure pulmonary edema: Discussing the physiological changes and clinical implications.
- Low-pressure pulmonary edema: Identifying causes and how they differ from high-pressure types.
Predict potential therapeutic targets to treat pulmonary edema, focusing on innovative treatment approaches and evidence-based practices.

Starling Forces and Fluid Homeostasis: Overview of forces affecting fluid movement across capillaries.
Source: Netter's Essential Physiology, Chapters 1, 2-11
Consequences of Capillary Hydrostatic Pressure: Discuss how increased capillary hydrostatic pressure leads to fluid leakage into interstitial spaces, contributing to edema.

The lymphatic system functions as an accessory route for interstitial fluid to return to the bloodstream. Its vital roles include:
- Creating a pumping system to facilitate fluid movement.
- Carrying proteins and large particles away from tissue spaces to maintain fluid homeostasis and prevent edema.

What is Edema?: Abnormal accumulation of fluid in interstitial spaces or body cavities, leading to tissue swelling and can result in various clinical manifestations depending on the severity and location.
Interstitial Space: Defined as the area between cells and capillaries where fluid exchange occurs. Contains extracellular matrix, composed mostly of collagen fibers, elastic fibers, and glycosaminoglycans (GAGs), which support tissue structure.

Inflammatory Edema:
- Caused by increased vascular permeability due to inflammation, resulting in fluid extravasation (e.g., in cases of infections, tissue injury).
- Typically mediated by cytokines and other inflammatory markers.
Non-inflammatory Edema:
- Results from mechanical and metabolic dysfunction without a clear inflammatory process (e.g., heart failure, hypoproteinemia).
- Often signifies systemic issues.

Inflammation: Characterized by active processes with fluid leaking from blood vessels causing stasis and local tissue swelling.
Congestion: Defined as a passive accumulation due to a decrease in outflow; increased hydrostatic pressure pushes fluid through vessel walls, contributing to edema.

Increased Vascular Permeability:
- Associated with inflammatory processes; causes include:
  - Infectious agents (Viruses, Bacteria, Rickettsia)
  - Immune-mediated conditions such as allergies and autoimmune diseases.
  - Neovascularization, particularly in cancer, affecting blood vessel integrity.
  - Anaphylaxis and exposure to toxins.
  - Clotting abnormalities impacting blood flow.
  - Various metabolic abnormalities (e.g., diabetes).
Increased Intravascular Hydrostatic Pressure:
- Often results from increased blood volume (congestion);
- Localized edema due to cardiac failure can occur:
  - Right Heart Failure: Leads to ascites (fluid accumulation in the abdominal cavity).
  - Left Heart Failure: Results in pulmonary edema.
Decreased Intravascular Oncotic Pressure:
- Occurs due to:
  - Decreased albumin production (e.g., malnutrition, liver disease).
  - Excessive albumin loss (gastrointestinal or renal disease).
  - Water intoxication (though this is rare).
Decreased Lymphatic Drainage:
- Results from lymphatic obstruction or compression (e.g., by tumors leading to lymphedema).
- Conditions such as intestinal lymphangiectasia can lead to protein-losing enteropathies, exacerbating fluid retention.

In a clinical scenario involving a dog with respiratory distress and a history of canine distemper virus exposure, potential signs suggest interstitial pulmonary edema.Mechanism options may include: A. Decreased pulmonary capillary oncotic pressureB. Increased pulmonary capillary hydrostatic pressureC. Increased endothelial permeabilityD. Obstruction of lymphatic drainageE. Compensatory fluid retention by kidneys

Pulmonary Edema: The accumulation of fluid in the lung's interstitium and alveoli, disrupting gas exchange.
Classification:
- High-pressure edema: Typically arises from left-sided heart failure (cardiogenic), which leads to increased pressure in pulmonary circulation.
- Low-pressure edema (noncardiogenic): Results from increased vascular permeability due to various inflammatory processes (e.g., infections).

Comparison of normal versus unhealthy pulmonary pressures is crucial; during heart failure:
- Increased pulmonary pressure results in interstitial edema and can cause excessive fluid accumulation leading to alveolar edema, potentially life-threatening.
Unilateral vs. Bilateral Heart Failure:
- Left heart failure tends to be more prevalent and primarily leads to pulmonary edema.
- Right heart failure typically results in peripheral edema and ascites.

This section engages students in identifying potential therapeutic approaches, focusing on both pharmacologic and non-pharmacological strategies to alleviate symptoms and address underlying causes.

Topics covered include:

Edema classification (inflammatory vs. non-inflammatory)
Lymphatic vessel function
Causes of edema
High-pressure vs. low-pressure pulmonary edema Prepare for upcoming discussions on Congestive Heart Failure, emphasizing the importance of early identification and management strategies for better clinical outcomes.