Edema and Fluid Retention

Edema Essentials - Swell Story Starters

• Edema: Palpable swelling from ↑ interstitial fluid volume.
• Governed by Starling equation:
  • $J_v = K_f [(\P_c - P_i) - \sigma (\pi_c - \pi_i)]$
  • $J_v$: Net filtration
  • $K_f$: Capillary filtration coefficient
  • $P_c$: Capillary hydrostatic pressure
  • $P_i$: Interstitial hydrostatic pressure
  • $\sigma$: Reflection coefficient
  • $\pi_c$: Capillary oncotic pressure
  • $\pi_i$: Interstitial oncotic pressure
• Primary Causes:
  • ↑ $P_c$ (e.g., heart failure, DVT)
  • ↓ $\pi_c$ (e.g., nephrotic syndrome, liver failure)
  • ↑ Capillary permeability (e.g., inflammation, sepsis)
  • Lymphatic obstruction (e.g., lymphedema)

⭐ The four primary Starling forces governing fluid movement across capillaries are: capillary hydrostatic pressure ($P_c$), interstitial hydrostatic pressure ($P_i$), capillary oncotic pressure ($\pi_c$), and interstitial oncotic pressure ($\pi_i$).

Edema Evaluation - Spotting the Swell

• History & Physical Exam: Onset, duration, location (unilateral/bilateral), associated symptoms (dyspnea, pain), drug history, systemic disease review.
• Characterize Edema:
  • Pitting vs. Non-pitting:

- **1+**: Mild, 2mm pit, disappears rapidly.
- **2+**: Moderate, 4mm pit, disappears in 10-15 sec.
- **3+**: Deep, 6mm pit, may last >1 min; extremity swollen.
- **4+**: Very deep, 8mm pit, lasts 2-5 min; extremity grossly distorted.

⭐ Unilateral edema often suggests local causes (e.g., DVT, cellulitis), while bilateral edema usually points to systemic conditions (e.g., heart failure, nephrotic syndrome, cirrhosis).

Systemic Swells - Body's Big Bloats

Systemic Swells (anasarca) arise from body-wide fluid dysregulation. Key mechanisms: ↑ capillary hydrostatic pressure ($P_c$), ↓ plasma oncotic pressure ($\pi_p$), ↑ capillary permeability, or lymphatic blockage.

• Common Systemic Causes & Features:

  System	Key Features & Associations
  Cardiac	Dependent, pitting edema (ankles, sacrum); worse evening. JVP ↑, dyspnea, orthopnea. (e.g., Heart Failure)
  Renal	Periorbital puffiness (esp. AM), then generalized. Proteinuria (Nephrotic: >3.5 g/24h), hematuria (Nephritic).
  Hepatic	Ascites often precedes peripheral edema. Jaundice, spider nevi, hypoalbuminemia. (e.g., Cirrhosis)
  Nutritional	Generalized, soft, pitting edema. Severe hypoalbuminemia (serum albumin <2.5 g/dL). (e.g., Kwashiorkor)

⭐ Mechanism of edema in nephrotic syndrome: Massive proteinuria leads to hypoalbuminemia and decreased plasma oncotic pressure, reducing fluid return to capillaries.

📌 Mnemonic: HARK! The Swelling! (Hepatic, Albumin-low/Nutritional, Renal, Cardiac).

Local Leaks & Lumps - Regional Risers

• 📌 DVT Risk (Virchow's Triad): SHE (Stasis, Hypercoagulability, Endothelial injury).

High‑Yield Points - ⚡ Biggest Takeaways

• Starling forces (hydrostatic & oncotic pressures) govern fluid movement across capillaries.
• Nephrotic syndrome causes generalized edema via severe hypoalbuminemia (↓ plasma oncotic pressure).
• Heart failure (especially right-sided) causes dependent edema from ↑ venous hydrostatic pressure.
• Cirrhosis leads to ascites & edema via portal hypertension and impaired albumin synthesis.
• Lymphedema is protein-rich, typically non-pitting, resulting from impaired lymphatic drainage.
• Common drug culprits: Calcium Channel Blockers (CCBs), NSAIDs, thiazolidinediones, steroids.
• Pitting edema signifies excess interstitial fluid; non-pitting suggests lymphedema or myxedema.