Fluid Volume Excess Mechanisms

Fluid Volume Excess (FVE)

• Definition: FVE occurs when the body retains excessive amounts of water and sodium, leading to an increase in blood volume and fluid in the interstitial spaces.

Pathophysiology of FVE

• Mechanism: Imbalances in the body's homeostatic mechanisms lead to sodium and water retention.
• Isotonic Nature: In FVE, the concentration of sodium remains relatively balanced, so serum sodium levels and serum osmolality stay within normal ranges.
• Fluid Distribution: The excess fluid typically remains within the extracellular space, causing edema.
• Edema Formation: Fluid shifts from blood capillaries to interstitial tissues creating edema, (swelling) which can be localized or generalized. This can be due to:
  • Increased capillary hydrostatic pressure or membrane permeability.
  • Venous obstruction (e.g., blood clots) preventing fluid return to the vascular system.
  • Decreased plasma oncotic pressure (insufficient albumin) as it can no longer keep fluids in the vascular system.
  • Lymphatic obstruction preventing drainage of excess fluid.
• Generalized Edema: Anasarca describes widespread edema throughout the body. Pitting edema is a clinical sign of fluid buildup where pressure leaves a visible indentation in the skin.

Etiologies of FVE

• Conditions causing sodium & water retention: Heart failure, cirrhosis, renal failure, adrenal gland disorders (e.g., Addison's and Cushing's), and stress. Note that heart failure or other underlying disease can initially prevent the heart from functioning as it should, thus causing the sodium and water retention, and not the other way around:
  • Heart Failure: Ineffective pumping leads to fluid buildup.
  • Cirrhosis: Impaired liver function causes fluid buildup in the abdomen.
• Other Causes: Excessive sodium intake (e.g., processed foods, canned foods, salt substitutes), certain medications (corticosteroids), and overhydration with intravenous fluids.
• Stress: Stress can increase the body's production of hormones that promote fluid retention, primarily ADH and aldosterone.

Risk Factors of FVE

• Preeclampsia, heart disease, kidney dysfunction, diabetes with peripheral vascular disease, and hypertension.

FVE: Prevention Strategies

• Managing underlying conditions that cause the excess fluid buildup.
• Use of appropriate medications like diuretics, and antihypertensives.
• Monitoring daily weights to detect early signs of fluid changes.
• Limiting sodium intake and consulting dietary professionals for assistance.

Clinical Manifestations of FVE

• Symptoms: Neurological: Cerebral edema causing altered mental status or agitation. Cardiac: Tachycardia, elevated blood pressure, bounding pulses, pitting edema, jugular venous distention (JVD), and weight gain. Respiratory: Shortness of breath, dyspnea, tachypnea, moist crackles or wheezes in the lungs. Peripheral edema. Gastrointestinal: distension, and ascites, skin: pale and taut skin surfaces. Other symptoms: nausea, polyuria, nocturia, and lower BUN/Cr levels. Low hematocrit due to fluid dilution.
• Diagnosis: Diagnostic tests like electrolyte panels, serum osmolality, and hematocrit assess fluid balance. Possible imaging studies: echocardiogram or ultrasound (kidneys) as well as liver function tests (LFTs).

Treatment of FVE

• Fluid Management: Restricting fluid intake; monitoring daily fluid intake (oral and intravenous).
• Dietary Management: Following a sodium-restricted diet, consulting with a registered dietitian for tailored plans.
• Pharmacologic Therapy: Loop diuretics (e.g., furosemide), thiazide-type diuretics, and potassium-sparing diuretics.