Fluid Regulation

Fluid States and Distribution

  • Providers assess patients' fluid state: wet vs. dry.

  • Importance of knowing where fluid is located (intravascular, interstitial, intracellular).

Hydrostatic Pressure

  • Defined as the outward force of fluid inside a vessel.

  • Generated by ventricular contraction; relates directly to blood pressure.

  • Higher in vessels than in tissues (interstitial space).

Colloid Osmotic Pressure

  • Also known as particle pull; attracts water towards particles.

  • Present in both the intravascular and interstitial spaces.

  • Determines fluid movement and balance in the body.

Lymphatic System

  • Maintains fluid balance and protects from infection.

  • Removes excess interstitial fluid; lymphatic drainage is crucial.

Osmolality

  • Describes solute concentration in the blood; normal range: 275−295275-295 mOsm/kg.

  • High osmolality indicates dehydration (more particles than expected).

Homeostasis Regulation

  • Anti-diuretic hormone (ADH) and renin-angiotensin-aldosterone system (RAAS) regulate fluid balance.

  • Hypothalamus monitors fluid levels and triggers thirst and ADH release when dehydrated.

  • Natriuretic peptides respond to fluid overload, promoting vasodilation and fluid displacement.

IV Fluids and Tonicity

  • Isotonic: Same concentration as blood (e.g., normal saline; 0.9 ext{% NaCl}).

  • Hypotonic: More water than particles; shifts fluid into cells (e.g., 0.45 ext{% NaCl}).

  • Hypertonic: More particles than water; pulls fluid into the vascular space (e.g., 3 ext{% NaCl}).

Edema Causes

  • Excessive fluid volume causing high hydrostatic pressure.

  • Low osmotic pressure due to inadequate plasma proteins (e.g., hypoalbuminemia).

  • Inflammatory mediators causing fluid leakage into tissues.

Types of Edema

  • Dependent edema: Fluid accumulation in areas closest to the ground due to gravity.

  • Pitting edema: Indentation remains after pressure is applied.

  • Third spacing: Fluid accumulation in abdomen (e.g., ascites).

Dehydration Causes

  • Low intake, excessive loss (surgery, exercise), or osmotic changes (e.g., uncontrolled diabetes).

Clinical Assessment of Dehydration

  • Signs: flushed skin, thirst, dry mouth, decreased urination, rapid heartbeat.

  • Expect high sodium levels if dehydrated due to fluid loss.

  • Evaluate hematocrit for signs of dehydration (increased due to fluid loss).