Ch 7: Fluid Imbalance Terms

Hydrostatic pressure

The force of fluid pressure in the bloodstream that pushes water out of the capillaries and into the interstitial space.

Osmotic pressure

Pressure exerted by solutes in a solution that pulls water into the bloodstream from the interstitial space.

Oncotic pressure

Also called “colloid osmotic pressure,” it is the force exerted specifically by albumin in the blood to keep fluid within the vessel.

Osmolality vs. Osmolarity

• Osmolality: Concentration of solutes per kg of solution.
• Osmolarity: Number of osmoles of solute per liter of solution.

Fluid Compartments: ICF, ECF, & ISF

1. Intracellular Fluid (ICF): Fluid inside the cells (2/3 of total body water).
2. Extracellular Fluid (ECF): Fluid outside the cells (1/3 of total body water).
3. Interstitial Fluid (ISF): Filtrate of blood located between the cells and capillaries.

Edema

The accumulation of excess fluid in the ISF and ICF compartments, often caused by elevated hydrostatic pressure or diminished osmotic/oncotic pressure.

Isotonic Solution

A solution with the same osmotic pressure as blood (e.g., 0.9\% \text{ NaCl}), resulting in no net fluid shift.

Hypotonic Solution

A solution with fewer particles than blood (e.g., 0.45\% \text{ NaCl}), causing water to shift out of the ECF and into the cells (cell swelling).

Hypertonic Solution

A solution with more particles than blood (e.g., 3\% \text{ NaCl} or Mannitol), causing water to shift out of the cells and into the ECF (cell shrinkage).

Electrolyte Normal Values

• Sodium (Na^{+}): 135-145 \text{ mEq/L}

• Potassium (K^{+}): 3.5-5.2 \text{ mEq/L}

• Calcium (Ca^{2+}): 8.5-10.5 \text{ mg/dL}

• Magnesium (Mg^{2+}): 1.5-2.5 \text{ mEq/L}

Hyponatremia

• Definition: Serum sodium level < 135 \text{ mEq/L}.
• Symptoms: Headache, confusion, muscle cramps, lethargy, and in severe cases, seizures and coma.

Hypernatremia

• Definition: Serum sodium level > 145 \text{ mEq/L}.
• Symptoms: Extreme thirst, dry/sticky mucous membranes, agitation, and CNS dysfunction due to cell dehydration.

Hypokalemia Symptoms & Diet

• Symptoms: Muscle weakness, leg cramps, and cardiac arrhythmias (U-wave on EKG).

• Dietary Management: Increase intake of potassium-rich foods like bananas, orange juice, potatoes, and spinach.

Hyperkalemia Symptoms

• Symptoms: Muscle cramping, diarrhea, and life-threatening cardiac changes (peaked T-waves).

Hypocalcemia

• Definition: Serum calcium level < 8.5 \text{ mg/dL}.
• Symptoms: Paresthesia around the mouth/fingers, muscle spasms, tetany, positive Chvostek’s sign, and positive Trousseau’s sign.

Hypercalcemia

• Definition: Serum calcium level > 10.5 \text{ mg/dL}.
• Symptoms: Muscle weakness, constipation, renal calculi (kidney stones), and lethargy/decreased reflexes.

Hypomagnesemia

• Definition: Serum magnesium level < 1.5 \text{ mEq/L}.
• Symptoms: Hyperactive deep tendon reflexes (HTN), tremors, muscle cramps, and dangerous arrhythmias like Torsades de Pointes.

Hypermagnesemia

• Definition: Serum magnesium level > 2.5 \text{ mEq/L}.
• Symptoms: Hyporeflexia (diminished reflexes), hypotension, bradycardia, and respiratory depression.

Aldosterone & ADH Effects

• Aldosterone: Stimulates the nephron to reabsorb Na^{+} and water into the blood and excrete K^{+} into the urine.
• ADH (Anti-diuretic Hormone): Stimulates the nephron to reabsorb only water into the blood.

Oliguria

Low urine output, defined as less than 400 \text{ mL} per day or less than 20 \text{ to } 30 \text{ mL} per hour.

Calcium Relationships

1. Calcium-Phosphate: Inverse relationship; when calcium is high, phosphate is low.
2. Calcium-Albumin: About half of calcium is bound to albumin; low albumin levels can lead to a low total calcium reading.

Fluid Volume Assessment

• Deficit (Dehydration): Dark urine, dry mucous membranes, poor skin turgor, hypotension, and tachycardia.
• Excess (Overload): Edema, jugular venous distension (JVD), crackles in lungs, and weight gain.

Ounce to mL Conversion

1 \text{ ounce (oz)} = 30 \text{ milliliters (mL)}

Hypophosphatemia

• Definition: Serum phosphate level < 2.5 \text{ mg/dL}.
• Symptoms: Muscle weakness, tremors, paresthesia, bone pain, and confusion.

Hyperphosphatemia

• Definition: Serum phosphate level > 4.5 \text{ mg/dL}.
• Symptoms: Tetany, muscle cramps, and paresthesia (often mimicking hypocalcemia) due to the inverse relationship with calcium.