NCLEX RN Review Notes

Fluids and Electrolytes

Physiologic homeostasis depends on normal fluid, electrolyte, and acid-base balance, essential for cell function and life.

Function of Water in the Body

Water is vital:

1. Medium for metabolic reactions.
2. Transporter of nutrients and wastes.
3. Lubricant and insulator.
4. Regulates body temperature.
5. Eliminates waste products.

Body Fluid Compartments

• Intracellular Fluid (ICF): Inside cells, 2/3 (70%) of body fluid.
• Extracellular Fluid (ECF): Outside cells, 1/3 (30%) of body fluid.
  • Interstitial fluid: Between cells, 2/3 of ECF.
  • Intravascular fluid (plasma): Within vascular system, 1/3 of ECF.
  • Lymph and Transcellular fluid: Includes digestive juice and CSF.

Factors Influencing Body Water

• Composition is 50-60% water by weight.
• Age: Infants have more ECF (70-80%), easily lost.
• Gender: Males (60% water) > Females (50% water).

Fluid Gains and Losses

• Intake: Drinking and eating.
• Output: Insensible water loss (600-900 ml/day via lungs/skin).
• Sensible perspiration: Excessive sweating loses water and electrolytes

Body Fluid Regulation

• Regulated by osmoreceptors, ADH, RAAS, ANP.
• Osmoreceptors: Hypothalamus neurons sense serum osmolality.
  • Increased osmolality: Stimulates ADH.
  • Decreased osmolality: Inhibits ADH.
  • ADH retains water in renal tubules
• Fluid shifts happen via osmosis, diffusion, filtration, active transport.

Osmosis & Diffusion

• Osmosis: Movement of water from lesser to higher concentration.
• Osmolality: $mOsm/kg$ of solvent.
• Osmolarity: $mOsm/L$ of solution.
• Diffusion: Movement from high to low concentration.
• Influenced by molecule size, concentration, temperature.

Starling's Law of Capillary Forces

• Hydrostatic pressure pushes fluid out of capillaries.
• Osmotic pressure pulls fluid into capillaries (especially oncotic pressure from albumin).

Filtration and Active Transport

• Filtration: Movement of solute and solvent from high to low pressure.
• Active Transport: Movement from low to high concentration using ATP (e.g., Na-K pump).

Intravenous Solutions

• Isotonic: 0.9% NSS, D5W.
• Hypertonic: higher concentration of solids (e.g., TPN, D50).
• Hypotonic: lower concentration of solids (e.g., 0.45% NaCl).

Fluid Balance Systems

• Kidneys: Fluid and electrolyte balance.
• Lungs: $CO_2$ levels, water vapor.
• Skin: Fluid elimination via perspiration.
• Endocrine: Hormone regulation.

Electrolytes

• Cations (+): Sodium $Na^+$, potassium $K^+$, calcium $Ca^+$, magnesium $Mg^+$, hydrogen ions $H^+$.
• Anions (-): Chloride $Cl^-$, bicarbonate $HCO_3^-$, phosphate, sulfate.

Sodium ($Na^+$, 135-145 mEq/L)

• Major ECF cation, determines plasma osmolality.
• Regulates fluid volume and ECF volume.
• Skeletal/heart muscle contraction, nerve impulse transmission.
• Regulated by thirst, ADH, RAAS.

Potassium ($K^+$, 3.5 – 5.0 mEq/L)

• Major ICF cation.
• Regulates protein synthesis, glucose use/storage, action potentials.
• Conduction of nerve impulses and muscle activity.
• Regulated by aldosterone (excretes K) and hydrogen ions.

Calcium ($Ca^{2+}$ 2.25 – 2.6 mmol/L or 8.8-10.5 mg/dL)

• Bone strength, enzyme activation, muscle contraction, nerve transmission, blood clotting.
• Regulated by Vitamin D, PTH, thyrocalcitonin.
• Inverse relationship with phosphorus.

Phosphorus ($P$, 2.5 – 4.5 mg/dl)

• Major ICF anion, mostly in bones.
• Activates B-complex vitamins, ATP, cell division, and metabolism.

Magnesium ($Mg^{++}$, 1.8 – 3.6 mg/dl)

• Skeletal muscle contractions, CHO metabolism, ATP formation, DNA synthesis.
• Regulates blood coagulation and skeletal muscle contractility.
• Regulated by the kidney and GIT.

Chloride ($Cl^-$, 98 – 106 mEq/L)

• Major ECF anion, maintains ECF osmotic pressure.
• Forms HCL in stomach, participates in chloride shift.

Electrolyte Imbalances

Potassium

• Hypokalemia: <3.5 mEq/L. Causes include diuretics, alkalosis, and GI losses. Symptoms involves cardiovascular, neuromuscular, and gastrointestinal systems.
• Hyperkalemia: >5.0 mEq/L. Causes include kidney failure, acidosis, and medications. Symptoms include cardiac, gastrointestinal, and muscular dysfunction.

Sodium

• Hyponatremia: <135 mEq/L. Causes include excess sweating, diuretics, and excess hypotonic fluids. Symptoms include neurological, muscular, and gastrointestinal changes.
• Hypernatremia: >145 mEq/L. Causes include decreased excretion, increased intake, and limited water. Symptoms include heart, brain and hydration issues.

Calcium

• Hypocalcemia: <9.0 mg/dL. Causes include absorption blockage, added excretion, and low ionized calcium. Symptoms: Chvostek's & Trousseau's Signs.
• Hypercalcemia: >10.5 mg/dL. Causes include high intake, impaired excretion, and greater bone breakdown. Symptoms involve muscle weakness, lethargy.

Magnesium

• Hypomagnesemia: <1.3 mEq/L. Causes include alcohol and malnutrition. Symptoms involve nerves and muscles.
• Hypermagnesemia: >2.1 mEq/L. Causes include large magnesium intake. Symptoms involve the heart muscle weakness, drowsiness.

Phosphorus

• Hypophosphatemia: <3.0 mg/dL. Causes include Lacks intake and overexcretion. Symptoms: pump failure, hard breathing, osteoporosis.
• Hyperphosphatemia: >4.5 mg/dL. Causes include kidney dysfunction. Symptoms are hyper calcemia and cramps, which are opposite symptoms of phophatemia.

Fluid Volume Imbalances

Hypovolemia

• Fluid volume deficit due to fluid loss exceeding intake.
• Manifestations: Acute weight loss,, oliguria, dizziness, thirst, increased pulse.
• Diagnostic: Increased Hgb , increased BUN, increased urine osmality.
• Corrected with oral or IV fluids, isotonic electrolyte solution.

Hypervolemia

• Fluid volume excess due to water and sodium retention.
• Manifestations: Peripheral edema, distended veins, bounding pulse.
• Diagnostic: Decreased serum osmality, decreased urine -Na, decreased specific gravity.
• Managed with diuretics, dietary sodium restriction.

Acid Base Balance

• Normal pH is maintained by chemical, respiratory & renal regulation. pH influenced by $H<em>2CO</em>3$ and $HCO_3$
• Buffer systems: Remove or release hydrogen ions to maintain pH

Respiratory and Renal Regulation

• Respiratory: Retains or eliminates $CO_2$
• Renal: Eliminates or retains $HCO_3$ and hydrogen ions.

Respiratory Acidosis

• Excess of carbonic acid, increased hydrogen concentration.
• Causes: Airway obstruction, CNS depression, hypoventilation.
• Manifestations: Drowsiness, decreased BP, headache and coma.

Respiratory Alkalosis

• Results from conditions that cause overstimulation of the respiratory system.
• Causes: Hypoxia, Hysteria, Pain.
• Symptoms: Fast breathing, confusion, and seizures.

Metabolic Acidosis

• Total concentration of buffer lowered by excess acid and loss of base.
• Causes: Diabetic ketoacidosis, kidney Disease, high-fat diet.
• Manifestations: Alterate brain function.

Metabolic Alkalosis

• Body to basic of not enough avid.
• Causes: Diuretics, Excessive vomiting, GI suctioning
• Symptoms: Foggy brain, abnormal heart.