Fluid Imbalances in Human Physiology

Fluid and Electrolyte Imbalance

• 60% of human body is fluid, mostly water
• Majority component in cells and bloodstream
• Solvent for body solutes/electrolytes
• Fluid constantly shifts between compartments

Body Fluid Compartments

• ICF: Intracellular fluid (within cells), 40% of total body weight
• ECF: Extracellular fluid (bloodstream), 20% of total body weight
• Interstitial fluid (between cells, tissue), part of ECF

Body Fluid Balance and Movement

• Homeostasis Goal: balance/equilibrium of solute and water across membrane
• Diffusion: passive movement from high to low concentration
• Osmosis: passive movement of water from high to low water concentration; semi-permeable membrane limits solute size
• Facilitated transport: active carrier proteins carry molecules through plasma membrane; ex: glucose facilitated by insulin
• Active transport: active movement against gradient; ex: Na+/K+ pump balances K+ ICF, Na+ ECF

Body Fluid Balance- Osmotic Movement

• Homeostasis: maintain equilibrium between body fluid (water) and solutes (electrolytes, proteins)
• Starling's law of capillary forces: osmotic and hydrostatic pressure in balance/opposition; more fluid may shift to ICF (swelling/edema) or ECF (dehydration)
• Hydrostatic pressure: water pushes fluid from vessels (high to low pressure) into cells
• Osmotic pressure: water pulled into cells from vessels (high to low)

Homeostasis Interrupted

• Fluid imbalances: fluid > or < “normal” inhibits body functions
• Body fluid functions: Universal biologic solvent; regulate electrolyte distribution in ECF and ICF; transport hormones, nutrients, toxins and waste products; transport O2 to cells; CO2 to lungs; regulate temperature

Fluid Homeostasis

• Fluid Homeostasis: balance of fluid intake & output
• Osmolarity: solute level in fluid, mechanism to monitor/assess body fluid status
• Mechanisms to maintain fluid homeostasis: thirst; ADH; renin-angiotensin-aldosterone system (RAAS); natriuretic peptides

Body Fluid Homeostasis: Renin-Angiotensin-Aldosterone System (RAAS)

• Hypotension, hypovolemia: low cardiac output (CO) and low fluid volume
• Low circulating fluid: reduced renal perfusion
• Kidneys: release renin, start RAAS compensation
• Renin converts angiotensin to angiotensin 1
• ACE (lungs) converts angiotensin 1 to angiotensin 2 (vasoconstrictor), increases blood pressure
• Triggers adrenal glands: release aldosterone (fluid retention), reabsorption of Na+, retention of Na + water
• Increased BP & fluid retention: return to normal blood volume

Fluid Imbalance: Edema

• Edema: swelling; increase in ISF and/or ICF
• Can hold 10-30L additional fluid
• Pitting edema: tissues displace; exceed tissue absorption capacity; usually in legs
• Nonpitting edema: firm; accumulations of plasma proteins (inflammation)
• Etiology (cause): high hydrostatic pressure, sodium retention, low osmotic pressure, inflammation, injury, low albumin

Fluid Imbalance: Assessment

• Symptoms determined by edema location: impaired movement, function (swelling)
• Increased extremity circumference: weight gain (1L=2.2 lbs) decreased blood flow (hypoxia)
• Wounds/ulcerations: skin susceptibility to injury
• Life-threatening edema: brain (cerebral), lungs (pulmonary), larynx (laryngeal)

Fluid Imbalances: Hypervolemia

• Excess fluid in body (overhydration), fluid volume overload
• Etiology (causes): high hydrostatic pressure (too much ECF); fluid shifts into interstitial fluid; Excess sodium; heart failure; Excess ADH (fluid retained)
• Excess ADH: **excess retention of fluid, (lack of diuresis) **; SIADH - dilutional hyponatremia; cirrhosis of liver - stimulates ADH release, impairs blood flow through liver and fluid accumulates (ascites)
• Assessment (clinical assessment): Jugular venous pressure; body weight; fluid balance

Fluid Imbalances: Hypovolemia

• Diminished fluid in body/bloodstream (dehydration); fluid volume deficit
• Causes: reduced fluid intake; excess fluid loss (ex: burn injuries, perspiration, diarrhea, vomiting); high osmotic pressure; insufficient ADH; diabetes insipidus; hypernatremia
• Complications: renal dysfunction related to decreased excretion of waste products
• Assessment : CV: low cardiac volume - hypotension (esp w/standing); tachycardia (elev HR to compensate low BP); reduced peripheral perfusion; weak/thready pulse; decreased arterial and venous pressure; Neuro: dizzy; weak; loss of consciousness; HA (poor cerebral blood/oxygen); Renal: low Urine output (<30ml/hr); high specific gravity

Electrolytes

• Electrolytes: charged ions (cations+, anions-)
• Essential for metabolism, energy production
• Cell function: nerve and muscle cells
• Impulse conduction: action potentials
• Muscle contraction
• Na+, K+: primary role in cell depolarization and repolarization
• Solutes: dissolved in ICF and ECF
• Protein molecules: essential body solute
• Maintains fluid balance, prevents fluid shift
• Transported substances throughout body

Electrolyte Balance- Concentration

• Normal Concentration: specific ranges varying between ICF and ECF.
• Sodium (Na+); Potassium (K+); Calcium (Ca++); Chloride (Cl-); Magnesium (Mg+); Phosphate

Electrolyte Balance - Movement

• Osmotic pressure: Electrolytes/solutes (proteins) pull water from cells (diffusion) and from ICF to ECF, to equalize concentration.
• Osmolarity: solutes/liter of body fluid; high serum osmolarity = excess electrolyte in blood; low serum osmolarity = reduced electrolyte in blood.
• Tonicity: osmotic pressure difference between two solutions; Isotonic; Hypotonic; Hypertonic.
• No fluid movement; Low; High osmolarity, respectively.

Sodium (Na+)

• Normal Range: 135-145 mEq/L
• 90% of ECF cations
• Imbalances: Hyponatremia (Serum Na++ < 135 mEq/L) ; Hypernatremia (Serum Na++ > 145 mEq/L)
• Primary role: Fluid volume balance
• Elevated Na+: Fluid retention
• Other functions: nerve impulse conduction; critical to muscle contraction
• Facilitates membrane transport through Na+/K+ pump

Sodium & Body Fluid

• Wherever sodium goes, water will follow: (sodium concentration regulates ECF volume and majority of osmotic activity)
• Hyponatremia: low ECF Na+ concentration; fluid shifts from ECF to ICF (cellular edema);
• Hypernatremia: High ECF Na+ concentration; fluid shifts from ICF to ECF (cellular dehydration)

Sodium Imbalance

• Severe Na imbalance: most dramatic to brain due to effect on cerebral fluid balance (or imbalance).
• Normal brain/normonatremia; Acute hyponatremia; Acute hypernatremia

Electrolyte Imbalance: Hyponatremia

• Hypervolemic: fluid overload dilutes Na+ (renal failure, heart failure); Excess fluid most common cause of hyponatremia; SIADH (syndrome of inappropriate ADH).
• Assessment: symptoms manifest <125 mEq/mL; Neuro/MS: HA, confusion, weakness, fatigue; muscle cramps; Severe (r/t cerebral edema): lethargy, seizure, coma, death; CV (excess volume): HTN, bounding pulse; Gl (excess volume, ascites): nausea, vomiting, diarrhea

Electrolyte Imbalance: Hypovolemic Hyponatremia

• Etiology: Renal loss (diuretics, renal disease); Non-renal loss (vomiting, Gl suctioning, wound drainage, sweating, burns); Symptoms manifest <125 mEq/mL
• Assessment: symptoms related to hypovolemia & hyponatremia/cell edema; Neuro/MS: HA, confusion, weakness, fatigue; muscle cramps; Severe (r/t cerebral edema): lethargy, seizure, coma, death; CV (hypovolemia): tachycardia, hypotn; Renal: low urine output (oliguria), azotemia; General (hypovolemia): thirst, poor skin turgor, dry mucosa

Electrolyte Imbalances: Hypernatremia

• Hypovolemic Hypernatremia: excess fluid loss (fluid lost, Na left behind); fever, diarrhea, tachypnea
• Assessment: Symptoms manifest >155 mEq/mL; symptoms r/t cellular dehydration; Neuro: restlessness, irritable, muscle twitching/spasms; Severe (r/t cerebral dehydration): lethargy, seizure, coma, death; CV: tachycardia, hypotn; General: thirst, fever

Electrolyte Imbalance: Hypervolemic Hypernatremia

• Etiology: hyperaldosteronism; excess salt intake, antacids with sodium bicarbs**
• Assessment: Symptoms manifest > 155 mEq/mL; Neuro: restless, irritable, muscle twitching/spasms, severe cerebral dehydration (seizure, coma, death); CV: tachycardia, hypotn; Resp: dyspnea, pulmonary congestion; general (hypervolemia): weight gain

Potassium (K+)

• Normal Range: 3.5-5 mEq/L
• Primary cation in ICF
• Hypokalemia: Serum K+< 3.5 mEq/ml
• Hyperkalemia: Serum K+ > 5 mEq/ml
• Primary role: Maintain action potentials; K+ gradient
• Other functions: cell depolarization, cardiac rhythms, muscle contraction, acid-base balance

Potassium & PH

• Intracellular pH Buffer: H+ and K+ ion exchange, shift between ICF and ECF to buffer pH; Alkalosis (high pH): H+ moves out of cell; K+ into cell (hypokalemia); Acidosis (low pH): H+ moves into cell; K+moves out (hyperkalemia)

Electrolyte Imbalance: Hypokalemia

• Etiology: Excess K+ excretion (renal); medication side effects (diuretics); severe GI loss(vomiting, diarrhea); inadequate intake of K+(NPO status, bariatric surgery); alkalosis
• Assessment: Decreases cell excitability; action potential; CV: hypoTN (low BP); Flattened T wave; prolonged PR interval; Neuro/MS: muscle fatigue, weakness, leg cramps; General: anorexia, n/v (decreased peristalsis)

Electrolyte Imbalance: Hyperkalemia

• Etiology: excess K+ retention; decreased K+ excretion (renal failure); massive injury/burn; acidosis
• Assessment: increases excitability; action potential; Decreases excitability threshold; CV: ventricular dysrhythmias; peaked T wave; widened QRS interval; Neuro/MS (early): numbness tingling, muscle cramps, confusion.

Calcium (Ca++)

• Normal Range: 8.7-10 mg/dL
• 99% of Ca+ bound in bones, teeth (primary mineral)
• 1% in circulation, ECF (measure serum levels)
• Hypocalcemia: Serum Ca++< 8.7 mg/dL
• Hypercalcemia: Serum Ca++ > 10 mg/dL
• Serum (free) calcium: nerve impulse conduction/excitability, muscle contraction; blood clotting factor
• Regulation: parathyroid hormone (PTH); decreased serum calcium stimulates PTH, calcium mobilized from bone to stabilize serum calcium

Electrolyte Imbalances: Hypocalcemia

• Etiology: insufficient supply of calcium; inadequate calcium or Vitamin D intake; hypoparathyroidism; increased excretion of calcium; renal disease, diarrhea; wound drainage.
• Assessment: increased neural excitability; neuro: muscle twitch/cramps , tetany, hyperreflexia, paresthesia (numbness, tingling); CV: hypoTN, arrhythmias; Resp: dyspnea, laryngospasm.

Electrolyte Imbalances: Hypercalcemia

• Etiology: metastatic cancer; immobility; hyperparathyroidism; excessive calcium or Vitamin D intake
• Assessment: decreased neural excitability; Neuro: muscle weakness, hyporeflexia/ataxia; CV: HyperTN, arrhythmias; MS: osteopenia, bone pain, pathologic Fx; GI: constipation, anorexia, n/v, cramps, hypoactive BS.

Phosphorus

• Normal Range: 2.5-4.5 mg/dL
• ICF anion: 14% in cells; 85% in bones
• Hypophosphatemia: Serum Phosphorus< 2.5 mg/dL
• Hyperphosphatemia: Serum Phosphorus > 4.5 mg/dL
• Roles: formation of teeth and bones; essential to carb, protein, lipid metabolism; ATP creation; building block of nucleic acids (RNA & DNA); regulate acid-base as buffer.
• Regulation: renal; PTH (elevated reduces phosphate retention; inverse relationship to calcium)

Hypophosphatemia & Hyperphosphatemia

• Hypophosphatemia: Serum Phosphorus <2.5mg/dL; decreased intestinal absorption (diarrhea, prolonged antacids, low Vit D); malnutrition; alcoholism; increased renal loss; alkalosis
• Assessment: decrease energy, deficiency in ATP; Neuro: tremors, paresthesia, weakness; MS: weak, joint stiffness; blood: Hemolytic anemia (hemolysis); impaired WBC & platelet function.
• Hyperphosphatemia: Serum Phosphorus > 4.5mg/dL; renal failure (reduced secretion); rhabdomyolysis (rapid production).
• Assessment: S/S related to complementary calcium deficit; Neuro: paresthesia, tetany; CV: Hypotension, arrhythmias.

Magnesium (Mg++)

• Normal Range: 1.5-2.5 mg/dL
• ICF cation: Majority stored in bone
• Hypomagnesemia: Serum magnesium <1.5mg/dL; Increased excretion/loss;
• Hypermagnesemia: Serum magnesium >2.5mg/dL; Decreased excretion
• Roles: Essential for absorption of Calcium & Vitamin D; Co-factor; enzymatic reactions; Facilitates ATP (Na-K pump); Transmits electrical impulses; Renal, Gl system; PTH stimulates magnesium reabsorption

Electrolyte Imbalance: Chloride (Cl-)

• Normal Range: 98-106 mEq/L
• ECF anion: majority stored in bone; Hypochloremia (serum chloride <98 mEq/L); Hyperchloremia (serum chloride > 106 mEq/L).
• Roles: essential for regulation of fluid (BP); pH balance; supports nerve impulse conduction, muscle contraction
• Facilitates absorption of nutrients
• Regulation: renal balances through selective absorption, excretion.

Hypochloremia & Hyperchloremia

• Hypochloremia: Serum Chloride < 98 mEq/L; increased excretion/loss of chloride, renal disease, excess sweating, pH imbalance (Chronic respiratory acidosis, metabolic alkalosis).
• Hyperchloremia: Serum Chloride > 106 mEq/L; rare; dehydration; medications (diuretics); heat exposure; decreased fluid intake; decreased excretion of chloride (renal disease).