Fluid and Electrolytes: Comprehensive Nursing Review

Comprehensive vocabulary flashcards covering fluid compartments, fluid and electrolyte regulatory mechanisms, clinical cues, diagnostic laboratory ranges, and nursing interventions.

Intracellular Fluid (ICF)

Body fluid located inside cells, constituting approximately $70\%$ of total body water and about $40\%$ of adult body weight. Its most prevalent cation is potassium ($K^+$) and its primary anions are phosphate/phosphorus ($PO_4^{3-}$) and magnesium ($Mg^{2+}$).

Extracellular Fluid (ECF)

Body fluid located outside cells, making up approximately $30\%$ of total body water. Its predominant cation is sodium ($Na^+$), and major anions include chloride ($Cl^-$) and bicarbonate ($HCO_3^-$). It is subdivided into interstitial, intravascular, and transcellular compartments.

Interstitial Fluid

The portion of extracellular fluid located in the spaces between tissue cells, comprising approximately $\frac{2}{3}$ of the total $ECF$.

Intravascular Fluid

The liquid plasma component of extracellular fluid contained within blood vessels, accounting for approximately $\frac{1}{3}$ of total $ECF$ and measured through blood lab tests.

Transcellular Fluid

A specialized fluid compartment containing approximately $1\,L$ of fluid, including cerebrospinal, pericardial, synovial, intraocular, pleural fluids, peritoneal fluid, and gastrointestinal secretions.

Third Spacing

The abnormal accumulation and trapping of fluid in an extracellular body compartment where it cannot readily exchange with circulating $ECF$ and is unavailable for physiological fluid exchange (e.g., ascites or pleural effusion).

Diffusion

The passive movement of solute molecules from an area of higher concentration to an area of lower concentration across a permeable membrane without requiring energy.

Active Transport

The process of moving substances across a cell membrane against a concentration gradient, requiring metabolic energy in the form of adenosine triphosphate ($ATP$), such as the sodium-potassium pump.

Osmosis

The movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, requiring no cellular energy.

Osmotic Pressure

The drawing force or amount of pressure required to stop the osmotic flow of water across a semipermeable membrane, determined by the concentration of solutes in solution.

Hydrostatic Pressure

The pushing force exerted by fluid against the walls of a compartment; at the capillary level, it acts as the primary force pushing water and solutes out of the vascular system into interstitial tissues.

Colloid Osmotic Pressure (Oncotic Pressure)

The osmotic pulling force exerted by large plasma proteins, predominantly albumin, that draws and holds water inside the vascular capillary bed.

First Spacing

The normal, physiologically balanced distribution of fluid within intracellular and extracellular compartments.

Second Spacing

The abnormal accumulation of fluid within interstitial spaces, clinically manifested as edema.

Anasarca

Severe, generalized massive edema involving diffuse swelling across subcutaneous tissues throughout the body.

Antidiuretic Hormone (ADH)

A hormone stored and released by the posterior pituitary gland when hypothalamic osmoreceptors detect increased serum osmolality or fluid deficit; it directs renal tubules to reabsorb free water, diluting serum solutes.

Aldosterone

A mineralocorticoid hormone released by the adrenal cortex with potent sodium-retaining and potassium-excreting capabilities that acts on distal renal tubules to increase circulating blood volume.

Renin-Angiotensin-Aldosterone System (RAAS)

A compensatory endocrine pathway initiated when decreased renal perfusion causes the release of renin from the glomeruli, converting angiotensinogen to angiotensin II, leading to systemic vasoconstriction and aldosterone release to retain sodium and water.

Atrial Natriuretic Factor (ANF / ANP)

A cardiac peptide hormone released by the atria in response to elevated atrial pressure and excess blood volume, causing vasodilation and increased renal excretion of sodium and water.

Insensible Water Loss

Invisible, non-measurable vaporization of water through the skin and lungs amounting to approximately $900\,mL/day$, occurring without electrolyte loss.

Hypovolemia (Fluid Volume Deficit)

An isotonic dehydration characterized by a proportional loss of both water and electrolytes resulting in decreased circulating blood volume, manifested by tachycardia, hypotension, poor skin turgor, flat neck veins, and oliguria.

Hypervolemia (Fluid Volume Excess)

An excess of fluid volume where both water and electrolytes are retained in excess within the extracellular compartment, leading to a bounding pulse, hypertension, crackles, jugular venous distention ($+JVD$), and acute weight gain.

Overhydration (Water Intoxication)

An excess of pure water causing hemodilution, making cellular and electrolyte concentrations appear falsely decreased and carrying severe risks of cerebral edema and pulmonary compromise.

Hemoconcentration

An increase in the relative concentration of red blood cells, hemoglobin, and other solutes in the blood caused by a loss of plasma volume, commonly seen in fluid volume deficit.

Hemodilution

A decreased concentration of cells and solutes in blood plasma resulting from an excess of fluid volume or water intoxication, lowering hematocrit and BUN values.

Orthopnea

Dyspnea or difficulty breathing that occurs when lying flat or supine, commonly relieved by sitting upright in a high Fowler's position in patients with fluid overload or congestive heart failure.

Oliguria

Abnormally low urine output, specifically between $10 - 30\,mL/hr$ during moderate fluid volume deficit, reflecting decreased renal filtration and volume conservation.

Hyponatremia

A serum sodium level below $135\,mEq/L$, frequently resulting in cerebral edema and neurological symptoms such as headache, lethargy, muscle twitching, confusion, and potential seizures.

Hypernatremia

A serum sodium level exceeding $145\,mEq/L$, causing intracellular dehydration and characterized by extreme thirst, dry and sticky mucous membranes, flushed dry skin, agitation, disorientation, and seizures.

Hypokalemia

A serum potassium level below $3.5\,mEq/L$, typically resulting from loop diuretic use or gastrointestinal losses; characterized by muscle weakness, hypoactive bowel sounds, flattened T waves, premature ventricular contractions ($PVCs$), and increased digoxin toxicity risk.

Hyperkalemia

A serum potassium level above $5.0\,mEq/L$, often caused by renal failure or potassium-sparing diuretics; characterized by flaccid muscle paralysis, depressed deep tendon reflexes, bradycardia, and potentially fatal cardiac arrhythmias.

Hypocalcemia

A total serum calcium level below $8.6\,mg/dL$ (or ionized calcium below $4.5\,mg/dL$), often occurring after thyroidectomy/parathyroid injury; characterized by perioral and extremity numbness/tingling, hyperactive deep tendon reflexes, muscle tetany, and laryngospasm.

Hypercalcemia

A total serum calcium level exceeding $10.2\,mg/dL$, commonly associated with hyperparathyroidism or malignancy; clinical cues include muscle weakness, constipation, decreased deep tendon reflexes, renal calculi, and cardiac dysrhythmias.

Chvostek's Sign

A clinical indicator of neuromuscular irritability in hypocalcemia and hypomagnesemia, manifested as ipsilateral facial twitching when tapping the facial nerve anterior to the ear and below the zygomatic bone.

Trousseau's Sign

A sign of latent tetany in hypocalcemia characterized by carpopedal spasm (flexion of the wrist and fingers) induced by inflating a blood pressure cuff above systolic pressure for several minutes.

Hypomagnesemia

A serum magnesium level below $1.3\,mEq/L$, presenting with increased neuromuscular excitability, hyperactive deep tendon reflexes, tremors, tetany, and cardiac dysrhythmias.

Hypermagnesemia

A serum magnesium level greater than $2.3\,mEq/L$, presenting with neuromuscular depression, lethargy, loss of deep tendon reflexes, hypotension, and respiratory depression.

Hypophosphatemia

A serum phosphorus level below $2.5\,mg/dL$, resulting in impaired cellular energy ($ATP$) production, acute respiratory muscle failure, generalized weakness, and altered mental status.

Hyperphosphatemia

A serum phosphorus level exceeding $4.5\,mg/dL$, frequently observed in end-stage renal disease ($ESRD$); it lowers serum calcium levels and triggers neuromuscular signs identical to hypocalcemia.

Isotonic IV Solution

An intravenous solution with an osmolality matching that of blood plasma (such as $0.9\%\,NaCl$ and Lactated Ringer's), expanding extracellular and intravascular volumes without causing net fluid shifts into or out of cells.

Hypotonic IV Solution

An intravenous fluid with lower osmolality than plasma (such as $0.45\%\,NaCl$) that causes water to shift into cells, making them swell.

Hypertonic IV Solution

An intravenous solution with higher osmolality than plasma (such as $3\%\,NaCl$ or $D5\,0.45\%\,NaCl$ in the bag) that draws water out of cells into the vascular space, causing cells to shrink.

Phlebitis

Inflammation of a vein wall associated with IV therapy, characterized by warmth, erythema, tenderness, and a palpable venous cord along the vein path.

Infiltration

The inadvertent leakage of non-vesicant intravenous fluid into surrounding subcutaneous tissues, characterized by localized coolness, swelling, blanching, and slowed infusion rate.

Extravasation

The inadvertent infiltration of a vesicant drug or solution into perivascular tissue, capable of causing severe pain, blistering, and tissue necrosis.

Hypoproteinemia

An abnormally low level of plasma proteins, specifically albumin, which reduces vascular colloid osmotic pressure and leads to fluid shifts into the interstitial space, producing systemic edema and ascites.