Fluid, Electrolyte, and Acid-Base Imbalances

Flashcards for Chapter 17: Fluid, Electrolyte, and Acid-Base Imbalances

Homeostasis

Maintenance of a stable internal environment in the body regarding fluid and electrolyte composition and volume.

Water Content of the Body

Ranges from 50% to 60% of adult body weight, varies with body mass, gender, and age. Lean body mass has a higher percentage of water than fat tissue.

Intracellular Fluid (ICF)

The fluid inside the body's cells, approximately 28 L in volume.

Extracellular Fluid (ECF)

The fluid outside the body's cells, includes plasma (3 L) and interstitial fluid (IF) (10 L).

Fluid Gain or Loss Calculation

1 L of water weighs 2.2 pounds (1 kg), and body weight change is an excellent indicator of overall fluid volume loss or gain.

Electrolytes

Substances whose molecules dissociate into ions when placed in water. Cations are positively charged, and anions are negatively charged. Concentration is expressed in milliequivalents (mEq)/L.

ICF Electrolyte Composition

Prevalent cation is K+ (potassium), prevalent anion is PO43− (phosphate).

ECF Electrolyte Composition

Prevalent cation is Na+ (sodium), prevalent anion is Cl− (chloride).

Diffusion

The movement of molecules from an area of higher concentration to an area of lower concentration.

Active Transport

The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy (ATP).

Osmosis

The movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Osmotic Pressure

The pressure required to prevent the flow of water across a semipermeable membrane via osmosis.

Plasma Osmolality

Calculated as (2 × Na) + (BUN / 2.8) + (glucose /18). Normal range is between 280 and 295 mOsm/kg.

Isotonic Solution

A solution with the same solute concentration as another solution, especially one in a cell or a body fluid.

Hypotonic Solution

A solution with a lower solute concentration than another solution; in cells, it is hypoosmolar.

Hypertonic Solution

A solution with a higher solute concentration than another solution; in cells, it is hyperosmolar.

Hydrostatic Pressure

The force of fluid within a compartment; in blood vessels, it is the blood pressure generated by the heart's contraction.

Oncotic Pressure

Also known as colloid osmotic pressure, it is the osmotic pressure caused by plasma proteins.

Edema

Caused by shifts of plasma to interstitial fluid due to elevation of venous hydrostatic pressure, decrease in plasma oncotic pressure, or elevation of interstitial oncotic pressure.

First Spacing

Normal distribution of fluid in ICF and ECF.

Second Spacing

Abnormal accumulation of interstitial fluid (edema).

Third Spacing

Fluid is trapped where it is difficult or impossible for it to move back into cells or blood vessels.

Hypothalamic-Pituitary Regulation of Water Balance

Osmoreceptors in hypothalamus sense fluid deficit or increase, stimulating thirst and ADH release. Decreased plasma osmolality suppresses ADH release.

Renal Regulation of Water Balance

The main organ for regulating fluid and electrolyte balance by adjusting urine volume and selectively reabsorbing water and electrolytes. Renal tubules are sites of action of ADH and aldosterone.

Adrenal Cortical Regulation of Water Balance

Releases hormones such as glucocorticoids (cortisol) and mineralocorticoids (aldosterone) to regulate water and electrolytes.

Cardiac Regulation of Water Balance

Natriuretic peptides are antagonists to the RAAS, suppressing aldosterone, renin, and ADH secretion to decrease blood volume and pressure.

GI Regulation of Water Balance

Oral intake accounts for most water. Small amounts of water are eliminated by the GI tract in feces. Diarrhea and vomiting can lead to significant fluid and electrolyte loss.

Gerontologic Considerations for Water Balance

Structural changes in kidneys decrease ability to conserve water; hormonal changes include a decrease in renin and aldosterone and increase in ADH and ANP; subcutaneous tissue loss leads to increased moisture loss.

Fluid Volume Deficit (FVD)

Also known as hypovolemia, it is an abnormal loss of body fluids, inadequate fluid intake, or plasma to interstitial fluid shift. Dehydration is the loss of pure water without a corresponding loss of sodium.

Fluid Volume Excess

Also known as hypervolemia, it is excess fluid intake, abnormal fluid retention, or interstitial-to-plasma fluid shift. Weight gain is the most common clinical manifestation.

Sodium (Na+)

Plays a major role in ECF volume and concentration, generating and transmitting nerve impulses, muscle contractility, and regulating acid-base balance.

Hypernatremia

High serum sodium that may occur with inadequate water intake, excess water loss, or sodium gain, causing hyperosmolality and cellular dehydration. Primary protection is thirst.

Hyponatremia

Results from loss of sodium-containing fluids and/or from water excess. Mild symptoms include headache, irritability, and difficulty concentrating. Severe symptoms include confusion, vomiting, seizures, and coma.

Potassium (K+)

Major ICF cation necessary for resting membrane potential of nerve and muscle cells, regulating intracellular osmoality, promoting cellular growth, maintenance of cardiac rhythms, and acid-base balance.

Hyperkalemia

High serum potassium caused by impaired renal excretion, shift from ICF to ECF, or massive intake of potassium. Most common in renal failure; manifestations include life-threatening arrhythmias, fatigue, confusion, muscle cramps, and weakness.

Hypokalemia

Low serum potassium caused by increased loss of K+ via the kidneys or gastrointestinal tract, increased shift of K+ from ECF to ICF, or decreased dietary K+. Cardiac issues are the most serious manifestations.

Calcium (Ca2+)

Functions include formation of teeth and bone, blood clotting, transmission of nerve impulses, myocardial contractions, and muscle contractions. Balance controlled by parathyroid hormone (PTH) and calcitonin.

Hypercalcemia

High levels of serum calcium caused by hyperparathyroidism or cancers. Manifestations include fatigue, lethargy, weakness, confusion, dysrhythmias, bone pain, fractures, nephrolithiasis, polyuria, and dehydration.

Hypocalcemia

Low serum calcium levels caused by decreased production of PTH, multiple blood transfusions, alkalosis, or increased calcium loss. Manifestations include positive Trousseau’s or Chvostek’s sign, laryngeal stridor, dysphagia, numbness and tingling, and dysrhythmias.

Phosphate (PO43-)

Primary anion in ICF, essential to function of muscle, red blood cells, and nervous system. Involved in acid-base buffering, ATP production, cellular uptake of glucose, and metabolism. Serum levels controlled by parathyroid hormone. Reciprocal relationship with calcium.

Hyperphosphatemia

High serum phosphate caused by acute kidney injury or CKD, excess intake of phosphate or vitamin D, or hypoparathyroidism. Manifestations include tetany, muscle cramps, paresthesias, hypotension, dysrhythmias, seizures, and calcified deposits in soft tissue.

Hypophosphatemia

Low serum phosphate caused by malnourishment/malabsorption, diarrhea, use of phosphate-binding antacids, or inadequate replacement during parenteral nutrition. Manifestations include CNS depression, muscle weakness and pain, respiratory and heart failure, rickets, and osteomalacia.

Magnesium (Mg2+)

Cofactor in enzyme for metabolism of carbohydrates, required for DNA and protein synthesis, blood glucose control, BP regulation, ATP production, acts on myoneural junction, important for normal cardiac function.

Hypermagnesemia

High serum magnesium caused by increased intake of products containing magnesium when renal insufficiency or failure is present or excess IV magnesium administration. Manifestations include hypotension, facial flushing, lethargy, nausea, vomiting, impaired deep tendon reflexes, muscle paralysis, respiratory and cardiac arrest.

Hypomagnesemia

Low serum magnesium caused by prolonged fasting or starvation, chronic alcoholism, fluid loss from GI tract, prolonged PN without supplementation, diuretics, proton-pump inhibitors, some antibiotics, or hyperglycemic osmotic diuresis. Manifestations resemble hypocalcemia, including muscle cramps, tremors, hyperactive reflexes, Chvostek’s and Trousseau’s signs, confusion, vertigo, seizures, and dysrhythmias.