Fluid and Electrolyte Balance - Key Terms

Vocabulary flashcards covering key terms and concepts from the lecture notes on fluid and electrolyte balance.

Sodium (Na+)

Major extracellular cation that helps regulate fluid balance and nerve/muscle function.

Potassium (K+)

Major intracellular cation essential for cellular function and electrical activity.

Chloride (Cl-)

Major extracellular anion that helps maintain electroneutrality and osmotic balance.

Water Content

Primary component of the body; about 60% of adult body weight; varies by gender, age, and body mass.

Intracellular Fluid (ICF)

Fluid located inside the cells; must abundant

Extracellular Fluid (ECF)

Fluid outside cells; subdivided into intravascular (plasma), interstitial, and transcellular compartments.

Interstitial Fluid

Fluid surrounding the cells in the extracellular space.

Intravascular Fluid (Plasma)

Liquid portion of blood inside the vessels; part of the extracellular fluid.

Transcellular Fluid

Small volume of fluid in specialized cavities (e.g., CSF, synovial, GI, pleural).

Osmosis

Movement of water from low solute concentration to high solute concentration; passive; requires a semipermeable membrane.

Diffusion

Movement of solutes from high to low concentration; passive; membrane must be permeable to solutes.

Facilitated Diffusion

Passive transport using carrier proteins to move solutes down their concentration gradient (e.g., insulin–glucose–K relationship).

Active Transport

Movement of solutes against their concentration gradient; requires energy (ATP).

Filtration

Water and dissolved solutes move across a membrane due to hydrostatic pressure gradients.

Hydrostatic Pressure: push or pull?

Pushes water; pressure within a compartment (e.g., blood vessels) that drives filtration.

Osmotic Pressure: push or pull?

Pulls water toward solutes; pressure exerted by solutes that draws water into a space.

Third Spacing

Loss of extracellular fluid into nonfunctional spaces, not available for physiologic use; can cause hemodynamic instability.

Renal Regulation

Kidneys regulate fluid/electrolyte balance by adjusting urine volume; ADH and aldosterone act on renal tubules.

Antidiuretic Hormone (ADH) / Vasopressin

Hormone that promotes water retention by the kidneys, diluting the blood and reducing urine output. Produced by the hypothalamus and released by the pituitary.

Osmoreceptors

Hypothalamic receptors that sense plasma osmolality and stimulate thirst and ADH release.

Renin-Angiotensin-Aldosterone System (RAAS)

System activated by decreased renal perfusion; leads to vasoconstriction (Angiotensin II) and aldosterone-mediated Na+/water retention.

Aldosterone

Hormone from the adrenal glands that promotes Na+ and water retention and K+ excretion, increasing fluid volume.

Angiotensin II

Vasoconstrictor that raises systemic vascular resistance and blood pressure.

Isotonic / Hypotonic / Hypertonic Solutions

Osmolality-matched (isotonic) fluids have similar osmolality to plasma; hypotonic fluids have lower osmolality; hypertonic fluids have higher osmolality.

Hematocrit

Proportion of blood volume occupied by red blood cells; increases with dehydration (hemoconcentration) and decreases with fluid overload (hemodilution).

STEP 1 of RAAS

Renin is released into the bloodstream by the kidneys in response to decreased perfusion. Renin turns angiotensinogen from the liver into Angiotensin I

STEP 2 of RAAS

Angiotensin Converting Enzyme (ACE) (produced by the lungs) converts Angiotensin I into II

STEP 3 of RAAS

Angiotensin II causes vasoconstriction of blood vessels and signals the kidneys to release aldosterone to increase the blood pressure

STEP 4 of RAAS

Aldosterone is released by the adrenal glands and causes the body to retain sodium and water and push potassium out. This increase blood volume and pressure

What lab values are indicative of kidney function?

BUN and creatinine, however, creatinine is most specific to kidney function because it is not influenced by hydration and diet.

Gerontological considerations

1) kidney structure and function decline

2) hormonal changes (ADH sensitivity decreases)

3) loss of subcutaneous tissue and reduced thirst mechanism

4) functional issues like mobility, cognition, and dysphasia affect hydration

What is the best indicator of fluid or volume status?

Daily weights

kg = lbs = L

1kg =2.2lbs = 1L

Which disease states can cause hypervolemia?

Renal failure, heart failure, liver failure, prolonged steroid use

SIADH

syndrome of inappropriate antidiuretic hormone - the body retains too much water due to the overproduction of ADH

What is the primary function of aldosterone in fluid balance?

Increase water and sodium reabsorption

Which hormone is responsible for regulating water balance by increasing water reabsorption by the kidneys?

Antidiuretic hormone (ADH)

Movement of water and solutes across a membrane due to hydrostatic pressure

Filtration

Movement of solutes against a concentration gradient, requiring energy

Active transport

Movement of solutes from an area of higher concentration to an area of lower concentration

Diffusion

Movement of water across a semipermeable membrane

Osmosis

Lab value - osmolality

• primarily serum

• Measures concentration of dissolved particles in the liquid portion of your blood, like sodium, glucose, and urea

• Assesses body’s water and electrolyte balance

Lab value - specific gravity

• Measure concentration of dissolved particles in urine reflecting how well the kidneys are regulating fluid and waste balance

• Higher specific gravity indicates more concentrated urine, Lower specific gravity indicates more diluted in urine

Lab value - BUN

• blood urea nitrogen is waste product of the liver breaking down protein

• Increase can be caused by decreased renal function, GI bleed, dehydration, increased protein intake

Lab value - creatinine

• A waste product muscle metabolism

• Increases with decrease in renal function

Hypovolemia - expected lab values: HCT, BUN, osmolality, and urine

• think “hemoconcentration”

• Elevated HCT

• elevated BUN - impaired kidney function from decreased perfusion causes elevated levels in the blood

• Elevated serum osmolality - higher concentration of solutes due to loss of water

• Elevated urine specific gravity - higher concentration of solutes due to water reabsorption

Causes of hypervolemia

• kidney failure

• Heart failure

• Liver disease

• Prolonged steroid use

• SIADH

Symptoms of hypervolemia and treatment

• shortness of breath

• Swelling/ weight gain

• High blood pressure

• Bounding pulse

Treatment: reduce fluid/sodium intake, diuretics, monitor I&Os, daily weights

Hypervolemia- expected lab values: HCT, BUN, osmolality, urine

• think dilution!

• HCT decreased

• Elevated BUN/ Creatinine (disruption in homeostatic regulation of kidneys, present in both hyper/hypo)

• Decreased serum osmolality

• Decreased urine specific gravity

Symptoms of hypovolemia and treatment

• rapid heart rate

• Rapid breathing (when blood volume decreases, less O2 to tissues)

• Dizziness/weakness

• Decreased urine output

Treatment: IV fluids, treat underlying reason, vital signs, I&Os, daily weights

Hypokalemia can occur:

• GI losses (vomiting, diarrhea, NG suction)

• Renal losses (diuretics, hyperaldosteronism)

• Magnesium deficiency (impairs K⁺ reabsorption)

• Insulin or β-agonists (drive K⁺ into cells)

Hyperkalemia can occur:

• Kidney failure → impaired excretion

• Medications (ACE inhibitors (prevent aldosterone), potassium-sparing diuretics)

• Addison’s disease (low aldosterone → ↓K⁺ excretion)

Hypernatremia can occur:

• Dehydration (water loss > Na⁺ loss)

• Diabetes insipidus (↓ADH effect → excess water loss)

• Excess Na⁺ intake (IV saline)

• Osmotic diuresis (uncontrolled diabetes, mannitol)

• Burns or excessive sweating without adequate water replacement

Hyponatremia can occur:

• Excess water intake

• SIADH (↑ADH → water retention dilutes Na⁺)

• Heart failure, cirrhosis, nephrotic syndrome (fluid overload → dilution)

• Vomiting, diarrhea, diuretics (Na⁺ loss > water loss)

• Adrenal insufficiency (low aldosterone → ↓Na⁺ reabsorption)