Fluids & Electrolytes

Flashcards covering key concepts related to fluids and electrolytes, including definitions of important terms and principles governing fluid balance.

Fluid Compartments

Body fluids are divided into intracellular (ICF) and extracellular (ECF) compartments.

Intracellular Fluid (ICF)

Comprises 2/3 of total body fluid and is located inside the cells.

Extracellular Fluid (ECF)

Comprises 1/3 of total body fluid and is located outside the cells.

Total Body Water

The total amount of water in the body. newborn

• 70% to 80% of body weight

• childhood

• 60% to 65% of body weight

• adults

• 50% to 60% of body weight

• older adults

• percent declines with ageand varies by gender and body composition.

Osmosis

The movement of water from an area of low solute concentration to an area of high solute concentration.

Diffusion

Movement of particles from an area of high solute concentration to an area of low solute concentration.

Active Transport

Movement of particles against their concentration gradient, requiring energy (ATP).

Starling Forces

The four forces that determine the net movement of fluid across capillary walls, balancing hydrostatic and oncotic pressures to regulate fluid exchange between the intravascular and interstitial compartments.

Capillary Hydrostatic Pressure

The outward pushing force exerted by the fluid within the capillaries against the capillary walls, promoting fluid movement out of the capillary and into the interstitial space.

Interstitial Hydrostatic Pressure

The inward pushing force exerted by fluid in the interstitial space against the outside of the capillary wall, promoting fluid movement into the capillary.

Capillary Colloid Osmotic Pressure

The inward pulling force exerted by plasma proteins (especially albumin) within the capillaries, drawing water from the interstitial space back into the capillary.

Interstitial Colloid Osmotic Pressure

The outward pulling force exerted by proteins in the interstitial fluid, drawing water out of the capillary and into the interstitial space.

Edema

The accumulation of fluid in interstitial spaces.

Edema causes

• increased capillary hydrostatic pressure (venous obstruction)

• decreased plasma oncotic pressure (losses or diminished production of albumin)

• increased capillary permeability (inflammation and immune response)

• lymphatic obstruction (lymphedema)

Third-Spacing

When too much fluid moves from the intravascular space into the interstitial or 'third' space causing it to become non-functional.

treatment of edema 

• Elevate edematous limbs

• Use compression stockings or devices

• Avoid prolonged standing

• Restrict salt intake

• Take diuretic drugs

• Treat underlying condition

Osmolality

Number of dissolved particles in 1 kg of water. Normal value is 280-294 mmol/kg (mOsm). Sodium, glucose, urea are most important.

Tonicity

Relative concentrations of two fluids separated by membrane

Hypovolemia or water deficit

concentration of particles too great or water content too little leading to decreased blood volume. Value greater than 294 mmol/kg

Hypovolemia or water deficit causes  

1) water deprivation. Related to: confusion or coma, inability to communicate, loss of thirst. 2) Water loss: watery diarrhea, vomiting, diabetes (osmotic effect of glucose), excessive diuresis, excessive diaphoresis. 3) a combination of these

Hypovolemia or water deficit diagnostics

Serum sodium levels >145 mmol/L (mEq/L) (hypernatremia), ECF osmolality >294 mmol/kg (mOsm), Urine specific gravity >1.030, Elevated hematocrit (Hct), elevated plasma proteins.

Hypovolemia or water deficit treatment

Oral fluids, IV 5% dextrose in water (D5, D5W), Diuretics

Hypervolemia or water excess

too little solute for amount of water or too much water for amount of solute, leading to increased blood volume. Value less than 280 mmol/kg (mOsm).

Hypervolemia or water excess causes

excessive fluid intake: compulsive water drinking causing water intoxication, excessive admin of IV solutions, tap water enemas. Abnormal retention of fluids: kidney injury/disease, heart failure, liver cirrhosis, SIADH.

Hypervolemia or water excess diagnostics

Dilutional effect

serum sodium levels <135 mmol/L (mEq/L) (hyponatremia)

ECF osmolality <280 mOsm and urine osmolality <100 mOsm, along with clinical signs of fluid overload such as edema and hypertension.

Hypervolemia or water excess treatment

Involves fluid restriction, diuretics to promote excretion of excess fluid, and treatment of underlying causes like heart or kidney issues.

electrocytes

charged particles that conduct electricity in the body, essential for nerve and muscle function.

3 most important electrocytes

Sodium (main ECF electrocyte), potassium (main ICF electrocyte), chloride (active in ICF).

Intracellular cations and anions

that help regulate cellular functions, including potassium (K+) as the primary cation and phosphate (HPO4-) as the primary anion and organic ions.

Extracellular cations and anions

that regulate fluid balance and nerve impulses, primarily sodium (Na+) as the main cation and chloride (Cl-) as the main anion, and bicarbonate (HCO3-)

isotonic

ECF equivalent to 0.9% salt solution; no net water movement i.e., no cell shrinking or swelling

Hypotonic

ECF less than 0.9% salt solution; water gain or solute loss; lower concentration of solutes than ICF; cells swell

Hypertonic

ECF greater than 0.9% salt solution; water loss or solute gain; higher concentration of solutes than ICF; cells shrink

ADH System

Is released when there is an increase in plasma osmolality decrease in circulating blood volume. is also called arginine vasopressin. increases water reabsorption

Osmolality receptors (osmoreceptors)

are specialized neurons in the hypothalamus that detect changes in plasma osmolality and help regulate fluid balance.

Baroreceptors

are sensory receptors that detect changes in blood pressure and help regulate fluid balance and blood volume.

RAAS System

is a hormone system that regulates blood pressure and fluid balance, involving renin, angiotensin, and aldosterone to control sodium and water retention.

Steps of RAAS

The steps of the RAAS system include the release of renin from the kidneys in response to low blood pressure, conversion of angiotensinogen to angiotensin I, conversion to angiotensin II by ACE, and the subsequent release of aldosterone, which promotes sodium and water retention.

NP System

Natriuretic peptides

• decreases tubular resorption, and promotes urinary excretion of sodium

• atrial natriuretic peptide

• brain natriuretic peptide

• urodilatin (kidney)

Sodium (Na+)

The primary electrolyte in extracellular fluid, essential for neuromuscular excitability and fluid balance.

Potassium (K+)

The primary electrolyte in intracellular fluid, important for cellular function and nerve signaling.

Calcium (Ca2+)

An important cation involved in bone health, muscle contractions, and nerve signaling.

Chloride (Cl−)

An anion that helps maintain acid-base balance and is involved in the digestive process.

Bicarbonate (HCO3-)

A key buffer in the blood that helps maintain pH balance.

Aldosterone

A hormone that increases sodium reabsorption in the kidneys, helping to regulate blood pressure.

Antidiuretic Hormone (ADH)

A hormone that promotes water retention in the kidneys and regulates osmotic pressure.

Natriuretic Peptides (NP)

Hormones produced by the heart that promote sodium and water excretion. ANP and BNP are made in cardiac cells.

Hypernatremia

A condition of elevated sodium levels in the blood, often due to dehydration or excessive sodium intake. Sodium level greater than 145 mmol/L/

Hypernatremia risk factors

advanced age, impaired mental state, fever, diarrhea, vomiting, uncontrolled diabetes, tube feedings, diuretics

Hypernatremia Manifestations

hypertonicity, seizures, muscle twitching, hyperreflexia, confusion, coma.

Hypernatremia evaluation

history, physical exam and labs: Serum Na+ > 145 mEq/l, Urine specific gravity > 1.030

Hypernatremia treatment

for hypovolemic hypernatremia-give oral water or isotonic salt-free fluid (D5W in water) until returns to normal. Fluid replacement is slow to prevent cerebral edema.

Hyponatremia

A condition of low sodium levels in the blood, often caused by excess water, or dilution of plasma. Sodium level less than 135 mmol/L.

Hyponatremia causes

sodium loss, inadequate sodium intake, dilution of sodium by water excess

Hyponatremia Manifestations

nausea and vomiting when sodium 125-130 mmol/L (mEq/L)

neurologic symptoms when <125 mmol/L (mEq/L)

lethargy, headache, confusion, apprehension, seizures, coma

Evaluation History, physical exam and lab levels: Serum Na+ < 135 mEq/l, urine specific gravity

< 1.010

Hyponatremia treatment

restrict water intake, hypertonic saline solutions (oral, IV)

potassium

is an essential electrolyte that plays a key role in maintaining fluid balance, muscle contractions, and nerve signaling in the body. Normal levels range from 3.5 to 5.0 mEq/L.

hyperkalemia

Serum level >5 mmol/L (mEq/L). caused by excessive consumption or renal pathology

Hypokalemia

serum level <3.5 mmol/L (mEq/L). often caused by use of non-potassium sparing diuretic

How does the body regulate potassium

The body regulates potassium primarily through the kidneys, which filter and excrete excess potassium, and through hormonal mechanisms involving aldosterone, which promotes potassium secretion in exchange for sodium. Changes in pH (causing acidosis or alkolosis) can also influence potassium regulation.

Calcium and Phosphate are regulated by

Parathyroid hormone (PTH), Vitamin D, Calcitonin

Parathyroid hormone

Increase plasma calcium levels via kidney reabsorption. 

Vitamin D

A fat-soluble steroid; increases calcium absorption from the GI tract.

Calcitonin

Decrease plasma calcium levels.

Hypocalcemia level

calcium level less than 8.5mg/dL

Hypocalcemia causes

Inadequate intake or absorption, Decreases in PTH, and vitamin D, Blood transfusions

Hypocalcemia manifestations

Increased neuromuscular excitability (partial depolarization), Muscle spasms, Chvostek and Trousseau signs, Convulsions, Tetany

Hypocalcemia Treatment

►Calcium gluconate, calcium replacement, decrease phosphate intake

Hypercalcemia level

calcium level more than 10.5mg/dL.

Hypercalcemia causes

Hyperparathyroidism, Bone metastasis, Excess vitamin D, Immobilization, Acidosis, Sarcoidosis

Hypercalcemia Manifestations

Decreased neuromuscular excitability, Weakness, Kidney stone, Constipation, Heart block

Hypercalcemia Treatment

Oral phosphate, IV normal saline, Bisphosphonates, Calcitonin, Denosumab

Hypophosphatemia level

phosphate level is less than 2.0mg/dL

Hypophosphatemia causes

Intestinal malabsorption and renal excretion, vitamin D deficiency, antacid use, alcohol abuse, malabsorption syndromes, refeeding syndromes

Hypophosphatemia manifestations

Diminished release of oxygen, osteomalacia (soft bones), muscle weakness, bleeding disorders (platelet impairment), leukocyte alterations, rickets

Hypophosphatemia treatment

Treat underlying condition such as respiratory alkalosis and hyperparathyroidism.

Hyperphosphatemia level

phosphate level more than 4.7 mg/dL.

Hyperphosphatemia causes

Exogenous or endogenous addition of phosphate to ECF, chemotherapy, long-term use of phosphate enemas or laxatives, renal failure

Hyperphosphatemia manifestations

Increased neuromuscular excitability (partial depolarization), Muscle spasms, Chvostek and Trousseau signs, Convulsions, Tetany with possible calcification of soft tissue.

Hyperphosphatemia treatment

Treat underlying condition, aluminum hydroxide, and dialysis.

Hypomagnesemia level

magnesium level below 1.5 mEg/L.

Hypomagnesemia causes

Malabsorption, Alcoholism, urinary losses (renal tubular dysfunction), associated with hypocalcemia and hypokalemia, neuromuscular irritability

Hypomagnesemia manifestations

Behavioural changes, irritability, increased reflexes, muscle cramps, ataxia, tetany, seizures, hypotension

Hypomagnesemia treatment

Treat underlying condition, magnesium sulfate

Hypermagnesemia level

magnesium level is higher than 3.0 mEg/L.

Hypermagnesemia causes

Malabsorption, Alcoholism, urinary losses (renal tubular dysfunction), Usually from renal failure, excessive intake of magnesium-containing antacids, adrenal insufficiency

Hypermagnesemia manifestations

Lethargy, drowsiness, loss of deep tendon reflexes, nausea and vomiting, muscle weakness, hypertension, bradycardia, respiratory depression or arrest, heart block, cardiac arrest.

Hypermagnesemia treatment

Treat underlying condition, avoid magnesium, dialysis.

Potassium Chloride indications for use

hypokalemia, mild forms of alkalosis

Potassium Chloride Mechanism of Action

prevents or treats K+ depletion

chloride corrects hypochloremia occurring with K+ deficiency.

Potassium Chloride Desired Effects

replacement for lost potassium

primary intracellular electrolyte

life-sustaining functions

maintenance of acid-base balance, isotonicity, electrodynamics of cell.

Potassium Chloride Adverse effects

GI: abd. pain, N/V, diarrhea, bleeding/ulceration d/t irritation with oral forms

local: pain and irritation at IV site, phlebitis

hyperkalemia

Crystalloids

fluids available as isotonic, hypotonic and hypertonic formulations

isotonic crystalloids are used to replace lost fluid and to promote urine output

hypotonic crystalloids shift fluid from ECF to ICF compartment

hypertonic crystalloids shift fluid from ICF to ECF compartment

Colloids

composed of proteins or starches that remain in blood vessels (not filtered by capillaries), drawing fluid from ICF and interstitum into vessels to increase plasma fluid volume.

Hypotonic Intravenous solutions

are IV fluids that have a lower osmolarity than blood, causing fluids to shift from the ECF into the ICF, thus hydrating cells. For example, 0.45% NaCl.

Isotonic Intravenous solutions

are IV fluids that have the same osmolarity as blood, maintaining fluid balance. For example, 0.9% NaCl is commonly used for hydration and electrolyte replacement.

Hypertonic Intravenous Solutions

are IV fluids that have a higher osmolarity than blood, causing fluids to shift from the ICF into the ECF, thus pulling fluid out of cells. For example, 3% NaCl.