Fluid & Electrolyte Balance

Fluid & Electrolyte Balance and Acid-Base Balance: Comprehensive Study Notes

• These notes summarize the key concepts from the provided transcript slides on Fluid & Electrolyte Balance, Perfusion, and Acid-Base Balance.

• They cover definitions, body fluid compartments, movement mechanisms, dehydration and overhydration, electrolyte imbalances (Na, K, Ca, Mg), and related nursing considerations.

• Equations and numeric thresholds are presented in LaTeX format where relevant.

Fluid and Electrolyte Balance: Core Concepts

• The body’s fluid content comprises both water and dissolved substances (solutes) including electrolytes and ions.

• Approximately 55\% - 60\% of body weight is fluid.

• Body fluids are made up of:

  • Solvent (water)

  • Solutes (electrolytes and non-electrolytes)

• Fluid compartments:

  • Intracellular Fluid (ICF): \approx \,\frac{2}{3} of body water (fluid within cells)

  • Extracellular Fluid (ECF): \approx \frac{1}{3} of body water (fluid outside cells)

  • Intravascular fluid (blood plasma)

  • Interstitial fluid (between cells)

  • Transcellular fluid (specialized spaces like CSF, synovial, GI)

• Fluid-electrolyte balance is closely linked to electrolyte concentrations and distribution across compartments.

• Normal hydration requires balanced intake and losses:

  • Fluid gains: from food and fluids

  • Fluid losses: sensible (urine, stool, wound drainage) and insensible (skin, lungs) water losses

• Minimum urine output to excrete waste: 400-600\ \,mL/24\,h

• Key homeostatic mechanisms include:

  • Thirst drive (drives water intake)

  • Antidiuretic hormone (ADH) regulating water reabsorption

  • Renal regulation of electrolytes (notably Na

• and K+) via transporters such as the Na+/K+-ATPase pump

• Movement of fluids and electrolytes occurs via:

  • Active transport (e.g., Na+/K+ pump: 3\ Na^+{out} + 2\ K^+{in} per ATP)

  • Passive transport: diffusion, filtration, osmosis

Key Terms (Foundational Concepts)

• Dehydration, Diffusion, Electrolytes, Filtration, Osmosis

• Hyperkalemia / Hypokalemia; Hypernatremia / Hyponatremia

• Hypermagnesemia / Hypomagnesemia; Hypercalcemia / Hypocalcemia

• Hypervolemia / Hypovolemia

• Acidosis / Alkalosis; Acids / Bases

• Hyperventilation / Hypoventilation; Kussmaul respirations

• Extracellular Fluid (ECF); Intracellular Fluid (ICF); Interstitial fluid; Intravascular fluid; Transcellular fluid

• Hypotonic (relative to plasma)

• Insensible water loss

• Osmolality; Osmolarity; Osmosis

Anatomy and Physiology Review

• Total body water is distributed between compartments as noted:

  • ICF (within cells): major portion

  • ECF (outside cells): smaller portion, includes intravascular and interstitial fluids plus transcellular fluids

• Fluid balance is essential for proper organ function; imbalance affects all systems.

• Fluid compartments are dynamically exchanged and regulated by pressures and osmolality.

Fluid Balance: Distribution and Regulation

• Two main compartments:

  • Intracellular (ICF): 2/3 of body water

  • Extracellular (ECF): 1/3 of body water

• ECF subdivisions:

  • Intravascular fluid (plasma)

  • Interstitial fluid (bathes tissues)

  • Transcellular fluids (e.g., CSF, synovial, GI lumen)

• Balance influenced by:

  • Fluid intake vs. loss

  • Thirst drive

  • Insensible water loss

• Important practical threshold: minimum urine output to excrete waste = 400-600\,\text{mL/24 h}

• Fluid gains vs. losses can be categorized into:

  • Gains: Food, Fluids

  • Losses: Sensible (urine, stool, wounds) and Insensible (skin, lungs)

Movement of Fluids and Electrolytes

• Active transport:

  • Na+/K+ pump: maintains intracellular/extracellular Na+ and K+ gradients; essential for cell function and volume regulation

  • Equation representing pump activity: \text{Na}^+{out} !:! 3\ Na^+ \,||!!\ \text{out} \,/\ \text{K}^+{in} !:! 2\ K^+ !!\in per ATP

• Passive transport:

  • Diffusion: movement down a concentration gradient

  • Filtration: movement driven by pressure differences (e.g., capillary filtration)

  • Osmosis: movement of water across semipermeable membranes from lower to higher solute concentration

• Osmolality vs Osmolarity:

  • Osmolality: \text{osmolality} = \frac{\text{Total solute particles}}{\text{kg of solvent}} \quad (\text{mOsm/kg})

  • Osmolarity: \text{osmolarity} = \frac{\text{Total solute particles}}{\text{L of solution}} \quad (\text{Osm/L})

Dehydration: Definition, Causes, Types, and Signs

• Dehydration: lack of fluid due to inadequate intake or excessive loss

• Major causes include:

  • GI losses (vomiting, diarrhea)

  • Third-spacing (fluid shifts into third spaces like edema)

  • Hemorrhage, fever, DKA, diuresis

  • Hyperventilation, fever, excessive Na+ intake

• Two main types:

  • Actual dehydration

  • Isotonic dehydration (hypovolemia) – equal loss of water and Na+ leading to reduced circulating volume

• Signs and symptoms (general):

  • Altered vital signs (VS) and mental status changes

  • GI symptoms

  • Oliguria (low urine output)

  • Decreased capillary refill

  • Flattened neck veins; Poor skin turgor

• 5 signs of dehydration (common quick checks):

  • Dry, chapped lips

  • Headaches

  • Dry skin

  • Achy joints

  • Fatigue

Dehydration: Laboratory Indicators and Nursing Care

• Laboratory findings in dehydration (fluid volume deficit / hypovolemia):

  • Hematocrit (Hct): Increased (hemoconcentration)

  • Blood Urea Nitrogen (BUN): Increased

  • Urine specific gravity: Greater than 1.030

  • Sodium (Na+): Greater than 145\,\text{mEq/L}

  • Blood osmolality: Greater than 295\,\text{mOsm/kg}

• Nursing care priorities:

  • Rehydration: oral or IV as appropriate

  • Monitor intake and output (I&O) and vital signs (VS)

  • Monitor mental status and gait stability

  • Encourage assistance via call light; help with position changes to prevent falls

Geriatric Dehydration Differences

• Less total water content in body

• Diminished thirst reflex → often under-recognized dehydration

• Decreased skin turgor can mask fluid loss

• Medication side effects can increase risk (e.g., diuretics, antihypertensives)

Pediatric Dehydration Differences

• Higher percentage of body water exposed to loss

• Reduced ability to concentrate and acidify urine

• Faster peristalsis and higher metabolic rate

• Larger body surface area relative to mass; greater insensible losses

• Immature immune system increases infection risk with dehydration

Dehydration in Pediatrics (Clinical Signs)

• Sunken fontanelle, reduced consciousness, dry mucous membranes, decreased tissue turgor

• Tachypnea, oliguria

• Weight loss, sunken eyes, tearless cry

• Reduced capillary refill time, hypotension in severe cases

Complications of Dehydration: Hypovolemic Shock

• Occurs with significant body fluid loss

• MAP decreases; organ perfusion compromised

• Nursing actions:

  • Administer oxygen and monitor oxygen saturation

  • Stay with unstable patient; frequent VS (e.g., every 15 minutes)

  • Fluid replacement (colloids: whole blood, PRBCs, plasma, synthetic plasma expanders; crystalloids: LR, NS)

  • Use vasoconstrictors as indicated; hemodynamic monitoring

Fluid Volume Excess: Overhydration / Hypervolemia

• Definition: Fluid volume excess due to excessive intake or impaired excretion

• Risk factors include:

  • Compromised regulatory systems

  • Overdose of fluids

  • Fluid shifts after burns

  • Prolonged corticosteroid use

  • Severe stress; hyperaldosteronism

• Common causes:

  • Excessive water intake

  • SIADH (syndrome of inappropriate antidiuretic hormone secretion)

  • Excessive use of hypotonic solutions (e.g., D5W)

• Expected findings (clinical):

  • Vital signs: tachycardia, bounding pulse, hypertension

  • Respiratory: tachypnea; possible dyspnea

  • Increased central venous pressure; edema; ascites

  • Neuromuscular: weakness, paresthesias; altered level of consciousness; seizures

  • GI: increased motility; anorexia, nausea

  • Weight gain; dependent edema; distended neck veins (JVD); crackles, cough

• Laboratory changes in fluid volume excess:

  • Hematocrit (Hct): decreased (dilutional)

  • Plasma osmolality: decreased

  • Urine specific gravity: decreased

  • BUN: decreased

• Nursing care and management:

  • I&O monitoring and daily weights

  • Assess breath sounds; monitor for edema and ascites

  • Restrict Na+ intake if ordered; monitor Na+ and K+ levels

  • Consider fluid restriction; position patient to ease breathing (semi-Fowler's to Fowler's)

  • Regular lab monitoring and diet adjustments

• Complications to watch for:

  • Pulmonary edema

  • Hyponatremia risk if excessive free water is given inappropriately

Complications of Overhydration: Pulmonary Edema

• Signs and symptoms:

  • Anxiety, tachycardia

  • Neck vein distention; edema; crackles; cyanosis may develop

  • Dyspnea at rest; productive cough with pink, frothy sputum

  • Altered mental status; decreased oxygenation

• Nursing actions:

  • Position in high-Fowler's position

  • Administer supplemental oxygen; consider CPAP/BiPAP or intubation if needed

  • Diuretics and vasodilators as prescribed (subject to BP status)

  • Monitor vitals, oxygenation, and fluid status closely

Check Your Knowledge (Practice Question)

• Question: The nurse is caring for a client with kidney failure who is dyspneic and has crackles on auscultation. Which additional sign/symptom would be anticipated?

  • Options (as presented):
    1) Rapid weight loss
    2) Flat hand and neck veins
    3) Weak and thready pulses
    4) An increase in blood pressure

  • Answer: 4) An increase in blood pressure (hypertension can accompany fluid overload and pulmonary edema in kidney failure)

Electrolyte Imbalances: Overview

• Electrolyte imbalances can occur in healthy individuals due to fluid balance changes and are more common in older adults and those with chronic illness.

• The main electrolytes covered: Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+).

The Main Electrolytes in Body Fluids

• Sodium (Na+)

• Chloride (Cl−)

• Potassium (K+

• Magnesium (Mg2+)

• Calcium (Ca2+)

• The electrolytes maintain: fluid balance and pH; electrical signaling for nerves and muscles.

Sodium: Regulation and Disorders

• Normal sodium range: 136-145\ \text{mEq/L}

• Fundamental concept: “Where sodium goes, water follows.” This principle drives fluid shifts with sodium imbalances.

• Hyponatremia and Hypernatremia reflect low/high plasma Na+ levels and have different risk factors and consequences.

Hyponatremia (Low Sodium)

• Risk factors:

  • Excessive sweating, diuretics, wound drainage, nephrotic syndrome, kidney disease, NPO status

  • Hyperglycemia; hypotonic fluid excess; freshwater submersion injuries

  • Certain medications (e.g., some SSRIs)

  • Older adults and chronically ill patients are at higher risk

• Associated lab/clinical considerations include decreased serum Na+ and potentially low serum osmolality depending on the etiology.

Hypernatremia (High Sodium)

• Risk factors:

  • Kidney failure, Cushings syndrome, aldosteronism, excessive intake of oral Na+

  • Water deprivation; hypertonic enteral feeds without adequate water; diabetes insipidus

  • Fever, heatstroke, burns

• Associated with increased serum osmolality and dehydration at the cellular level (water moves from cells to extracellular space).

Quick Lab/Mnemonic Guidance for Acute vs Chronic Na+ Changes (from the slides)

• Acute low Na+ (Sodium):

  • Seizures; Low serum osmolality; Diarrhea; Increased ICP risk; Low urine osmolality; Diuretic use; Respiratory failure considerations; Oral tube suctioning may contribute to losses.

• Chronic high Na+ (Sodium):

  • Hypertension risk cues with high serum osmolality; Diabetes insipidus; Head trauma; Mannitol therapy; D5W treatment; Renal failure; Addison's disease; High specific gravity of urine; family of signs (BUN, electrolytes, glucose) indicates sodium imbalance.

• Practical note: monitoring Na+ and osmolality is critical when managing fluids, diuretics, and conditions like SIADH or diabetes insipidus.

Potassium (K+): Regulation and Disorders

• Normal range: 3.5\ -\ 5.0\ \text{mEq/L}

• Approximately 98\% of body potassium is inside cells; even small shifts can cause major clinical effects.

• Potassium balance is tightly linked to acid-base status and renal function.

Hypokalemia (Low Potassium)

• Risk factors:

  • Excessive diuretic use, Cushing’s syndrome, increased aldosterone, vomiting/diarrhea, NG suctioning, NPO status, kidney disease, alkalosis

  • Hyperinsulinism, total parenteral nutrition (TPN), water intoxication

• Clinical features (typical):

  • Muscle cramps, weakness, fatigue; shallow respirations in severe cases due to muscle weakness of the respiratory muscles

  • Palpitations and arrhythmias; tachycardia or bradycardia depending on compensatory mechanisms

  • Hyporeflexia or diminished deep tendon reflexes

  • Alkalosis may accompany hypokalemia and contribute to symptoms

• Note: signs such as fatigue, cramps, and ECG changes require careful monitoring and correction of K+ levels.

Hyperkalemia (High Potassium)

• Risk factors:

  • Overconsumption of high-potassium foods; rapid IV K+ administration; RBC transfusions; adrenal insufficiency; kidney failure; acidosis (e.g., DKA)

  • Tissue damage (sepsis, trauma, surgery, fever, MI); older adults may be at greater risk

• Clinical features:

  • Muscle twitches, cramping, paresthesias; irritability and anxiety

  • Elevated blood pressure; ECG changes including tall peaked T waves; widened QRS; PR prolongation; potential dysrhythmias

  • Abdominal cramping and diarrhea

• Monitoring: rising potassium levels can cause life-threatening dysrhythmias; watch for fatigue, weakness, and changes in reflexes.

Potassium: Practical Considerations

• Potassium balance is critical in planning IV fluids and medications; watch for signs of both hypo- and hyperkalemia.

• Potassium chloride (IV and PO) must be used carefully; both excess retention and rapid shifts can be dangerous.

• Education and dietary guidance are important for long-term management and prevention of imbalance-related complications.

Calcium (Ca2+) and Magnesium (Mg2+): Roles and Disorders

• Calcium:

  • Normal range: 1.3-2.1\ \text{mg/dL}

  • Critical roles: skeletal muscle contraction, carbohydrate metabolism, ATP formation, B-complex vitamin synthesis, DNA and protein synthesis, membrane stabilization

  • Calcium balance is linked to parathyroid hormone (PTH) and vitamin D; deficiencies or excesses can cause neuromuscular and cardiovascular symptoms.

• Common causes of hypocalcemia:

  • Chronic renal failure; high phosphate; low calcium

  • Hypoparathyroidism; dietary calcium and vitamin D deficiency

• Common causes of hypercalcemia:

  • Cancer metastasis to bone; hyperparathyroidism; vitamin D poisoning

• Magnesium:

  • Normal range and roles not explicitly listed in the transcript beyond causes; hypo/hyper magnesium conditions can affect neuromuscular and cardio-respiratory function and often co-occur with other electrolyte disturbances

• Calcium-related problems are often interconnected with vitamin D status and parathyroid function; monitoring Ca2+ is essential in patients with renal disease, bone disease, or endocrine disturbances.

Practical Clinical Connections and Real-World Relevance

• Fluid and electrolyte balance underpins perfusion, organ function, and acid-base homeostasis; disturbances can lead to organ dysfunction if not corrected timely.

• Elderly and pediatric populations require special attention due to physiological differences (thirst response, total body water content, and organ reserve).

• Practical nursing priorities across dehydration and overload include: accurate I&O, daily weights, vitals, mental status, breath sounds, edema assessment, orthostatic precautions, and careful electrolyte monitoring.

• Management strategies depend on balance of fluids and electrolytes: choose crystalloids vs colloids, modulate electrolyte intake, and adjust rate of administration to avoid rapid shifts that could cause complications.

Summary of Normal Values and Thresholds (Quick Referenced Ranges)

• Total body water: 55\% - 60\% of body weight

• ICF: \frac{2}{3} of body water

• ECF: \frac{1}{3} of body water

• Urine output to excrete waste: 400-600\ \text{mL/24 h}

• Sodium (Na+): 136-145\ \text{mEq/L}

• Potassium (K+): 3.5-5.0\ \text{mEq/L}

• Calcium (Ca2+): 1.3-2.1\ \text{mg/dL}

• Magnesium (Mg2+): (value not explicitly provided in the transcript section; typically ~1.7-2.2 mg/dL in adults in many references, but use local lab reference when available)

• Osmolality (serum): typically >295\ \text{mOsm/kg} in dehydration; lower in some fluid overload states depending on the situation

• Serum osmolality and urine osmolality values are used to differentiate causes of hyponatremia/hypernatremia and to guide treatment decisions

End of notes.