Fluids And Lytes

Normal Physiology: Fluid Balance

Fluid Compartments

  • Intracellular

  • Extracellular

    • Intravascular (in blood vessels)

    • Interstitial (between cells)

    • Lymph

    • Transcellular (CSF, fluid in various body spaces)

Movement of Fluid Between Compartments

  • Between Cells and Interstitium: Related to tonicity or osmolality of extracellular fluid.

    • Hypertonic: Water pulled out of cells.

    • Hypotonic: Water moves into cells.

    • Isotonic: No change.

  • Between Interstitium and Intravascular Space: Determined by:

    • Capillary Hydrostatic Pressure: Pushes fluid out of capillary.

    • Capillary Colloidal Osmotic Pressure: Pulls fluid into capillary.

    • Tissue Hydrostatic Pressure: Opposes pushing of fluid out of capillary (pushes fluid out of tissue into capillary).

    • Tissue Colloidal Osmotic Pressure: Pulls fluid into interstitium.

Primary Functions

  • Maintain vascular volume.

  • Provide environment for cellular metabolism.

Sources of Gain

  • Oral intake.

  • Oxidation of nutrients.

Sources of Loss

  • Urine.

  • Insensible losses through skin and lungs.

  • Stool.

Regulatory Mechanisms

  • Thirst: Affects fluid intake.

  • ADH: Affects fluid output (increases water reabsorption in the collecting duct of nephron).

Pathological Changes

  • Isotonic Decrease in Extracellular Fluid Compartment: Proportionate losses of sodium and water.

Predisposing Factors (PF)

  • Impaired Fluid Intake:

    • Inability to obtain fluids (e.g., decreased mobility, coma, decreased access).

    • Impaired thirst.

    • Impaired swallowing.

  • Excessive Fluid Losses:

    • GI loss (e.g., vomiting, diarrhea).

    • Renal loss (e.g., polyuria, diuretic therapy).

    • Skin loss (e.g., increased sweating due to fever or exercise, burns).

Nursing Problem

  • Example of Disorder: Isotonic fluid volume deficit.

Assessment Findings

  • Fluid shifts from cells to different compartments leading to hypovolemia.

  • Assessment of sodium concentration, detecting hypovolemia indicating decreased blood volume which may lead to impaired circulation.

  • Physical signs include hypotension and 'thready' pulse.

Interventions

  • Fluid replenishment using isotonic IV fluid to replace lost electrolytes effectively.

Normal Physiology: Electrolyte Balance

Sodium

  • Cation; mostly found extracellularly. Normal Serum Level: 135-148 mEq/L.

Primary Functions

  • Regulates extracellular and vascular volume (related to osmolality).

  • Maintains resting membrane potential, generating action potentials in nerve and muscle tissue.

Normal Sources of Gain

  • Dietary.

Normal Sources of Loss

  • Kidneys.

  • GI tract (small amounts with normal stool).

  • Skin (through sweat).

Pathological Changes

  • Decreased Serum Sodium (<135 mEq/L):

    • Increased sodium/water loss (e.g., excessive sweating, burns, vomiting).

    • Excessive water intake relative to output (dilutional hyponatremia).

Predisposing Factors (PF)

  • Increased Loss:

    • Skin (e.g., excessive sweating).

    • GI loss (e.g., vomiting).

    • Renal (e.g., aggressive diuretic therapy).

Nursing Problem

  • Example of Disorder: Hyponatremia.

Assessment Findings

  • Symptoms relate to muscle function, potentially affecting nervous system function due to low sodium levels.

Pathological Changes

  • Increased Serum Sodium (>148 mEq/L):

    • Excess water loss (e.g., polyuria, watery diarrhea).

    • Excessive sodium intake (oral or IV).

Nursing Problem

  • Example of Disorder: Hypernatremia.

Assessment Findings

  • Typically presents with changes in pulse quality (e.g., full and bounding), peripheral or pulmonary edema.

Potassium

  • Cation; mostly found intracellularly. Normal Serum Level: 3.5-5.0 mEq/L.

Primary Functions

  • Regulates intracellular osmolality, helps maintain resting membrane potential, influences acid-base balance.

Normal Sources of Gain

  • Dietary.

Normal Sources of Loss

  • Mainly through kidneys, stool, sweat.

Pathological Changes

  • Decreased Serum Levels (<3.5 mEq/L):

    • Inadequate intake, excessive losses from renal, GI, skin, or transcompartmental shifts.

Nursing Problem

  • Example of Disorder: Hypokalemia.

Assessment Findings

  • Symptoms of muscle weakness, fatigue, constipation, and polyuria.

Pathological Changes

  • Increased Serum Levels (>5.0 mEq/L):

    • Decreased elimination (e.g., renal failure) or excessive intake.

Nursing Problem

  • Example of Disorder: Hyperkalemia.

Assessment Findings

  • Affects cardiac function; potential for severe complications.

Calcium

  • Normal Serum Levels: 8.5-10.5 mg/dL.

Distribution

  • Primarily in the bone; small vital amounts extracellularly.

Primary Functions

  • Influences membrane potential and permeability; required for muscle contraction.

Pathological Changes

  • Decreased Serum Levels (<8.5 mg/dL):

    • Results from impaired absorption, renal loss, or increased protein binding due to alkaline pH.

Nursing Problem

  • Example of Disorder: Hypocalcemia.

Assessment Findings

  • Symptoms may include spasms and dysrhythmias.

Pathological Changes

  • Increased Serum Levels (>10.5 mg/dL):

    • Can lead to hyperactivity of the parathyroid hormone or excessive dietary calcium intake.

Nursing Problem

  • Example of Disorder: Hypercalcemia.

Assessment Findings

  • Symptoms may include muscle weakness and lethargy.

Acid-Base Balance

General Concepts

  • pH must remain within 7.35-7.45 for normal function.

  • Alterations in pH affect membrane excitability and enzyme function.

  • pH determined by hydrogen ion concentration:

    • Acid: Releases H+ ions → lower pH.

    • Base: Accepts H+ ions → higher pH.

Regulation of pH

  • Primary Routes for Acid Excretion:

    • Lungs excrete carbonic acid as carbon dioxide (CO2).

    • Kidneys excrete all other acids.

  • Buffer Systems prevent large changes in pH pending respiratory and renal function.

Bicarbonate Buffer System

  • Critical for maintaining pH balance in the body.

Arterial Blood Gases (ABGs)

  • Assessing pCO2, HCO3, and pH to evaluate acid-base imbalances.

  • Normal Ranges:

    • pCO2: 35-45 mmHg.

    • HCO3: 22-26 mEq/L.

Interpreting ABGs

  • Assessing pH, pCO2, and HCO3 helps identify acidosis/alkalosis and its causes.

Clinical Conditions

  • Metabolic Acidosis: Caused by excess metabolic acids or loss of bicarbonate.

  • Metabolic Alkalosis: Caused by excessive bicarbonate or loss of acids.

  • Respiratory Acidosis: Caused by impaired ventilation causing increased pCO2.

  • Respiratory Alkalosis: Caused by hyperventilation resulting in decreased pCO2.