Fluid, Electrolyte, and Acid-Base Imbalances

CHAPTER 17: Fluid, Electrolyte, and Acid-Base Imbalances

Normal Physiology

• Homeostasis is maintained by keeping the composition and volume of fluids and electrolytes within narrow limits.

• Fluid and electrolyte imbalances are common in patients with major illnesses or injuries.

• Imbalances are classified as deficits or excesses.

Water Content of the Body

• Water content varies with body mass, gender, and age.

• Lean body mass has a higher percentage of water.

• Fat tissue has a lower percentage of water.

• Adult body weight is 50-60% water.

Body Fluid Compartments

• Intracellular Fluid (ICF): 28 L

• Extracellular Fluid (ECF)

  • Plasma: 3 L

  • Interstitial Fluid (IF): 10 L

Calculation of Fluid Gain or Loss

• 1 L of water weighs 2.2 pounds (1 kg).

• Body weight change is a good indicator of overall fluid volume loss or gain.

Electrolytes

• Substances that dissociate into ions when placed in water.

• Cations: positively charged ions.

• Anions: negatively charged ions.

• Electrolyte concentration is expressed in milliequivalents (mEq)/L.

Electrolyte Composition

• ICF

  • Prevalent cation: K^+ potassium

  • Prevalent anion: PO_4^{3-} phos

• ECF

  • Prevalent cation: Na^+ ssodium

  • Prevalent anion: Cl^- chloride

Concentrations of Cations and Anions

• Refer to the provided diagrams for specific concentrations of cations and anions in plasma and intracellular fluid (ICF).

Mechanisms Controlling Fluid and Electrolyte Movement

• Diffusion: Movement of molecules from an area of high concentration to an area of low concentration.

• Active Transport: Requires energy (ATP) to move electrolytes against a concentration gradient (e.g., sodium-potassium pump).

• Osmosis: Movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.

Osmotic Pressure

• The osmolality of fluid surrounding cells affects them.

  • Isotonic: Same solute concentration as the cell interior.

  • Hypotonic: Lower solute concentration than the cell interior (hypoosmolar).

  • Hypertonic: Higher solute concentration than the cell interior (hyperosmolar).

Osmotic Movement of Fluids

• Plasma Osmolality Calculation:

  • Plasma\ Osmolality = (2 \times Na) + (BUN / 2.8) + (glucose / 18)

  • Normal plasma osmolality: 280-295 mOsm/kg

  • Greater than 295 mOsm/kg: water deficit

  • Less than 275 mOsm/kg: water excess

Hydrostatic and Oncotic Pressure

• Hydrostatic Pressure: Force of fluid in a compartment; blood pressure generated by the heart's contraction.

• Oncotic Pressure: Colloid osmotic pressure; osmotic pressure caused by plasma proteins.

Fluid Movement in Capillaries

• Determined by:

  • Capillary hydrostatic pressure

  • Plasma oncotic pressure

  • Interstitial hydrostatic pressure

  • Interstitial oncotic pressure

Fluid Shifts

• Edema is caused by:

  • Shifts of plasma to interstitial fluid

  • Elevation of venous hydrostatic pressure

  • Decrease in plasma oncotic pressure

  • Elevation of interstitial oncotic pressure

Fluid Spacing

• First Spacing: Normal distribution in ICF and ECF.

• Second Spacing: Abnormal accumulation of interstitial fluid (edema).

• Third Spacing: Fluid trapped where it's difficult or impossible to move back into cells or blood vessels.

Regulation of Water Balance

• Hypothalamic-Pituitary Regulation

  • Osmoreceptors in hypothalamus sense fluid deficit or increase.

  • Deficit stimulates thirst and antidiuretic hormone (ADH) release.

  • Decreased plasma osmolality (water excess) suppresses ADH release.

• Renal Regulation

  • Main organ for regulating fluid and electrolyte balance.

  • Adjusts urine volume.

  • Selective reabsorption of water and electrolytes.

  • Renal tubules are sites of action of ADH and aldosterone.

• Adrenal Cortical Regulation

  • Releases hormones to regulate water and electrolytes.

  • Glucocorticoids (e.g., cortisol).

  • Mineralocorticoids (e.g., aldosterone).

Factors Affecting Aldosterone Secretion

• Renal perfusion:

  • ↓Renal perfusion → ↑ Renin secretion → ↑ Plasma angiotensin II → ↑ Aldosterone secretion

• Other factors:

  • Stress, physical trauma, ↑ Serum K^+, ↓ Serum Na^+, ↑ ACTH

Effects of Stress on Fluid and Electrolyte Balance

• Stress → Hypothalamus (CRH) → Anterior pituitary (↑ ACTH secretion) + Posterior pituitary (↑ ADH secretion).

• Adrenal cortex (↑ Aldosterone, ↑ Cortisol) → Kidney (↑ Na^+ reabsorption, ↑ K^+ excretion, ↑ H_2O reabsorption)

Regulation of Water Balance (Continued)

• Cardiac Regulation

  • Natriuretic peptides are antagonists to the RAAS.

  • Hormones made by cardiomyocytes in response to increased atrial pressure.

  • They suppress secretion of aldosterone, renin, and ADH to decrease blood volume and pressure.

• GI Regulation

  • Oral intake accounts for most water.

  • Small amounts of water are eliminated by GI tract in feces.

  • Diarrhea and vomiting can lead to significant fluid and electrolyte loss.

Gerontologic Considerations

• 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 lost.

Fluid Volume Imbalances

• Fluid Volume Deficit (FVD) or Hypovolemia

  • Abnormal loss of body fluids, inadequate fluid intake, or plasma to interstitial fluid shift.

  • Dehydration: Loss of pure water without a corresponding loss of sodium.

  • FVD Interprofessional Care: Correct underlying cause and replace water and electrolytes (orally, blood products, isotonic IV solutions).

• Fluid Volume Excess (Hypervolemia)

  • Excess fluid intake, abnormal fluid retention, or interstitial-to-plasma fluid shift.

  • Clinical manifestations related to excess volume (weight gain is the most common).

  • Interprofessional Care: Remove fluid without changing electrolyte composition or osmolality of ECF (diuretics, fluid restriction, possible sodium restriction, removal of fluid to treat ascites or pleural effusion).

Nursing Management: Fluid Imbalances

• Assessment:

  • Health history (kidney, heart, GI, or respiratory problems).

  • Prior fluid balance problems.

  • Recent changes in body weight.

  • Exercise pattern/activity level.

  • Current and past medications.

  • Dialysis or surgeries.

  • Monitor laboratory results when available.

• Clinical Problems:

  • Hypervolemia, hypovolemia

  • Deficient knowledge- fluid volume management

  • Impaired tissue perfusion

  • Altered blood pressure

  • Impaired respiratory system function

  • Impaired urinary system function

  • Risk for injury

  • Risk for impaired skin integrity

• Implementation:

  • Daily weights, I & O

  • Cardiovascular care, respiratory care

  • Patient safety, skin care

Assessment of Skin Turgor

• Refer to the provided images for assessing skin turgor.

Fluid Therapy

• Give IV fluids as ordered.

• Carefully monitor rate of infusion.

• Maintain adequate oral intake.

• Assess ability to obtain adequate fluids independently, express thirst, and swallow effectively.

• Assist those with physical limitations.

Sodium

• Imbalances typically associated with parallel changes in osmolality.

• 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 may occur with inadequate water intake, excess water loss, or sodium gain.

• Causes hyperosmolality leading to cellular dehydration.

• Primary protection is thirst.

• Clinical manifestations: thirst, changes in mental status (drowsiness, restlessness, confusion, lethargy, seizures, coma), symptoms of fluid volume deficit.

• Treatment: Treat underlying cause.

Differential Assessment of ECF Volume

• Extracellular contraction (Volume deficit resulting from H_2O deficiency): Hypernatremia

• Normal: Isotonic ECF deficit (Normal Na^+)

• Extracellular expansion (Volume excess resulting from H_2O excess): Hyponatremia

• Normal: Isotonic ECF excess (Normal Na^+)

Imbalances in ECF Volume

• Net loss > H_2O loss: Hypoosmolar imbalance

• Sodium and water: Isotonic loss (Osmolar balance)

• H_2O loss > Na^+ loss: Hyperosmolar imbalance

• Net gain > H_2O gain: Hyperosmolar imbalance

• Sodium and water: Isotonic gain (Osmolar balance)

• H_2O gain > Na^+ gain: Hypoosmolar imbalance

Hyponatremia

• Results from loss of sodium-containing fluids and/or from water excess.

• Clinical manifestations: Mild (headache, irritability, difficulty concentrating); More severe (confusion, vomiting, seizures, coma).

• If the cause is water excess:

  • Fluid restriction may be the only treatment

  • Loop diuretics and demeclocycline.

  • Severe symptoms (seizures): Give small amount of IV hypertonic saline solution (3% NaCl).

• If the cause is abnormal fluid loss:

  • Fluid replacement with isotonic sodium-containing solution.

  • Encouraging oral intake.

  • Withholding diuretics.

  • Drugs that block vasopressin (ADH): Convaptan (Vaprisol) IV, Tolvaptan (Samsca) oral.

Potassium

• 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.

• Sources: Protein-rich foods, fruits and vegetables, salt substitutes, potassium medications (PO, IV), stored blood.

• Regulated by kidneys.

Hyperkalemia

• High serum potassium caused by impaired renal excretion, shift from ICF to ECF, massive intake of potassium, some drugs.

• Most common in renal failure.

• Manifestations: Life-threatening arrhythmias, fatigue, confusion, tetany, muscle cramps, weak or paralyzed skeletal muscles, abdominal cramping or diarrhea.

ECG Effects of Hyperkalemia

• Tall, peaked T wave.

• Prolonged PR interval.

• Widened QRS.

• Depressed ST segment.

• Wide, flat P wave.

Nursing and Interprofessional Management of Hyperkalemia

• Stop oral and IV K^+ intake.

• Increase K^+ excretion (thiazide diuretics, dialysis).

• patiromer (Veltessa), sodium zirconium cyclosilicate (ZS-9, Lokelma), and/or sodium polystyrene sulfonate (Kayexalate).

• Force K^+ from ECF to ICF by IV regular insulin with dextrose and a b-adrenergic agonist or sodium bicarbonate.

• Stabilize cardiac cell membrane by administering calcium chloride or calcium gluconate IV.

• Use continuous ECG monitoring.

Hypokalemia

• Low serum potassium caused by increased loss of K^+ via the kidneys or gastrointestinal tract, increased shift of K^+ from ECF to ICF, decreased dietary K^+ (rare).

• Renal losses from loop or potassium-depleting diuresis

• Low magnesium level.

• Clinical manifestations: Cardiac most serious, skeletal muscle weakness and paresthesia, weakness of respiratory muscles, decreased GI motility, hyperglycemia.

ECG Effects of Hypokalemia

• Slightly prolonged PR interval.

• ST depression.

• Slightly peaked P wave.

• Shallow T wave.

• Prominent U wave.

• Decreased R wave amplitude.

Nursing and Interprofessional Management of Hypokalemia

• KCl supplements orally or IV.

• Always dilute IV KCl.

• NEVER give KCl via IV push or as a bolus.

• Should not exceed 10 mEq/hr.

• Use an infusion pump.

Calcium

• Functions: Formation of teeth and bone, blood clotting, transmission of nerve impulses, myocardial contractions, muscle contractions.

• Major source is dietary intake. Need vitamin D to absorb.

• Present in bones and plasma. Ionized or free calcium is biologically active.

• Changes in pH and serum albumin affect levels.

• Balance controlled by parathyroid hormone (PTH) and calcitonin.

  • Parathyroid hormone (PTH): Increases bone resorption, GI absorption, and renal tubule reabsorption of calcium.

  • Calcitonin: Increases calcium deposition into bone, increases renal calcium excretion, and decreases GI absorption.

Hypercalcemia

• High levels of serum calcium caused by hyperparathyroidism (two-thirds of cases), cancers, especially kidney, breast, prostate, ovarian, hematologic, and lung cancers.

• Manifestations: Fatigue, lethargy, weakness, confusion, hallucinations, seizures, coma, dysrhythmias, bone pain, fractures, nephrolithiasis, polyuria, dehydration.

Nursing and Interprofessional Management of Hypercalcemia

• Low calcium diet.

• Stop medications related to hypercalcemia.

• Increased weight-bearing activity.

• Increased fluid intake (3000 to 4000 ml daily, cranberry or prune juice)

• Hydration with isotonic saline infusion.

• Bisphosphonates—gold standard.

• Calcitonin.

Hypocalcemia

• Low serum Ca levels caused by decreased production of PTH, multiple blood transfusions, alkalosis, increased calcium loss.

• Manifestations: Positive Trousseau’s or Chvostek’s sign, laryngeal stridor, dysphagia, numbness and tingling around the mouth or in the extremities, dysrhythmias.

Tests for Hypocalcemia

• Refer to the provided images demonstrating Trousseau's and Chvostek's signs.

Nursing and Interprofessional Management of Hypocalcemia

• Treat cause.

• Calcium and Vitamin D supplements.

• IV calcium gluconate.

• Rebreathe into paper bag.

• Treat pain and anxiety to prevent hyperventilation-induced respiratory alkalosis.

Phosphate

• Primary anion in ICF.

• Essential to function of muscle, red blood cells, and nervous system.

• Involved in acid-base buffering system, ATP production, cellular uptake of glucose, and metabolism of carbohydrates, proteins, and fats.

• Serum levels controlled by parathyroid hormone.

• Maintenance requires adequate renal functioning.

• Reciprocal relationship with calcium.

Hyperphosphatemia

• High serum PO_4^{3-} caused by acute kidney injury or CKD, excess intake of phosphate or vitamin D, hypoparathyroidism.

• Manifestations: Tetany, muscle cramps, paresthesias, hypotension, dysrhythmias, seizures (hypocalcemia), calcified deposits in soft tissue such as joints, arteries, skin, kidneys, and corneas (cause organ dysfunction, notably renal failure).

• Management: Identify and treat underlying cause, restrict intake of foods and fluids containing phosphorus, oral phosphate-binding agents, hemodialysis, volume expansion and forced diuresis, correct any hypocalcemia.

Hypophosphatemia

• Low serum PO_4^{3-} caused by malnourishment/malabsorption, diarrhea, use of phosphate-binding antacids, inadequate replacement during parenteral nutrition.

• Manifestations: CNS depression, muscle weakness and pain, respiratory and heart failure, rickets and osteomalacia.

• Management: Increasing oral intake with dairy products, oral supplements, IV administration of sodium or potassium phosphate, monitor serum calcium and phosphorus levels every 6 to 12 hours.

Magnesium

• Cofactor in enzyme for metabolism of carbohydrates.

• Required for DNA and protein synthesis, blood glucose control, BP regulation.

• Needed for ATP production.

• Acts directly on myoneural junction.

• Important for normal cardiac function.

• 50% to 60% contained in bone, 30% in cells, only 1% in ECF.

• Absorbed in GI tract, excreted by kidneys.

Hypermagnesemia

• High serum Mg caused by increased intake of products containing magnesium when renal insufficiency or failure is present, excess IV magnesium administration.

• Manifestations: Hypotension, facial flushing, lethargy, nausea and vomiting, impaired deep tendon reflexes, muscle paralysis, respiratory and cardiac arrest.

• Management: Prevention first—stop magnesium-containing drugs and limit dietary intake of magnesium-containing foods, IV calcium gluconate if symptomatic, fluids and diuretics to promote urinary excretion, dialysis.

Hypomagnesemia

• Low serum Mg caused by prolonged fasting or starvation, chronic alcoholism, fluid loss from GI tract, prolonged PN without supplementation, diuretics, proton-pump inhibitors, some antibiotics, hyperglycemic osmotic diuresis.

• Manifestations: Resembles hypocalcemia, muscle cramps, tremors, hyperactive deep tendon reflexes, Chvostek’s and Trousseau’s signs, confusion, vertigo, seizures, dysrhythmias.

• Management: Treat underlying cause, oral supplements, increase dietary intake, IV magnesium when severe.