Fluid, Electrolyte, and Acid-Base Balance (NUR 314)

Intracellular Fluid (ICF) Volume

28 L

Extracellular Fluid (ECF) Volume

14 L (3L = Plasma & 11 L = Interstitial)

ECF Volume Deficit (Description, Assessment Findings, Lab Values)

Description: Sodium and water intake less than output (isotonic loss)

Assessment: Overnight weight loss (> 2 lbs.), orthostatic hypotension, tachycardia, dry membranes, poor turgor, dark urine, oliguria (< 30 mL/h)

Labs: ↑ Hematocrit, ↑ BUN > 20 mg/dL, urine specific gravity > 1.030

ECF Volume Excess (Description, Assessment Findings, Lab Values)

Description: Sodium and water intake greater than output (isotonic gain)

Assessment: Overnight weight gain (> 2 lbs.), dependent edema, lung crackles, confusion, pulmonary edema

Labs: ↓ Hematocrit, ↓ (< 10 mg/dL)

Antidiuretic Hormone (ADH)

ADH (vasopressin) is secreted by the posterior pituitary gland to cause renal cells to reabsorb water

Renin-Angiotensin-Aldosterone System (RAAS)

Hormone system that regulates ECF volume by influencing the amount of sodium and water excreted in urine; critical for blood pressure homeostasis

Atrial Natriuretic Peptide (ANP)

Weak hormone that regulates ECV by influencing the amount of sodium and water excreted in urine; secreted by atrial cells when they are “stretched”

Brain Natriuretic Peptide (BNP)

Hormone that regulates ECV by influencing the amount of sodium and water excreted in urine; secreted by left ventricular cells under increased pressure

Normal Range of Potassium (K⁺)

3.5 mEq/L to 5 mEq/L

Normal Range of Sodium (Na⁺)

136 mEq/L to 145 mEq/L

Normal Range of Chloride (Cl^-)

98 mEq/L to 106 mEq/L

Normal Range of Magnesium (Mg²⁺)

1.3 mEq/L to 2.1 mEq/L

Normal Range of Total Calcium (Ca²⁺)

9.0 mg/dL to 10.5 mg/dL

Normal Range of Ionized Calcium (Ca²⁺)

4.5 mg/dL to 5.6 mg/dL

Normal Range of Phosphate (PO^3-₄)

2.5 mg/dL to 4.5 mg/dL

Hypernatremia (Description, Assessment Findings, Lab Values)

Description: Loss of relatively more water than salt; gain of relatively more salt than water

Assessment: ↓ LOC, thirst, seizures (rapid/severe onset)

Labs: Serum Na⁺ > 145 mEq/L

Etiologies of Hypernatremia

1.) Loss of relatively more salt than water

• Diabetes insipidus (ADH insufficiency)

• Osmotic diuresis

• Total output > intake

2.) Gain of relatively more salt than water

• Administration of hypertonic feedings/fluids

• Lack of access to water

• Dysfunction of thirst drive

Hyponatremia (Description, Assessment Findings, Lab Values)

Description: Gain of relatively more water than salt; loss of relatively more salt than water

Assessment: ↓ LOC, seizures (rapid/severe onset)

Labs: Serum Na⁺ > 136 mEq/L

Etiologies of Hyponatremia

1.) Gain of relatively more water than salt

• Excessive ADH

• Excessive water intake

• Excessive IV administration of D₅W

• Hypotonic irrigation

• Tap-water enemas

2.) Loss of relatively more salt than water

• Replacement of fluid output with water (but no salt)

Hyperkalemia (Description, Assessment Findings, Lab Values)

Description: High serum K⁺ concentration

Assessment: Bilateral muscle weakness (quads), ABD cramps, diarrhea, dysrhythmias, cardiac arrest (severe)

Labs: Serum K⁺ > 5 mEq/L, peaked T waves, widened QRS complex, PR interval prolongation

Etiologies of Hyperkalemia

1.) ↑ K⁺ intake

• Administration of large amounts of IV K⁺

• Rapid infusion of stored blood

• Excess ingestion of salt substitutes

2.) Extracellular shift of K⁺

• Cellular damage (trauma, cytotoxic chemo)

• Insufficient insulin

3.) ↓ K⁺ output

• Acute/chronic oliguria

• Potassium-sparing diuretics

• Adrenal insufficiency (cortisol/aldosterone deficit)

Hypokalemia (Description, Assessment Findings, Lab Values).)

Description: Low serum K⁺ concentration

Assessment: Bilateral muscle weakness (quads → respiratory muscles), ABD distension, ↓ bowel sounds, constipation, dysrhythmias

Labs: Serum K⁺ < 3.5 mEq/L, U waves, flattened/inverted T waves, ST segment depression

Etiologies of Hypokalemia

1.) ↓ K⁺ intake

• Excessive use of K⁺-free IV solutions

2.) Intracellular shift of K⁺

• Alkalosis

• Insulin

3.) ↑ K⁺ output

• Acute/chronic diarrhea

• GI losses

• Potassium-wasting diuretics

• Aldosterone excess

• Polyuria

Hypercalcemia (Description, Assessment Findings, Lab Values)

Description: High serum Ca²⁺ concentration

Assessment: Anorexia, nausea/vomiting, constipation, diminished reflexes, ↓ LOC, personality change, cardiac arrest (severe)

Labs: Total serum Ca²⁺ > 10.5 mg/dL, serum ionized Ca²⁺ > 5.6 mg/dL, heart block, shortened ST segments

Etiologies of Hypercalcemia

1.) ↑ Ca²⁺ intake/absorption

• Milk-alkali syndrome

2.) Extraosseous shift of Ca²⁺

• Prolonged immobilization

• Hyperparathyroidism

• Bone tumors

• Secretion of bone-resorbing factors (non-osseous cancers)

3.) ↓ Ca²⁺ output

• Thiazide diuretics

Hypocalcemia (Description, Assessment Findings, Lab Values)

Description: Low serum Ca²⁺ concentration

Assessment: Numbness/tingling of fingers/toes/mouth, + Chvostek sign, hyperactive reflexes, muscle twitching/cramping, laryngospasm, seizures, dysrhythmias

Labs: Total serum Ca²⁺ < 9.0 mg/dL, serum ionized Ca²⁺ < 4.5 mg/dL, prolonged ST segment

Etiologies of Hypocalcemia

1.) ↓ Ca²⁺ intake/absorption

• Calcium-deficient diet

• Vitamin D deficiency

• Chronic diarrhea

• Laxative misuse

2.) Intraosseous shift of Ca²⁺

• Hypoparathyroidism

• Rapid administration of citrated blood

• Hypoalbuminemia

• Alkalosis

• Pancreatitis

• Hyperphosphatemia

3.) ↑ Ca²⁺ output

• Chronic diarrhea

Hypermagnesemia (Description, Assessment Findings, Lab Values)

Description: High serum Mg²⁺ concentration

Assessment: Lethargy, hypoactive deep tendon reflexes, bradycardia, hypotension, flushing/warmth, ↓ respiration rate/depth, dysrhythmias, cardiac arrest

Labs: Serum Mg² > 2.1 mEq/L, prolonged PR interval

Etiologies of Hypermagnesemia

1.) ↑ Mg²⁺ intake/absorption

• Magnesium-containing laxatives/antacids

• Parenteral overload

2.) ↓ Mg²⁺ output

• Oliguric end-stage renal disease

• Adrenal insufficiency

Hypomagnesemia (Description, Assessment Findings, Lab Values)

Description: Low serum Mg²⁺ concentration

Assessment: + Chvostek sign, hyperactive deep tendon reflexes, muscle cramps/twitching, grimacing, dysphagia, seizures, insomnia, tachycardia, hypertension, dysrhythmias

Labs: Serum Mg²⁺ > 1.3 mEq/L, prolonged QT interval

Etiologies of Hypomagnesemia

1.) ↓ Mg²⁺ intake/absorption

• Malnutrition

• Chronic alcoholism

• Chronic diarrhea

• Laxative misuse

2.) Shift of Mg²⁺ into inactive form

• Rapid administration of citrated blood

3.) ↑ Mg²⁺ output

• Chronic diarrhea

• GI losses

• Thiazide/loop diuretics

• Excess aldosterone

Normal Range of pH

7.35 to 7.45

Normal Range of PaCO₂

35 to 45

Normal Range of HCO₃^-

21 to 28

Normal Range of PaO₂

80 to 100