Electrolytes and Acid-Base Balance

Overview

This lecture reviews key concepts of fluid and electrolytes, including major electrolyte functions, sources, ranges, signs of imbalances, and acid-base balance for nursing students.

Major Electrolytes and Their Functions

• Potassium maintains resting membrane potential of skeletal, smooth, and cardiac muscles; normal range is 3.5–5 mEq/L.
• Calcium influences excitability of nerve and muscle cells and muscle contraction; normal range is 8.5–10.5 mg/dL.
• Phosphate has an inverse relationship with calcium; normal range is 2.8–4.5 mg/dL.
• Magnesium is essential for neuromuscular junction function and found in whole grains and dark green leafy vegetables; normal range is 1.7–2.2 mEq/L.
• Sodium regulates fluid balance; normal range is 135–145 mEq/L.

Signs and Symptoms of Electrolyte Imbalances

• Hypokalemia/Hyperkalemia: Muscle weakness, cardiac dysrhythmias, possible death.
• Hypocalcemia: Muscle/nerve irritability, tetany, positive Trousseau's and Chvostek's signs.
• Hyponatremia & Hypovolemia: Hypotension, tachycardia, thready pulse, dry mucous membranes, dark yellow urine, poor skin turgor.

Dietary Sources and Restrictions

• High Sodium Foods: Canned, frozen, packaged foods, soups, deli meats; avoid in hypertension/CHF.
• Calcium Sources: Canned fish with bones, broccoli, oranges, dairy products; requires vitamin D for absorption.

Acid-Base Balance

• Normal pH Range: 7.35–7.45.
• O2 Sat: 95–100%.
• PaO2: 80–100 mmHg.
• Bicarbonate (HCO3-): 22–26 mEq/L (regulated by kidneys).
• CO2: 35–45 mmHg (regulated by lungs).
• Lungs: Increase or decrease CO2 levels by changing respiratory rate.
• Kidneys: Control bicarbonate levels.

Acid-Base Imbalance Examples

• Respiratory Acidosis: Caused by pneumonia, airway obstruction, COPD (CO2 retention).
• Respiratory Alkalosis: Seen in severe anxiety, acute pain, hyperventilation (CO2 loss).
• Metabolic Acidosis: Caused by diarrhea or ketoacidosis (loss of base or increased acids).

Key Terms & Definitions

• Hypokalemia/Hyperkalemia — low/high blood potassium.
• Hypocalcemia/Hypercalcemia — low/high blood calcium.
• Hyponatremia — low blood sodium.
• Tetany — muscle spasms due to low calcium.
• Oliguria — low urine output.
• Trousseau’s/Chvostek’s sign — clinical signs of hypocalcemia.

Action Items / Next Steps

• Review electrolyte normal ranges, sources, and signs of imbalance.
• Study acid-base balance and compensation mechanisms.
• Be able to identify foods high in sodium or calcium for patient teaching.