ACID BASE IMBALANCES book

Acid-Base Balance Overview

  • The hydrogen ion (H+) balance is crucial for the optimal functioning of membrane excitability, enzyme systems, and chemical reactions.

  • Normal pH range for extracellular body fluids: 7.35 to 7.45.

  • Acid-base balance mechanisms generate, buffer, and eliminate acids and bases.

Mechanisms of Acid-Base Balance

Acid-Base Chemistry

  • Acids release H+, while bases accept H+.

  • Dissociation examples:

    • Hydrochloric acid (HCl) dissociates to form H+ and Cl− ions.

    • Bicarbonate (HCO3 −) combines with H+ to form carbonic acid (H2CO3).

  • Buffer Systems: Mixtures of weak acids/bases and their conjugates that help stabilize pH.

Production of Metabolic Acids and Bicarbonate

  • Metabolic Acids: Produced from metabolic processes (e.g., from sulfuric acid via amino acids).

  • Volatile acids (H2CO3) can leave via the lungs, while nonvolatile acids (e.g., sulfuric, phosphoric) are managed by the kidneys.

Calculation of pH

  • The Henderson-Hasselbalch equation:

    • pH = 6.1 + log10(HCO3 − / (PCO2 × 0.03))

  • Normal pH when HCO3 − concentration to H2CO3 ratio is 20:1.

Regulation of pH

  1. Chemical Buffer Systems: Immediate buffer response using bicarbonate, proteins, etc.

  2. Respiratory Control: Regulation of volatile carbonic acid.

  3. Renal Control: Excretion of H+ and reabsorption/generation of HCO3 −.

Laboratory Tests for Acid-Base Balance

  • Arterial Blood Gases (ABGs): Assesses blood pH, CO2 content, HCO3 − levels, base excess/deficit, and anion gap.

Disorders of Acid-Base Balance

Metabolic Disorders

  • Metabolic Acidosis: Decrease in pH due to reduced HCO3 − (causes: excess fixed acids, loss of bicarbonate).

    • Manifestations: Weakness, hyperventilation (Kussmaul breathing).

  • Metabolic Alkalosis: Increase in pH due to excess HCO3 − (causes: loss of fixed acids, gain of bicarbonate).

    • Manifestations: Confusion, tetany, compensatory hypoventilation.

Respiratory Disorders

  • Respiratory Acidosis: Elevated PCO2 due to impaired ventilation leading to decreased pH.

    • Manifestations: Headache, confusion, lethargy.

  • Respiratory Alkalosis: Decreased PCO2 from hyperventilation (increased pH).

    • Manifestations: Dizziness, tingling, tetany.

Compensatory Mechanisms

  • Acidosis/Alkalosis: The body employs compensatory mechanisms (respiratory and renal) to stabilize pH.

  • Examples of compensation include altered ventilation rates and bicarbonate reabsorption.

Key Takeaways

  • Many metabolic and respiratory disorders can lead to acidosis or alkalosis, each with specific causes and compensatory mechanisms.

  • Regulation of pH is a constant dynamic process involving interplay between respiratory and renal systems.