Acid-Base Imbalances lecture

ASID-BASE IMBALANCES

Introduction

  • Discussed by Assoc. Prof. Kameliya Bratoeva, M.D., PhD at MU-Varna.

Importance of pH in the Body

  • The body is highly sensitive to extracellular pH levels.

    • Outside the acceptable pH range, proteins denature, enzymes lose functionality, and can lead to death.

Understanding pH

  • pH reflects a fluid's acidity or alkalinity.

  • pH is the negative logarithm of hydrogen ion (H+) concentration.

    • Normal H+ concentration is ~40 nmol/L (or 40 x 10^-9 mol/L), leading to a normal pH of 7.40.

Acid-Base Balance

  • Changes in pH result from changes in hydrogen ion concentration.

    • High pH: Few H+ ions, indicative of an alkaline solution.

    • Low pH: Many H+ ions, indicative of an acidic solution.

Regulation of Acid-Base Balance

  • Critical for maintaining blood pH between 7.35 and 7.45.

  • Regulated by:

    • Buffering agents (e.g., bicarbonate).

    • Respiratory system: adjusts carbonic acid levels by regulating CO2.

    • Renal system: regulates bicarbonate and hydrogen ion excretion.

Acid and Base Definitions

  • Acids: Molecules that release hydrogen ions (e.g., carbonic acid).

  • Bases (Alkalis): Substances that accept H+ ions (e.g., bicarbonate).

  • Certain proteins act as weak bases, with hemoglobin being important for buffering.

pH and Hydrogen Ion Concentration

  • Relates directly to pH levels.

    • Low pH = high H+ concentration.

    • High pH = low H+ concentration.

Normal Acid-Base Physiology

Metabolism and pH

  • Cells produce H+ and CO2 during macronutrient metabolism.

  • Respiratory system: Removes CO2 to decrease H+ levels, aiding in pH balance.

  • Renal system: Adds bicarbonate and removes acids through urine.

    • Normal ranges: pH = 7.35-7.45; HCO3 = 22-26 mEq/L; pCO2 = 38-42 mmHg.

Buffers in the Body

  • Buffer systems present in all body fluids to resist pH changes.

    • Bicarbonate System: Main buffer in the blood, maintains a 20:1 ratio of bicarbonate to carbonic acid.

    • Phosphate System: Operates in renal and bodily fluids.

    • Protein Buffers: Utilize amino acids and hemoglobin for pH balance.

Compensation Mechanisms

  • Respiratory compensation: Adjusts ventilation to regulate CO2 and H2CO3 levels.

  • Renal compensation: Slow, powerful response to regulate H+ and bicarbonate.

Acid-Base Imbalances

Definitions

  • Acidosis: pH < 7.35 (caused by increased H+ concentration).

  • Alkalosis: pH > 7.45 (caused by decreased H+ concentration).

Compensation Mechanisms

  • Body attempts to restore normal pH; involves varying degrees of compensation via respiratory or renal pathways.

Common Acid-Base Disorders

  • Metabolic Acidosis: Bicarbonate deficiency (HCO3- < 22 mEq/L). Cause examples include renal dysfunction or high acid production.

  • Respiratory Acidosis: Excess CO2, causes include CNS depression, lung disease.

  • Metabolic Alkalosis: Bicarbonate excess ( HCO3- > 26 mEq/L); causes include vomiting, diuretics, or antacid use.

  • Respiratory Alkalosis: Low CO2, usually due to hyperventilation.

Case Studies

Case Study 1

  • Post-surgery patient on Morphine exhibits:

    • pH: 7.15 (low)

    • CO2: 68 mmHg (high)

    • HCO3: 22 mEq/L (normal)

    • Conclusion: Uncompensated Respiratory Acidosis.

Case Study 2

  • Asthma patient exhibits:

    • pH: 7.36 (normal)

    • CO2: 69 mmHg (high)

    • HCO3: 36 mEq/L (high)

    • Conclusion: Compensated Respiratory Acidosis.

Case Study 3

  • Post-abdominal surgery patient with large NG tube drainage exhibits:

    • pH: 7.52 (high)

    • CO2: 35 mmHg (normal)

    • HCO3: 29 mEq/L (high)

    • Conclusion: Uncompensated Metabolic Alkalosis.

Conclusion

  • Understanding acid-base imbalances is essential for diagnosing and managing patients effectively, as disturbances can have profound impacts on physiological functions.