Acid-Base Balance

Acid-Base Balance in the Body

Acid-Base Balance and Blood Gases

  • Acid is a substance that yields hydrogen or hydronium ions in water.

    • Sources of H+ in the body include acid from food, carbonic acid formation, inorganic acids, and organic acids.

  • Base is a substance that yields hydroxyl ions in water.

  • Plasma pH is crucial for physiological processes and has a narrow range of 7.35-7.45.

  • Acidosis causes decreased pH, while alkalosis leads to increased plasma pH.

  • Regulation Mechanisms include chemical buffers, respiratory mechanisms, and renal mechanisms.

Lungs and Acid-Base Balance

  • CO2 and Hydrogen ions have a direct proportional relationship in the lungs.

  • Ventilation plays a crucial role in removing carbon dioxide and regulating hydrogen ion concentration.

  • Hypoventilation leads to carbon dioxide accumulation and increased hydrogen ion concentration.

  • Hyperventilation decreases hydrogen ion concentration.

Kidneys and Acid-Base Balance

  • Kidneys play a vital role in excreting acid and base for regulation.

  • Main Role: Reclaim bicarbonate and excrete excess acid or base.

  • Excretion: Considerable amounts of acid and base daily.

  • IV Infusion: Lactate, acetate, and HCO3 can impact HCO3 levels.

Blood Buffers and Handerson-Hasselbach Equation

  • Blood Buffers: Bicarbonate, carbonic acid, plasma protein, hemoglobin, and inorganic phosphate.

  • Handerson-Hasselbach Equation: Expresses acid-base balance relationship.

  • Parameters of Interest: pH, pCO2, HCO3, pO2.

Evaluation of pH and Ventilation

  • Normal pH: 7.35-7.45, with 7.40 being optimal for arterial blood.

  • Ventilation Evaluation: Normal pCO2 is 35-45 mmHg.

  • Respiratory Alkalosis: pCO2 < 35 mmHg.

  • Respiratory Acidosis: pCO2 > 45 mmHg.

  • Total CO2: 19-24 mmol/L (Arterial), 22-26 mmol/L (Venous).

By understanding these concepts and mechanisms, healthcare professionals can assess and manage acid-base imbalances effectively.

Metabolic Process Evaluation

  • Normal HCO3 Levels: 21-28 mEq/L

    • <21 mEq/L: Metabolic Acidosis

    • 28 mEq/L: Metabolic Alkalosis

  • Kidneys' Role: Regulate pH by reabsorbing bicarbonate and excreting excess acid and base

Oxygenation Assessment

  • pO2 Levels:

    • Normal: 81-100 mmHg

    • Hypoxemia: <81 mmHg

    • Types of Hypoxemia based on blood levels:

      • Mild: 61-80 mmHg

      • Moderate: 41-60 mmHg

      • Severe: ≤40 mmHg

  • Association with Hemoglobin: Determines oxygen's association or dissociation

  • Effects of Excessive Oxygen: Can lead to Acidosis

  • Altitude Impact: Individuals in high altitudes show a lower range of arterial pO2

Four Basic Abnormal States

  • REMEMBER Acronym:

    • R = Respiratory

    • O = Opposite (high pCO2, high HCO3- vs low pH)

    • M = Metabolic

    • E = Equal (high pCO2, high HCO3- vs high pH)

A. Metabolic Acidosis

  • Characteristics:

    • Low pH, Low pCO2, Low HCO3-

  • Causes:

    • Bicarbonate Deficiency

    • Conditions like DKA, Lactic Acidosis, Renal Failure

  • Compensatory Mechanism:

    • Increased Breathing Rate (Hyperventilation)

B. Metabolic Alkalosis

  • Characteristics:

    • High pH, High pCO2, High HCO3-

  • Causes:

    • Bicarbonate Excess

    • Factors like Vomiting with Chloride Loss

  • Compensatory Mechanism:

    • Decreased Breathing Rate

C. Respiratory Acidosis

  • Characteristics:

    • High HCO3-, Low pH, High pCO2

  • Causes:

    • Excessive Carbon Dioxide Accumulation

    • Associated with COPD, Myasthenia Gravis, etc.

  • Compensatory Mechanism:

    • Kidneys retain HCO3 due to increased pCO2

D. Respiratory Alkalosis

  • Characteristics:

    • High pH, Low pCO2, Low HCO3-

  • Causes:

    • It Is Due To Excessive Carbon Dioxide Loss.

    • associated with Anxiety, Severe pain, etc.

  • Compensatory Mechanism:

    • Decreased Reabsorption Of Hco3 (Acidification)