Biochemical Mixtures: Buffer Systems, Analysis and Clinical Applications

1. Buffer Systems in the Body

The human body requires maintaining a stable internal environment, particularly the pH of blood. Normal blood pH fluctuates within a range of 7.35 – 7.45 mmol/L, regulated by buffer systems. Buffer systems consist of a pair of substances capable of binding to H+ or OH- ions to neutralize pH changes.

Note: Ideal blood pH is 7.38 – 7.42, allowing for optimal biochemical reactions.

Plasma Buffer Systems:

• Bicarbonate (H2CO3/NaHCO3): This is the primary buffer system in the body, playing a critical role in regulating blood pH.
• Phosphate (NaH2PO4/Na2HPO4): This buffer system acts as an auxiliary, less effective than bicarbonate.
• Protein/Proteinate Na: Proteins in the blood can bind to H+ or OH- ions to maintain pH.
• Organic Acids/Sodium Salts of Organic Acids: This buffer system has a limited role, primarily related to the metabolism of organic acids.

Blood Cell Buffer Systems:

• Hemoglobin (HHb/KHb (not carrying O2), HHbO2/KHbO2 (carrying O2): Hemoglobin in red blood cells plays a crucial role in CO2 and O2 transport, and also acts as a buffer.
• Phosphate (KH2PO4/K2HPO4): This buffer system is similar to the phosphate buffer system in plasma.
• Bicarbonate (H2CO3/KHCO3): This buffer system is similar to the bicarbonate buffer system in plasma.
• Organic Acids/Potassium Salts of Organic Acids: This buffer system is similar to the organic acid/sodium salt buffer system in plasma.

Note:

• Buffer systems in the blood work in parallel and complement each other to maintain stable pH.
• The hemoglobin buffer system in red blood cells is more effective at buffering CO2 than the bicarbonate buffer system due to hemoglobin’s high affinity for CO2.

2. Mixed Acid-Base Analysis: Evaluating Acid-Base Status

Mixed acid-base analysis involves analyzing blood arterial pH, PCO2, and HCO3 parameters to assess acid-base status in the body.

a. Blood Arterial pH Analysis:

• Significance: Arterial blood pH reflects the buffering capacity of the body’s buffer systems.
• Evaluation:
  • Acidosis: Decreased arterial blood pH (<7.35).
  • Alkalosis: Increased arterial blood pH (>7.45).

b. PCO2 Analysis:

• Significance: PCO2 is the partial pressure of CO2 in arterial blood, reflecting alveolar ventilation capacity.
• Evaluation:
  • Decreased PCO2: Often occurs due to increased alveolar ventilation.
  • Increased PCO2: Often occurs due to decreased alveolar ventilation.

c. HCO3 (Actual Bicarbonate) Analysis:

• Significance: HCO3 reflects the buffering capacity of the bicarbonate buffer system, the primary buffer system in the body.
• Normal value: 22 – 28 mEq/L
• Evaluation:
  • Decreased HCO3: May be due to bicarbonate loss through the gastrointestinal tract, kidneys, or increased acid in the body.
  • Increased HCO3: May be due to acid deficiency or increased alkalosis.

Note:

• Blood arterial pH analysis is often prioritized in assessing acid-base status as it most accurately reflects blood pH.
• Mixed acid-base analysis should be combined with clinical examination, medical history, and additional tests for an accurate diagnosis of the cause of acid-base imbalance.

3. Types of Acid-Base Imbalances

a. Respiratory Acidosis:

• Cause: Decreased alveolar ventilation leading to increased PCO2 in the blood.
• Test results:
  • Decreased blood pH
  • Increased blood PCO2
  • Normal or slightly increased blood HCO3.

b. Respiratory Alkalosis:

• Cause: Increased alveolar ventilation leading to decreased PCO2 in the blood.
• Test results:
  • Increased blood pH
  • Decreased blood PCO2
  • Normal or slightly decreased blood HCO3.

c. Metabolic Acidosis:

• Cause: Increased acid in the blood due to metabolic disturbances, such as diabetes, kidney failure.
• Test results:
  • Decreased blood pH
  • Normal or slightly increased blood PCO2
  • Decreased blood HCO3.

d. Metabolic Alkalosis:

• Cause: Acid loss or increased alkalosis, for example, vomiting, diuretic use.
• Test results:
  • Increased blood pH
  • Normal or slightly decreased blood PCO2
  • Increased blood HCO3.

e. Mixed Acidosis:

• Cause: Combination of respiratory acidosis and metabolic acidosis.
• Test results:
  • Significantly decreased blood pH
  • Increased blood PCO2
  • Decreased blood HCO3.

Note:

• Mixed acid-base imbalances are often difficult to distinguish from simple acid-base imbalances.
• Accurate identification of the type of acid-base imbalance is crucial for treatment and prevention of complications.

4. Mechanism of Bicarbonate Buffer System

The bicarbonate buffer system operates based on the chemical equilibrium reaction between carbonic acid (H2CO3) and bicarbonate (HCO3-).

• When acid enters the body (increased H+): HCO3- in the blood will combine with H+ to form H2CO3. H2CO3 will decompose into CO2 and H2O, with CO2 being exhaled through the lungs.
• When base enters the body (increased OH-): H2CO3 in the blood will release H+ to neutralize OH-.

Note:

• The kidneys play a crucial role in regulating bicarbonate levels in the blood, helping to maintain pH balance.
• In acidosis, the kidneys will increase H+ excretion and retain HCO3- to increase bicarbonate levels in the blood.
• In alkalosis, the kidneys will decrease H+ excretion and excrete HCO3- to decrease bicarbonate levels in the blood.

5. Clinical Applications

Mixed acid-base analysis is used in:

• Diagnosing and monitoring diseases related to acid-base imbalances, such as respiratory failure, kidney failure, diabetes, vomiting, diarrhea.
• Adjusting treatment based on test results for optimal effectiveness.
• Monitoring the effectiveness of acid-base treatment methods, such as mechanical ventilation, fluid administration, dietary adjustments.

Note:

• Mixed acid-base analysis should be performed under standard conditions to ensure accuracy.
• Results should be combined with clinical examination and additional tests for accurate conclusions and effective treatment.

Conclusion:

Buffer systems and mixed acid-base analysis are essential tools in maintaining blood pH balance and treating diseases related to acid-base imbalances. A solid understanding of biochemical mixtures helps to improve diagnosis, treatment, and prevention of complications associated with acid-base imbalances.