Electrolytes Part 3: Bicarbonate, Lactate, and Phosphate

Key Electrolytes Discussed

1. Bicarbonate
2. Lactate
3. Phosphate

Bicarbonate

• Role and Function:

  • Second most abundant anion in the extracellular fluid (ECF) after chloride.
  • Central to acid-base balance in the body.
  • Originates from carbon dioxide in the blood.
  • Involved in major buffering system in the blood with carbonic acid.
  • Helps maintain normal pH between 7.35 and 7.45.

• Process:

  • Carbon dioxide + water = carbonic acid (via carbonic anhydrase).
  • Carbonic acid dissociates into hydrogen ions + bicarbonate.
  • Total carbon dioxide includes dissolved carbon dioxide, carbonic acid, and bicarbonate.

• Clinical Relevance:

  • Bicarbonate levels can indicate metabolic disorders such as acidosis and alkalosis.
  • The kidneys regulate bicarbonate through excretion or reabsorption to maintain pH balance.

Phosphate

• Role and Function:

  • Widespread in the body, located in bones, ATP, DNA, and RNA.
  • Acts as a reservoir of biochemical energy.

• Regulation:

  • Absorbed in intestines, regulated by kidneys, Vitamin D, and parathyroid hormone (PTH).
  • Vitamin D increases phosphate absorption; PTH decreases it.

• Clinical Relevance:

  • Hypophosphatemia (low phosphate) occurs in conditions like sepsis, diabetes, and renal disease.
  • Hyperphosphatemia (high phosphate) can be due to renal failure or excessive intake.

Lactate

• Role and Function:

  • Byproduct of anaerobic metabolism.
  • Indicates tissue hypoxia (low oxygen levels).
  • Converted back to glucose by the liver (Cori cycle).

• Clinical Relevance:

  • Indicator of oxygen deprivation and severity in critical illnesses.
  • Elevated in conditions causing hypoxia or severe systemic illness.

Anion Gap and Other Concepts

• Anion Gap:

  • Difference between measured cations (sodium and potassium) and anions (chloride and bicarbonate).
  • Used to identify unmeasured anions in the blood.

• Clinical Relevance:

  • Elevated anion gap seen in conditions like renal failure, ketoacidosis, lactic acidosis.
  • Low anion gap may indicate hypoalbuminemia or severe hypercalcemia.

Testing and Specimen Handling

• Bicarbonate: Measured using ion-selective electrodes.

• Phosphate: Measured using ammonium molybdate complex formation.

• Lactate: Measures tissue hypoxia; enzymatic methods involve lactate oxidase.

• Specimen Collection:

  • Use of closed systems to prevent air exposure.
  • Anaerobic collection important for accurate results.
  • Proper temperature maintenance necessary (e.g., ice water slurry for lactate).

Summary

• Understanding these electrolytes and their functions is crucial for diagnosing and managing metabolic disorders.
• Each electrolyte plays a distinct role in maintaining physiological balance and responding to changes in the body.