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Sample

Indication

Pathophysiology

  1. Bicarbonate is the most important buffer in the blood which maintains the pH (acid-base balance).
  2. Bicarbonate is the measure of a metabolic (Kidney) component of acid-base balance.
  3. Bicarbonate is easily regulated by the kidney which excretes it in excess and retains when needed.
  4. In the body most of the CO2 is in the form of HCO3, So CO2 level in blood is the measure of HCO3.
    1. The CO2 contents measure H2CO3, dissolved CO2, and the bicarbonate ions HCO3 that is present in the blood.
  5. Bicarbonate level is affected by a variety of respiratory and metabolic disturbances which affect acid-base balance.
    1. HCO3 ion is a measure of the metabolic kidney part of the acid-base balance.
  6. HCO3 is exchanged for other ions like Chloride and Phosphate to maintain electroneutrality. 

  1. When HCO3 level increases, the pH also increases.
  2. Kidneys play important role in the balance of the acid-base system.
    1. In respiratory acidosis, kidney compensates by increased reabsorption of HCO3.
    2. In respiratory alkalosis, kidney compensates by increased excretion of HCO3.

NORMAL

Lower-than-normal levels may be seen in:

  1. Addison disease
  2. Diarrhea
  3. Ethylene glycol poisoning
  4. Ketoacidosis
  5. Kidney disease
  6. Lactic acidosis
  7. Metabolic acidosis
  8. Starvation.
  9. diabetic ketoacidosis.
  10. Methanol poisoning
  11. Salicylate toxicity (such as aspirin overdose)
  12. Liver disease

Higher-than-normal levels may be seen in:

  1. Breathing disorders (compensated respiratory acidosis)
  2. Cushing syndrome
  3. Excessive vomiting
  4. Hyperaldosteronism
  5. Ingestion of excessive amount of antacid, diuretics and steroids
  6. Severe vomiting.

The following conditions may also alter bicarbonate levels:

  1. Alkalosis
  2. Delirium
  3. Dementia
  4. Renal tubular acidosis, distal.
  5. Renal tubular acidosis, proximal.

Acid-base balance

  1. Respiratory acidosis: There is an absolute CO2 excess that results in decreased pH and increased pCO2 and a base deficit.
  2. Respiratory alkalosis: There is an absolute CO2 deficit that results in increased pH and decreased pCO2 and a base excess.
  3. Metabolic acidosis: There is an absolute HCO3 deficit resulting in decreased pH and HCO3.
  4. Metabolic alkalosis: There is absolute HCO3 excess, resulting in increased pH and HCO3 level.
  HCO3  pCO2 pH  
Normal values  22 to 26 meq/L 35 to 45 mm HG 7.35 to 7.45 Etiology
Metabolic alkalosis  Increased Normal increased Prolonged vomiting, nasogastric drainage or NaHCO3 overdoses
Metabolic acidosis Decreased Normal Decreased Diabetes, intestinal fistula, and kidney disease
Respiratory alkalosis Normal Decreased Increased Hyperventilation
Respiratory acidosis Normal Increased Decreased Drugs causing respiratory depression

Possible References Used

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