Bicarbonate Level (HCO3-), Acid-Base Balance
- It is done on serum or plasma of the patient (plasma arterial or venous can be used).
- The best anticoagulant is heparin.
- The test should be done as soon as possible and minimize the time interval between a sample taken and analyzed.
- Collect samples anaerobically and heparin is the preferred anticoagulant.
- It assists in evaluating the pH of the patient.
- It also assists to evaluate electrolyte balance.
- The bicarbonate ion is the measure of a metabolic (renal) component of the acid-base equilibrium.
- Bicarbonate is the most important buffer system in the blood which maintains the pH (acid-base balance).
- H+ + HCO3 –↔ H2O + CO2
- Buffer pair = HCO3– / H2CO3
- The ratio = HCO3– / H2CO3 = 20:1
- HCO3 = 24 meq/L
- Carbonic acid = 1.2 meq/L
- Normal pH = 7.4
- Correction occurs when the values for both components of the buffer pair (HCO3 / H2CO3) return to normal.
- Bicarbonate is the measure of a metabolic (Kidney) component of acid-base balance.
- Bicarbonate is easily regulated by the kidney which excretes it in excess and retains when needed.
- This buffer pair (HCO3– / H2CO3) operates both in the kidneys and the lungs, and major extracellular buffer.
- H+ + HCO3 –↔ H2O + CO2
- In the body most of the CO2 is in the form of HCO3, So the CO2 level in blood is the measure of HCO3.
- The CO2 contents measure H2CO3, dissolved CO2, and the bicarbonate ions HCO3 that is present in the blood.
- CO2 is carried in the blood as:
- Dissolved in the plasma (pCO2).
- As bicarbonate (HCO3).
- Carbamino compound.
- Bicarbonate level is affected by a variety of respiratory and metabolic disturbances which affect acid-base balance.
- HCO3 ion is a measure of the metabolic kidney part of the acid-base balance.
- HCO3 is exchanged for other ions like Chloride and Phosphate to maintain electroneutrality.
- When the HCO3 level increases, the pH also increases.
- Kidneys play an important role in the balance of the acid-base system (c0mpensation).
- Kidneys compensate by producing more acidic or more alkaline urine.
- In respiratory acidosis, the kidney compensates by increased reabsorption of HCO3–.
- In respiratory alkalosis, the kidney compensates by increased excretion of HCO3–.
- Lungs compensate by increased or decreased blow off of CO2.
- Arterial blood = 21 to 28 meq/L
- Venous blood = 22 to 29 meq/L
- Peritoneal fluid = 24 to 29 meq/L
- Duodenal fluid = 4 to 21 meq/L
- Pancreatic fluid = 66 to 127 meq/L
- For SI unit multiplication factor is 1, that will be in mmol/L
lower-than-normal levels may be seen in:
- Addison disease
- Ethylene glycol poisoning
- Kidney disease
- Lactic acidosis
- Metabolic acidosis
- diabetic ketoacidosis.
- Methanol poisoning
- Salicylate toxicity (such as aspirin overdose)
- Liver disease
Higher-than-normal levels may be seen in:
- Breathing disorders (compensated respiratory acidosis)
- Cushing syndrome
- Excessive vomiting
- Ingestion of excessive amount of antacid, diuretics, and steroids
- Severe vomiting.
The following conditions may also alter bicarbonate levels:
- Renal tubular acidosis, distal.
- Renal tubular acidosis, proximal.
- Acidemia means arterial blood pH <7.4.
- Acidosis means a systemic increase in H+ ions.
- Alkalemia means arterial blood pH >7.4.
- Alkalosis means a systemic decrease in H+ ions.
- Respiratory acidosis: There is an absolute CO2 excess that results in decreased pH and increased pCO2 and a base deficit.
- Respiratory alkalosis: There is an absolute CO2 deficit that results in increased pH and decreased pCO2 and base excess.
- Metabolic acidosis: There is an absolute HCO3 deficit resulting in decreased pH and HCO3.
- Metabolic alkalosis: There is absolute HCO3 excess, resulting in increased pH and HCO3 levels.
|Normal values||22 to 26 meq/L||35 to 45 mm Hg||7.35 to 7.45|
|Metabolic alkalosis||Increased||Normal||increased||Prolonged vomiting, nasogastric drainage or NaHCO3 overdose|
|Metabolic acidosis||Decreased||Normal||Decreased||Diabetes, intestinal fistula, and kidney disease|
|Respiratory acidosis||Increased||Increased||Decreased||Drugs causing respiratory depression|