Bicarbonate is an indicator of the buffering capacity of the blood. Low bicarbonate indicates that a larger pH change will occur for a given amount of acid or base produced.
Bicarbonate in the blood is calculated from the pH and PCO2 using the Henderson-Hasselbalch equation.
Normal range:
Arterial: 21 " �28 mEq/L
Venous: 22 " �29 mEq/L
Use
Significant indicator of electrolyte dispersion and anion deficit.
Together with pH determination, bicarbonate measurements are used in the diagnosis and treatment of numerous potentially serious disorders associated with acid " �base imbalance in the respiratory and metabolic systems. Some of these conditions are diarrhea, renal tubular acidosis, carbonic anhydrase inhibitors, hyperkalemic acidosis, renal failure, and ketoacidosis.
Interpretation
Increased In
Primary metabolic alkalosis
Primary respiratory acidosis
Severe vomiting
Lung disease (COPD)
Cushing syndrome
Diuretics
Primary hyperaldosteronism
Laxative abuse
Decreased In
Primary metabolic acidosis
Primary respiratory alkalosis
Addison disease
Ethylene glycol or methanol poisoning
Chronic diarrhea
Salicylate overdose
Limitations
Bicarbonate can be determined by titration, but this is rarely done.
HCO3 � � � is the largest fraction contributing to the total CO2. Therefore, both parameters usually change in the same direction.
The standard HCO3 � � � is the concentration of HCO3 � � � in whole blood at 38 � �C equilibrated at a PCO2 of 40 mm Hg with the blood Hb fully oxygenated.