Saturday, March 29, 2008


The determination of blood gas is considered a special test in the local setting.
pCO2, pH and HCO3 are usually assayed. The results help in the evaluation whether a patient has acidosis or alkalosis.


Values : pH - decreased , PCO2 normal, HCO3 - decreased
Condition - metabolic acidosis
Compensatory mechanism - hyperventilation , increase excretion of CO2
decreased retention of CO2

Values: pH increased, HCO3 - increased , PCO2-normal
Condition - metabolic alkalosis
Compensatory mechanism - hypoventilation, decreased excretion of CO2
increased retention of CO2

Values : pH- increased , PCO2 - decreased , HCO3 -normal
Condition - respiratory alkalosis
Compensatory mechanism : increased retention of HCO3
decreased excretion of H+

Values: pH-decreased , PCO2 -increased, HCO3 -normal
Condition: respiratory acidosis
Compensatory mechanism : increased retention of HCO3,
increased excretion of H+

Henderson=Hasselbalch Equation: (H & H)

pH = 6.1 + log (HCO3)/DCO2


DCO2 = PCO2 X 0.031

Where: pH =indicates the acidity or alkalinity of a solution (hydrogen ion concentration.
HCO3 - bicarbonate
DCO2 - dissolved carbon dioxide
TCO2 - total carbon dioxide

Sample Problems:

Based on the following lab results obtained,
1. What is the acid base status of the patient?
2. What further test would you recommend?
3. What may be the possible causes of the condition?
4. Show all computations.

laboratory data:

TCO2 = 20 mmol/L
PCO2 = 30 mmHg

For more on blood gas analysis, visit the site below:

labtests on line

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