11. Components of ABG
1. pH – measures hydrogen concentration in blood,
shows acidity or alkalinity
2. pCO2 – partial pressure of CO2 dissolved in blood,
shows respiratory parameter
3. pO2 – partial pressure of O2 dissolved in blood
4. HCO3 – reflects kidney’s ability to retain or excrete
bicarbonate, shows metabolic parameter
12. Components of ABG
5. SaO2 - measures the percentage of Hb combined
with O2
6. Base excess - amount of acid or base (in mmol)
required to titrate 1 L of blood to pH 7.4, at 37◦C and
pCO2 of 40mmHg.
16. Classic approach
• Based on this approach – 6 primary disorders:
1. Metabolic acidosis (high or normal AG)
2. Metabolic alkalosis
3. Acute and chronic respiratory acidosis
4. Acute and chronic respiratory alkalosis
17. Stewart approach
• Non bicarbonate based
• Variables :
1. Respiratory – pCO2
2. Metabolic – strong ion difference (SID) and total
weak acids (ATOT)
SID : [cations]-[anions]
ATOT : represent all non bicarbonate buffer
21. Compensation
• Maintainance of acid base balance
• Goal : to return pH back to normal
• Accomplished by buffer system (by changing H+)
• Respiratory compensation faster than metabolic
• No complete compensation (only 50 – 75%)