How to interprit a Arterial Blood gas report - basic steps

1. Interpretation of arterial
blood gas report
DR. Manori Gamage
Dept of Paediatrics
Faculty Of medical Sciences
University Of Sri Jayewardenepura

2. Important to remember
• In neonates PaO2 normal value is lower than infants/
children.
• VBG/ CBG is ok, but need to be careful during
interpretation.

3. What are the information you can obtain from an ABG
▪ Correct oxygenation
▪ Acid base status
▪ True picture of alveolar ventilation

4. What are the parameters you check in an ABG
Parameter
pH
PaCO2
PaO2
HCO3
Anion gap
Base excess
Normal range
7.35 - 7.45
35 - 45 mmHg (4.7 - 6 kPa)
75 - 98 mmHg (10 - 13 kPa)
22 - 26 mmol/L
8 - 16 mmol/L

5. How to interpret oxygenation
Oxygen in blood,
(a) could be bound to haemoglobin or
(b) dissolved in plasma
Pulse oxymeter - detects oxygen bound to Hb.
PaO2 - detects oxygen dissolved in plasma.
PaO2 gives oxygen tension in the blood and is the best
indicator of rate of oxygen transfer at lung level.

6. How to interpret Oxygen and CO2
(a) PaO2 - Low in hypoxic respiratory failure
(b) PaCO2 - indicates hypoventilation
indicates hyperventilation.
at alveolar level.

7. ABG Interpretation
Normal pH - 7.35. - 7.45
pH - < 7.35 - Acidosis
pH - > 7.45 - Alkalosis

8. Acidosis
Metabolic
• Occur due to
(a) Organic acids
(b) HCO3
Occur due to either of those
status
Respiratory
• Hypoventilation and
accumulation of CO2 causes
Respiratory acidosis.
Causes
 Respiratory failure due to
Bronchiolitis/ penumonia/ BA
 Central hypoventilation due to
neurological issues.

9. How to analyse metabolic acidosis further
Acidosis due to
increased organic acids
(increased anion gap)
 Lactic acidosis
 DKA
 Renal failure
Acidosis due to
HCO3 loses
(normal anion gap)
 Diarrhoea
 RTA

10. Base excess
It is a measurement of amount of acid base needed to
retain pH to 7.4.
So in Acidosis,
BE = Negative (-ve)
In Alkalosis,
BE = Positive (+ve)

11. Look at the pH
Alkalosis
Step 2
 Look at Pco2 value
in respiratory alkalosis
 Look at HCO3 value
in metabolic alkalosis
Acidosis
Step 2
 Look at CO2 value
in respiratory acidosis
 Look at HCO3 value
in metabolic acidosis

12. How to identify compensatory mechanism
Step 1 = pH (normal due to compensation)
IIry compensatory metabolic acidosis
CO2
HCO3
IIry compensatory respiratory acidosis
CO2
HCO3

13. If uncompensatory acid - base disorder detected,
Need to correct it.
Metabolic acidosis
NaHCO3 to correct acidosis.
Respiratory acidosis
Support ventilation
Respiratory alkalosis
Adjust ventilator settings in a
ventilator.
Metabolic alkalosis
Need to identify other associated
metabolic and electrolyte
anomalies and correct it.