1. ABG INTERPRETATION By: Dr. Ashraf Al Tayar, MD,MRCP(I),
Assistant Consultant Critical Care, KKNGH.

2. ABG Interpretation: Comprises 4 steps.
Determine the process
Determine the primary disorder
Sharpen the diagnosis
Determine compensation

3. I. Step 1:
Use pH to determine
Acidosis - < 7.35
Alkalosis - > 7.45

4. - Metabolic acidosis pH PCO2 HCO3 - Metabolic alkalosis
II. Determine metabolic vs. Respiratory
Metabolic disorders:
- pH changes in same direction as
PCO2 and HCO3
- Metabolic acidosis pH
PCO2
HCO3
- Metabolic alkalosis

5. Respiratory disorders:
- pH change in opposite direction of
HCO3 and PCO2
- Respiratory acidosis pH
PCO2
HCO3
- Respiratory alkalosis

6. Sharpen the Diagnosis - Calculate the AG - Calculate Osm. Gap
- Calculate Urinary AG

7. AG:
Na – ( CL + HCO3)
normal 10 (+/-) 2

8. AG:
- Paraproteinaemia
- Hyperchloraemia
- Hypoalbumenaemia
( AG 2.5 / 1 gm /dL in albumin)
- Hypermagnesaemia
- Hyponatraemia

9. AG : Metabolic acidosis (DD) (MUDPILERS)
Methanol
Uremia
DKA
Paraldehyde
Isopropyl alcohol – Isoniazide
Lactic acid
Ethylene glycol
Rhabdomyolosis
Salycylate

10. Normal AG Metabolic acidosis (Hyperchloremia)
A. Hypokalemia
- Diarrhea
- Urethral diversion
- RTA
- Mineralocorticorticoid deficiency
- CAI: Acetazolamide
B. Hyperkalemia
- Renal failure (Early)
- Renal disease: SLE
Amylodosis
Sickle cell
- Sulphur toxicity

11. Urine AG
- < - 10
extra renal causes
- > + 10
Renal causes

12. Osmolal Gap
- measured serum osm. – calc. osm.
normal (10 – 15)
OG DD:
( MEDIE )
Methanol
Ethylene glycol
Diuretic : Mannitol
Isoprophyl alcohol
Ethanol

13. Determine Compensation
Metabolic acidosis
PCO2 = 40 + BE
Metabolic alkalosis
PCO2 = X BE

14. Respiratory acidosis Acute :HCO3 = PCO2 – 40 / 10 + 24
Chronic : HCO3 = PCO2 – 40 /
Respiratory alkalosis:
Acute : 40 – PCO2 /
Chronic: 40 – PCO2 /

15. Example 1:
pH: 7.07
PCO2: 28
HCO3: 8
SBE: - 20

16. Example 2:
pH : 7.33
PCO2 : 20
HCO3 : 12
BE : 12

17. Example 3
pH : 7.48
PCO2 : 28
HCO3: 22
BE : 2

18. Effects of Acid base change
Acidosis alkalosis
CVS Inotropy Inotropy
Conduction- defect Altered coronary flow
Arterial VD Digoxin toxicity
Venous VD
Oxygen Delivery
O2 Hb binding Affinity
2, 3 DPG , 3 DPG
Neuromuscular
Resp. dep NM excitability
Sensorium Encephalopathy
Seizures
Resp. dep
Electrolytes
Hyper K Hypo K+
Hyper Ca+ Hypo Ca+
Hyperuricaemia Hypophosphatemia

19. THANK YOU