ABG INTERPRETATION

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 - lt 7.35
• Alkalosis - gt 7.45

4

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

5

• Respiratory disorders
• - pH change in opposite direction of
• HCO3 and PCO2
• - Respiratory acidosis
• pH
• PCO2
• HCO3
• - Respiratory alkalosis
• pH
• PCO2
• HCO3

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
• - lt - 10
• extra renal causes
• - gt 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 40 0.6 X BE

14

• Respiratory acidosis
• Acute HCO3 PCO2 40 / 10 24
• Chronic HCO3 PCO2 40 / 3 24
• Respiratory alkalosis
• Acute 40 PCO2 / 5 24
• Chronic 40 PCO2 / 2 24

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 2, 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