ABG INTERPRETATIONABG INTERPRETATION

By: Dr. Ashraf Al Tayar, By: Dr. Ashraf Al Tayar, MD,MRCP(I), MD,MRCP(I),

Assistant Consultant Critical Care, Assistant Consultant Critical Care, KKNGH.KKNGH.

ABG Interpretation: Comprises 4 steps.ABG Interpretation: Comprises 4 steps.

• Determine the process• Determine the primary disorder• Sharpen the diagnosis• Determine compensation

I. Step 1:

Use pH to determine

Acidosis - < 7.35

Alkalosis - > 7.45

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

Respiratory disorders:

- pH change in opposite direction of

HCO3 and PCO2

- Respiratory acidosis

pH

PCO2

HCO3

- Respiratory alkalosis

pH

PCO2

HCO3

- Calculate the AG

- Calculate Osm. Gap

- Calculate Urinary AG

Sharpen the DiagnosisSharpen the Diagnosis

AG:

Na – ( CL + HCO3)

normal 10 (+/-) 2

• AG:

- Paraproteinaemia

- Hyperchloraemia

- Hypoalbumenaemia

( AG 2.5 / 1 gm /dL in albumin)

- Hypermagnesaemia

- Hyponatraemia

AG : Metabolic acidosis (DD) (MUDPILERS)

Methanol

Uremia

DKA

Paraldehyde

Isopropyl alcohol – Isoniazide

Lactic acid

Ethylene glycol

Rhabdomyolosis

Salycylate

Normal AG Metabolic acidosis (Hyperchloremia)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

Urine AG

- < - 10

extra renal causes

- > + 10

Renal causes

Osmolal Gap- measured serum osm. – calc. osm.

normal (10 – 15)OG DD:( MEDIE )MethanolEthylene glycolDiuretic : MannitolIsoprophyl alcoholEthanol

Determine CompensationDetermine Compensation

Metabolic acidosis

PCO2 = 40 + BE

Metabolic alkalosis

PCO2 = 40 + 0.6 X BE

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

Example 1:

pH: 7.07

PCO2: 28

HCO3: 8

SBE: - 20

Example 2:

pH : 7.33

PCO2 : 20

HCO3 : 12

BE : 12

Example 3

pH : 7.48

PCO2 : 28

HCO3: 22

BE : 2

Effects of Acid base changeEffects 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. depElectrolytes Hyper K+ Hypo K+

Hyper Ca+ Hypo Ca+ Hyperuricaemia Hypophosphatemia

THANK YOU