Abg interpretation copy

ABG Interpretation
DR ANKIT GAJJAR
MBBS, MD, IDCCM, IFCCM, EDIC
CONSLUTANT INTENSIVIST

Collecting ABG
• Radial is ideal
• Preheparinised syringe
• Flush syringe with 0.5 ml heparin and empty
• Heparin not emptied adequately
- Low HCO3
- Low PCO2

• 50% of the syringe should be filled by blood
• Avoid contact with air
– Increase PO2 if PO2 <150
– Decrease in PCO2
• Marked elevation in WBC
– Decrease in PO2
• Maintain cold chain

Know your machine
• Measured variables
– pH
– PCO2
– PO2
• Calculated variables
– HCO3
- Lactate
- SpO2
- PaO2
- Electrolytes

What does ABG tells us
• Acid Base disorder
– Metabolic acidosis
– Metabolic alkalosis
• Blood gas abnormalities
– Respiratory acidosis
– Respiratory alkalosis
– Hypoxia
– Carbon monoxide poisoning
– Methemoglobinaemia

The Blood Gas Report:
The essentials
• pH 7.4 (7.35-7.45)
• PCO2 40 (35-45)
• PO2 80 (80-100)
• HCO3 24 (24-28)

STEP 1 - Is your ABG valid?
• Henderson-Hasselbalch equation
• [H+]= 24 X pCO2/HCO3
• 80 – (H+) = Decimals after 7

Ph 7.40
PCO2 40
PO2 88
HCO3 24
Na 137
Cl 102

• Step 1 - pH
• Step 2 – Metabolic / Respiratory
• Step 3 – Respiratory acute v/s Chronic
– change in pH = 0.08 x PCO2 / 10
• Step 4 Respiratory compensation
– Rule of 1,2,4,5
• Step 5 Metabolic compensation
– Expected pCO2 = (1.5 x HCO3)+8
– Expected pCO2 = (0.7x HCO3)+21
• Step 6 Anion gap
• Step 7 Delta ratio

STEP – 1 Acidemic or Alkalemic
• pH < 7.4 - Acidosis
• pH > 7.4 - Alkalosis

STEP 2 – METABOLIC / RESPIRATORY

Metabolic Acidosis
• Increase acid production
• Decrease acid excretion
• Increase alkali excretion
• In ABG
– pH < 7.40
– HCO3 < 24

Anion gap
• Serum AG = Measured cations - measured
anions = Unmeasured anions - unmeasured
cations
• Serum AG = Na - (Cl + HCO3)
• Reference range is 8 to 16 mmol/l (an average
of 12 mmol/l)
• AG falls by 2.5 meq/L for every 1 g/dL
reduction in the serum albumin concentration

pH 7.05
PCO2 31
PO2 88
HCO3 10
Na 137
Cl 102

Increase anion gap
• Increase unmeasured anions (MUD-PILES)
– Methanol
– Uremia
– DKA
– Paraldehyde
– Isoniazid
– Lactic Acidosis (shock, sepsis, metformin, linezolid, drugs)
– Ethylene Glycol
– Salicylates
• Decrease unmeasured cations
– Ca, Mg, K

Normal anion gap acidosis
• Loss of bicarb (HARD UP)
– Hyperchloremic acidosis (Excessive normal saline)
– Acetazolamide
– RTA
– Diarrhea
– Ureterosigmoidostomy / colonic fistula
– Post hypocapnia

Delta gap
• AG – Normal AG = Δ Gap
• Δ gap SHOULD BE = Δ Bicarbonate
• Δ gap/ Δ Bicarbonate = Delta Ratio
• Δ ratio < 1 – Another metabolic acidemia
• Δ ratio > 1 – Another metabolic alkalemia

Look for compensation
• Expected pCO2 = (1.5 x HCO3) + 8 ± 2
• If CO2 is higher then expected concomitant
respiratory acidosis
• If CO2 is lower then expected concomitant
respiratory alkalosis

Ph 7.05 7.43
PCO2 32 16
PO2 88 88
HCO3 10 10
Na 137 137
Cl 102 102

Management of metabolic acidosis
• Identify underlying etiology
• Treat according to underlying etiology
• HCO3
– HCO3 losing pathology
– severe acidosis
• If inadequate respiratory compensation
INTUBATION AND HYPERVENTILATION

Metabolic alkalosis
• Ph > 7.40
• HCO3 > 26

Look for compensation
• Expected pCO2 = (0.7 x HCO3) + 21 ± 2
• PCO2 higher then expected associated
respiratory acidosis
• PCO2 lower then expected respiratory alkalosis

Ph 7.58
PCO2 50
PO2 88
HCO3 44
Na 145
Cl 88

Causes
• Chloride responsive (U Chloride < 20)
– Vomiting / Gastric suction
– Prior use of diuretics
– Posthypercapnia
• Chloride resistant (U Chloride > 20)
– Severe hypokalemia
– Hyperaldosteronism
– Active use of diuretics
– Milk alkali syndrome

Treatment of metabolic alkalosis
• Normal saline
• Potassium replacement
• Acetazolamide

Respiratory acidosis
• pH < 7.35
• PCO2 > 45

Acute v/s Chronic
• Expect change in pH = 0.008 x PCO2
• If pH is higher then expected pH it is chronic

Ph 7.31
PCO2 76
PO2 68
HCO3 38
Na 137
Cl 94

Compensation (Rule of 1,4,2,5)
• Increase in HCO3
• <24 hrs: Expected [HCO3] = 24+[1/10x (PCO2-40)]
10 mmhg increase in PaCO2 increase in HCO3
by 1 mmol/L
• >24 hrs: Expected [HCO3] = 24+[4/10x (PCO2-40)]
10 mmhg increase in PaCO2 increase in HCO3
by 4 mmol/L

Respiratory alkalosis
• Ph > 7.45
• PCO2 > 45

Acute v/s Chronic
• Expect change in pH = 0.008 x PCO2
• If pH is lower then expected pH it is chronic

Compensation (Rule of 1,4,2,5)
• Decrease in HCO3
• <24 hrs: Expected [HCO3] = 24 – [2/10x (40-PCO2)]
10 mmhg decrease in PaCO2 decrease in HCO3 by
2 mmol/L
• >24 hours:Expected [HCO3] = 24 –[5/10 x (40-PCO2)]
10 mmhg decrease in PaCO2 decrease in HCO3 by
5 mmol/L

Ph 7.52
PCO2 30
PO2 66
HCO3 22
Na 130
Cl 100

• Step 1 - pH
• Step 2 – metabolic/respiratory
• Step 3 – resp acute v/s chronic
• Step 4 resp compensation
– Rule of 1,2,4,5
• Step 5 metabolic compensation
– Expected pCO2 = (1.5 x HCO3) + 8
– Expected pCO2 = (0.7x HCO3) + 21
• Step 7 delta ratio

ARE WE READY FOR THE CHALLENGE

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.39
PCO2 93.8
PO2 69.6
HCO3 55.7
Na 145
Cl 86

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.18
PCO2 16
PO2 114
HCO3 6
Na 135
Cl 95

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.25
PCO2 80
PO2 46
HCO3 20
Na 134
Cl 104

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.23
PCO2 23
PO2 64
HCO3 14
Na 130
Cl 94

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.14
PCO2 59.1
PO2 66.3
HCO3 18
Na 138
Cl 102

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.23
PCO2 23
PO2 110
HCO3 14
Na 130
Cl 100

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.26
PCO2 18
PO2 128
HCO3 7
Na 136
Cl 113

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.31
PCO2 33
PO2 88
HCO3 16
Na 134
Cl 113

• Step 1 - pH
– Rule of 1,2,4,5
Ph 7.64
PCO2 32
PO2 75
HCO3 33
Na -
Cl -

One more gap – Saturation gap
• ABG machiene gives SaO2 from PaO2 – SaO2
chart
• In case of Methemoglobinemia ABG will give
SaO2 higher then SpO2
• ABG machine with co oxymetry will give
measured
– SaO2
– Meth HB
– Carboxy Hb

Abg interpretation copy

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