Analysis of ABG

8/6/2019 Analysis of ABG

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Analysis of ABGDr. Ashwinikumar Aiyangar

Dept of NephrologyKamineni Hospital


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Why Order an ABG?

Aids in establishing a diagnosis

Helps guide treatment plan

Aids in ventilator management

Improvement in acid/base management

allows for optimal function of medications

Acid/base status may alter electrolyte levels

critical to patient status/care


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Acid Base Balance

The body produces acids daily

15,000 mmol CO2

50-100 mEq Nonvolatile acids

The lungs and kidneys attempt to maintain

balance


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Acid Base Balance

Assessment of status via bicarbonate-carbon dioxide buffer system

CO2 + H2O H2CO3 HCO3-+ H+

ph = 6.10 + log ([HCO3] / [0.03 x PCO2])


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The Terms

ACIDS

Acidemia

Acidosis

Respiratory

oCO2

Metabolic

qHCO3

BASES

Alkalemia

Alkalosis

Respiratory

qCO2

Metabolic

oHCO3


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Respiratory Acidosis

qph, oCO2,qVentilation

Causes

CNS depression Pleural disease

COPD/ARDS

Musculoskeletal disorders

Compensation for metabolic alkalosis


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Respiratory Alkalosis

opH, qCO2,oVentilation

q CO2 q HCO3 (oCl to balance charges

hyperchloremia)

Causes

Intracerebral hemorrhage

Salicylate and Progesterone drug usage

Anxiety qlung compliance

Cirrhosis of the liver

Sepsis


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Metabolic Acidosis

High AG Acidosis M - Methanol

U - Uremia

D - DKA P - Paraldehyde

I - INH

L - Lactic Acidosis

E - Ehylene Glycol S - Salicylate

Normal AG Metabolic

Acidosis

Hyperalimentation

Acetazolamide

RTA (Calculate urine

anion gap)

Diarrhea

Pancreatic Fistula


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Metabolic Alkalosis

opH, oHCO3

Causes

Vomiting

Diuretics

Chronic diarrhea

Hypokalemia Renal Failure


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Normal Values (in ABG)

pH 7.4

HCO3 24

pCO2 - 40


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Prediction ofCompensation for Simple

Acid-Base Disorders

Metabolic Acidosis (fall in HCO3)

Pco2 = 1.5[HCO3]+ 8 2 Pco2 = last 2 digits of pH 100

Pco2 = 15 + [HCO3]

Metabolic Alkalosis (rise in HCO3) Pco2 = + 0.6 mm Hg for [HCO3] of 1 mEq/L

Pco2 = 15 + [HCO3]


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Respiratory Acidosis (rise in pCO2)

Acute [HCO3-] = +1 mEq/L for each Pco2 of 10mm Hg

Chronic [HCO3-] = +4 mEq/L for each Pco2 of 10

mm Hg

Respiratory Alkalosis (fall in pCO2)

Acute [HCO3-] = - 2 mEq/L for each Pco2 of 10

mm Hg

Chronic [HCO3-] = - 5 mEq/L for each Pco2 of 10mm Hg


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Step by Step analysis


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Step 1

Is there acidosis or alkalosis ?

Look at pH (normal between 7.35 and 7.45)

pH7.45 - alkalosis


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Step 2

Determine the primary acid base defect

If pH < 7.35 (acidosis)

Metabolic low HCO3

Respiratory high pCO2

If pH > 7.45 (alkalosis) Metabolic high HCO3

Respiratory low pCO2


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pH - 7.30

HCO3 14

pCO2 - 32


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pH - 7.28

HCO3 30

pCO2 - 55


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pH - 7.50

HCO3 30

pCO2 - 45


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pH - 7.50

HCO3 21

pCO2 - 25


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Step 3

Calculate the expected compensation

Use the rules

If expected and actual compensation match

confirms primary disorder simple acid basedisorder


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pH - 7.3

HCO3 14

pCO2 29

Diabetic h/o fever since 1 week, c/o

breathlessness


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Acid-Base Disorders



Pco2 = 15 + [HCO3]


Pco2 = 15 + [HCO3]


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pH - 7.32

HCO3 30

pCO2 55

Obese male, BMI 44, admitted for sleep study


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mm Hg



mm Hg



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pH - 7.50

HCO3 30

pCO2 45

40 yr male, c/o vomiting since 1 week


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Acid-Base Disorders



Pco2 = 15 + [HCO3]


Pco2 = 15 + [HCO3]


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pH - 7.50

HCO3 21

pCO2 25

25 year old girl, admitted with sudden onset

breathlessness


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mm Hg



mm Hg



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Step 4

Determine presence of mixed disorder

Rule of same direction HCO3 and pCO2change in the same direction in simpledisorders, opposite directions think of mixeddisorder

If expected and actual compensation DO NOTmatch there is a mixed disorder


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pH - 7.26

HCO3 16

pCO2 - 26


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Acid-Base Disorders


Pco2

= 1.5[HCO3]

+

8 2

Pco2 = last 2 digits of pH 100

Pco2 = 15 + [HCO3]


Pco2 = 15 + [HCO3]


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pH - 7.25

HCO3 26

pCO2 - 55


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mm Hg



mm Hg



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Step 5

Calculate anion gap

If there is presence of metabolic acidosis

If HCO3, pCO2 are normal and yet there is suspicion of

acid base disorder eg. Sick patients in ICU


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Anion Gap

AG = Na (Cl + HCO3) (N 10 to 12)

>12 - high anion gap

High AG is a foot print of metabolic acidosis

sometimes in mixed acid base disorders pH,

HCO3 and pCO2 are normal


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Step 6

In case AG is high

Compare the fall in HCO3 (HCO3) with rise inAG (AG)

If AG = HCO3, then pure HAGMA

If AG > HCO3, it is HAGMA + asso. Met Alk

If AG < HCO3, it is HAGMA + NAGMA


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43 yr male, alcoholic, noteaten for 3 days, came

with increased RR and

vomiting

pH - 7.24

HCO3 - 18

pCO2 - 28

Na 136

K 3.8

Cl 95

AG = 23

AG = 23-12 = 11

HCO3 = 24-18 = 6


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28 yr female, diarrhea

since 4 days came with

oliguria and creatinine

of 4.0

pH - 7.24 HCO3 11

pCO2 - 25

Na 132 K 3.4

Cl 104

AG 17

AG = 17-12 = 5

HCO3 = 24-11 = 13


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THANK YOU

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Analysis of ABG