ABG interpretation Dr Ayman Sabri

Case

• A 50-Year old woman underwentintestinal bypass for morbid obesity .She has 10-15 watery stool motion perday , she was treated by tincture ofopium . Next day she was foundsomnolent and hypotensive. The plasmavalue were:


2

Laboratory data

PH 7.02

PaCO2 30

HCO3(mEq/L)

10 What isyour

Diagnosis ?

HCO3(mEq/L)

Na(mEq/L)

130

K(mEq/L)

3.2

CL(mEq/L)

1023

What isyour

Diagnosis ?

1. History taking and physical examination2. Assess accuracy of data (validity).3. Identify the primary disturbance

1. Check arterial pH-------- acidosis or alkalosis2. HCO3

- & pCO2 analysis---primary disorder.4. Compensatory responses5. Calculate AG6. Assess delta ratio7. Urine anion gab8. Formulate acid-base diagnosis




• Step 1.History taking and physical examination

Comprehensive history taking and physicalexamination can often give clues as to theunderlying acid-base disorder

• Step 1.History taking and physical examination

Comprehensive history taking and physicalexamination can often give clues as to theunderlying acid-base disorder

Respiratory alkalosisPulmonary embolus

Respiratory acidosisCOPD

Metabolic acidosisDehydration or shock

Hyperkalaemia

Metabolic alkalosisVomiting , Hypokalaemia Metabolic alkalosisVomiting , Hypokalaemia

Metabolic acidosisSevere diarrhea

salisylates or alcohol intoxication

Metabolic acidosisRenal failure

metabolic acidosisHyperglycaemia (DKA? if ketonespresent

Respiratory alkalosisCirrhosis

ValidityValidity

1.Arterial pH2.Look at PCO2, HCO3

• Principle – The body does not fullycompensate for primary acid-base disorders.

i.e.PH < 7.4 ……. acidosis

PH > 7.4 ……. alkalosis

• Principle – The body does not fullycompensate for primary acid-base disorders.

i.e.PH < 7.4 ……. acidosis

PH > 7.4 ……. alkalosis

Acidosis AlkalosisAcidosis

- If PCO2 is the initial chemical change, thenprocess is respiratory.

- if HCO3- is the initial chemical change, thenprocess is metabolic.

- If PCO2 is the initial chemical change, thenprocess is respiratory.

- if HCO3- is the initial chemical change, thenprocess is metabolic.

PCO2HCO3PH

AcidosisAcidosis

AlkalosisAlkalosis

MetabolicMetabolic

MetabolicMetabolic

AcidosisAcidosis

AlkalosisAlkalosis

AlkalosisAlkalosis MetabolicMetabolic

RespiratoryRespiratory

RespiratoryRespiratory

Metabolic acidosisExpected pCO2 = 1.5 x [HCO3] + 8 (range: +/- 2)

Metabolic alkalosisExpected pCO2 = 0.7 [HCO3] + 20 (range: +/- 5)

“If the actual pCO2 or [HCO3-]

is different from the predicted values,You must suspect a 2nd acid-base disorder”

Metabolic acidosisExpected pCO2 = 1.5 x [HCO3] + 8 (range: +/- 2)

Metabolic alkalosisExpected pCO2 = 0.7 [HCO3] + 20 (range: +/- 5)

“If the actual pCO2 or [HCO3-]

is different from the predicted values,You must suspect a 2nd acid-base disorder”

• Acute Respiratory :The [HCO3] will increase by 1 mmol/l for every 10

mmHg elevation in pCO2 above 40 mmHg.Expected [HCO3] = 24 + { (Actual pCO2 - 40) / 10 }

• Chronic Respiratory :The [HCO3] will increase by 4 mmol/l for every 10

mmHg elevation in pCO2 above 40mmHg.Expected [HCO3] = 24 + 4 { (Actual pCO2 - 40) / 10}

• Acute Respiratory :The [HCO3] will increase by 1 mmol/l for every 10

mmHg elevation in pCO2 above 40 mmHg.Expected [HCO3] = 24 + { (Actual pCO2 - 40) / 10 }

• Chronic Respiratory :The [HCO3] will increase by 4 mmol/l for every 10

mmHg elevation in pCO2 above 40mmHg.Expected [HCO3] = 24 + 4 { (Actual pCO2 - 40) / 10}

• Acute RespiratoryThe [HCO3] will decrease by 2 mmol/l for every 10

mmHg decrease in pCO2 below 40 mmHg.Expected [HCO3] = 24 - 2 { ( 40 - Actual pCO2) / 10 }

• Chronic RespiratoryThe [HCO3] will decrease by 5 mmol/l for every 10

mmHg decrease in pCO2 below 40 mmHg.Expected [HCO3] = 24 - 5 { ( 40 - Actual pCO2 ) / 10 }(range: +/- 2)

• It takes 2 to 3 days to reach maximal renal compensation

• Acute RespiratoryThe [HCO3] will decrease by 2 mmol/l for every 10

mmHg decrease in pCO2 below 40 mmHg.Expected [HCO3] = 24 - 2 { ( 40 - Actual pCO2) / 10 }

• Chronic RespiratoryThe [HCO3] will decrease by 5 mmol/l for every 10

mmHg decrease in pCO2 below 40 mmHg.Expected [HCO3] = 24 - 5 { ( 40 - Actual pCO2 ) / 10 }(range: +/- 2)

• It takes 2 to 3 days to reach maximal renal compensation

• The anion gap is defined as the quantity ofanions not balanced by cations.

• (Na + K) + Unmeasured cations =(Cl + HCO3) + Unmeasured anions

• Anion Gap=measured cation- measured anion.

• Anion gap = [Na + K] – (Cl + HCO3)• Value: 12 ± 4 meq/L

• The anion gap is defined as the quantity ofanions not balanced by cations.

• (Na + K) + Unmeasured cations =(Cl + HCO3) + Unmeasured anions

• Anion Gap=measured cation- measured anion.

• Anion gap = [Na + K] – (Cl + HCO3)• Value: 12 ± 4 meq/L

Anions and Cations in Serum(Values in mEq/L)

CATIONSANIONS

Calcium 5Organic acids 5

Magnesium 1.5Sulfates 1

Potassium 4.5Phosphates 2

Actually there is no gap

Potassium 4.5Phosphates 2

Sodium 140Proteins 15

Bicarbonates 24

Chlorides 104

Total 151Total 151

High Anion Gap Normal anion gap

• 1. Ketoacidosis- Diabetic- Alcoholic- Starvation

• 2. Lactic acidosis• 3. Toxicosis

- Ethylene glycol- Methanol- Salicylates

• 4. Advanced renal failure

• 1. GIT HCO3- loss

- Diarrhea- External fistulas

• 2. Renal HCO3- loss

- Proximal RTA- Distal RTA- Hyperkalemic RTA

metabolic acidosis

(MUD PILES)(MUD PILES)MethanolUremiaDiabetic ketoacidosisPropylene glycolIsoniazid intoxicationLactic acidosisEthanol ethylene glycolSalicylates

• 1. Ketoacidosis- Diabetic- Alcoholic- Starvation

• 2. Lactic acidosis• 3. Toxicosis

- Ethylene glycol- Methanol- Salicylates

• 4. Advanced renal failure

• 1. GIT HCO3- loss

- Diarrhea- External fistulas

• 2. Renal HCO3- loss

- Proximal RTA- Distal RTA- Hyperkalemic RTA

(MUD PILES)(MUD PILES)MethanolUremiaDiabetic ketoacidosisPropylene glycolIsoniazid intoxicationLactic acidosisEthanol ethylene glycolSalicylates

Osmolal gap

Step 1:Calculate Osm = 2[Na+] + glucose/18 + BUN/2.8

Step 2: Measure Osm

Step 3: Osmolal gap (measured - calc) should be ≤ 10

.ىرخأ ةرم اھجاردإ مث ةروصلا فذح ىلإ رطضت دق ،رھظت ءارمحلاxةمالع تلظ اذإ .ىرخأ ةرم فلملا حتفا مث ،رتویبمكلا لیغشت ةداعإب مق .ةفلات ةروصلا نوكت دق وأ ةروصلا حتفل رتویبمكلا ىلع ةركاذلل ةیفاك ةحاسم كانھ نوكت ال دق .ةروصلا ضرع نكمي ال

Low Anion Gap

- Hypoalbuminemia

- Plasma cell dyscrasia

- Monoclonal protein

- Bromide intoxication

- Normal variant

Corrected AG=Anion Gap + 2.5 x

(4- Albumin)

- Hypoalbuminemia

- Plasma cell dyscrasia

- Monoclonal protein

- Bromide intoxication

- Normal variant

Corrected AG=Anion Gap + 2.5 x

(4- Albumin)

• If a metabolic acidosis is diagnosed, then theDelta Ratio should be checked

Delta ratio= ∆ Anion gap/∆ [HCO3-]∆ Anion gap = (12-AG)∆ [HCO3-] = (24 - [HCO3-])

Delta ratio Assessment Guidelines

< 0.4 Hyperchloremic normal anion gap acidosis< 1 High AG & normal AG acidosis

1 to 2 Pure Anion Gap AcidosisLactic acidosis: average value 1.6DKA more likely to have a ratio closer to 1due to urine ketone loss

Pure Anion Gap AcidosisLactic acidosis: average value 1.6DKA more likely to have a ratio closer to 1due to urine ketone loss

> 2 High AG acidosis and a concurrent metabolicalkalosisor a pre-existing compensated respiratoryacidosis

Urine anion gab= (N a +K) -Cl

POSITIVEurinary anion gab

NEGATIVEurinary anion gab

(normal NH(normal NH33 excreationexcreation))

POSITIVEurinary anion gab

NEGATIVEurinary anion gab

(normal NH(normal NH33 excreationexcreation))

GUT causesNEGATIVEn bowel

causes

Urinary causes

Final DiagnosisFinal DiagnosisFinal DiagnosisFinal Diagnosis

Case



45

Laboratory data

PH 7.02

PaCO2 30

HCO3(mEq/L)

10

H = (PCO2/ HCO3) ×24 =PH-7.8 ×100H= (30/10)X24=7.02-7.8X100

Validity

PH= acidosis------Hco3= Met acidosisPrimarydefect

Expected pCO2 = 1.5 x [HCO3] + 8(range: +/- 2)=1.5X10+8= 22pco2 30 added respiratory acidosis.

CompensationHCO3(mEq/L)

10

Na(mEq/L)

130

K(mEq/L)

3.2

CL(mEq/L)

10246

Expected pCO2 = 1.5 x [HCO3] + 8(range: +/- 2)=1.5X10+8= 22pco2 30 added respiratory acidosis.

Compensation

= [Na+] – [HCO3-] – [Cl-]

=130-(10+ 102)= 18High AG

AG

Anion gap/∆ [HCO3-]=18-12/24-10= <1 (0.42).High AG & normal AG acidosis

Delta ratio

Final diagnosis:

• Normal Anion gap and high Anion gapmetabolic acidosis+ combined respiratoryacidosis.– Lactic acidosis (hypotension)– Metabolic acidosis due to HCO3 loss (diarrhea).– Respiratory acidosis due to respiratory

depression by opiate.

• Normal Anion gap and high Anion gapmetabolic acidosis+ combined respiratoryacidosis.– Lactic acidosis (hypotension)– Metabolic acidosis due to HCO3 loss (diarrhea).– Respiratory acidosis due to respiratory

depression by opiate.

Case

• A 23y old women with rheumatoid artheritisincreased her dose of salicylate because offlare up. She developed epigastric pain andvomiting that persist for 2 days. She went tolocal hospital where the following blood resultobtained:

• PH =7.61 Pco2 25mmHg, Hco3 =33mmol/l.• What is your acid base diagnosis?

• A 23y old women with rheumatoid artheritisincreased her dose of salicylate because offlare up. She developed epigastric pain andvomiting that persist for 2 days. She went tolocal hospital where the following blood resultobtained:

• PH =7.61 Pco2 25mmHg, Hco3 =33mmol/l.• What is your acid base diagnosis?

Laboratory data

PH 7.61

PaCO2 25mmHg.What is

yourDiagnosis ?

PaCO2 25mmHg.

HCO3(mEq/L)

33mmol/l.

49

What isyour

Diagnosis ?

Laboratory data

PH 7.61PaCO2 25mmHg.

HCO3(mEq/L)

33mmol/l.

H = (PCO2/ HCO3) ×24 =PH-7.8×100

H= (25/33)X24=7.61-7.8X100Validity

PH= alkalosis------increased Hco3=Metabolic alkalosis

Primarydefect

Metabolic alkalosisExpected pCO2 = 0.7x [HCO3] + 20(range: +/- 2)=0.7X33+ 20=43So compansation is not adaqauterespiratory alkalosis.

CompensationHCO3(mEq/L)

33mmol/l.

50

Metabolic alkalosisExpected pCO2 = 0.7x [HCO3] + 20(range: +/- 2)=0.7X33+ 20=43So compansation is not adaqauterespiratory alkalosis.

Compensation

Final diagnosis

Combined Metabolic alkalosis (GIT loss Vomiting )and respiratory alkalosis with salicylate.

Let’s play tic-tac-toe

PH 7.26 PaCO2 42 HCO3 17

AlkalineNormalAcidic

PH Pa CO2

HCO3

Metabolic acidosis

PH 7.49 PaCO2 30 HCO3 23


PHHCO3

Pa CO2

Respiratory alkalosis

PH 7.26 PaCO2 52 HCO3 34


PH HCO3

Pa CO2

Respiratory acidosis withcompensation (Partial)

PH 7.48 PaCO2 51 HCO3 29


PH

Pa CO2 HCO3

Metabolic alkalosis withcompensation (Partial)

PH 7.36 PaCO2 50 HCO3 34


PHPa CO2 HCO3

Respiratory acidosis withcompensation (complete)

PH 7.43 PaCO2 49 HCO3 30


PHPa CO2 HCO3

Metabolic alkalosis withcompensation (complete)

ABG interpretation Dr Ayman Sabri

Health & Medicine

Transcript of ABG interpretation Dr Ayman Sabri