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Arterial Blood Gas Interpretation Dr. Tauhid Iqbali

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Page 1: Arterial Blood Gas Interpretation

Arterial Blood Gas Interpretation

Dr. Tauhid Iqbali

Page 2: Arterial Blood Gas Interpretation

OBJECTIVESABG-Procedure and Precautions

Maintaining acid-base balance in the body

Working principle of ABG analyzer

Anatomy of ABG report

Interpretation of ABG

Question and Answer stretch

Page 3: Arterial Blood Gas Interpretation

ABG – Procedure and Precautions Site- (Ideally) Radial Artery Femoral Artery

Ideally - Pre-heparinised ABG syringes - Syringe should be FLUSHED with 0.5ml

of 1:1000 Heparin solution and emptied. DO NOT LEAVE EXCESSIVE HEPARIN IN THE

SYRINGEHEPARIN DILUTIONAL HCO3

EFFECT PCO2

Only small 0.5ml Heparin for flushing and discard itSyringes must have > 50% blood. Use only 2ml or less syringe.

Page 4: Arterial Blood Gas Interpretation

Ensure No Air Bubbles. Syringe must be sealed immediately after withdrawing sample.– Contact with AIR BUBBLES Air bubble = PO2 150 mm Hg , PCO2 0 mm HgAir Bubble + Blood = PO2 PCO2

ABG Syringe must be transported at the earliest to the laboratory for EARLY analysis via COLD CHAIN

Page 5: Arterial Blood Gas Interpretation

Patients Body Temperature affects the values of PCO2 and HCO3.

ABG Analyser is controlled for Normal Body temperatures

Any change in body temp at the time of sampling leads to alteration in values detected by the electrodes

Cell count PO2

ABG Sample should always be sent with relevant information regarding O2, FiO2 status and Temp.

Page 6: Arterial Blood Gas Interpretation

MAINTAINING ACID-BASE BALANCE

Page 7: Arterial Blood Gas Interpretation

Acid Base Balance o H+ ion concentration in the body is precisely

regulatedo The body understands the importance of H+

and hence devised DEFENCES against any change in its concentration

BICARBONATE BUFFER SYSTEMActs in few seconds

RESPIRATORY REGULATIONActs in few minutes

RENAL REGULATIONActs in hours to days

ACID

BASE

Page 8: Arterial Blood Gas Interpretation

Regulation of Acid Base

1. Bicarbonate Buffer System

CO2 + H2O carbonic anhydrase H2CO3 H+ + HCO3-

In Acidosis - Acid = H+

H+ + HCO3 H2CO3 CO2 + H2O

In Alkalosis - Alkali + Weak Acid = H2CO3

CO2 + H20 H2CO3 HCO3- + H+

+

ALKALI

Page 9: Arterial Blood Gas Interpretation

2. Respiratory Regulation of Acid Base Balance:

H+ PaCO2

H+ PaCO2

ALVEOLARVENTILATION

ALVEOLARVENTILATION

Page 10: Arterial Blood Gas Interpretation

3. Renal Regulation of Acid Base Balance: Kidneys control the acid-base balance by excreting

either an acidic or a basic urine.This is achieved in the following ways:

Reabsorption Secretion of H+

of HCO3 ions in tubules

in blood and excretion

• Proximal Convulated Tubules (85%)• Thick Ascending Limb of Loop of Henle (10%)• Distal Convulated Tubule• Collecting Tubules(5%)

Page 11: Arterial Blood Gas Interpretation

Another mechanism by which the kidney controls the acid base balance is by the Combination of excess H+ ions in urine with AMMONIA and other buffers- A mechanism for generating NEW Bicarbonate ions

In CKD, the dominant mechanism by which acid is eliminated by the Kidneys is excretion of NH4+

GLUTAMINE

2HCO3- 2NH4

+REABSORBED EXCRETED +H+, Cl-

Page 12: Arterial Blood Gas Interpretation

WORKING PRINCIPLE OF ABG ANALYZIER

Page 13: Arterial Blood Gas Interpretation

ABG ELECTRODES pH (Sanz Electrode)   Measures H+ ion concentration of sample against a

known pH in a reference electrode, hence potential difference. Calibration with solutions of known pH (6.384 to 7.384).

P CO2 (Severinghaus Electrode)

CO2 reacts with solution to produce H+ higher CO2- more H+ higher P CO2 measured.

P O2 (Clark Electrode)    O2 diffuses across membrane producing an electrical

current measured as P O2.

Page 14: Arterial Blood Gas Interpretation

Measured Values

Temperature Correction:Is there any value to it?

Calculated Data:Which are the useful ones?

Entered Data:Derived from other sources

The Anatomy of a Blood Gas Report

Page 15: Arterial Blood Gas Interpretation

The Anatomy of a Blood Gas Report

----- XXXX Diagnostics ------

Blood Gas Report248 05:36 Jul 22 2000Pt ID 2570 / 00

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

CpH 7.439pCO2 47.6 mm HgpO2 123.5 mm Hg

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %ct CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Measured Values

Temperature Correction:Is there any value to it?

Calculated Data:Which are the useful ones?

Entered Data:Derived from other sources

Page 16: Arterial Blood Gas Interpretation

Temperature Correction:“ There is no scientific basis ... for applying temperature corrections to blood gas measurements…” Shapiro BA, OTCC, 1999.

Uncorrected pH & pCO2 are reliable reflections of in-vivo acid base status

Temperature correction of pH & pCO2 do not affect calculated bicarbonate

pCO2 reference points at 37o C are well established as reliable reflectors of alveolar ventilation

Reliable data on DO2 and oxygen demand are unavailable at temperatures other than 37o C

----- XXXX Diagnostics ------

Blood Gas Report

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

CpH 7.439pCO2 47.6 mm HgpO2 123.5 mm Hg

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Page 17: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

C

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Bicarbonate is calculated on the basis of the Henderson equation:

[H+] = 24 pCO2 / [HCO3-]

Bicarbonate:

Page 18: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

C

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Standard Bicarbonate:Plasma HCO3 after equilibrationto a PCO2 of 40 mm Hg

: reflects non-respiratory acid base change: does not quantify the extent of the buffer base abnormality : does not consider actual buffering capacity of blood

Base Excess: D base to normalise HCO3 (to 24) with PCO2 at 40 mm Hg(Sigaard-Andersen)

: reflects metabolic part of acid base D: no info. over that derived from pH, pCO2 and HCO3

: Misinterpreted in chronic or mixed disorders

Page 19: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

C

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Oxygenation Parameters:O2 Content of blood:Hb x O2 Sat x Const. + Dissolved O2

Oxygen Saturation:

Alveolar / arterial gradient:

Arterial / alveolar ratio:

Page 20: Arterial Blood Gas Interpretation

Interpretation of ABG OXYGENATION ACID BASE

Page 21: Arterial Blood Gas Interpretation

OXYGENATION ASSESSMENT

Artery

CO2 O2

Page 22: Arterial Blood Gas Interpretation

PaO2 (Partial pressure of arterial oxygen)PaO2 is dependant upon Age, FiO2, Patm

As Age the expected PaO2

• PaO2 = 109 - [0.4 (Age)]• Normal PaO2: 75-100 mmHg

As FiO2 the expected PaO2

• Alveolar Gas Equation:• PAO2= (PB-P h2o) x FiO2- pCO2/R

OXYGENATION

PAO2 = partial pressure of oxygen in alveolar gas, PB = barometric pressure(760mmHg), Ph2o = water vapor pressure (47 mm Hg), FiO2 = fraction ofinspired oxygen, PCO2 = partial pressure of CO2 in the ABG, R = respiratoryquotient (0.8)

Page 23: Arterial Blood Gas Interpretation

PaO2 / FiO2 ratio:

Inspired Air FiO2 = 21% PiO2 = 150 mmHg

PalvO2 = 100 mmHg

PaO2 = 90 mmHg

O2CO2

PaO2/FiO2 Ratio Inference>300 Normal<300 Acute Lung Injury<200 ARDS (along with other criteria)

Page 24: Arterial Blood Gas Interpretation

PaO2/ FiO2 ratio ( P:F Ratio ) Gives understanding that the patients OXYGENATION

with respect to OXYGEN delivered is more important than simply the PO2 value.

Example

Patient 1On Room Air

Patient 2On MV

PO2 60 90

FiO2 21% (0.21) 50% (0.50)

P:F Ratio 285 180

Page 25: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured37.0o

CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg

Corrected38.6o

C

Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79

Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %

Oxygenation:O2 Content of blood:Hb x O2 Sat x 1.34 + Dissolved O2 (given by Pao2x0.003)Useful in oxygen transport calculationsDerived from calculated saturationOxygen Saturation:Ideally measured by co-oximetryCalculated values may be error-proneAlveolar / arterial gradient:Hypoxemia causes differentiated by A-a GradienEstimate of normal A–a gradient <[age in years/4] + 4An abnormally increased A–a gradient suggests :• Defect in diffusion• V/Q (ventilation/perfusion ratio) mismatch• right-to-left shuntNormal A-a Gradient:• Hypoventilation

Neuromuscular disorders Central nervous system disorder

• Low inspired FIO2 (e.g. high altitude)Arterial / alveolar ratio:Remains stable with change in FIO2Low a/A (<0.6) = Shunt , V/Q mismatch, diffusion defect

Page 26: Arterial Blood Gas Interpretation

Alveolar-arterial DifferenceInspired O2 = 21%= piO2 = (760-45) x .21=150 mmHg ( So at room air PiO2=150 mmHg)

O2

CO2

palvO2 = piO2 - pCO2 / RQ= 150 - 40/0.8= 150 – 50 = 100 mm Hg( Calculated)

partO2 = 90 mmHg (Measured)

(palvO2- partO2 ) D = 10 mmHg (Normal= =<[age in years/4] + 4)

Page 27: Arterial Blood Gas Interpretation

Alveolar-arterial Difference

O2

CO2

Oxygenation Failure (Type 1 Resp. Failure)piO2 = 150

pCO2 = 40

palvO2= 150 – 40/.8=150-50 =100

pO2 = 45

(palvO2 - pO2)

D = 100-45 = 55

Ventilation Failure (Type 2 Resp. Failure)piO2 = 150

pCO2 = 80

palvO2= 150-80/.8 =150-100

= 50

pO2 = 45 (palvO2 - pO2)

D = 50-45 = 5

Page 28: Arterial Blood Gas Interpretation

ACID-BASE ASSESSMENT

Page 29: Arterial Blood Gas Interpretation

Definitions and TerminologyACIDOSIS: Presence of a process which tends to pH by

virtue of gain of H +  or loss of HCO3-

ALKALOSIS: Presence of a process which tends to pH by

virtue of loss of H+ or gain of HCO3-

If these changes, change pH, suffix ‘emia’ is addedACIDEMIA : Reduction in arterial pH    (pH<7.35)ALKALEMIA : Increase in arterial pH (pH>7.45)

Page 30: Arterial Blood Gas Interpretation

Simple Acid Base Disorder/ Primary Acid Base disorder A single primary process  of acidosis or alkalosis due to

an initial change in PCO2 and HCO3

Compensation The normal response of the  respiratory system or

kidneys to change in pH induced by a primary acid-base disorder

Note: The Compensatory responses to a primary Acid Base disturbance are never enough to correct the change in pH , they only act to reduce the severity

Mixed Acid Base Disorder Presence of more than one acid base disorder

simultaneously

Page 31: Arterial Blood Gas Interpretation

6-STEP APPROACH TO INTERPRETATION

OF ACID-BASE

Page 32: Arterial Blood Gas Interpretation

STEP 0 • Is this ABG Authentic?

STEP 1 • ACIDEMIA or ALKALEMIA?

STEP 2 • RESPIRATORY or METABOLIC?

STEP 3• If Respiratory – ACUTE or

CHRONIC?

STEP 4 • Is COMPENSATION adequate?

STEP 5• If METABOLIC – ANION

GAP?

STEP 6• If High gap Metabolic Acidosis–

GAP GAP?

Page 33: Arterial Blood Gas Interpretation

If the pH and the [H+] are inconsistent, the ABG is probably not valid.[H+] = 24(PaCO2)

[HCO3-]

H+ ion (mmol/L) pH100 7.0079 7.1063 7.2050 7.3045 7.3540 7.4035 7.4532 7.5025 7.60

STEP0: Is this ABG Authentic?

Page 34: Arterial Blood Gas Interpretation

Look at pH<7.35 : acidemia>7.45 : alkalemia

NOTE – An acid base abnormality is present even if either the pH or PCO2 are Normal.

ACIDEMIA OR

ALKALEMIA?

STEP 1

Page 35: Arterial Blood Gas Interpretation

PRIMARY DISORDER

PRIMARY RESPONSES COMPENSATORYRESPONSESH+ ion pH Primary

Conc. Defect

MetabolicAcidosis H+

pH HCO3

PCO2Alveolar

Hyperventilation

Metabolic Alkalosis H+ pH

HCO3

PCO2Alveolar

Hypoventilation

RespiratoryAcidosis H+ pH PCO2 HCO3

RespiratoryAlkalosis H+ pH PCO2 HCO3

RESPIRATORY or METABOLIC?STEP 2

RULE- If either the pH or PCO2 is Normal, there is a mixed metabolic and respiratory acid base disorder.

Page 36: Arterial Blood Gas Interpretation

IF RESPIRATORY, IS IT ACUTE OR CHRONIC?oAcute respiratory disorder : ∆pH(e-acute) = 0.008x ∆Pco2 oChronic respiratory disorder : ∆pH(e-chronic)= 0.003x ∆pCO2oCompare, pHmeasured (pHm) v/s pHexpected (pHe)

Respiratory acidosis: pH(e-chronic)=7.40–0.008( PCO2-40) pH(e-acute)=7.40–0.003(PCO2-40) Respiratory alkalosis: pH(e-chronic)=7.40+0.008(40-PCO2) pH(e-acute)=7.40+0.003(40-PCO2)

IF RESPIRATOR

Y- ACUTE/CHR

ONIC?

STEP 3

pH(m) = pH(e- acute)

pH(m) = between pH(e- acute) & pH(e-

chronic)

pH(m) = pH(e-chronic)

ACUTE RESPIRATORYDISORDER

PARTIALLY COMPENSATED CHRONIC RESPIRATORY DISORDER

Page 37: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured 37.0o

CpH 7.301pCO2 76.2 mm HgpO2 45.5 mm Hg

Calculated DataHCO3 act 36.1 mmol / L

O2 Sat 78 %pO2 (A - a) 9.5 mm Hg DpO2 (a / A) 0.83

Entered DataFiO2 21 %

Case 1

60 year old male smokerwith progressiverespiratory distressand somnolence.

D CO2 =76-40=36Ac D pH = 36/10 x0.08=0.29Exp Acute pH = 7.40-0.29=7.11

Chronic D pH= 36/10 x0.03=0.10Exp Chr pH = 7.40-0.10=7.30

Chronic resp. acidosis

pH <7.35 ; acidemia

pCO2 >45; respiratory acidemia

HypoxiaNormal A-a gradientDue to hypoventilation

Page 38: Arterial Blood Gas Interpretation

----- XXXX Diagnostics ------

Blood Gas Report

Measured 37.0o

CpH 7. 232pCO2 60.1 mm HgpO2 66.3 mm Hg

Calculated DataHCO3 act 24.5 mmol / L

O2 Sat 92 %pO2 (A - a) mm Hg DpO2 (a / A)

Entered DataFiO2 30 %

Case 218-year-old male asthmatic;3 days of cough, dyspneaand orthopnea notresponding to usualbronchodilators.

O/E: Respiratory distress;suprasternal and intercostal retraction;tired looking; on 4 L NC.

D CO2 = 60 - 40 = 20Expect Acute D pH = 20/10x0.08= 0.16Expect Ac pH = 7.40 - 0.16 = 7.24Acute resp. acidosis

pH <7.35 ; acidemia

pCO2 >45; respiratory acidemia

Hypoxemia

piO2 = (760-45)x.3=214.5 / palvO2 = 214-60/.8=129

129-66= 63

Oxygenation failure

Page 39: Arterial Blood Gas Interpretation

ADEQUATE COMPENSA

TION?STEP 4

IS THE COMPENSATORY RESPONSE ADEQUATE OR NOT?

METABOLIC DISORDER PCO2 expected

Metabolic acidosis: PaCO2(e)= (1.5 x [HCO3-]) +8± 2Metabolic alkalosis:PaCO2(e)= (0.7 x [HCO3-])+ 21 + 2

PCO2measured ≠ PCO2expected MIXED DISORDER

RESPIRATORY DISORDER pHexpected (acute-chronic)

pHm ≠ pHe range MIXED DISORDER

Page 40: Arterial Blood Gas Interpretation

CASE 1Mr. Shamshuddin, 62/M,Nagina k/c/o COPD Breathlessness,

progressively increased, aggravated on exertion, 2 days

Chronic smoker O/E RS- B/L expiratory rhonchi

22/7/11 7:30 ampH 7.20

PCO2 92 mmHg

PO2 76 mmHg

Actual HCO3

21.00 mmol/l

SO2 89

FiO2 37%

Page 41: Arterial Blood Gas Interpretation

STEP 1 – ACIDEMIA STEP 2 – pH PCO2

Respiratory STEP 3 – pH expected

pH acute = 7.40 – 0.008(92-40) 7.40 – 0.008(52) 6.984

pH chronic = 7.40 – 0.003(92-40) 7.244

pH b/w 6.98 to 7.244

Primary Respiratory Acidosis,partially compensated

Page 42: Arterial Blood Gas Interpretation

METABOLIC ACIDOSIS-

ANION GAP?STEP 5

IN METABOLIC ACIDOSIS WHAT IS THE ANION GAP?ANION GAP(AG) = Na – (HCO3 + Cl)

Normal Value = 12 + 4 ( 8- 16 Meq/l)

Adjusted Anion Gap = Observed AG +2.5(4.5- S.Albumin)50% in S. Albumin 75% in Anion Gap !!!

Metabolic Acidosis

High Anion Gap Metabolic Acidosis

Normal Anion Gap Acidosis

Page 43: Arterial Blood Gas Interpretation

Anion GapAG based on principle of electroneutrality:

Total Serum Cations = Total Serum AnionsM cations + U cations = M anions + U anionsNa + (K + Ca + Mg) = HCO3 + Cl + (PO4 + SO4

+ Protein + Organic Acids)Na + UC = HCO3 + Cl + UABut in Blood there is a relative abundance of Anions, hence Anions > CationsNa – (HCO3 + Cl) = UA – UC Na – (HCO3 + Cl) = Anion Gap

Page 44: Arterial Blood Gas Interpretation

CASE 3 Mr.Dharam Dutt, 63/M,Bijnor k/c/o CRF(conservativeRx) Breathlessness Decreased Urine Otpt. 2days Vomiting 10-15 O/E

No pedal edema, dehydration +

RS – B/L A/E Normal

31/7/11 11:30pm

pH 7.18

PCO2 21.00

PO2 90

Actual HCO3

7.80

Base Excess -18.80

SO2 95

Na 140.6

Chloride 102

T.Protein 6

Albumin 2.4

Page 45: Arterial Blood Gas Interpretation

STEP 1 – ACIDEMIA STEP 2 – pH PCO2

METABOLIC STEP 4 – PCO2expected PCO2exp = (1.5 x HCO3)+8+2

(1.5X7.80)+8+2 19.7+2= 17.7 –

21.7 STEP5 – ANION GAP = Na – (HCO3 +Cl)

= 140.6-(7.80+102) = 30.8

AG corrected for albumin = 30.8+5.25AG = 36.05

HIGH AG Met. Acidosis

Page 46: Arterial Blood Gas Interpretation

High Anion Gap Metabolic Acidosis

M

U

D

P

I

L

E

S

METHANOL

UREMIA - ARF/CRF

DIABETIC KETOACIDOSIS & other KETOSIS

PARALDEHYDE, PROPYLENE GLYCOL

ISONIAZIDE, IRON

LACTIC ACIDOSIS

ETHANOL, ETHYLENE GLYCOL

SALICYLATE

Page 47: Arterial Blood Gas Interpretation

Non Anion Gap Metabolic Acidosis

U

S

E

D

C

R

A

P

URETEROENTEROSTOMIES

SMALL BOWEL FISTULA

EXCESS CHLORIDE

DIARRHOEA

CARBONIC ANHYDRASE INHIBITOR

RTA

ADDISSION’S DISEASE

PANCREATOENTEROSTOMIES

Page 48: Arterial Blood Gas Interpretation

CO EXISTANT

METABOLIC DISORDER – “Gap Gap”?

STEP 6

If an increased anion gap is present:Assess the ratio of the change in the anion gap (∆AG ) to the change in [HCO3-] (∆[HCO3-]): ∆AG/∆[HCO3-] ∆ Anion Gap = Measured AG – Normal AG

Measured AG – 12

∆ HCO3 = Normal HCO3 – Measured HCO3

24 – Measured HCO3

Ideally, ∆Anion Gap = ∆HCO3

For each 1 meq/L increase in AG, HCO3 will fall by 1 meq/L ∆AG/D HCO3

- = 1 Pure High AG Met AcidosisD AG/D HCO3

- > 1 Assoc Metabolic AlkalosisD AG/D HCO3

- < 1 Assoc Non AG Met Acidosis

Page 49: Arterial Blood Gas Interpretation

CASE 4 Mr.Dharam Dutt, 63/M,Bijnor k/c/o CRF(conservativeRx) Breathlessness Decreased Urine Otpt. 2days Vomiting 10-15 O/E

No pedal edema, dehydration +

RS – B/L A/E Normal

31/7/11 11:30pm

pH 7.18

PCO2 21.00

PO2 90

Actual HCO3

7.80

Base Excess -18.80

SO2 95

Na 140.6

Chloride 102

T.Protein 6

Albumin 2.4

Page 50: Arterial Blood Gas Interpretation

STEP 1 – ACIDEMIA STEP 2 – pH PCO2

METABOLIC STEP 4 – PCO2expected PCO2exp = (1.5 x HCO3)+8+2

(1.5X7.80)+8+2 19.7+2= 17.7 – 21.7

COMPENSATED STEP5 – ANION GAP = Na – (HCO3 +Cl)

= 140.6-(7.80+102) = 30.8

AG corrected for albumin = 30.8+5.25AG = 36.05

HIGH AG Met. Acidosis

Page 51: Arterial Blood Gas Interpretation

STEP 6 – GAP GAP = (AG-12)/(24-HCO3) = 36.05-12/24-7.80

= 24.05/16.2 = 1.48

Gap/gap > 1 = add. Metabolic alkalosis

∆sis – Primary Metabolic Acidosis,High Anion Gap, compensated

Cause- CRF -Add. Metabolic AlkalosisCause - ? Vomiting

Page 52: Arterial Blood Gas Interpretation

Normal AG= 12; D Gap = 16 - 12 = 4Normal HCO3=24;DHCO3 = 24 -14 = 10D AG/D HCO3

- < 1(4/10)Indicates additional non-gap Met.acidosis

----- XXXX Diagnostics ------

Blood Gas Report

Measured 37.0o

CpH 7.236pCO2 34 mm HgpO2 110.5 mm Hg

Calculated DataHCO3 act 14 mmol / L

O2 Sat %pO2 (A - a) mm Hg DpO2 (a / A)

Entered DataFiO2 21.0 %

Case 5

28 year old diabetic withrespiratory distressfatigue andloss of appetite.

pH <7.35 ; acidemia

HCO3 <22; metabolic acidemia

Limits:Expected pCO2 = (1.5 x HCO3)+8 + 2

= (1.5 x 14)+ 8 + 2 = 29 + 2 = 27 to 31

Met. Acidosis + Resp. acidosis

If Na = 130, Cl = 100Anion Gap = 130 - (100 + 14)

= 130 - 114= 16

Page 53: Arterial Blood Gas Interpretation
Page 54: Arterial Blood Gas Interpretation

Question1.A 45 year-old woman with a history of inhalant abuse presents to the emergency room complaining of dyspnea. She has an SpO2 of 99% on room air and is obviously tachypneic on exam with what appears to be Kussmaul’s respirations. A room air arterial blood gas is performed and reveals: pH 6.95, PCO2 9, PO2 128, HC3- 2. A chemistry panel revealed sodium of 130, chloride 98, HCO3- 2. Answer1.The patient has a very low pH (acidemia)The low pH in conjunction with the low bicarbonate tells us that the metabolic acidosis is the primary process The anion gap is elevated at 30[130-(98+2)]. This tells us that the patient has a primary elevated anion gap metabolic acidosis. Compensated as PaCO2 (e)=9-13(1.5x2+8+-2)delta AG is 30-12 = 18 Delta AG/D HCO3

- < 1( 18/22) ,So there is an additional non-gap metabolic acidosis as well. Combined elevated anion gap and non-gap metabolic acidoses with compensatory respiratory alkalosis.

Page 55: Arterial Blood Gas Interpretation

Question2.A 45 year-old man with a history of very severe COPD (FEV1~ 1.0L, < 25% predicted) and chronic carbon dioxide retention (Baseline PCO2 58) presents to the emergency room complaining of worsening dyspnea and an increase in the frequency and purulence of his sputum production over the past 2 days. His oxygen saturation is 78% on room air. Before he is placed on supplementaloxygen, a room air arterial blood gas is drawn and reveals: pH 7.25, PCO2 68, PO2 48, HCO3-31.Answer2.The patient has a low pH (acidemia)The combination of the low pH and the high PCO2 tells us that the respiratory acidosis is the primary process. pH(e-acute)=7.2 and pH(e-chronic)=7.3 (If pH(m) = between pH(e- acute) & pH(e- chronic)

- partially compensated metabolic alkalosis.The alveolar-arterial oxygen difference is 17 mmHg(As ABG is taken before placing him on supplemental oxygen, So PiO2 will be 150 and RQ will be 0.8). palvO2= piO2 - pCO2 / RQ= 150-68/0.8=65 , And A-a gradient= palvO2 –PaO2=65-48=17

This value is elevated, suggesting that the hypoxemia is due to either shunt or areas of low V/Q (the more likely explanation in a patient with COPD) and cannot be explained by hypoventilation alone.

Primary respiratory acidosis with partially compensated metabolic alkalosis with hypoxemia due to either shunt or V/Q mismatch.

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for not becoming comatose!