arterial blood gas interpretation
TRANSCRIPT
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Arterial Blood Gas Interpretation
Dr. Tauhid Iqbali
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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
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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.
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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
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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.
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MAINTAINING ACID-BASE BALANCE
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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
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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
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2. Respiratory Regulation of Acid Base Balance:
H+ PaCO2
H+ PaCO2
ALVEOLARVENTILATION
ALVEOLARVENTILATION
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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%)
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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-
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WORKING PRINCIPLE OF ABG ANALYZIER
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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.
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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
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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
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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 %
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----- 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:
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----- 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
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----- 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:
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Interpretation of ABG OXYGENATION ACID BASE
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OXYGENATION ASSESSMENT
Artery
CO2 O2
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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)
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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)
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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
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----- 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
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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)
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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
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ACID-BASE ASSESSMENT
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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)
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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
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6-STEP APPROACH TO INTERPRETATION
OF ACID-BASE
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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?
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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?
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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
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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.
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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
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----- 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
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----- 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
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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
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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%
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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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Any Questions?
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for not becoming comatose!