ABG

Dr. Meena

1. ARTERIAL BLOOD GAS ANALYSIS
S.MEENATCHI SUNDARI,
II YEAR PG.
A.Y.T 1

2. DEFINITION
It is a diagnostic procedure in which a
blood is obtained from an artery directly
by an arterial puncture or accessed by a
way of indwelling arterial catheter
A.Y.T 2

3. EQUIPMENT
Blood gas kit OR
• 1ml /2ml syringe
•23-26 gauge needle
•Stopper or cap
•Alcohol swab
•Disposable gloves
•Plastic bag & crushed ice
•Lidocaine (optional)
•Vial of heparin (1:1000)
•Par code or label
A.Y.T 3

4. Preparatory phase:
•Record patient inspired oxygen concentration
•Check patient temperature
•Explain the procedure to the patient
•Provide privacy for client
•If not using hepranized syringe , hepranize
the needle
•Perform Allen's test
•Wait at least 20 minutes before drawing
blood for ABG after initiating, changing, or
discontinuing oxygen therapy, or settings of
mechanical ventilation, after suctioning the
patient or after extubation.
A.Y.T 4

5. EXCESSIVE HEPARIN
Dilutional effect on results ¯ HCO
3
-
& PaCO2
Only .05 ml heperin required for 1 ml blood.
So syringe be emptied of heparin after flushing or only dead
space volume is sufficient or dry heperin should be used

6. ALLEN’S TEST
It is a test done to determine that
collateral circulation is present from the
ulnar artery in case thrombosis occur in
the radial
A.Y.T 6

7. Sites for obtaining abg
•Radial artery ( most common )
•Brachial artery
•Femoral artery
Radial is the most preferable
site used because:
•It is easy to access
•It is not a deep artery which
facilitate palpation,
stabilization and puncturing
•The artery has a collateral
blood circulation
A.Y.T 7

8. Performance phase:
•Wash hands
•Put on gloves
•Palpate the artery for maximum pulsation
•If radial, perform Allen's test
•Place a small towel roll under the patient
wrist
•Instruct the patient to breath normally
during the test and warn him that he may
feel brief cramping or throbbing pain at the
puncture site
•Clean with alcohol swab in circular motion
•Skin and subcutaneous tissue may be
infiltrated with local anesthetic agent if
needed
A.Y.T 8

9. •Insert needle at 45 radial ,
60 brachial and 90 femoral
•Withdraw the needle and
apply digital pressure
•Check bubbles in syringe
•Place the capped syringe in
the container of ice
immediately
•Maintain firm pressure on
the puncture site for 5
minutes, if patient has
coagulation abnormalities
apply pressure for 10 – 15
minutes
A.Y.T 9

10. AIR BUBBLES
:
1.PO2 ~150 mmHg & PCO2 ~0 mm Hg in air bubble(R.A.)
2.Mixing with sample, lead to ­ PaO2 & ¯ PaCO2
To avoid air bubble, sample drawn very slowly and
preferabily in glass syringe
Steady State:
Sampling should done during steady state after change in
oxygen therepy or ventilator parameter
Steady state is achieved usually within 3-10 minutes

11. Follow up phase:
•Send labeled, iced specimen to the lab
immediately
•Palpate the pulse distal to the puncture site
•Assess for cold hands, numbness, tingling or
discoloration
•Documentation include: results of Allen's
test, time the sample was drawn,
temperature, puncture site, time pressure
was applied and if O2 therapy is there
•Make sure it’s noted on the slip whether the
patient is breathing room air or oxygen. If
oxygen, document the number of liters . If
the patient is receiving mechanical
ventilation, FIO2 should be documented
A.Y.T 11

12. complication
•Arteriospasm
•Hematoma
•Hemorrhage
•Distal ischemia
•Infection
•Numbness
A.Y.T 12

13. ABG component
•PH:
measures hydrogen ion concentration in the
blood, it shows blood’ acidity or alkalinity
•PCO2 :
It is the partial pressure of CO2 that is carried
by the blood for excretion by the lungs, known as
respiratory parameter
•PO2:
It is the partial pressure of O2 that is dissolved in
the blood , it reflects the body ability to pick up
oxygen from the lungs
•HCO3 :
known as the metabolic parameter, it reflects the
kidney’s ability to retain and excrete bicarbonate
A .Y .T 13

14. Parameter37 C (Change
every 10 min)
4 C (Change
every 10 min)
¯ pH
0.01 0.001
­ PCO2
1 mm Hg 0.1 mm Hg
¯ PO2
0.1 vol % 0.01 vol %
Temp Effect On Change of ABG Values

15. A.Y.T15

16. Steps for ABG analysis
1.What is the pH? Acidemia or Alkalemia?
2.What is the primary disorder present?
3.Is there appropriate compensation?
4.Is the compensation acute or chronic?
5.Is there an anion gap?
6.If there is a AG check the delta gap?

17. Normal values:
PH = 7.35 – 7.45
PCO2 = 35 – 45 mmhg
PO2 = 80 – 100 mmhg

HCO3 = 22 – 28
meq/L
A.Y.T17

18. Calculation of pH
203.0
log10.6
3
PaCO
HCO
pH
´
+=
-
[ ]
-
+
´=
3
2
24
HCO
PaCO
H
Henderson-
Hesselbach
equation

19. Step 1
Look at the pH: is the blood acidemic or alkalemic?
pH normal value 7.35-7.45
ACIDIC:below 7.35
ALKALOSIS:above 7.45

20. Step 2: What is the primary disorder?
What disorder
is present?
pH pCO2 HCO3
Respiratory
Acidosis
pH low high high
Metabolic
Acidosis
pH low low low
Respiratory
Alkalosis
pH high low low
Metabolic
Alkalosis
pH high high high
ROME

21. Step 4:
Calculation of compensation
Mean "whole body" response equations for simple acid-base disturbances.
Note: The formula calculates the change in the compensatory parameter.
DisorderpHPrimary
change
Compensatory
Response
Equation
Metabolic
Acidosis
¯¯ [HCO
3
-
] ¯ PCO
2
ΔPCO
2
» 1.2 ´ ΔHCO
3
Metabolic
Alkalosis
­­ [HCO
3
-
] ­ PCO
2
ΔPCO
2
» 0.7 ´ ΔHCO
3
Respiratory
Acidosis
¯ ­ PCO
2
­ [HCO
3
-
] Acute:
ΔHCO
3
-
» 0.1 ´ ΔPCO
2
Chronic:
ΔHCO
3
-
» 0.3 ´ ΔPCO
2
Respiratory
Alkalosis
­ ¯ PCO
2
¯ [HCO
3
-
] Acute:
ΔHCO
3
-
» 0.2 ´ ΔPCO
2
Chronic:
ΔHCO
3
-
» 0.5 ´ ΔPCO
2

22. 1.2
0.7
0.1 0.3
0.2 0.5
Compensation Formula Simplified
Acute Chronic
Metabolic
Respiratory
Acidosis
Alkalosis
Acidosis
Alkalosis

23. Step 3-4: Is there appropriate
compensation? Is it chronic or acute?
Respiratory Acidosis
Acute (Uncompensated): for every 10 increase in pCO2 -> HCO3
increases by 1 and there is a decrease of 0.08 in pH
Chronic (Compensated): for every 10 increase in pCO2 -> HCO3
increases by 4 and there is a decrease of 0.03 in pH
Respiratory Alkalosis
Acute (Uncompensated): for every 10 decrease in pCO2 -> HCO3
decreases by 2 and there is a increase of 0.08 in PH
Chronic (Compensated): for every 10 decrease in pCO2 -> HCO3
decreases by 5 and there is a increase of 0.03 in PH

Partial Compensated: Change
in pH will be between 0.03 to
0.08 for every 10 mmHg
change in PCO2

24. Step 3-4: Is there appropriate
compensation?
Metabolic Acidosis
Winter’s formula: Expected pCO2 = 1.5[HCO3] + 8 ± 2
OR
D pCO2 = 1.2 (D HCO3)
If serum pCO2 > expected pCO2 -> additional
respiratory acidosis and vice versa
Metabolic Alkalosis
Expected PCO2 = 0.7 × HCO3 + (21 ± 2)
OR
D pCO2 = 0.7 (D HCO3)
If serum pCO2 < expected pCO2 - additional respiratory
alkalosis and vice versa

25. Step 5: Calculate the anion gap
AG used to assess acid-base status esp in D/D of
metabolic acidosis
D AG & D HCO
3
-
used to assess mixed acid-base
disorders
AG based on principle of electroneutrality:
Total Serum Cations = Total Serum Anions
Na + (K + Ca + Mg) = HCO3 + Cl + (PO4 + SO4
+ Protein + Organic Acids)
Na + UC = HCO3 + Cl + UA
Na – (HCO3 + Cl) = UA – UC

Na – (HCO3 + Cl) = AG
 Normal =12 ± 2

26. Contd…
AG corrected = AG + 2.5[4 – albumin]
If there is an anion Gap then calculate the
Delta/delta gap (step 6) to determine
additional hidden nongap metabolic acidosis
or metabolic alkalosis
If there is no anion gap then start analyzing
for non-anion gap acidosis

27. Step 6: Calculate Delta Gap
Delta gap = (actual AG – 12) + HCO3
Adjusted HCO3 should be 24 (+_ 6) {18-30}
If delta gap > 30 -> additional metabolic alkalosis
If delta gap < 18 -> additional non-gap metabolic
acidosis
If delta gap 18 – 30 -> no additional metabolic
disorders

28. Step 5: Calculate the “gaps”
Anion gap = Na
+
− [Cl
−
+ HCO
3
−
]
Δ AG = Anion gap − 12
Δ HCO
3
= 24 − HCO
3
Δ AG = Δ HCO
3
−
, then Pure high AG Met. Acidosis
Δ AG > Δ HCO
3
−
, then High AG Met Acidosis + Met. Alkalosis
Δ AG < Δ HCO
3
−
, then High AG Met Acidosis + HCMA

29. Nongap metabolic acidosis
For non-gap metabolic acidosis, calculate the urine anion
gap
URINARY AG
Total Urine Cations = Total Urine Anions
Na + K + (NH4 and other UC) = Cl + UA
(Na + K) + UC = Cl + UA
(Na + K) – Cl = UA – UC
(Na + K) – Cl = AG

Distinguish GI from renal causes of loss of HCO3 by estimating
Urinary NH4+ .
Hence a -ve UAG (av -20 meq/L) seen in GI, while +ve value (av
+23 meq/L) seen in renal problem.
UAG = UNA + UK – UCL

30. Metobolic acidosis: Anion gap acidosis

31. Causes of nongap metabolic acidosis - DURHAM
Diarrhea, ileostomy, colostomy, enteric fistulas
Ureteral diversions or pancreatic fistulas
RTA type I or IV, early renal failure
Hyperailmentation, hydrochloric acid administration
Acetazolamide, Addison’s
Miscellaneous – post-hypocapnia, toulene, sevelamer, cholestyramine ingestion

32. Dictums in ABG AnalysisDictums in ABG Analysis
1.Primary change & Compensatory change always
occur in the same direction.
2.pH and Primary parameter change in the same
direction suggests a metabolic problem.
pH and Primary parameter change in the opposite
direction suggests a respiratory problem.
3.Renal and pulmonary compensatory mechanisms
return pH toward but rarely to normal.
Corollary:
A normal pH in the presence of changes in PCO
2
or
HCO
3
suggets a mixed acid-base disorder.

33. Steps for ABG analysis
1.What is the pH? Acidemia or Alkalemia?
2.What is the primary disorder present?
3.Is there appropriate compensation?
4.Is the compensation acute or chronic?
5.Is there an anion gap?
6.If there is a AG check the delta gap?