Very detailed metabolic acidosis,alkalosis

1. PAEDIATRICS.
ABGs
DR NYIRENDA

2. OBJECTIVE
1. What is an ABG test?
2. Indications
3. Normal parameters of ABGs
4. How to collect a sample/Handling of sample
5. Disorders of ABGs
6. How to interpret step by step ABGs
7. Calculate the anion gap

3. Introduction
• The major function of the pulmonary system (lungs and
pulmonary circulation) is to deliver oxygen to cells and remove
carbon dioxide from the cells.
• If the patient’s history and physical examination reveal
evidence of respiratory dysfunction, diagnostic test will help
identify and evaluate the dysfunction.
• ABG analysis is one of the first tests ordered to assess
respiratory status because it helps evaluate gas exchange in the
lungs.
• An ABG test can measure how well the person's lungs and
kidneys are working and how well the body is using energy.

4. 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

5. Indication
• To obtain information about patient ventilation (PCO2) ,
oxygenation (PO2) and acid base balance
• Monitor gas exchange and acid base abnormalities for patient
on mechanical ventilator or not
• To evaluate response to clinical intervention and diagnostic
evaluation ( oxygen therapy )
• An ABG test may be most useful when a person's breathing rate
is increased or decreased or when the person has very high
blood sugar levels, a severe infection, or heart failure
5

6. COMPONENTS OF THE ABG
• pH: Measurement of acidity or alkalinity, based on the
hydrogen (H+). 7.35 – 7.45
• Pao2 :The partial pressure oxygen that is dissolved in arterial
blood. 80-100 mm Hg.
• PCO2: The amount of carbon dioxide dissolved in arterial
blood. 35– 45 mmHg
• HCO3 : The calculated value of the amount of bicarbonate
in the blood. 22 – 26 mmol/L
• SaO2:The arterial oxygen saturation.
>95%
❑pH,PaO2 ,PaCO2 , Lactate and electrolytes are measured
Variables
❑HCO3 (Measured or calculated)

7. 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
7

8. Normal values:
• PH = 7.35 – 7.45
• PCO2 = 35 – 45
mmhg
• PO2 = 80 – 100
mmhg
• HCO3 = 22 – 28
meq/L
8 A.Y.T

9. Normal Values
Variable Normal Normal
Range(2SD)
pH 7.40 7.35 - 7.45
pCO2 40 35-45
Bicarbonate 24 22-26
Anion gap 12 10-14
Albumin 4 4

10. EQUIPMENT
Blood gas kit OR
• 1ml 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 10 A.Y.T

11. 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.
11 A.Y.T

12. 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
12

13. Sites for obtaining ABGs
• 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
13 A.Y.T

14. 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
14

15. • 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
15

16. 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
16

17. Delayed Analysis
• Consumptiom of O2 & Production of CO2 continues
after blood drawn
➢Iced Sample maintains values for 1-2 hours
➢Uniced sample quickly becomes invalid within 15-20
minutes
•PaCO2  3-10 mmHg/hour
•PaO2 
•pH  d/t lactic acidosis generated by glycolysis in
R.B.C.

18. Parameter 37 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

19. FEVER OR HYPOTHERMIA
1. Most ABG analyzers report data at N body temp
2. If severe hyper/hypothermia, values of pH &
PCO2 at 37 C can be significantly diff from pt’s
actual values
3. Changes in PO2 values with temp also predictable
❑ If Pt.’s temp < 37C
Substract 5 mmHg Po2, 2 mmHg Pco2 and Add
0.012 pH per 1C decrease of temperature

20. 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

21. ❑ TYPE OF SYRINGE
1. pH & PCO2 values unaffected
2. PO2 values drop more rapidly in plastic syringes (ONLY
if PO2 > 400 mm Hg)
❑ Differences usually not of clinical significance so plastic
syringes can be and continue to be used
❑Risk of alteration of results  with:
1. size of syringe/needle
2. vol of sample
❑ HYPERVENTILATION OR BREATH HOLDING
May lead to erroneous lab results

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

23. CENTRAL EQUATION OF ACID-BASE PHYSIOLOGY
➢ Henderson Hasselbach Equation:
➢where [ H+] is related to pH by
• To maintain a constant pH, PCO2/HCO3- ratio should be
constant
• When one component of the PCO2/[HCO3- ]ratio is altered, the
compensatory response alters the other component in the
same direction to keep the PCO2/[HCO3- ] ratio constant
❑ [H+] in nEq/L = 24 x (PCO2 / [HCO3 -] )
❑ [ H+] in nEq/L = 10 (9-pH)

24. Compensatory response or regulation of pH
By 3 mechanisms:
➢ Chemical buffers:
➢ React instantly to compensate for the addition or
subtraction of H+ ions
➢ CO2 elimination:
➢ Controlled by the respiratory system
➢ Change in pH result in change in PCO2 within minutes
➢ HCO3- elimination:
➢ Controlled by the kidneys
➢ Change in pH result in change in HCO3-
➢ It takes hours to days and full compensation occurs in 2-5
days

25. 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

26. 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. What is the differential for the clinical
processes?

27. ➢Metabolic Conditions are suggested if
•pH changes in the same direction as pCO2 or
pH is abnormal but pCO2 remains unchanged
➢Respiratory Conditions are suggested if:
•pH changes in the opp direction as pCO2 or
pH is abnormal but HCO3- remains unchanged

28. Compensation
• The respiratory and metabolic system works together to keep the body’s
acid-base balance within normal limits.
• The respiratory system responds to metabolic based PH imbalances in the
following manner:
* metabolic acidosis: ↑ respiratory rate and depth (↓PaCO2)
* metabolic alkalosis: ↓ respiratory rate and depth (↑PaCO2)
• The metabolic system responds to respiratory based PH imbalances in the
following manner:
*respiratory acidosis: ↑ HCO3 reabsorption
*respiratory alkalosis: ↓HCO3 reabsorption
28

29. a. Respiratory acidosis
Phase PH PaCO2 HCO3
UNCOMPENSATED ↓ ↑ ------
Because there is no response from the kidneys yet to
acidosis the HCO3 will remain normal
29
Phase PH PaCO2 HCO3
FULL COMPENSATED N ↑ ↑
Phase PH PaCO2 HCO3
PARTIAL COMPENSATED ↓ ↑ ↑
PH return to normal PaCO2 & HCO3 levels are still high to
correct acidosis
The kidneys start to respond to the acidosis by increasing
the amount of circulating HCO3

30. B. Respiratory alkalosis
Phase PH PaCO2 HCO3
UNCOMPENSATED ↑ ↓ ------
Because there is no response from the kidneys yet to
acidosis the HCO3 will remain normal
30
Phase PH PaCO2 HCO3
FULL COMPENSATED N ↓ ↓
Phase PH PaCO2 HCO3
PARTIAL COMPENSATED ↑ ↓ ↓
PH return to normal PaCO2 & HCO3 levels are still low to
correct alkalosis
The kidneys start to respond to the alkalosis by
decreasing the amount of circulating HCO3

31. C. Metabolic acidosis
Phase PH PaCO2 HCO3
UNCOMPENSATED ↓ ------- ↓
Because there is no response from the lungs yet to
acidosis the PaCO2 will remain normal
31
Phase PH PaCO2 HCO3
FULL COMPENSATED N ↓ ↓
Phase PH PaCO2 HCO3
PARTIAL COMPENSATED ↓ ↓ ↓
PH return to normal PaCO2 & HCO3 levels are still low to
correct acidosis
The lungs start to respond to the acidosis by decreasing
the amount of circulating PaCO2

32. D. Metabolic alkalosis
Phase PH PaCO2 HCO3
UNCOMPENSATED ↑ ------- ↑
Because there is no response from the lungs yet to
alkalosis the PaCO2 will remain normal
32
Phase PH PaCO2 HCO3
FULL COMPENSATED N ↑ ↑
Phase PH PaCO2 HCO3
PARTIAL COMPENSATED ↑ ↑ ↑
PH return to normal PaCO2 & HCO3 levels are still high to
correct alkalosis
The lungs start to respond to the alkalosis by increasing
the amount of circulating PaCO2

33. Metobolic acidosis: Anion gap acidosis

34. Calculate the anion gap
• AG used to assess acid-base status esp in D/D of met acidosis
•  AG &  HCO3
- 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

35. THE END.
THANK YOU.