1. Arterial blood gas By
Maha Subih

2. What is an ABG Arterial Blood Gas
Drawn from artery- radial, brachial, femoral
It is an invasive procedure.
Caution must be taken with patient on anticoagulants.
Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.

3. What Is An ABG? pH [H+] PCO2 Partial pressure CO2
PO Partial pressure O2
HCO3 Bicarbonate
BE Base excess
SaO2 Oxygen Saturation

4. Acid/Base Balance
The pH is a measurement of the acidity or alkalinity of the blood.
no. of (H+) in the blood.
The normal pH range is
in an acidic state decreases the force of cardiac contractions, decreases the vascular response to catecholamines, and a diminished response to the effects and actions of certain medications.
An alkalotic state interferes with tissue oxygenation and normal neurological and muscular functioning.

5. Acid/Base Relationship
H2O + CO  H2CO  HCO H+

6. Buffers There are two buffers that work in pairs
H2CO NaHCO3 Carbonic acid base bicarbonate
These buffers are linked to the respiratory and renal compensatory system

7. The Respiratory buffer response
This triggers the lungs to either increase or decrease the rate and depth of ventilation , start to occur within 1-3 minutes

8. The Renal Buffer Response
The kidneys excrete or retain bicarbonate(HCO3-).
Renal system may take from hours to days to correct the imbalance.

9. ACID BASE DISORDER Res. Acidosis
a pH less than 7.35 with a paco2 greater than 45 mmHg.

10. Causes
Central nervous system depression r/t medications such as narcotics, sedatives, or anesthesia.
Impaired muscle function r/t spinal cord injury, neuromuscular diseases, or neuromuscular blocking drugs.
Pulmonary disorders such as atelectasis, pneumonia, pneumothorax, pulmonary edema
Massive pulmonary embolus
Hypoventilation due to pain.

11. Management Increase the ventilation.
Causes can be treated rapidly if not treated may need M.V

12. Respiratory alkalosis
Psychological responses, anxiety or fear.
Pain
Increased metabolic demands such as fever, sepsis, pregnancy or thyrotoxicosis.
Medications such as respiratory stimulants.
RX: Resolve the underlying problem
Monitor for respiratory muscle fatigue

13. Metabolic Acidosis Management: Treat the cause
Bicarbonate less than 22mEq/L with a pH of less than 7.35.
Renal failure
Diabetic ketoacidosis
Management: Treat the cause
Hypoxia → Restore tissue perfusion to the hypoxic tissues
The use of bicarbonate is indicated

14. Metabolic Alkalosis High PH, high HCO3, high CO2.
Caused by: prolonged vomiting or NG suctioning, prolonged diuretic.

15. STEPS TO AN ABG INTERPRETATION
Assess the pH –acidotic/alkalotic
If above 7.45 – alkalotic
If below 7.35 – acidotic

16. Contd….. Step 2: Assess the paCO2 level.
pH decreases below 7.35, the paCO2 should rise.
If pH rises above 7.45 paCO2 should fall.
If pH and paCO2 moves in opposite direction – primary respiratory problem.

17. contd Step:2 Assess HCO3 value
If pH increases the HCO3 should also increase
If pH decreases HCO3 should also decrease
They are moving in the same direction
primary problem is metabolic

18. Step 3 Assess pao2 < 80 mm Hg - Hypoxemia
For a resp. disturbance : acute, chronic
If the change in paco2 is associated with the change in pH, the disorder is acute.
In chronic process the compensatory process brings the pH to within the clinically acceptable range ( 7.30 – 7.50)

19. Respiratory acidosis pH
PaCo2
HC03
normal
Respiratory
Alkalosis
Metabolic Acidosis
Metabolic Alkalosis

20. J is a 45 years old female admitted with the severe attack of asthma
J is a 45 years old female admitted with the severe attack of asthma. She has been experiencing increasing shortness of breath since admission three hours ago. Her arterial blood gas result is as follows:
pH : 7.22
paCO2 : 55
HCO3 : 25
Follow the steps
pH is low – acidosis
paCO2 is high – in the opposite direction of the pH.
Hco3 is Normal.
Respiratory Acidosis

21. Mr. D is a 55 years old admitted with recurring bowel obstruction has been experiencing intractable vomiting for the last several hours. His ABG is:
pH : 7.5
paCO2 :42
HCO3 : 33
Metabolic alkalosis

22. COMPENSATION
A patient can be uncompensated or partially compensated or fully compensated
pH has returned within normal range- fully compensated though other values may be still abnormal

23. Mrs. H is admitted, he is kidney dialysis patient who has missed his last 2 appointments at the dialysis centre his ABG results:
pH : 7.32
paCo2 :
HCO3 :
Pao2 :
Partially compensated metabolic Acidosis

24. Mr. K with COPD.His ABG is:
pH : 7.35
PaCO2 :
HCO3 : 28
PaO2 : 90
Fully compensated Respiratory Acidosis

25. Mr. S is a 53 year old man presented to ED with the following ABG.
pH : 7.51
PaCO2 : 50
HCO3 : 40
Pao2 : 40 (21%O2)
He has metabolic alkalosis

26. Precautions Excessive Heparin Decreases bicarbonate and PaCO2
Large Air bubbles not expelled from sample PaO2 rises, PaCO2 may fall slightly.
Fever may lead to erroneous lab results
Care must be taken to prevent bleeding

27. It’s not magic understanding ABG’s, it just takes a little practice!

28. Practice ABG’s PaO2 90 SaO2 95 pH 7.48 PaCO2 32 HCO3 24

29. Answers to Practice ABG’s
Respiratory alkalosis
Respiratory acidosis
Metabolic acidosis
Compensated Respiratory acidosis
Metabolic alkalosis
Compensated Metabolic alkalosis

30. Any Questions?