Arterial blood gas

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 PO2 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 7.35-7.45. • 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 + CO2  H2CO3  HCO3 + H+

6. Buffers • There are two buffers that work in pairs • H2CO3 NaHCO3Carbonic 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 • 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 • Step:1 • 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)

20. 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 : 32 • HCO3 : 18 • Pao2 : 88 • Partially compensated metabolic Acidosis

24. Mr. K with COPD.His ABG is: • pH : 7.35 • PaCO2 : 48 • 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 • PaO2 60 SaO2 90 pH 7.32 PaCO2 48 HCO3 25 • PaO2 95 SaO2 100 pH 7.30 PaCO2 40 HCO3 18 • PaO2 87 SaO2 94 pH 7.38 PaCO2 48 HCO3 28 • PaO2 94 SaO2 99 pH 7.49 PaCO2 40 HCO3 30 • 6. PaO2 62 SaO2 91 pH 7.35 PaCO2 48 HCO3 27 • PaO2 93 SaO2 97 pH 7.45 PaCO2 47 HCO3 29 • PaO2 95 SaO2 99 pH 7.31 PaCO2 38 HCO3 15 • PaO2 65 SaO2 89 pH 7.30 PaCO2 50 HCO3 24 • 10. PaO2 110 SaO2 100 pH 7.48 PaCO2 40 HCO3 30

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

30. Any Questions?