1. Arterial Blood Gas Analysis

2. Learning outcomes By the end of this session you should understand:
The normal ranges for arterial blood gas values
How to use the 5-step approach to arterial blood gas interpretation
Some of the common causes of arterial blood gas abnormalities and what to do to correct them

3. 5-step approach to arterial blood gas interpretation

4. 5-step approach to arterial blood gas interpretation
How is the patient?
Will provide useful clues to help with interpretation of the results

5. 5-step approach to arterial blood gas interpretation
How is the patient?
Will provide useful clues to help with interpretation of the results
Assess oxygenation
Is the patient hypoxaemic?
The PaO2 should be > 10 kPa (75 mmHg) breathing air and about 10 kPa less than the % inspired concentration

6. 5-step approach to arterial blood gas interpretation
How is the patient?
Will provide useful clues to help with interpretation of the results
Assess oxygenation
Is the patient hypoxaemic?
The PaO2 should be > 10 kPa (75 mmHg) breathing air and about 10 kPa less than the % inspired concentration
Determine the pH (or H+ concentration)
Is the patient acidaemic; pH < 7.35 (H+ > 45 nmol l-1)
Is the patient alkalaemic; pH > 7.45 (H+ < 35 nmol l-1) respiratory component

7. 5-step approach to arterial blood gas interpretation
How is the patient?
Will provide useful clues to help with interpretation of the results
Assess oxygenation
Is the patient hypoxaemic?
The PaO2 should be > 10 kPa (75 mmHg) breathing air and about 10 kPa less than the % inspired concentration
Determine the pH (or H+ concentration)
Is the patient acidaemic; pH < 7.35 (H+ > 45 nmol l-1)
Is the patient alkalaemic; pH > 7.45 (H+ < 35 nmol l-1)
Determine the respiratory component
If the pH < 7.35, is the PaCO2 > 6.0 kPa (45 mmHg) – respiratory acidosis
If the pH > 7.45, is the PaCO2 < 4.7 kPa (35 mmHg) – respiratory alkalosis

8. 5-step approach to arterial blood gas interpretation
How is the patient?
Will provide useful clues to help with interpretation of the results
Assess oxygenation
Is the patient hypoxaemic?
The PaO2 should be > 10 kPa (75 mmHg) breathing air and about 10 kPa less than the % inspired concentration
Determine the pH (or H+ concentration)
Is the patient acidaemic; pH < 7.35 (H+ > 45 nmol l-1)
Is the patient alkalaemic; pH > 7.45 (H+ < 35 nmol l-1)
Determine the respiratory component
If the pH < 7.35, is the PaCO2 > 6.0 kPa (45 mmHg) – respiratory acidosis
If the pH > 7.45, is the PaCO2 < 4.7 kPa (35 mmHg) – respiratory alkalosis
Determine the metabolic component
If the pH < 7.35, is the HCO3- < 22 mmol l-1 (base excess < -2 mmol l-1) – metabolic acidosis
If the pH > 7.45, is the HCO3- > 26 mmol l-1 (base excess > +2 mmol l-1) – metabolic alkalosis

9. Case study 1 Initial Information
A 21-year-old woman is thrown from her horse at a local event. On the way to hospital she has become increasingly drowsy and the paramedics have inserted an oropharyngeal airway and given high-flow oxygen via a face-mask. An arterial blood gas sample has been taken.

10. Case study 1 (continued)
Initial Information
A 21-year-old woman is thrown from her horse at a local event. On the way to hospital she has become increasingly drowsy and the paramedics have inserted an oropharyngeal airway and given high-flow oxygen via a face-mask. An arterial blood gas sample has been taken.
Step 1: How is the patient?

11. Case study 1 (continued)
Initial Information
A 21-year-old woman is thrown from her horse at a local event. On the way to hospital she has become increasingly drowsy and the paramedics have inserted an oropharyngeal airway and given high-flow oxygen via a face-mask. An arterial blood gas sample has been taken.
Step 1: How is the patient?
The reduced level of consciousness will impair oxygenation and ventilation, causing an increased PaCO2 , a respiratory acidosis

12. Case study 1 (continued)
Initial Information
A 21-year-old woman is thrown from her horse at a local event. On the way to hospital she has become increasingly drowsy and the paramedics have inserted an oropharyngeal airway and given high-flow oxygen via a face-mask. An arterial blood gas sample has been taken.
Step 1: How is the patient?
The reduced level of consciousness will impair oxygenation and ventilation, causing an increased PaCO2 , a respiratory acidosis
There is unlikely to be much compensation (change in bicarbonate) because of the acuteness of the situation

13. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?

14. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?
Step 2: Assess oxygenation
Is the patient hypoxaemic?
The PaO2 should be about 10 kPa less than the % inspired concentration

15. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?

16. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?
Step 3: Determine the pH (or H+ concentration)
Is the patient acidaemic; pH < 7.35?
Is the patient alkalaemic; pH > 7.45?

17. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?

18. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?
Step 4: Determine the respiratory component
If the pH < 7.35, is the PaCO2 > 6.0 kPa (45 mmHg)? – respiratory acidosis
If the pH > 7.45, is the PaCO2 < 4.7 kPa (35 mmHg)? – respiratory alkalosis

19. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?

20. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
What are you going to do now?
Step 5: Determine the metabolic component
If the pH < 7.35, is the HCO3- < 22 mmol l-1 (base excess < -2 mmol l-1) – metabolic acidosis
If the pH > 7.45, is the HCO3- > 26 mmol l-1 (base excess > +2 mmol l-1) – metabolic alkalosis

21. Case study 1 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4)
normal values
PaO kPa > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa 4.7 – 6.0 kPa
Bicarbonate mmol l – 26 mmol l-1
Base excess mmol l-1 +/- 2 mmol l-1
In summary:
An acute respiratory acidosis with impaired oxygenation. 21

22. Case study 2 Initial Information
A 60-year-old man is brought to the ED after a witnessed out-of-hospital cardiac arrest. The paramedics arrived after 7 min, during which CPR had not been attempted. His initial rhythm was VF and the paramedics subsequently restored a spontaneous circulation after the 3rd shock.
On arrival:
Intubated, ventilated with 50% oxygen
HR 120 min-1, BP 150/95 mmHg
Comatose (GCS 3)
Use the 5-step approach to analyse the results of an arterial blood sample

23. Case study 2 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 50% (FiO2 0.5)
normal values
PaO kPa (56 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO2 6.2 kPa (47 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1

24. Case study 2 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 50% (FiO2 0.5)
normal values
PaO kPa (56 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO2 6.2 kPa (47 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1
In summary:
This is a typical ABG result after prolonged cardiac arrest.
There is a mixed metabolic and respiratory acidosis – the predominant component is metabolic, with significant impairment of oxygenation.

25. Case study 3 Initial Information
A 65-year-old man with severe COPD has been found collapsed in the respiratory unit. On initial assessment by the ward nurse he is apnoeic but has an easily palpable carotid pulse. The nurse is attempting to ventilate his lungs with a bag-mask and supplemental oxygen (with reservoir) and has called the cardiac arrest team.
On arrival:
Oropharyngeal airway, ventilated with bag-mask, oxygen at 15 l min-1
Carotid pulse palpable, 90 min-1, SpO2 99%
Comatose (GCS 3)
Use the 5-step approach to analyse the results of an arterial blood sample

26. Case study 3 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 85% (FiO2 0.85) estimated
normal values
PaO kPa (147 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (135 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO3- 36 mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1

27. Case study 3 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 85% (FiO2 0.85) estimated
normal values
PaO kPa (147 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (135 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO3- 36 mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1
In summary:
The significant acidaemia (pH 7.10) indicate an additional acute respiratory acidosis as a result of the respiratory arrest. In the
pre-existing compensated chronic respiratory acidosis,
the pH would have been close to normal.

28. Case study 4 Initial Information
A 75-year-old woman is admitted to the ED following a VF cardiac arrest, witnessed by paramedics. This had been preceded by 30 min of severe central chest pain. Spontaneous circulation restored after 2 shocks, but the patient remained apnoeic and unresponsive. The paramedics intubated her trachea and ventilated her with an automatic ventilator.
On arrival:
Tube confirmed in trachea, tidal volume of 900 ml, rate of 18 breaths min-1, 100% oxygen
Pulse 100 min-1, BP 90/54 mmHg
Comatose (GCS 3)
Use the 5-step approach to analyse the results of an arterial blood sample

29. Case study 4 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 1.0)
normal values
PaO kPa (192 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (20 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE - 4 mmol l-1 +/- 2 mmol l-1

30. Case study 4 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 1.0)
normal values
PaO kPa (192 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (20 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE - 4 mmol l-1 +/- 2 mmol l-1
In summary:
A respiratory alkalosis, mild metabolic acidosis and
impaired oxygenation.

31. Case study 5 Initial Information On arrival:
An 18-year-old insulin dependent diabetic is admitted to the ED. He has been vomiting for 48 h and because he was unable to eat, he has taken no insulin.
On arrival:
Breathing spontaneously RR 35 min-1, oxygen 4 l min-1 via Hudson mask, SpO2 98%
HR 130 min-1, BP 90/65 mmHg
GCS 12 (E3, M5, V4)
Use the 5-step approach to analyse the results of an arterial blood sample

32. Case study 5 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 0.3) estimated
normal values
PaO kPa (129 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (19 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1
The blood glucose is 30 mmol l-1 and there are ketones +++ in the urine

33. Case study 5 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 0.3) estimated
normal values
PaO kPa (129 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (19 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1
The blood glucose is 30 mmol l-1 and there are ketones +++ in the urine
In summary:
These blood gas results are consistent with severe diabetic ketoacidosis. Further evidence is the presence of ketones in his urine and the very high blood glucose. There is a primary metabolic acidosis with partial compensation provided by the respiratory alkalosis.

34. Case study 6 Initial Information
A 75-year-old man is on the surgical ward 2 days after a laparotomy for a perforated sigmoid colon secondary to diverticular disease. He has become increasingly hypotensive over the last 6 h, despite ml 0.9% saline.
On arrival:
RR 35 min-1, SpO2 92% on 6 l min-1 oxygen via facemask
HR 120 min-1, sinus tachycardia, warm peripheries, BP 70/40 mmHg
Urine output 90 ml in the last 6 h
GCS 13 (E3, M6, V4)
Use the 5-step approach to analyse the results of an arterial blood sample

35. Case study 6 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4) estimated
normal values
PaO kPa (62 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO2 4.5 kPa (34 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1

36. Case study 6 (continued)
Arterial blood gas analysis reveals:
Inspired oxygen 40% (FiO2 0.4) estimated
normal values
PaO kPa (62 mmHg) > 10 kPa (75 mmHg) on air
pH – 7.45
PaCO2 4.5 kPa (34 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg)
HCO mmol l – 26 mmol l-1
BE mmol l-1 +/- 2 mmol l-1
In summary:
There is a primary metabolic acidosis with slight compensation provided by the mild respiratory alkalosis. The degree of this is probably limited by the presence of an acute abdomen. The most likely diagnosis is sepsis syndrome secondary to intra-abdominal infection. The plasma lactate would be elevated.

37. Any questions?

38. Summary This workshop has covered:
The terms used to describe the results of arterial blood gas analysis
The normal ranges for arterial blood gas values
How respiration and metabolism are linked
How to use the 5-step approach to arterial blood gas interpretation
Some of the common causes of arterial blood gas abnormalities and what to do to correct them

39. Advanced Life Support Course Slide set
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© Resuscitation Council (UK) 2010