1) Arterial blood gases (ABGs) measure pH, partial pressures of oxygen and carbon dioxide, and bicarbonate levels in arterial blood and can help diagnose respiratory and metabolic conditions. 2) Low pH and high PCO2 indicate respiratory acidosis as seen in asthma, while low pH and low HCO3 indicate metabolic acidosis as seen in heart failure. 3) Case studies presented ABG results from patients with asthma, COPD, and heart failure and the summaries identified the primary acid-base abnormality in each case based on pH, PCO2, and HCO3 levels.

1. ARTERIAL BLOOD GASES

6. Carto

8. Respiratory failure: PO2<60 SaO2<90
paO2 SaO2
97 97 Young patient
80 95 Old patient
70 93 Inferior limit of normal
60
40
30
20
90 Respiratory failure
75 Severe Respiratory failure or
Normal venous blood
60 Loss of counciousness
36 Death by hypoxemia

9. • Diffusion of CO2 from the bloodstream to
alveoli is so efficient that CO2 elimination is
actually limited by how quickly we can “blow-
off” the CO2 in our alveoli.

10. ABG
• pH=7,35-7,45
• paCO2=35-45mmHg
• SaO2=95-98%
• paO2=80-100mmHg
• HCO3=24-26mEq/l

12. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

13. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

14. Case 1
• A patient presents with a one-day history of
productive cough, and increasing dyspnea after
pollen exposure.
• In the ER, the chest x-ray shows normal lungs. His
oxygen saturation is 90% on room air.
• An arterial blood gas is obtained and it reveals a
• pH 7.55
• PCO2 30
• PO2 63
• HCO3- 22

15. Answer
• Step 1: The pH is high (alkalemia)
• pH 7.55
• PCO2 30
• PO2 63
• HCO3- 22

16. Answer
• Step 1: The pH is high (alkalemia)
• Step 2: The PCO2 is low (respiratory alkalosis)
and the bicarbonate is low.
• pH 7.55
• PCO2 30
• PO2 63
• HCO3- 22

17. Answer
• Step 1: The pH is high (alkalemia)
• Step 2: The PCO2 is low (respiratory alkalosis)
and the bicarbonate is low.
• A high pH with a low PCO2 indicates that the
primary process is a respiratory alkalosis

18. Figure 2-17. As air trapping and alveolar hyperinflation develop in obstructive lung diseases,
breath sounds progressively diminish.

19. Time and Progression of Disease
100
50
30
80
0
10
20
40
Alveolar Hyperventilation
60
70
90 Point at which PaO2
declines enough to
stimulate peripheral
oxygen receptors
PaO2
Disease OnsetPaO2orPaCO2
Figure 4-2. PaO2 and PaCO2 trends during acute alveolar hyperventilation.

20. Arterial Blood Gases
Mild to Moderate Asthma Episode
 Acute alveolar hyperventilation with hypoxemia
pH PaCO2 HCO3
- PaO2
   (Slightly) 

21. Case 2
• A patient with acute asthmatic crisis arrives with
SMURD. She presented severe crisis after
cleaning all the house and important dust
exposure
• An arterial blood gas is obtained and it reveals a
• pH 7.25
• PCO2 76
• PO2 58
• HCO3 33
• SaO2 85%

22. Answer
• Step 1: The pH is low (acidosis)
• pH 7.25
• PCO2 56
• PO2 58
• HCO3 33
• SaO2 85%

23. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is high (respiratory acidosis)
– and the bicarbonate is high in order to compensate
the acidosis  no result
• pH 7.25
• PCO2 76
• PO2 58
• HCO3 33
• SaO2 85%

24. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is high (respiratory
acidosis)
– and the bicarbonate is high in order to
compensate the acidosis  no result
• A low pH with a high PCO2 indicates that the
primary process is a respiratory acidosis

25. Time and Progression of Disease
100
50
30
80
0
10
20
40
Alveolar Hyperventilation
60
70
90
Point at which PaO2
declines enough to
stimulate peripheral
oxygen receptors
Acute Ventilatory FailureDisease Onset
Point at which disease becomes
severe and patient begins to
become fatigued
Pa02orPaC02
Figure 4-7. PaO2 and PaCO2 trends during acute ventilatory failure.

26. Arterial Blood Gases
Severe Asthmatic Episode (Status Asthmaticus)
 Acute ventilatory failure with hypoxemia
pH PaCO2 HCO3
- PaO2
   (Significantly) 

27. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

28. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

29. Case 3
• A big smoker: 2 packs/day from the age of 11
years old comes to the ED.
• He had no money for his spray so he stopped
medication.
• An arterial blood gas is obtained and it reveals a
• pH 7.31
• PCO2 55
• PO2 70
• HCO3 27
• SaO2 87%

30. Answer
• Step 1: The pH is low (acidosis)
• pH 7.31
• PCO2 55
• PO2 70
• HCO3 27
• SaO2 87%

31. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is high (respiratory acidosis)
– and the bicarbonate is normal.
• pH 7.31
• PCO2 55
• PO2 70
• HCO3 27
• SaO2 87%

32. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is high (respiratory
acidosis)
– and the bicarbonate is normal
• A low pH with a high PCO2 indicates that the
primary process is a respiratory acidosis.

33. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

34. ABG
What you should know
HEART
FAILURE
ASTHMA
COPD

35. Case 4
• An 80-yr-old man was admitted with severe
congestive heart failure.
• He was hypotensive and oliguric.
• He had both pulmonary and peripheral edema.
• creatinine was 2.5 mg/dl.
• his baseline creatinine was known to be 1.6
mg/dl.
• On arrival at the emergency department, his
plasma Na was 135 mEq/L, K was 4 mEq/L
• The blood lactate level was 20 mmol/L.

36. Case 4
• An arterial blood gas is obtained and it reveals
• pH 7.1
• PCO2 20
• PO2 64
• HCO3 6 mEq/l
• SaO2 77 %

37. Answer
• Step 1: The pH is low (acidosis)
• pH 7.1
• PCO2 20
• PO2 64
• HCO3 6 mEq/l
• SaO2 77 %

38. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is low HCO3(metabolic
acidosis)
• pH 7.1
• PCO2 20
• PO2 64
• HCO3 6 mEq/l
• SaO2 77 %

39. Answer
• Step 1: The pH is low (acidosis)
• Step 2: The PCO2 is low HCO3(metabolic
acidosis) pH 7.1
• A low pH with a low HCO3 indicates that the
primary process is a metabolic acidosis.

40. • arterial lactate: 0.5-1.6 mmol/L
venous lactate: 0.5-2.2 mmol/L
•  intubation, ventilation, dobutamine 
pH=7,2

41. Case 5
• Internal medicine resident took a sample from a
cardiology resident
• An arterial blood gas is obtained and it reveals
• pH 7.32
• PCO2 48
• PO2 42
• HCO3 22 mEq/l
• SaO2 67 %

42. VENOUS BLOOD GAS
• The venous pO2 is easy. Venous pO2 is normally 40 mm
Hg.
• This is the same as the normal arterial pCO2, making it
easy to remember

44. VENOUS BLOOD GAS
• SvO2 =75 %
• PO2 =40 %
• pCO2= 46
• pH=7.32-7.42
• HCO3 =22-24.
• +6
• 0.003
• 2

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