Interpretation of Arterial Blood Gases (ABG)

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1 Interpretation of Arterial Blood Gases (ABG) Prof. Dr. W. Vincken Head Respiratory Division Universitair Ziekenhuis Brussel (UZ Brussel) Vrije Universiteit Brussel (VUB) W Vincken - UZ Brussel - VUB 1

2 ABG: puncture Patient At rest for 5-15 Minimize anxiety/pain (hyperventilation) A. radialis puncture at non-dominant side Allen test Strictly aseptic W Vincken - UZ Brussel - VUB 2

3 ABG: puncture Syringe Glass > plastic (gas-permeable) Polypropylene > polystyrol Dry heparin Max 5% of sample volume Draw blood slowly up (avoid hemolysis) W Vincken - UZ Brussel - VUB 3

4 ABG: puncture Remove air bubbles before mixing/cooling Mix sample thoroughly turn 5 x up and down slowly and roll horizontally for 5 Immediate transport (within 10 ) If not: Store at 0-4 C in icewater Do not store directly on ice (hemolysis) W Vincken - UZ Brussel - VUB 4

5 Before interpretation of ABG Make/take note of F I O 2 : room air (0.21) or under O 2 therapy Body posture: sitting or supine At rest or during exercise W Vincken - UZ Brussel - VUB 5

6 ABG: parameters Parameters of oxygenation P a O 2 S a O 2 P A-a O W Vincken - UZ Brussel - VUB 7

7 ABG: parameters Parameters of oxygenation Parameters of alveolar ventilation and acid-base status P a O 2 S a O 2 P A-a O 2 P a CO 2 ph [HCO 3- ] Base Excess (BE) W Vincken - UZ Brussel - VUB 8

8 ABG: normal values Parameters of oxygenation P a O mmhg* [105 (age/3)] S a O 2 > 97 % P A-a O 2 <10 mmhg (up to 20 mmhg in elderly) *7.5 mmhg = 1 kpa W Vincken - UZ Brussel - VUB 9

9 ABG: normal values Parameters of alveolar ventilation and acid-base status P a CO 2 40 mmhg (35 45 mmhg) ph 7.4 ( ) [HCO 3- ] 24 mmol/l Base Excess (BE) 0 mmol/l W Vincken - UZ Brussel - VUB 10

10 Abnormal ABG: hyperoxemia High P a O 2 No pathophysiological substrate (except mild hyperoxemia in extreme alveolar hyperventilation) Usually indicates sampling error (air in blood sample) or high F I O 2 (oxygen administration) W Vincken - UZ Brussel - VUB 11

11 Abnormal ABG: hypoxemia Low P a O 2 Desaturation : low S a O W Vincken - UZ Brussel - VUB 12

12 Hypoxemia calculate P A-a O 2 Hypoxemia with P A-a O 2 = respiratory failure type I = oxygenation (lung) failure Hypoxemia with normal P A-a O 2 = respiratory failure type II = ventilatory (pump) failure W Vincken - UZ Brussel - VUB 15

13 Hypoxemia: calculate the Alveolo-arterial PO 2 gradient P A-a O 2 (mmhg) = P A O 2 - P a O 2 P A O 2 is calculated using the alveolar gas equation P A O 2 = P I O 2 [P A CO 2 / R] P A O 2 = [(P b - P H 2O) x F I O 2 ] [P a CO 2 / 0.8] P A O 2 = [(760-47) x 0.21] [P a CO 2 x 1.25] P A O 2 = 149 [P a CO 2 x 1.25] P a O 2 and P a CO 2 are measured (ABG) Normal P A-a O 2 < 5 10 mmhg (up to 20 mmhg in elderly) W Vincken - UZ Brussel - VUB 17

14 Hypoxemia: 3 main causes P A-a O 2 = P A O 2 P a O 2 P a O 2 = P A O 2 P A-a O 2 (1) Reduced P A O 2 (2) Increased P A-a O 2 (3) Reduced P v O W Vincken - UZ Brussel - VUB 18

15 Hypoxemia (1): due to reduced P A O 2 * P a O 2 = P A O 2 P A-a O 2 P A O 2 = P I O 2 [P A CO 2 / R] P A O 2 = [( P b - P H 2O) x F I O 2 ] [P A CO 2 / R] Reduced P I O 2 Reduced P b : high altitude Reduced F I O 2 : inhalation of hypoxic gas mixtures Increased P A CO 2 = hypercapnia = Ventilatory failure or Type II Respiratory Failure * and normal P A-a O W Vincken - UZ Brussel - VUB 19

16 Hypoxemia (2): due to increased P A-a O 2 P a O 2 = P A O 2 P A-a O 2 = Failure of the lung as a gas exchanger = Intrapulmonary mechanism/cause of hypoxemia = Oxygenation failure or Type I Respiratory Failure Ventilation/perfusion mismatch Diffusion limitation Right Left shunt W Vincken - UZ Brussel - VUB 20

17 Hypoxemia (2): Oxygenation failure Ventilation/Perfusion mismatch (R>L shunt-like effect of regions with low V/Q ratio) obstructive lung diseases (COPD, asthma, ) parenchymal lung disease (pneumonia, atelectasis, ILD, ) vascular lung disease W Vincken - UZ Brussel - VUB 21

18 Hypoxemia (2): Oxygenation failure Diffusion limitation (with exercise and reduced transit time of RBCs in pulmonary capillaries) increased thickness of alveolocapillary membrane Interstitial lung diseases reduced surface area of alveolocapillary membrane Emphysema W Vincken - UZ Brussel - VUB 22

19 Hypoxemia (2): Oxygenation failure Anatomic R L shunt (leads to refractory hypoxemia) intracardiac (ASD, VSD, ) intrapulmonary (A-V malformations, fistulas) W Vincken - UZ Brussel - VUB 23

20 Hypoxemia: consequences (1) Desaturation central cyanosis Chemoreceptor stimulation Central respiratory drive Output respiratory muscles V E and WOB : dyspnea V A and hypocapnia & respiratory alkalosis W Vincken - UZ Brussel - VUB 29

21 Hypoxemia: consequences (2) Tissue hypoxia organ disfunction: CNS, CV, kidneys anaerobic metabolism lactic acidosis Pulmonary vasoconstriction pulmonary hypertension cor pulmonale & right heart failure Increased renal erythropoetin production secondary polycythemia W Vincken - UZ Brussel - VUB 30

22 Abnormal ABG: hypercapnia High P a CO 2 (> 45 mmhg) Respiratory acidosis : low ph (< 7.35) ph = pk + log [HCO 3- ] / 0.03 x PCO W Vincken - UZ Brussel - VUB 31

23 Hypercapnia: 4 main causes P a CO 2 = VCO 2 / V A VCO 2 = CO 2 production V A = alveolar ventilation = V E - V D (1) Increased VCO 2 (2) Reduced V A (reduced V E and normal V D ) (3) Increased V D (4) Severe V/Q mismatching W Vincken - UZ Brussel - VUB 35

24 Hypercapnia (1): increased VCO 2 P a CO 2 = VCO 2 / V A Exercise with extreme effort Fever and other hypermetabolic states in patients unable to increase V E and V A, e.g., mechanically ventilated patient W Vincken - UZ Brussel - VUB 36

25 Hypercapnia (2): reduced V A P a CO 2 = VCO 2 / V A Reduced V A = alveolar hypoventilation = Ventilatory failure or Type II respiratory failure Any hypoxemia is secondary to hypercapnia, i.e., the P A-a O 2 is normal Extrapulmonary mechanism/cause of hypoxemia: Severe UAO Failure of the ventilatory pump W Vincken - UZ Brussel - VUB 37

26 Hypercapnia (2): Failure of the ventilatory pump (a) Reduced respiratory drive (central controller) CNS disorders Drug (illicit or not) overdose Metabolic disorders Obesity-hypoventilation syndrome (Pickwick syndrome) Central alveolar hypoventilation (Ondine s curse, ) W Vincken - UZ Brussel - VUB 39

27 Hypercapnia (2): Failure of the ventilatory pump (b) Dysfunction of respiratory neuromuscular apparatus Motor neurons (ALS, poliomyelitis, ) Peripheral nerve (Guillain-Barré, phrenic neuropathy, ) Myoneural junction (myastenia, drugs, ) Muscle (myopathy, metabolic disorders, malnutrition, ) W Vincken - UZ Brussel - VUB 40

28 Hypercapnia (2): Failure of the ventilatory pump (c) Chest wall disorders including severe obesity Kyphoscoliosis TBC sequellae incl. thoracoplasty Severe obesity W Vincken - UZ Brussel - VUB 41

29 Hypercapnia: consequences Hypoxemia with normal P A-a O 2 P a O 2 decreases with 1.25 mmhg/mmhg P a CO 2 increase Respiratory acidosis: reduced ph If persistent: HCO 3- retention by the kidneys increased [HCO 3- ] and positive BE the reduced ph will increase towards 7.4 (normal) but not overshoot it ph = pk + log [HCO 3- ] / 0.03 x PCO 2 ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 Compensatory metabolic alkalosis Acutely, Δ HCO 3- = 0.1 x Δ P a CO 2 Chronically, Δ HCO 3- = 0.35 x Δ P a CO W Vincken - UZ Brussel - VUB 44

30 Clinical signs of hypercapnia CNS: cerebral vasodilatation increased cerebral Q intracranial hypertension headache, papilledema asterixis lethargy, confusion progressing to coma carbonarcosis Peripheral vasodilatation full bounding pulses with warm, cherry-red skin W Vincken - UZ Brussel - VUB 45

31 Abnormal ABG: hypocapnia Low P a CO 2 (< 35 mmhg) Respiratory alkalosis: high ph (> 7.45) ph = pk + log [HCO 3- ] / 0.03 x PCO W Vincken - UZ Brussel - VUB 47

32 Hypocapnia: 1 main mechanism P a CO 2 = VCO 2 / V A Increased V A = alveolar hyperventilation W Vincken - UZ Brussel - VUB 48

33 Hypocapnia ~ alveolar hyperventilation: causes Stimulation of chemoreceptors Hypoxemia Metabolic acidosis Pulmonary J-receptor stimulation Interstitial/parenchymal lung diseases Tissue hypoxia Anemia, CO-, sulf- or methb Sepsis, hypotension, shock (also stimulation of baroreceptors) Fever, thyrotoxicosis, strenuous exercise Psychogenic : hyperventilation syndrome = diagnosis of exclusion W Vincken - UZ Brussel - VUB 49

34 Hypocapnia: consequences Respiratory alkalosis: increased ph If persistent: HCO 3- excretion by the kidneys reduced [HCO 3- ] and negative BE (= base deficit) increased ph will decrease towards (but not below) 7.4 ph = pk + log [HCO 3- ] / 0.03 x PCO 2 ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 Compensatory metabolic acidosis Acutely, Δ HCO 3- = 0.2 x Δ P a CO 2 Chronically, Δ HCO 3- = 0.5 x Δ P a CO W Vincken - UZ Brussel - VUB 50

35 Abnormal ABG: acid-base disorders Acidosis: low ph Respiratory Metabolic Alkalosis: high ph Respiratory Metabolic W Vincken - UZ Brussel - VUB 51

36 Metabolic acidosis ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 ph due to HCO 3- and negative BE (base deficit), due to Acid [H + ] accumulation (and buffering by HCO 3- ) renal failure diabetes mellitus: ketoacidosis tissue hypoxia/hypoperfusion (shock): lactic acidosis intoxications: ASA, antifreeze, methanol, paraldehyde Loss of HCO 3 - diarrhea W Vincken - UZ Brussel - VUB 52

37 Metabolic acidosis If persistent, the ph (hence increase in [H + ]) leads to: chemoreceptor stimulation increased central respiratory drive increased V E and V A : hyperventilation hypocapnia the low ph rises towards normal (not exceeding 7.4) compensatory respiratory alkalosis Δ P a CO 2 = 1 à 1.3 x Δ HCO 3 - ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 ph = pk + log [ HCO 3- ] / 0.03 x PCO W Vincken - UZ Brussel - VUB 53

38 Metabolic alkalosis ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 ph due to HCO 3- and positive BE, due to HCO 3- accumulation Excessive ingestion of alkali Drug intake: diuretics, corticosteroids Cushing syndrome Hypokalemia Loss of acid Loss of gastric acid: prolonged vomiting, nasogastric suction Via kidneys W Vincken - UZ Brussel - VUB 54

39 Metabolic alkalosis If persistent, the ph (hence reduction in [H + ]) leads to: reduced chemoreceptor stimulation reduced central respiratory drive reduced V E and V A : hypoventilation hypercapnia the increased ph will decrease towards normal (but not below 7.4) compensatory respiratory acidosis Δ P a CO 2 = 0.6 x Δ HCO 3 - ph = pk + log [ HCO 3- ] / 0.03 x PCO 2 ph = pk + log [ HCO 3- ] / 0.03 x PCO W Vincken - UZ Brussel - VUB 55

40 Arterial Blood Gases : main use Note sampling conditions Careful sampling and handling Detection of Respiratory Failure Detection of Acid-Base disturbances W Vincken - UZ Brussel - VUB 56

41 Interpretation of ABG Oxygenation Look at P a O 2 and S a O 2 Calculate P A-a O 2 Alveolar ventilation Look at P a CO 2 Acid-Base status Look at ph, HCO 3- and BE W Vincken - UZ Brussel - VUB 57

42 Thank you for listening Hope you learned something, or at least enjoyed it Prof. Dr. W. Vincken Head Respiratory Division UZ Brussel, VUB W Vincken - UZ Brussel - VUB 58

43 Interpretation of ABG 10 examples W Vincken - UZ Brussel - VUB 59

44 Interpretation of ABG : example 1 P a O 2 mmhg 69 S a O 2 % 91 P A-a O 2 mmhg calculate P a CO 2 mmhg 60 ph 7.2 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 60

45 Interpretation of ABG : example 1 P a O 2 mmhg 69 S a O 2 % 91 P A-a O 2 mmhg x = 5 P a CO 2 mmhg 60 ph 7.2 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 61

46 Interpretation of ABG : example 1 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal P a CO 2 mmhg 60 ph 7.2 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 62

47 Interpretation of ABG : example 1 Oxygenation Reduced P a O 2 and S a O 2 69/91% = mild hypoxemia and arterial desaturation Normal P A-a O 2 5 = hypoxemia is due to Ventilatory failure = Failure of the respiratory air pump, or Reduced P A O 2, or Reduced P v O W Vincken - UZ Brussel - VUB 63

48 Interpretation of ABG : example 1 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal P a CO 2 mmhg 60 Hypercapnia ph 7.2 Acidosis HCO 3 - meq/l 24 Normal BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 64

49 Interpretation of ABG : example 1 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal Type II RF P a CO 2 mmhg 60 Hypercapnia Respiratory ph 7.2 Acidosis Acidosis HCO - 3 meq/l 24 Normal Acute BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 65

50 Interpretation of ABG : example 2 P a O 2 mmhg 69 S a O 2 % 91 P A-a O 2 mmhg calculate P a CO 2 mmhg 60 ph 7.37 HCO - 3 meq/l 34 BE meq/l W Vincken - UZ Brussel - VUB 66

51 Interpretation of ABG : example 2 P a O 2 mmhg 69 S a O 2 % 91 P A-a O 2 mmhg x = 5 P a CO 2 mmhg 60 ph 7.37 HCO - 3 meq/l 34 BE meq/l W Vincken - UZ Brussel - VUB 67

52 Interpretation of ABG : example 2 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal P a CO 2 mmhg 60 ph 7.37 HCO - 3 meq/l 34 BE meq/l W Vincken - UZ Brussel - VUB 68

53 Interpretation of ABG : example 2 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal P a CO 2 mmhg 60 Hypercapnia ph 7.37 Minimal acidosis HCO - 3 meq/l 34 Increased BE meq/l + 10 Positive W Vincken - UZ Brussel - VUB 69

54 Interpretation of ABG : example 2 P a O 2 mmhg 69 Hypoxemia S a O 2 % 91 Desaturation P A-a O 2 mmhg 5 Normal Type II RF P a CO 2 mmhg 60 Hypercapnia Respiratory ph 7.37 Minimal acidosis Acidosis HCO 3 - meq/l 34 Increased Chronic BE meq/l + 10 Positive Compensatory metabolic alkalosis W Vincken - UZ Brussel - VUB 70

55 Interpretation of ABG : example 3 P a O 2 mmhg 99 S a O 2 % 98 P A-a O 2 mmhg calculate P a CO 2 mmhg 30 ph 7.50 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 71

56 Interpretation of ABG : example 3 P a O 2 mmhg 99 S a O 2 % 98 P A-a O 2 mmhg x = 12.5 P a CO 2 mmhg 30 ph 7.50 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 72

57 Interpretation of ABG : example 3 P a O 2 mmhg 99 Normal S a O 2 % 98 Normal P A-a O 2 mmhg 12.5 Normal P a CO 2 mmhg 30 Hypocapnia ph 7.50 Alkalosis HCO 3 - meq/l 24 Normal BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 73

58 Interpretation of ABG : example 3 P a O 2 mmhg 99 Normal S a O 2 % 98 Normal P A-a O 2 mmhg 12.5 Normal P a CO 2 mmhg 30 Hypocapnia Respiratory ph 7.50 Alkalosis Alkalosis HCO - 3 meq/l 24 Normal Acute BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 74

59 Interpretation of ABG : example 4 P a O 2 mmhg 99 S a O 2 % 98 P A-a O 2 mmhg 12.5 P a CO 2 mmhg 30 ph 7.42 HCO - 3 meq/l 20 BE meq/l W Vincken - UZ Brussel - VUB 75

60 Interpretation of ABG : example 4 P a O 2 mmhg 99 Normal S a O 2 % 98 Normal P A-a O 2 mmhg 12.5 Normal P a CO 2 mmhg 30 ph 7.42 HCO - 3 meq/l 20 BE meq/l W Vincken - UZ Brussel - VUB 76

61 Interpretation of ABG : example 4 P a O 2 mmhg 99 Normal S a O 2 % 98 Normal P A-a O 2 mmhg 12.5 Normal P a CO 2 mmhg 30 Hypocapnia ph 7.42 Minimal alkalosis HCO 3 - meq/l 20 Reduced BE meq/l - 4 Negative W Vincken - UZ Brussel - VUB 77

62 Interpretation of ABG : example 4 P a O 2 mmhg 99 Normal S a O 2 % 98 Normal P A-a O 2 mmhg 12.5 Normal P a CO 2 mmhg 30 Hypocapnia Respiratory ph 7.42 Minimal alkalosis Alkalosis HCO 3 - meq/l 20 Reduced Chronic BE meq/l - 4 Negative Compensatory metabolic acidosis W Vincken - UZ Brussel - VUB 78

63 Interpretation of ABG : example 5 P a O 2 mmhg 60 S a O 2 % 88 P A-a O 2 mmhg calculate P a CO 2 mmhg 32 ph 7.49 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 79

64 Interpretation of ABG : example 5 P a O 2 mmhg 60 S a O 2 % 88 P A-a O 2 mmhg x = 49 P a CO 2 mmhg 32 ph 7.49 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 80

65 Interpretation of ABG : example 5 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased P a CO 2 mmhg 32 ph 7.49 HCO - 3 meq/l 24 BE meq/l W Vincken - UZ Brussel - VUB 81

66 Interpretation of ABG : example 5 Oxygenation reduced P a O 2 and S a O 2 60/88% = hypoxemia and arterial desaturation Increased P A-a O 2 49 = hypoxemia is due to Oxygenation failure Failure of the lung as a gas exchanger Intrapulmonary disease Ventilation/perfusion mismatch Diffusion limitation Right>Left shunt W Vincken - UZ Brussel - VUB 82

67 Interpretation of ABG : example 5 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased P a CO 2 mmhg 32 Hypocapnia ph 7.49 Alkalosis HCO 3 - meq/l 24 Normal BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 83

68 Interpretation of ABG : example 5 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased Type I RF P a CO 2 mmhg 32 Hypocapnia Respiratory ph 7.49 Alkalosis Alkalosis HCO - 3 meq/l 24 Normal Acute BE meq/l 0 Normal W Vincken - UZ Brussel - VUB 84

69 Interpretation of ABG : example 6 P a O 2 mmhg 60 S a O 2 % 88 P A-a O 2 mmhg 49 P a CO 2 mmhg 32 ph 7.42 HCO - 3 meq/l 18 BE meq/l W Vincken - UZ Brussel - VUB 85

70 Interpretation of ABG : example 6 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased P a CO 2 mmhg 32 ph 7.42 HCO - 3 meq/l 18 BE meq/l W Vincken - UZ Brussel - VUB 86

71 Interpretation of ABG : example 6 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased Type I RF P a CO 2 mmhg 32 Hypocapnia ph 7.42 Minimal alkalosis HCO 3 - meq/l 18 Reduced BE meq/l - 6 Negative W Vincken - UZ Brussel - VUB 87

72 Interpretation of ABG : example 6 P a O 2 mmhg 60 Hypoxemia S a O 2 % 88 Desaturation P A-a O 2 mmhg 49 Increased Type I RF P a CO 2 mmhg 32 Hypocapnia Respiratory ph 7.42 Minimal alkalosis Alkalosis HCO 3 - meq/l 18 Reduced Chronic BE meq/l - 6 Negative Compensatory Metabolic acidosis W Vincken - UZ Brussel - VUB 88

73 Interpretation of ABG : example 7 P a O 2 mmhg 92 S a O 2 % 94 P A-a O 2 mmhg calculate P a CO 2 mmhg 40 ph 7.27 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 89

74 Interpretation of ABG : example 7 P a O 2 mmhg 92 S a O 2 % 94 P A-a O 2 mmhg x = 7 P a CO 2 mmhg 40 ph 7.27 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 90

75 Interpretation of ABG : example 7 P a O 2 mmhg 92 Normoxemia S a O 2 % 94 Normal P A-a O 2 mmhg 7 Normal P a CO 2 mmhg 40 ph 7.27 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 91

76 Interpretation of ABG : example 7 P a O 2 mmhg 92 Normoxemia S a O 2 % 94 Normal P A-a O 2 mmhg 7 Normal P a CO 2 mmhg 40 Normocapnia ph 7.27 Acidosis HCO 3 - meq/l 16 Reduced BE meq/l - 7 Negative W Vincken - UZ Brussel - VUB 92

77 Interpretation of ABG : example 7 P a O 2 mmhg 92 Normoxemia S a O 2 % 94 Normal P A-a O 2 mmhg 7 Normal P a CO 2 mmhg 40 Normocapnia Acute ph 7.27 Acidosis Acidosis HCO - 3 meq/l 16 Reduced Metaboli c BE meq/l - 7 Negative W Vincken - UZ Brussel - VUB 93

78 Interpretation of ABG : example 8 P a O 2 mmhg 100 S a O 2 % 97 P A-a O 2 mmhg calculate P a CO 2 mmhg 30 ph 7.37 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 94

79 Interpretation of ABG : example 8 P a O 2 mmhg 100 S a O 2 % 97 P A-a O 2 mmhg x = 12 P a CO 2 mmhg 30 ph 7.37 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 95

80 Interpretation of ABG : example 8 P a O 2 mmhg 100 Normoxemia S a O 2 % 97 Normal P A-a O 2 mmhg 12 Normal P a CO 2 mmhg 30 ph 7.37 HCO - 3 meq/l 16 BE meq/l W Vincken - UZ Brussel - VUB 96

81 Interpretation of ABG : example 8 P a O 2 mmhg 100 Normoxemia S a O 2 % 97 Normal P A-a O 2 mmhg 12 Normal P a CO 2 mmhg 30 Hypocapnia ph 7.37 Minimal acidosis HCO 3 - meq/l 16 Reduced BE meq/l - 7 Negative W Vincken - UZ Brussel - VUB 97

82 Interpretation of ABG : example 8 P a O 2 mmhg 100 Normoxemia S a O 2 % 97 Normal P A-a O 2 mmhg 12 Normal P a CO 2 mmhg 30 Hypocapnia Compensatory Respiratory ph alkalosis 7.37 Minimal acidosis Acidosis HCO 3 - meq/l 16 Reduced Metabolic BE meq/l - 7 Negative W Vincken - UZ Brussel - VUB 98

83 Interpretation of ABG : example 9 P a O 2 mmhg 95 S a O 2 % 96 P A-a O 2 mmhg calculate P a CO 2 mmhg 40 ph 7.50 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 99

84 Interpretation of ABG : example 9 P a O 2 mmhg 95 S a O 2 % 96 P A-a O 2 mmhg x = 4 P a CO 2 mmhg 40 ph 7.50 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 100

85 Interpretation of ABG : example 9 P a O 2 mmhg 95 Normoxemia S a O 2 % 96 Normal P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 40 ph 7.50 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 101

86 Interpretation of ABG : example 9 P a O 2 mmhg 95 Normoxemia S a O 2 % 96 Normal P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 40 Normocapnia ph 7.50 Alkalosis HCO 3 - meq/l 32 Increased BE meq/l + 8 Positive W Vincken - UZ Brussel - VUB 102

87 Interpretation of ABG : example 9 P a O 2 mmhg 95 Normoxemia S a O 2 % 96 Normal P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 40 Normocapnia Acute ph 7.50 Alkalosis Alkalosis HCO - 3 meq/l 32 Increased Metabolic BE meq/l + 8 Positive W Vincken - UZ Brussel - VUB 103

88 Interpretation of ABG : example 10 P a O 2 mmhg 83 S a O 2 % 91 P A-a O 2 mmhg calculate P a CO 2 mmhg 50 ph 7.43 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 104

89 Interpretation of ABG : example 10 P a O 2 mmhg 83 S a O 2 % 91 P A-a O 2 mmhg x = 4 P a CO 2 mmhg 50 ph 7.43 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 105

90 Interpretation of ABG : example 10 P a O 2 mmhg 83 Normoxemia S a O 2 % 91 Borderline P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 50 ph 7.43 HCO - 3 meq/l 32 BE meq/l W Vincken - UZ Brussel - VUB 106

91 Interpretation of ABG : example 10 P a O 2 mmhg 83 Normoxemia S a O 2 % 91 Borderline P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 50 Hypercapnia ph 7.43 Minimal alkalosis HCO 3 - meq/l 32 Increased BE meq/l + 8 Positive W Vincken - UZ Brussel - VUB 107

92 Interpretation of ABG : example 10 P a O 2 mmhg 83 Normoxemia S a O 2 % 91 Borderline P A-a O 2 mmhg 4 Normal P a CO 2 mmhg 50 Hypercapnia Compensatory Respiratory ph acidosis 7.43 Minimal alkalosis Alkalosis HCO 3 - meq/l 32 Increased Metabolic BE meq/l + 8 Positive W Vincken - UZ Brussel - VUB 108

93 Definition of Respiratory Failure Abnormal Arterial Blood Gases Hypoxemia with P a O 2 < 60 mmhg without or with Hypercapnia with P a CO 2 > 50 mmhg Without ABGs No Diagnosis of RF W Vincken - UZ Brussel - VUB 109

94 Classification of Respiratory Failure According to type of onset/duration Acute Respiratory Failure Chronic Respiratory Failure Acute on Chronic Respiratory Failure W Vincken - UZ Brussel - VUB 110

95 Classification of Respiratory Failure According to type of ABG abnormality Respiratory Failure Type I Hypoxemia with (due to) increased P A-a O 2 Normocapnia or hypocapnia Respiratory Failure Type II Hypoxemia with (due to) hypercapnia Normal P A-a O W Vincken - UZ Brussel - VUB 111

96 Classification of Respiratory Failure According to type of ABG abnormality Type I RF ~ Oxygenation Failure Failure of the lung as a gas exchanger (O 2 and CO 2 ) Increased P A-a O 2 Type II RF ~ Ventilatory Failure Failure of the respiratory system as an air pump Normal P A-a O 2 Mixed Failure W Vincken - UZ Brussel - VUB 112

97 Oxygenation Failure Reduced P a O 2 (hypoxemia) Increased P A-a O 2 Reduced P a CO 2 (hypocapnia) Increased ph (respiratory alkalosis) If persistent: compensatory metabolic acidosis (renal bicarbonate excretion) Acutely, Δ HCO 3- = 0.2 x Δ P a CO 2 Chronically, Δ HCO 3- = 0.5 x Δ P a CO W Vincken - UZ Brussel - VUB 113

98 Oxygenation Failure Abnormal Chest X-Ray Diffuse pulmonary diseases Localised pulmonary diseases Normal Chest X-Ray Anatomic R>L shunts Asthma (except for hyperinflation) Pulmonary embolism/vascular disease W Vincken - UZ Brussel - VUB 114

99 Ventilatory Failure Increased P a CO 2 (hypercapnia) Reduced ph (respiratory acidosis) Reduced P a O 2 (pro rata hypoxemia) Normal P A-a O 2 If persistent: compensatory metabolic alkalosis (renal bicarbonate retention) Acutely, Δ HCO 3- = 0.1 x Δ P a CO 2 Chronically, Δ HCO 3- = 0.35 x Δ P a CO W Vincken - UZ Brussel - VUB 115

100 Classification of Respiratory Failure Type I Type II Acute Hypoxemia with Hypoxemia with Chronic increased P A-a O 2 Hypocapnia Respiratory alkalosis Hypoxemia Hypocapnia Compensated respiratory alkalosis Due to HCO 3- excretion and metabolic acidosis normal P A-a O 2 Hypercapnia Respiratory acidosis Hypoxemia Hypercapnia Compensated respiratory acidosis Due to HCO 3- retention and metabolic alkalosis W Vincken - UZ Brussel - VUB 116

101 Classification of Respiratory Failure Acute P a O 2 P A-a O 2 P a CO 2 ph Chronic P a O 2 P A-a O 2 P a CO 2 ph HCO 3 - BE Type I Low High Low High Low High Low High normal Low negative Type II Low Normal High Low Low Normal High Low normal High positive W Vincken - UZ Brussel - VUB 117

102 Thank you for listening Hope you learned something, or at least enjoyed it Prof. Dr. W. Vincken Head Respiratory Division UZ Brussel, VUB W Vincken - UZ Brussel - VUB 118

Interpretation of Arterial Blood Gases. Prof. Dr. W. Vincken Head Respiratory Division Academisch Ziekenhuis Vrije Universiteit Brussel (AZ VUB)

Interpretation of Arterial Blood Gases Prof. Dr. W. Vincken Head Respiratory Division Academisch Ziekenhuis Vrije Universiteit Brussel (AZ VUB) Before interpretation of ABG Make/Take note of Correct puncture