1 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 5 Oxygenation Assessments Oxygenation Assessments

2 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Transport Review Oxygen is carried in the blood in two ways: 1. As dissolved oxygen in the blood plasma 2. Bound to the hemoglobin (Hb)  Most oxygen is carried to the tissue cell bound to the hemoglobin.

3 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Dissolved in the Blood Plasma  At normal body temperature, about mL of oxygen (O 2 ) will dissolve in each 100 mL of blood for every 1 mm Hg of PO 2.  Thus when the PaO 2 is 100 mm Hg, about 0.3 mL of dissolved O 2 exists in every 100 mL of plasma: × 100 mm Hg = 0.3 mL  Clinically, written as 0.3 volume percent (vol%)  0.3 vol% O 2

4 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Hb value in normal man: 14 to 16 g/100 mL  Hb value in normal woman: 12 to 15 g/100 mL  Clinically, the weight measurement of hemoglobin, in reference to 100 mL of blood, is known as the grams percent hemoglobin (g% Hb) Oxygen Bound to Hemoglobin

5 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Each g% Hb can carry 1.34 mL of O 2  Thus if the Hb level is 12 g% and if the Hb is fully saturated, about vol% of O 2 will be bound to the Hb: O 2 bound to Hb = 1.34 mL O 2 × 12 g% Hb = vol% O 2 O 2 bound to Hb = 1.34 mL O 2 × 12 g% Hb = vol% O 2 Oxygen Bound to Hemoglobin (Cont’d)

6 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  At a normal PaO 2 of 100 mm Hg, however, the Hb saturation (SaO 2 ) is only about 97% because of these normal physiologic shunts:  Thebesian venous drainage into the left atrium  Bronchial venous drainage into the pulmonary veins Oxygen Bound to Hemoglobin (Cont’d)

7 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Thus the amount of arterial oxygen in the calculation must be adjusted to 97%: vol% O vol% O 2 ×.97 × vol% O vol% O 2 Oxygen Bound to Hemoglobin (Cont’d)

8 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  To calculate the total amount of oxygen in 100 mL of blood, the following must be added together:  Dissolved oxygen  Oxygen bound to hemoglobin Total Oxygen Content

9 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. A 44-year-old woman with a long history of asthma arrives in the emergency room in severe respiratory distress. Her vital signs are respiratory rate 36 breaths/min, heart rate 130 bpm, and blood pressure 160/95 mm Hg. Her hemoglobin concentration is 10 g%, and her PaO 2 is 55 mm Hg (SaO 2 85%). Based on these data, the patient’s total oxygen content is determined on the next slide: Case Example

10 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 55 PaO 2 55 PaO 2 × (dissolved O 2 factor) × (dissolved O 2 factor) vol% O vol% O 2 1. Dissolved O 2

11 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 2. Oxygen Bound to Hemoglobin 10 g% Hb 10 g% Hb × 1.34 (O 2 bound to Hb factor) × 1.34 (O 2 bound to Hb factor) 13.4 vol% O 2 (at SaO 2 of 100%) 13.4 vol% O 2 (at SaO 2 of 100%) Above answer is then followed by the SaO 2 factor: 13.4 vol% O vol% O 2 ×.85 SaO 2 ×.85 SaO vol% O 2 (at SaO 2 of 85%) vol% O 2 (at SaO 2 of 85%)

12 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc vol% O 2 (bound to hemoglobin) vol% O 2 (bound to hemoglobin) vol% O 2 (dissolved O 2 ) vol% O 2 (dissolved O 2 ) vol% O 2 (total amount of O 2 /100 mL of blood) vol% O 2 (total amount of O 2 /100 mL of blood) 3. Total Oxygen Content.

13 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. The total oxygen content can be calculated in the patient’s:  Arterial blood (CaO 2 )  Venous blood (CvO 2 )  Pulmonary capillary blood (CcO 2 ) Total Oxygen Content (Cont’d)

14 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. CaO 2 = Oxygen content of arterial blood (Hb × 1.34 × SaO 2 ) + (PaO 2 × 0.003) (Hb × 1.34 × SaO 2 ) + (PaO 2 × 0.003) CvO 2 = Oxygen content of mixed venous blood CvO 2 = Oxygen content of mixed venous blood (Hb × 1.34 × Sv O 2 ) + (Pv O 2 × 0.003) (Hb × 1.34 × Sv O 2 ) + (Pv O 2 × 0.003) CcO 2 = Oxygen content of pulmonary capillary blood (Hb × 1.34) + (PAO 2 × 0.003) (Hb × 1.34) + (PAO 2 × 0.003) Total Oxygen Content (Cont’d)

15 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygenation Indices  Oxygen tension–based indices  Oxygen saturation and content indices

16 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Tension–Based Indices  Arterial oxygen tension (PaO 2 )  Alveolar-arterial oxygen tension difference (P[A-a]O 2 )

17 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial Oxygen Tension (PaO 2 )  Good indicator of the patient’s oxygenation status  The PaO 2, however, may be misleading in these clinical situations:  Low Hb  Decreased cardiac output  Peripheral shunting  Carbon monoxide and cyanide exposure

18 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Alveolar-Arterial Oxygen Tension Difference (P[A-a]O 2 )  The P(A-a)O 2 is the oxygen tension difference between the alveoli and arterial blood.

19 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Alveolar-Arterial Oxygen Tension Difference (P[A-a]O 2 ) (Cont’d) PAO 2 = FIO 2 (P B − PH 2 O ) − PaCO 2 (1.25)

20 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Study Example If a patient is receiving an FIO 2 of 0.30 on a day when the barometric pressure is 750 mm Hg, and if the patient’s PaCO 2 is 70 mm Hg and PaO 2 is 60 mm Hg, the P(A-a)O 2 can be calculated as shown on the next slide:

21 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Study Example (Cont’d) PAO 2 = FIO 2 (P B − P H 2 O ) − PaCO 2 (1.25) = 0.30 (750 − 47) − 70 (1.25) = (703) 0.30 − 87.5 = (210.9) − 87.5 = mm Hg

22 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Study Example (Cont’d) Using the PaO 2 obtained from the ABG: (PAO 2 ) (PAO 2 ) − 60.0 (PaO 2 ) − 60.0 (PaO 2 ) 63.4 mm Hg [P(A-a)O 2 ] 63.4 mm Hg [P(A-a)O 2 ] The normal P(A-a)O 2 ranges from 7 to 15 mm Hg and should not exceed 30 mm Hg.

23 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. P(A-a)O 2 Increases  Oxygen diffusion disorders  Decreased V/Q ratios  Right-to-left cardiac shunting  Age

24 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Note: The P(A-a)O 2 Loses sensitivity in patients breathing high FIO 2

25 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Saturation– and Content–Based Indices

26 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Saturation– and Content–Based Indices  CaO 2 = (Hb × 1.34 × SaO 2 ) + (PaO 2 × 0.003)  CvO 2 = (Hb × 1.34 × SvO 2 ) + (PvO 2 × 0.003)  CcO 2 = (Hb × 1.34) + (PAO 2 × 0.003)

27 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Most Common Oxygen Saturation–and Content–Based Indices  Total oxygen delivery  Arterial-venous oxygen content difference  Oxygen consumption  Oxygen extraction ratio  Mixed venous oxygen saturation  Pulmonary shunting

28 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Total Oxygen Delivery DO 2 = Q T × (CaO 2 × 10) The total oxygen delivery is the amount of oxygen delivered to the peripheral tissue cells.

29 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Total Oxygen Delivery DO 2 = Q T × (CaO 2 × 10) (Cont’d) For example, if a patient has a cardiac output of 4 L/min and a CaO 2 of 15 vol%, the DO 2 is 600 mL of oxygen per minute—as calculated on the next slide:

30 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Total Oxygen Delivery DO 2 = Q T × (CaO 2 × 10) = 4 L/min × (15 vol% × 10) = 600 mL O 2 per minute Normally, about 1000 mL/min

31 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Total Oxygen Delivery (Cont’d) Decreases:  Low PaO 2  Low SaO 2  Low Hb  Low cardiac output

32 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Total Oxygen Delivery (Cont’d) Increases:  Increased PaO 2  Increased SaO 2  Increased Hb  Increased cardiac output

33 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial-Venous Oxygen Content Difference C(a-v)O 2 = CaO 2 − CvO 2 The arterial-venous oxygen content difference (C[a-v]O 2 ) is the difference between the CaO 2 and the CvO 2 —that is, CaO 2 − CvO 2.

34 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial-Venous Oxygen Content Difference C(a-v)O 2 = CaO 2 − CvO 2 (Cont’d) For example, if a patient’s CaO 2 is 15 vol% and the CvO 2 is 8 vol%, the C(a-v)O 2 is 7 vol%—as calculated on the next slide:

35 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial-Venous Oxygen Content Difference C(a-v)O 2 = CaO 2 − CvO 2 = 15 vol% − 8 vol% = 7 vol% Normally, 5 vol% Normally, 5 vol%

36 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial-Venous Oxygen Content Difference (Cont’d) Increases:  Decreased cardiac output  Exercise  Seizures  Hyperthermia

37 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Arterial-Venous Oxygen Content Difference (Cont’d) Decreases:  Increased cardiac output  Skeletal relaxation  Peripheral shunting  Cyanide  Hypothermia

38 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Consumption VO 2 = Q T [C(a-v)O 2 ] × 10 Oxygen (VO 2 ) consumption is the amount of oxygen consumed by the peripheral tissue cells during a 1-minute period.

39 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Consumption VO 2 = Q T [C(a-v)O 2 ] × 10 (Cont’d) For example, if a patient has a cardiac output of 4 L/min and a C(a-v)O 2 of 6 vol%, the total amount of oxygen consumed by the tissue cells in 1 minute would be 240 mL—as calculated on the next slide:

40 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Consumption VO 2 = Q T [C(a-v)O 2 ] × 10 VO 2 = Q T [C(a-v)O 2 ] × 10 = 4 L/min × 6 vol% × 10 = 240 mL O 2 /min Normal is 250 mL O 2 /min

41 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Consumption (Cont’d) Increases:  Seizures  Exercise  Hyperthermia  Body size

42 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Consumption (Cont’d) Decreases:  Skeletal muscle relaxation  Peripheral shunting  Certain poisons (e.g., cyanide)  Hypothermia

43 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Extraction Ratio O 2 ER = CaO 2 − CvO 2 CaO 2 The O 2 ER is the amount of oxygen consumed by the tissue cells divided by the total amount of oxygen delivered.

44 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Extraction Ratio O 2 ER = CaO 2 − CvO 2 CaO 2 (Cont’d) For example, if a patient’s CaO 2 is 15 vol% and the CvO 2 is 10 vol%, the O 2 ER would be 33%— as calculated on the next slide:

45 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Extraction Ratio O 2 ER = CaO 2 − CvO 2 CaO 2 CaO 2 = 15 vol% − 10 vol% 15 vol% 15 vol% = 5 vol% 15 vol% 15 vol% = 0.33 Normal is 0.25%

46 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Extraction Ratio (Cont’d) Increases:  Decreased cardiac output  Periods of increased O 2 consumption  Exercise, seizures, hyperthermia  Anemia  Decreased arterial oxygenation  ↓ Hb, ↓ PaO 2

47 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Oxygen Extraction Ratio (Cont’d) Decreases:  Increased cardiac output  Skeletal muscle relaxation  Peripheral shunting  Certain poisons (e.g., cyanide)  Hypothermia  Increased arterial oxygenation  ↑ Hb, ↑ PaO 2

48 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Mixed Venous Oxygen Saturation SvO 2 Signals changes in the:  C(a-v)O 2  VO 2  O 2 ER Normally about 75% Normally about 75%

49 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Mixed Venous Oxygen Saturation SvO 2 (Cont’d) Decreases:  Decreased cardiac output  Exercise  Seizures  Hyperthermia

50 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Mixed Venous Oxygen Saturation SvO 2 (Cont’d) Increases:  Increased cardiac output  Skeletal muscle relaxation  Peripheral shunting  Certain poisons (e.g., cyanide)  Hypothermia

51 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Pulmonary Shunt Faction Q s = CcO 2 − CaO 2 Q T CcO 2 − CvO 2

52 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Ventilated Alveolus Ventilated Alveolus Pulmonary capillary Oxygenated blood Nonoxygenated blood Normal alveolar-capillary unit.

53 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Ventilated Alveolus Ventilated Alveolus Pulmonary capillary Oxygenated blood Nonoxygenated blood Anatomic shunt. Anatomic shunt

54 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Alveolus Pulmonary capillary Nonoxygenated blood Collapsed Alveolus or Consolidated or Fluid-Filled Alveolus Collapsed Alveolus or Consolidated or Fluid-Filled Alveolus Types of capillary shunts.

55 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Alveolus Pulmonary capillary Nonoxygenated blood Alveolus with Decreased Ventilation or Alveolus with a Diffusion Defect Alveolus with Decreased Ventilation or Alveolus with a Diffusion Defect Types of relative or shuntlike effects.

56 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Pulmonary Shunting Need following information:  Barometric pressure  PaO 2  PaCO 2  PvO 2  Hb concentration  PAO 2 (partial pressure of alveolar oxygen)  FIO 2

57 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim A 22-year-old man is on a volume-cycled mechanical ventilator on a day when the barometric pressure is 755 mm Hg. The patient is receiving an FIO 2 of The following clinical data are obtained:  Hb: 15 g/dL  PaO 2 : 65 mm Hg (SaO 2 = 90%)  PaCO 2 : 56 mm Hg  PvO 2 : 35 mm Hg (SvO 2 = 65%)

58 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) With this information the following can now be calculated:  PAO 2  CcO 2  CaO 2  CvO 2

59 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) PAO 2 = (P B − PH 2 O) FIO 2 − PaCO 2 (1.25) = (755 − 47) 0.60 − 56 (1.25) = (708) 0.60 − 70 = − 70 = 354.8

60 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) CcO 2 = (Hb × 1.34) + (PAO 2 × 0.003) = (15 × 1.34) + (354.8 × 0.003) = = (vol% O 2 )

61 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) CaO 2 = (Hb × 1.34 × SaO 2 ) + (PaO 2 × 0.003) = (15 × 1.34 × 0.90) + (65 × 0.003) = = (vol% O 2 )

62 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) CvO 2 = (Hb × 1.34 × SvO 2 ) + (PvO 2 × 0.003) CvO 2 = (Hb × 1.34 × SvO 2 ) + (PvO 2 × 0.003) = (15 × 1.34 × 0.65) + (35 × 0.003) = (15 × 1.34 × 0.65) + (35 × 0.003) = = = (vol% O 2 ) = (vol% O 2 )

63 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Case Example: Automobile Accident Victim (Cont’d) Q S = CcO 2 − CaO Q T CcO 2 − CvO 2 = − − = =0.36

64 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 5-2. Clinical Significance of Pulmonary Shunting

65 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 5-3. Oxygenation Index Changes Commonly Seen in Respiratory Diseases

66 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Hypoxemia  Hypoxemia refers to an abnormally low arterial oxygen tension (PaO 2 ) and is frequently associated with hypoxia.  Although hypoxemia may suggest tissue hypoxia, it does not necessary mean the absolute existence of tissue hypoxia.  For example, a low arterial oxygen level may be offset by an increased cardiac output.

67 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 5-4. Hypoxemia Classifications*

68 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Hypoxia  Hypoxia refers to low or inadequate oxygen for aerobic cellular metabolism.

69 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 5-5. Types of Hypoxia

70 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Cor Pulmonale  The term used to denote:  Pulmonary arterial hypertension  Right hypertrophy  Increased right ventricular work  Right ventricular failure

71 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Cor Pulmonale (Cont’d)  Three major causes:  Increased viscosity of blood (polycythemia)  Increased vascular resistance Caused by hypoxic vasoconstriction Caused by hypoxic vasoconstriction  Obliteration of the pulmonary capillary bed

72 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Polycythemia  Increased red blood cell level

73 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Hypoxic Vasoconstriction of the Lungs  Caused by decreased PAO 2  Generalized pulmonary vasoconstriction combined with polycythemia leads to:  Cor pulmonale  Distended neck veins  Peripheral edema and pitting edema

74 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Pitting edema. (From Bloom A, Ireland J: Color atlas of diabetes, ed 2, London, 1992, Mosby-Wolfe.)

75 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Distended Neck Veins Distended neck veins (arrows).