Chapter 5 Oxygenation Assessments Mosby items and derived

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

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) Ø Most oxygen is carried to the tissue cell bound to the hemoglobin. Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 2

Oxygen Dissolved in the Blood Plasma At normal body temperature, about 0. 003 m. L of oxygen (O 2) will dissolve in each 100 m. L of blood for every 1 mm Hg of PO 2. Thus when the Pa. O 2 is 100 mm Hg, about 0. 3 m. L of dissolved O 2 exists in every 100 m. L of plasma: 0. 003 × 100 mm Hg = 0. 3 m. L Clinically, written as 0. 3 volume percent (vol%) Ø 0. 3 vol% O 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 3

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

Oxygen Bound to Hemoglobin (Cont’d) Each g% Hb can carry 1. 34 m. L of O 2 Thus if the Hb level is 12 g% and if the Hb is fully saturated, about 15. 72 vol% of O 2 will be bound to the Hb: O 2 bound to Hb = 1. 34 m. L O 2 × 12 g% Hb = 15. 72 vol% O 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 5

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

Oxygen Bound to Hemoglobin (Cont’d) Thus the amount of arterial oxygen in the calculation must be adjusted to 97%: 15. 72 vol% O 2 ×. 97 15. 24 vol% O 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 7

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

Case Example 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 Pa. O 2 is 55 mm Hg (Sa. O 2 85%). Based on these data, the patient’s total oxygen content is determined on the next slide: Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 9

1. Dissolved O 2 55 Pa. O 2 × 0. 003 (dissolved O 2 factor) 0. 165 vol% O 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 10

2. Oxygen Bound to Hemoglobin 10 g% Hb × 1. 34 (O 2 bound to Hb factor) 13. 4 vol% O 2 (at Sa. O 2 of 100%) Above answer is then followed by the Sa. O 2 factor: 13. 4 vol% O 2 × . 85 Sa. O 2 11. 39 vol% O 2 (at Sa. O 2 of 85%) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 11

3. Total Oxygen Content. 11. 39 vol% O 2 (bound to hemoglobin) + 0. 165 vol% O 2 (dissolved O 2) 11. 555 vol% O 2 (total amount of O 2/100 m. L of blood) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 12

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

Total Oxygen Content (Cont’d) Ca. O 2 = Oxygen content of arterial blood (Hb × 1. 34 × Sa. O 2) + (Pa. O 2 × 0. 003) Cv. O 2 = Oxygen content of mixed venous blood (Hb × 1. 34 × Sv. O 2) + (Pv. O 2 × 0. 003) Cc. O 2 = Oxygen content of pulmonary capillary blood (Hb × 1. 34) + (PAO 2 × 0. 003) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 14

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

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

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

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. Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 18

Alveolar-Arterial Oxygen Tension Difference (P[A-a]O 2) (Cont’d) PAO 2 = FIO 2 (PB − PH 2 O) − Pa. CO 2 (1. 25) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 19

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 Pa. CO 2 is 70 mm Hg and Pa. O 2 is 60 mm Hg, the P(A-a)O 2 can be calculated as shown on the next slide: Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 20

Case Study Example (Cont’d) PAO 2 = FIO 2 (PB − PH 2 O) − Pa. CO 2 (1. 25) = 0. 30 (750 − 47) − 70 (1. 25) = (703) 0. 30 − 87. 5 = (210. 9) − 87. 5 = 123. 4 mm Hg Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 21

Case Study Example (Cont’d) Using the Pa. O 2 obtained from the ABG: 123. 4 (PAO 2) − 60. 0 (Pa. 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. Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 22

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

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

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

Oxygen Saturation– and Content–Based Indices Ca. O 2 = (Hb × 1. 34 × Sa. O 2) + (Pa. O 2 × 0. 003) Cv. O 2 = (Hb × 1. 34 × Sv. O 2) + (Pv. O 2 × 0. 003) Cc. O 2 = (Hb × 1. 34) + (PAO 2 × 0. 003) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 26

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 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 27

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

Total Oxygen Delivery DO 2 = QT × (Ca. O 2 × 10) (Cont’d) For example, if a patient has a cardiac output of 4 L/min and a Ca. O 2 of 15 vol%, the DO 2 is 600 m. L of oxygen per minute—as calculated on the next slide: Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 29

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

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

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

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

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

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

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

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

Oxygen Consumption VO 2 = QT [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. Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 38

Oxygen Consumption VO 2 = QT [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 m. L—as calculated on the next slide: Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 39

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

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

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

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

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

Oxygen Extraction Ratio O 2 ER = Ca. O 2 − Cv. O 2 Ca. O 2 = 15 vol% − 10 vol% 15 vol% = 5 vol% 15 vol% = 0. 33 Normal is 0. 25% Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 45

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

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

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

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

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

Pulmonary Shunt Faction Qs = Cc. O 2 − Ca. O 2 QT Cc. O 2 − Cv. O 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 51

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

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

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

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

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

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 0. 60. The following clinical data are obtained: Hb: 15 g/d. L Pa. O 2: 65 mm Hg (Sa. O 2 = 90%) Pa. CO 2: 56 mm Hg Pv. O 2: 35 mm Hg (Sv. O 2 = 65%) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 57

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

Case Example: Automobile Accident Victim (Cont’d) PAO 2 = (PB − PH 2 O) FIO 2 − Pa. CO 2 (1. 25) = (755 − 47) 0. 60 − 56 (1. 25) = (708) 0. 60 − 70 = 424. 8 − 70 = 354. 8 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 59

Case Example: Automobile Accident Victim (Cont’d) Cc. O 2 = (Hb × 1. 34) + (PAO 2 × 0. 003) = (15 × 1. 34) + (354. 8 × 0. 003) = 20. 1 + 1. 064 = 21. 164 (vol% O 2) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 60

Case Example: Automobile Accident Victim (Cont’d) Ca. O 2 = (Hb × 1. 34 × Sa. O 2) + (Pa. O 2 × 0. 003) = (15 × 1. 34 × 0. 90) + (65 × 0. 003) = 18. 09 + 0. 195 = 18. 285 (vol% O 2) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 61

Case Example: Automobile Accident Victim (Cont’d) Cv. O 2 = (Hb × 1. 34 × Sv. O 2) + (Pv. O 2 × 0. 003) = (15 × 1. 34 × 0. 65) + (35 × 0. 003) = 13. 065 + 0. 105 = 13. 17 (vol% O 2) Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 62

Case Example: Automobile Accident Victim (Cont’d) QS = Cc. O 2 − Ca. O QT Cc. O 2 − Cv. O 2 = 21. 164 − 18. 285 21. 164 − 13. 17 = 2. 879 7. 994 = 0. 36 Mosby items and derived items © 2011, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 63

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

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

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

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

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

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

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

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

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

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

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

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