Chapter 5 Oxygenation Assessments Mosby items and derived

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

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

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

Note: The P(A-a)O 2 Loses sensitivity in patients breathing high FIO 2 Mosby items

Oxygen Saturation– and Content –Based Indices Mosby items and derived items © 2011, 2006

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

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

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

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.

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

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 ©

Table 5 -3. Oxygenation Index Changes Commonly Seen in Respiratory Diseases Mosby items and

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

Hypoxia refers to low or inadequate oxygen for aerobic cellular metabolism. Mosby items and

Table 5 -5. Types of Hypoxia Mosby items and derived items © 2011, 2006

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

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