Pathophysiology and General Management of Failure of Arterial Oxygenation

1. Pathophysiology and General Managementof Failure of Arterial Oxygenation Dong Soo Kim, M.D. aruma@khu.ac.kr www.nopain365.com

2. Respiration ; exchange of oxygen and carbon dioxide between humans and the atmosphere • Human respiration ; - Ventilation - Arterial oxygenation - Oxygen transport - Oxygen extraction and utilization • Respiratory failure ; BGA abnormalities of high PaCO2 and low PaO2 or both

3. Standards for Basic Anesthetic Monitoring • Standard IQualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care.(Approved by the ASA House of Delegates on Oct. 15, 2003)

4. Standards for Basic Anesthetic Monitoring • Standard IIDuring all anesthetics, the patient’s oxygenation, ventilation, circulation, and temperature shall be continually evaluated.(Approved by the ASA House of Delegates on Oct. 15, 2003)

5. Relationship of PaO2 and SaO2

6. Definition of Hypoxemia • PaO2 = 105 – Age / 2 - PaO2 of 50 year-old man ; 80 mm Hg - PaO2 of 80 year-old man ; 65 mm Hg • Defining Hypoxemia - Harrison’s (1998) :PaO2< 80 mm Hg -Shapiro BA (1998): relative deficiency of oxygen tension in the arterial blood -Morgan GE(2006): PaO2< 60 mm Hg

7. Objective and Methods for Oxygenation Monitoring • Objective ;To ensure adequate O2 concentration in the inspired gas and the blood during all anesthetics • Methods ; - Inspired gas : During every administration of general anesthesia using an anesthesia machine, theconcentration of O2 in the breathing system shall be measured by an O2 analyzer with a low O2concentration limit alarm in use.(Approved by the ASA House of Delegates on Oct. 15, 2003)

8. Objective and Methods for Oxygenation Monitoring • Objective ;To ensure adequate O2 concentration in the inspired gas and the blood during all anesthetics • Methods ; - Blood oxygenation : During all anesthetics, a quantitative method of assessing oxygenation such as pulse oximetry shall be employed. Adequate illumination and exposure of the patient are necessary to assess color.(Approved by the ASA House of Delegates on Oct. 15, 2003)

9. Monitoring during Anesthesia • BP, heart rate • ECG • CVP • Pulse oximetry • Capnography • Urine output • Temperature • BIS (bispectral index) • Cardiac output • Cerebral metabolic rate of oxygen (CMRO2)

10. Tracheobronchial Tree

11. Subdivisions and Structure of Intrapulmonary Airways

12. Pathways of O2 and CO2 Diffusion

13. Ultrastructure of Pulmonary Alveoli and Capillaries

14. Transfer of O2 and CO2 Between Alveolar Air and Capillary Blood

15. Process of Oxygenation • External respiration • Blood oxygen transport • Internal respiration

16. Oxygen Transport Cascade

17. External Respiration • Transfer of oxygen molecules from atmosphere to blood • Alveolar oxygen tension (PAO2) is the major limiting factor in the oxygenation of desaturated blood • Major factors involved in determining the PAO2 - Fraction of inspired oxygen (FiO2) - Alveolar gas exchange - Mixed venous oxygen content - Distribution of ventilation

18. Oxygen Transport

19. Mixed Venous PO2 as an Indicator • The most reliable single physiologic indicator for monitoring the overall balance between oxygen supply and demand • PvO2 < 28 mm Hg ; - anaerobic metabolic state - blood lactate levels ↑ Hyperdynamic 45 Normal 35 Compromised PvO2 27 Metabolic disruption 20 Death

20. Critical level of PvO2 20 18 16 Blood lactate (mEq/L) 14 Survivors 12 Nonsurvivors 10 8 6 Upper limit of normal lactate conc. 4 2 0 20 22 24 26 28 30 32 34 36 38 40 PvO2(mm Hg) Relation between blood lactate and PvO2 JAMA 1976;236:570

21. Aerobic Glucose ↓ Pyruvate ↓ CO2 + H2O + ATP Anaerobic Glucose ↓ Pyruvate ↓ Lactate + ATP Cellular Metabolism

22. Pathophysiology of Impaired Tissue Oxygenation • Failure of arterial oxygenation • Failure of oxygen transport • Failure of tissue oxygen extraction

23. Oxyhemoglobin Dissociation Curve

24. Mechanisms of Hypoxemia • Low alveolar O2 tension • - Low inspired O2 tension • - Alveolar hypoventilation • - Third gas effect (diffusion hypoxia) • - Increased O2 consumption • Increased alveolar - arterial O2 gradient • - Shunting • - Ventilation / perfusion mismatch • - Low mixed venous O2 tension • - Decreased cardiac output • - Increased O2 consumption • - Decreased Hb concentration

25. Common Factors Causing Intraoperative and/or Postoperative Hypoxemia • Low inspired O2 concentration • Hypoventilation • Ventilation / perfusion mismatch • Increased intrapulmonary Rt to Lt shunt - Atelectasis ; main contributor • Pneumothorax • Pulmonary edema • Pulmonary embolism

26. Low Alveolar Oxygen Tension Diffusion Hypoxia

27. Theoretical Respiratory Unit

28. Theoretical Respiratory Unit

29. Subdivisions of Physiological Shunt

30. Normal Shunts

31. Increased A – a Oxygen Gradient Abnormal Shunts

32. Increased A – a Oxygen Gradient Endobronchial Intubation

33. Increased A – a Oxygen Gradient V/Q Mismatch Shunt ↓V/Q ratio(shunt effect)

34. Increased A – a Oxygen Gradient V/Q Mismatch ↑V/Q ratio Deadspace

35. Effect of Anesthesia on Gas Exchange • During anesthesia, - Deadspace (normal ventilation, no perfusion) ↑ - Alveolar ventilation ↓ (rate and/or tidal volume) - intrapulmonary shunting ↑ (5-10% ↑, as a result of atelectasis, airway obstruction) • Prolonged administration of high concentration of O2(> 50%) may be associated with increases in absolute shunt(absorption atelectasis) • Inhalation anestheticsinhibithypoxic pulmonary vasoconstriction(ED50 ; 2 MAC)

36. Mucociliary Blanket • Normal defense mechanism of the pulmonary tree • Submucosal gland ; mucus produce (100 mL/d) • Mucus ; water (95%), glycoprotein (2%), carbohydrate (1%) • Mucus blanket moves mucus and foreign bodies toward the larynx (2 cm/min) • Inhalation anesthetics, smoke ; ciliary movement ↓

37. Potential Results of Retained Secretions Inflammation and partial plugging Airflow resistance ↑ Work of breathing ↑ Uneven distribution of ventilation Shunt effect Hypoxemia Total plugging Absorption atelectasis Lung compliance ↓ Stasis pneumonia Fever

38. Various Factors as Causes of Clinically Detectable Atelectasis following Major Surgery Bendixen HH. Respiratory care. 1974

39. Consequences of Hypoxemia • CNS ; cerebral vasodilation, confusion, convulsion, unconsciousness, coma • CV ; myocardial depression, coronary vasodilation, bradycardia, dysrhythmia, heart failure, shock • Resp ; hypoxic pulmonary vasoconstriction • Renal ; dec RBF and tubular function

40. Events Associated with Decreased PaO2 Snyder JV. Oxygen transport in the critical ill. 1995

41. Classification of Hypoxia

42. “삼순이 없는 세상 살아서 뭐하나……”

43. “누굴 놀리나……”

44. General Management of Hypoxemia • Directed at the cause • O2 therapy • Reserve normal CV function • PEEP • Chest physical therapy

45. Effect of O2 Therapy on Variable Types of Hypoxemia

46. Effect of Hypoventilation on Oxygen Therapy Braun HA. Introduction to Respiratory Physiology. 1990

47. Effect of Ventilation / Perfusion Mismatching on Oxygen Therapy Braun HA. Introduction to Respiratory Physiology. 1990

48. Effect of Shunt on Oxygen Therapy Braun HA. Introduction to Respiratory Physiology. 1990

49. Effect of Varying Amounts of Shunt on Arterial Oxygen Tension Br J Anaesth 1973;45:711

50. Hypoxemia and Oxygen Therapy • Refractory hypoxemia; Secondary to true shunt mechanism • Responsive hypoxemia ; Secondary to shunt effect