Respiratory failure

1. Chaper 13 Respiratory failure Zhao Mingyao BMC.ZZU

2. Respiration = ventilation + gas exchange Ventilation: alveoli enlarging to set up P gradient airway fluency to let gas flow gas exchange: area distance efficiency (V/Q) ------ physiology view

4. 1.Concept of Repiratory Failure Respiratory system fails to adequately oxygenate the blood with/without retention of CO2, it is generally defined as a PaO2 < 60mmHg, with /without PaCO2 >50mmHg

5. Acute : minutes to days Chronic: over months to years Central : head injury, encephalitis Peripheral: asthma, pneumonia, emphysema 2.Classification of ~ According to (1)duration (2)primary site

6. (3)blood-gas Type I : PaO2  Type II: PaO2 + PaCO2 (4)pathogenesis ventilation blood gas exchange: diffusion V/Q anatomy shunt

7. Section 1 Etiology and pathogenesis Respiration = ventilation + gas exchange

8. Mechanism of RF 1. Hypoventilation Extralung intralung (1)restrictive ~ (2)obstructive ~ Central airway ~ Peripheral airway ~

9. Ventilation (does work) = dynamic force overcomes resistant force (elastic ~ + nonelastic ~) ----physics view

10. (1) Restrictive ~ Major Causes: CNS and nerves Respiratory muscles, chest wall and pleura Lung( Alveoli) distension  Alveoli distensibility 

11. 1)Extrapulmonary disease ①CNS: ②Respiratory muscles: ③Chest wall and pleura:

12. 2)Intrinsic disease ①Pulmonary elastic structure  ②Alveolar surfactant substance

13. Function of surfactant substances 1. Reduces surface tension 2. Increases compliance, stabilize alveoli Keep alveoli dry; Prevent pulmonary edema

14. 3)Blood gas change PACO2PAO2=PiO2  ———— R • PAO2 P O2 in alveoli • PiO2： PO2 in inhaling air • PACO2：PCO2 in alveoli • R：respiratory quotient

15. PCO2 in alveoli 0.863Vco2 PaCO2= PACO2 = —————— VA PACO2： PCO2 in alveoli Vco2：CO2 production/min VA：alveolar ventilation volume

16. Blood gas change PACO2 PAO2= PiO2  —————— R • 0.863Vco2 • PaCO2= PACO2 = ——————VA

17. Blood-Gas changes Ventilatory disorder Restrictive obstructive Alveolar ventilatory volume  PaO2 and PaCO2 proportionately PaO2 + PaCO2

18. (2) Obstructive ventilatory disorders Tracheobronchial tree narrowing

19. 1)Central airway obstruction Airway above or below carina Variable narrowing Fixed narrowing

20. Variable expiration inspiration outside thorax---inspiratory dyspnea

21. Retractions ( supraclavicular, intercostal and subcostal areas) on inspiration

22. Variable inspiration expiration inside thorax---expiratory dyspnea

23. 2)Peripheral airway obstruction

24. Peripheral airway (Φ <2mm ) 1. thinner wall, without cartilage support 2. caliber changes with respiration 3. close junction with adjacent tissues

25. Peripheral airway obstruction 1.mucosa edema 2.fibrosis 3.inflammatory infiltration 4.secretions in lumen thickness diameter

26. 0 0 Isobaric point 10 20 25 10 15 20 20 20 20 20 30 20 35 +35 20 20 +35 25 20 Normal expire Emphysema expire Isobaric point upshift in Emphysema

27. Mechanism of RF due to COPD ?

28. CNS, NS Ventilation disorders Respiratory muscle Extrapulmonary Chest wall, pleura Restrictive Elastic structure intrapulmonary Surfactant substances  outside inspiratory variable Central expiratory inside Obstructive fixed  both Peripheral isobaric point upshift caliber decrease expiratory

29. 3)Blood gas change PO2 ? PCO2 ?

30. 2. Diffusion disorder a disruption in the exchange of O2 or CO2 or both across the alveolar-capillary membrane

31. Total diffusion AREA is large 50~100 m2 Diffusion PATH is very small, <1 µm

32. 1) Diffusion area  Alveolar area : 80m2 at rest: 40 m2 Causes of decreased area: Emphysema Pulmonary tumor Pulmonary lobectomy

33. 2) Diffusion distance Pulmonary edema, congestion Pulmonary fibrosis Alveolar epithelium hyperplasia Alveolar-capillary membrane thickness

34. 3) Diffusion time↑ alveolar normal Thick alveolar membrane Pul vein Pul Artery

35. 3) Blood gas change distance PaO2 area  Blood stream time  solubility PaCO2 Normal or or  diffusion ability Diffusion disorder

36. 3. Mismatching Ventilation/perfusion

37. 1)V/Q Causes: Bronchial asthma, chronic bronchitis, obstructive pulmonary emphysema, pulmonary fibrosis Mechanism: venous admixture alveolar ventilation  V/Q<0.8 Perfusion normal (functional shunt)

38. 2)V/Q Causes: Pulmonary arteriosclerosis, pulmonary thrombosis bronchiectasis, pulmonary tuberculosis Mechanism: alveolar ventilation normal deadspace-like ventilation V/Q>0.8 perfusion 

39. Gas exchange disorder diffusion area ↓ diffusion distant ↑ efficiency (V/Q) V/Q ↓ －functional shunt V/Q ↑ －dead space-like ventilation

40. 3)Blood gas change V/Q(-) V/Q: ventilation  V/Q: perfusion  V/Q V/Q  PaO2 , PaCO2 N or  or 

41. 4.Anatomic shunt (Right-to-left shunt) Causes: atelectasis, pulmonary consolidation, bronchiectasis, A-V shunt open Mechanism: Admixture with unoxygenated blood

42. 3)Blood gas change PO2 ? PCO2 ?

43. summary restrictive inadequate alveolar ventilation ventilatory (PaO2↓ PaCO2↑) obstructive Respiratory failure diffusion disorder Gas exchange （PaO2↓ PaCO2↑↓N） Ventilation-perfusion dismatching Anatomic shunt（V/Q=0）

44. Mechanism of ARDS ? ?

45. Mechanism of ARDS Pathogenic factors Inflammatory cells and platelet activated Release proteinase, inflammatory mediators Microthrombosis Alveolar-capillary membrane damaged Permeability  (continue)

46. pulmonary edema diffusion disorder hypoxemia atelectasis functional shunt bronchus spasm dead space-like ventilation vascular constriction microthrombosis

47. Section 2 Alterations of function and metabolism in ~

48. decompensation compensation Respiratory failure Acid-base, electrolytes disorder abnormal blood-gas reaction of systems

49. 1. Acid-base and electrolytes disturbance Respiratory acidosis type II ~ retention of CO2 K+ Metabolic acidosis---hypoxia anaerobic glycolysis  lactic acid  K+

50. Respiratory alkalosis type I RF with hyperventilation K+ Mixed acidosis Res acidosis & met acidosis type II RF---hypoxia and hypercapnia K+ Res acidosis & met alkalosis Remove CO2 too fast hypokalemia