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Acute respiratory failure

Acute respiratory failure. Definitions. acute respiratory failure occurs when: pulmonary system is no longer able to meet the metabolic demands of the body hypoxaemic respiratory failure: PaO 2  60mmHg when breathing room air hypercapnic respiratory failure: PaCO 2  50mmHg kPa.

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Acute respiratory failure

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  1. Acute respiratory failure

  2. Definitions • acute respiratory failure occurs when: • pulmonary system is no longer able to meet the metabolic demands of the body • hypoxaemic respiratory failure: • PaO2 60mmHg when breathing room air • hypercapnic respiratory failure: • PaCO2  50mmHg kPa

  3. Basic respiratory physiology

  4. CO2 O2

  5. Oxygen in • Depends on • PAO2 • Diffusing capacity • Ventilation • Perfusion • Ventilation-perfusion matching

  6. Oxygen Carbon dioxide Water vapour Nitrogen

  7. Oxygen Carbon dioxide Water vapour Nitrogen

  8. Oxygen Carbon dioxide Water vapour Nitrogen

  9. Oxygen in • Depends on • PAO2 • FIO2 • Alveolar pressure • PACO2 • Ventilation • Ventilation-perfusion matching • Perfusion • Diffusing capacity

  10. Ventilation-perfusion matching

  11. V/Q relationships No. of lung units 1 Ventilation:perfusion ratio

  12. Carbon dioxide out • Largely dependent on alveolar ventilation • Anatomical dead space constant but physiological dead space depends on ventilation-perfusion matching

  13. Carbon dioxide out • Respiratory rate • Tidal volume • Ventilation-perfusion matching

  14. Pathophysiology

  15. Pathophysiology • Low inspired Po2 • Hypoventilation • Ventilation-perfusion mismatch • Shunting • Dead space ventilation • Diffusion abnormality

  16. 100% 75% PAO2=110mmHg PACO2=38mmHg

  17. Pathophysiology • Low inspired oxygen concentration • Hypoventilation • Shunting • Dead space ventilation • Diffusion abnormality

  18. PAO2=75 mm Hg PACO2=77 mm Hg PAO2=110 mm Hg PACO2=38 mm Hg

  19. Sites at which disease may cause hypoventilation

  20. Pathophysiology • Low inspired oxygen concentration • Hypoventilation • Shunting • Dead space ventilation • Diffusion abnormality

  21. Shunt

  22. 75% 75% 100% 75% 87.5%

  23. 75% 75% 100% 75% 90%

  24. Shunting • Intra-pulmonary • Pneumonia • Pulmonary oedema • Atelectasis • Collapse • Pulmonary haemorrhage or contusion • Intra-cardiac • Any cause of right to left shunt • eg Fallot’s, Eisenmenger, • Pulmonary hypertension with patent foramen ovale

  25. Pathophysiology • Low inspired oxygen concentration • Hypoventilation • Shunting • Dead space ventilation • Diffusion abnormality

  26. Dead space

  27. V/Q relationships No. of lung units Diseased Normal 1 Ventilation:perfusion ratio

  28. Pathophysiology • Low inspired oxygen concentration • Hypoventilation • Shunting • Dead space ventilation • Diffusion abnormality

  29. Respiratory monitoring

  30. Clinical • Respiratory compensation • Sympathetic stimulation • Tissue hypoxia • Haemoglobin desaturation

  31. Clinical • Respiratory compensation • Tachypnoea • Accessory muscles • Recesssion • Nasal flaring • Sympathetic stimulation • Tissue hypoxia • Haemoglobin desaturation

  32. Clinical • Respiratory compensation • Sympathetic stimulation • HR • BP (early) • sweating • Tissue hypoxia • Haemoglobin desaturation

  33. Clinical • Respiratory compensation • Sympathetic stimulation • Tissue hypoxia • Altered mental state • HR and BP (late) • Haemoglobin desaturation

  34. Clinical • Respiratory compensation • Sympathetic stimulation • Tissue hypoxia • Haemoglobin desaturation • cyanosis

  35. Pulse oximetry 90 Hb saturation (%) 60 PaO2 (mmHg)

  36. Oxygen delivery

  37. Sources of error • Poor peripheral perfusion • Poorly adherent/positioned probe • False nails or nail varnish • Lipaemia • Bright ambient light • Excessive motion • Carboxyhaemoglobin or methaemoglobin

  38. 123 8040 87% HR=95

  39. Summary • worry if • RR > 30/min (or < 8/min) • unable to speak 1/2 sentence without pausing • agitated, confused or comatose • cyanosed or SpO2 < 90% • deteriorating despite therapy • remember • normal SpO2 does not mean severe ventilatory problems are not present

  40. Treatment

  41. Treatment • Treat the cause • Supportive treatment • Oxygen therapy • CPAP • Mechanical ventilation

  42. Oxygen therapy • Progressive hypercarbia due to loss of hypoxic drive is RARE • Hypoxia KILLS • The appropriate response to progressive hypercarbia is assisted ventilation NOT removal of oxygen

  43. Oxygen therapy • Fixed performance devices • Variable performance devices

  44. Variable performance device 30 37% O2 Flow 6 l/min O2 6 0 Time

  45. Variable performance device 24 l/min air 30 37% O2 6 l/min O2 Flow 6 0 Time

  46. Fixed performance device 60% O2 30 l/min 60% O2 15 l/min air 100% O2 15 l/min

  47. Other devices • Bag valve resuscitator

  48. Other devices • Reservoir face mask

  49. CPAP • reduces shunt by recruiting partially collapsed alveoli

  50. Lung compliance and FRC • reduces work of breathing Volume Pressure

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