1. ACUTE RESPIRATORY FAILURE
Ihab B Abdalrahman, MBBS, MD, ABIM, SSBB
Ihab Tarawa
Consultant of Acute Care Medicine, Soba University Hospital
10/2/2012 1

2. BASIC RESPIRATORY
PHYSIOLOGY
Ihab Tarawa 10/2/2012 2

3. Respiratory system made
ridiculously easy
 It is as simple as moving the air in and out.
 Allowing gas exchange.
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4. CO2 O2
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5. 1,2,3
 Bottom line of the respiratory system is to
 Let oxygen in,
 And carbon dioxide out.
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6. Definitions
 acute respiratory failure occurs when:
 pulmonary system is no longer able to meet the
metabolic demands of the body
 hypoxaemic respiratory failure:
 PaO2  8 kPa when breathing room air
 hypercapnic respiratory failure:
 PaCO2  6.7 kPa
Ihab Tarawa 10/2/2012 6

7. Oxygen in
Depends on
 Ventilation
 PAO2
 Perfusion
 Ventilation-perfusion matching
 Diffusing capacity
Ihab Tarawa 10/2/2012 7

8. PAO2
 The alveolar pressure is equal to the sum of
the partial pressures of the gases within the
alveolus.
 The partial pressure of each gas is
proportional to the concentration of the gas.
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9. Oxygen
Carbon
dioxide
Water
vapour
Nitrogen
Alveolarpressure PAO2  PACO2  PAH2O  PAN2
Ihab Tarawa 10/2/2012 9

10. Oxygen
Carbon
dioxide
Water
vapour
Nitrogen
Alveolarpressure PAO2  PACO2  PAH2O  PAN2
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11. Oxygen
Carbon
dioxide
Water
vapour
Nitrogen
Alveolarpressure PAO2  PACO2  PAH2O  PAN2
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12. Oxygen in
 Depends on
 PAO2
 FIO2
 Alveolar pressure
 PACO2
 Ventilation
 Ventilation-perfusion matching
 Perfusion
 Diffusing capacity
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13. Ventilation-perfusion
matching
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14. Carbon dioxide out
 Largely dependent on alveolar ventilation
Alveolar ventilation  RR x (V - V ) T D
 Anatomical dead space constant but
physiological dead space depends on ventilation-
perfusion matching
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15. Carbon dioxide out
 Respiratory rate
 Tidal volume
 Ventilation-perfusion matching
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16. PATHOPHYSIOLOGY
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17. Normal
ventilation &
perfusion
PAO2=14.74 kPa
PACO2=5 kPa
75% 100%
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18. Pathophysiology
 Low inspired Po2
 Although, in theory, acute respiratory failure may
result from a low inspired PO2 this is rarely a
problem in Intensive Care except in locations at
high altitude.
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19. Pathophysiology
 Low inspired oxygen concentration
 Hypoventilation
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20. Oxygen
Carbon
dioxide
Water
vapour
Nitrogen
Alveolarpressure PAO2  PACO2  PAH2O  PAN2
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21. Hypoventilation
PAO2=9.74 kPa
PACO2=10 kPa
75%
92%
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22. Brainstem
Spinal cord
Airway Nerve root
Lung Nerve
Pleura
Neuromuscular
Chest wall junction
Respiratory
muscle
Sites at which disease may cause hypoventilation
Ihab Tarawa 10/2/2012 22

23. Brainstem
Spinal cord
Airway Nerve root
Lung Nerve
Pleura
Neuromuscular
Chest wall junction
Respiratory
muscle
Sites at which disease may cause hypoventilation
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24. Pathophysiology
 Low inspired oxygen concentration
 Hypoventilation
 Shunting
 Dead space ventilation
 Diffusion abnormality
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25. Shunt
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26. oxygen therapy
has relatively
little effect on
hypoxia due to
shunting.
75% 75%
100% 75%
87.5%
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27. hypoxic vasoconstriction
↓perfusion to non-ventilated alveoli
↑perfusion to ventilated alveoli,
↓ magnitude of the shunt
↑and increasing the arterial saturation
75% 75%
100% 75%
90%
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28. 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
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29. Pathophysiology
 Low inspired oxygen concentration
 Hypoventilation
 Shunting
 Dead space ventilation
 Diffusion abnormality
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30. Dead space
ventilated but not
perfused
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31. Pathophysiology
 Low inspired oxygen concentration
 Hypoventilation
 Shunting
 Dead space ventilation
 Diffusion abnormality
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32. Ihab Tarawa 10/2/2012 32

33. Diffusion abnormalities.
 These can result from a failure of diffusion
across the alveolar membrane
 or a reduction in the number of alveoli
resulting in a reduction in the alveolar surface
area.
 Causes include ARDS and fibrotic lung
disease
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34. RESPIRATORY MONITORING
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35. Clinical
 Respiratory compensation
 Sympathetic stimulation
 Tissue hypoxia
 Haemoglobin desaturation
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36.  Bottom line of the respiratory system is to let
oxygen in and CO2 out.
 Some sensors will go off
 Hypoxia
 Acidosis
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37. Ihab Tarawa 10/2/2012 37

38. Clinical
 Respiratory compensation
 Tachypnoea
 Accessory muscles
 Recession
 Nasal flaring
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39. Clinical
 Sympathetic stimulation
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40. Clinical
 Sympathetic stimulation
 HR
 BP (early)
 sweating
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41. Point of making a difference
 Coming for help
 Or coming with a coffin
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42. Clinical
 Tissue hypoxia
 Altered mental state
 HR and BP (late)
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43. Clinical
 Haemoglobin
desaturation
 cyanosis
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44. If we wait for the
patient to become
cyanosed
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45. Pulse oximetry, notice the
sigmoid curve
90
Hb saturation (%)
8
PaO2 (kPa) Ihab Tarawa 10/2/2012 45

46.  The oxygen content of blood is mainly
dependent on:
 the haemoglobin saturation,
 with the a very small contribution from dissolved
oxygen.
Ihab Tarawa 10/2/2012 46

47. Oxygen delivery
O2 delivery  Cardiac output  O2 content  10
O2 content  O2 saturation Hb  1.37  0.003  PaO2
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48. Monitoring
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49. 123
80
40
87%
HR=95
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50. Sources of error
 Poor peripheral perfusion
 Poorly adherent/positioned probe
 False nails or nail varnish
 Lipaemia
 Bright ambient light
 Excessive motion
 Carboxyhaemoglobin or methaemoglobin
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51. Thing to remember
Saturation is not a
measure of
ventilation
Ihab Tarawa 10/2/2012 51

52. 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
Ihab Tarawa 10/2/2012 52

53. TREATMENT
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54. Treatment
 Treat the cause
 Supportive treatment
 Oxygen therapy
 CPAP
 Mechanical ventilation
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55. Oxygen therapy
 Fixed performance
devices
 Variable performance
devices
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56.  Nasal canula
 Simpler mask
 Other
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57. Other devices
 Reservoir face mask
 Bag valve resuscitator
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58. CPAP
 reduces shunt by recruiting partially collapsed
alveoli
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59. Ihab Tarawa 10/2/2012 59

60. Lung compliance and FRC
 reduces work of breathing
Volume
Pressure Ihab Tarawa 10/2/2012 60

61. Mechanical ventilation
 Decision to ventilate
 Complex
 Multifactorial
 No simple rules
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62. Ventilate?
 Severity of respiratory failure
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63. Ventilate?
 Severity of respiratory failure
 Cardiopulmonary reserve
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64. Ventilate?
 Severity of respiratory failure
 Cardiopulmonary reserve
 Adequacy of compensation
 Ventilatory requirement
Ihab Tarawa 10/2/2012 64

65. Ventilate?
 Severity of respiratory failure
 Cardiopulmonary reserve
 Adequacy of compensation
 Ventilatory requirement
 Expected speed of response
 Underlying disease
 Treatment already given
Ihab Tarawa 10/2/2012 65

66. Ventilate?
 Severity of respiratory failure
 Cardiopulmonary reserve
 Adequacy of compensation
 Ventilatory requirement
 Expected speed of response
 Underlying disease
 Treatment already given
 Risks of mechanical ventilation
Ihab Tarawa 10/2/2012 66

67. Ventilate?
 Severity of respiratory failure
 Cardiopulmonary reserve
 Adequacy of compensation
 Ventilatory requirement
 Expected speed of response
 Underlying disease
 Treatment already given
 Risks of mechanical ventilation
 Non-respiratory indication for intubation
Ihab Tarawa 10/2/2012 67

68. Ventilate?
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 68

69. Yes
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 69

70. Yes
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask O2
O2
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 70

71. Yes
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 71

72. Yes
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 72

73. Yes
 43 year old male
 Community acquired pneumonia
 Day 1 of antibiotics
 PaO2 8 kPa (60 mmHg), PaCO2 4 kPa (30
mmHg), pH 7.15 on 15 l/min O2 via reservoir
facemask
 Respiratory rate 35/min
 Agitated
Ihab Tarawa 10/2/2012 73

74. Ventilate?
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 74

75. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 75

76. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 76

77. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 77

78. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 78

79. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 79

80. No
 24 year old woman
 Presents to A&E with acute asthma
 SOB for 2 days
 Salbutamol inhaler, no steroids
 PFR 60 L/min, HR 105/min
 pH 7.25 PaCO2 6.8 kPa (51 mmHg), PaO2 42 kPa
(315 mmHg) on FiO2 0.6
 RR 35/min
 Alert
Ihab Tarawa 10/2/2012 80

81. Pathway
 Airway patent
 Secure airway
 Patient breathing
 Ventilat
 Is he hypoxic
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82. Hypoxic
Yes No
Acidosis
Shock
PE
Asthma
Pumonary
edema
Anxiety
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83. Hypoxic
Pco2
Low Pco2
High /normal
pneumonia
ARDS
Pulmonary
edema
Aspiration
PE
pneumothorax
Ihab Tarawa 10/2/2012 83

84. Hypoxic
Pco2
Low Pco2
High /normal
Normal A-a High A-a
gradient gradient
Breathing Breathing Fatigue from
hard normally hypoxia
Acute on
Asthma CND
chronic
COPD Drugs
PE
Ihab Tarawa 10/2/2012 84

85. Ihab Tarawa 10/2/2012 85

86. QUESTIONS?
Ihab Tarawa 10/2/2012 86