1. Physiology of respiratory failure:
S.Mahadevan,MD,
V.R.Pattabhiraman,MD,DNB,FCCP
Arjun Srinivasan,MD,DM
Pulmonology Associates
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2. Hypoxia Hypoxaemia Low oxygen in the blood. Low oxygen in the tissues.
Sepsis
Hypotension
Low cardiac output state
Poisoning, cellular toxins
Low hemoglobin
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3. Ventilation Perfusion The blood that are in the pulmonary arteries.
The air that you breathe that takes part in respiration.
Minute Ventilation=Tidal volumeX Respiratory rate.
Perfusion
The blood that are in the pulmonary arteries.
Alveolar
Respiratory
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4. Dead space Anatomical dead space Physiological
The air in the conducting space of the airways like the nasal cavity , trachea , main bronchus , bronchioles, alveolar ducts.
Physiological
The air in the air sacs that do not take part in gas exchange.
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6. Muscles of respiration:
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7. Diaphragmatic response to respiratory failure:
Maximal blood flow due to greater capillary density.
Oxygen uptake is greater.
Increased mitochondrial density.
Oxidative fibers are more (80% vs 40%).
Fast twitch muscle fibers are designed to contract at low stimulus.
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9. Respiratory physiology:
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10. Alveolar gas exchange.
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11. 9PM,breathless,severe pain,Sao2 89%,RR 24,HR 100
Clinical scenario:
40 year old male , BMI 33,underwent emergency upper abdominal surgery under GA , shifted.
9PM,breathless,severe pain,Sao2 89%,RR 24,HR 100
Tried NIV and oxygen , Saturation dropped to 85% and hence he was put on 10 liters O2 and for pain morphine was given.
Oxygen monitored ,> 97%
At about 4AM he was unresponsive ,with shallow breathing ????
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12. Carbon dioxide elimination
Respiratory Failure
Clinical syndrome
Failure of the lung to fulfill it’s function
Oxygenation
Carbon dioxide elimination
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13. Classification of Respiratory Failure
Fig. 68-2
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14. Hypoxemia : Physiological causes
High Altitude
Diffusion
Hypoventilation
Ventilation : Perfusion mismatch
Shunting
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15. Altitude and pAo2 relationship:
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16. Hypoxemia due to high altitude
As you go up in altitude the oxygen content in the blood is lesser.
Total barometric pressure (air pressure ) at sea level is 760 mm Hg
Oxygen is 21%
(760mmHg-47mmHg) x .21=150 mmHg pA O2
At 19,000 feet,
(380mmHg-47mm Hg)x.21=70 mmHg
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17. Hypoxemia due to high altitude
Low Total Barometric pressure.
100% oxygen Pa02 responds.
Normal A-a gradient.
Body responds with hyperventilation.
paCo2 goes down.
Can affect normal individuals.
Acclimatization by climbing slowly can reduce the incidence of pulmonary edema.
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18. Diffusion Limitation
Fig. 68-5
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19. Diffusion abnormality and hypoxemia.
Pulmonary fibrosis.
Hypoxemia during exercise.
Red cells doesn't have enough contact time for oxygenation.
Increased A-a gradient.
Hypoxemia responds to 100% oxygen.
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20. Hypoventilation and hypoxemia.
Respiratory rate and tidal volume are lesser.
Increased pCO2.
Seen in narcotics, obesity, brainstem stroke.
Normal A-a gradient.
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22. Regional difference in perfusion
V/Q
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23. Hypoxemic pulmonary vasoconstriction:
Blood chasing oxygen.
Alveoli sends neural impulse to produce vasoconstriction of the adjacent arterioles.
This ensures optimization of V/Q ratio on other units.
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24. V:Q mismatch and hypoxemia
Pulmonary artery pressures are low and hence gravity accounts for distribution of blood in lungs.
Top part of the lung has high V/Q ratio due to lower perfusion and higher ventilation.
Zero ventilation is shunt and zero perfusion is dead space.
Certain areas of lung have high V/Q ratio and certain areas of lung have low V/Q ratio and is known as V/Q mismatch.
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25. Ventilation without perfusion
FIO2
Ventilation without perfusion
(deadspace ventilation)
Hypoventilation
Diffusion abnormality
The opposite extreme of ventilation-perfusion mismatch is deadspace ventilation
Normal
Perfusion without ventilation (shunting)
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26. V/Q is the most common cause for hypoxemia.
Pneumonia, COPD , Bronchial Asthma, Pulmonary embolism , COPD ,pulmonary fibrosis , PHT .
It responds to 100 % oxygen
Increased A-a gradient
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27. Shunting and hypoxemia:
Shunt refers to perfusion without ventilation.
Intrapulmonary shunt refers to areas in the lung where perfusion exceeds ventilation.
Pulmonary shunting is minimized by the normal reflex pulmonary vasoconstriction to hypoxia.
Because shunt represents areas where gas exchange does not occur, 100% inspired oxygen is unable to overcome the hypoxia caused by shunting
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28. Shunting: FIO2 Ventilation without perfusion (deadspace ventilation)
Hypoventilation
Diffusion abnormality
Shunting is the most common cause for hypoxaemic respiratory failure in ICU patients.
It is a form of ventilation-perfusion mismatch in which alveoli which are not ventilated (eg due to collapse or pus or oedema fluid) are still perfused.
Normal
Perfusion without ventilation (shunting)
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29. Respiratory failure due to shunting is relatively resistant to oxygen therapy. Increasing the inspired oxygen concentration has little effect because it can not reach alveoli where shunting is occurring and blood leaving normal alveoli is already 100% saturated
75%
75%
100%
75%
87.5%
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30. Dead space ventilation and hypoxemia:
FIO2
Ventilation without perfusion
(deadspace ventilation)
Hypoventilation
Diffusion abnormality
The opposite extreme of ventilation-perfusion mismatch is deadspace ventilation
Normal
Perfusion without ventilation (shunting)
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31. Alveolar-capillary interface destroyed e.g emphysema
Blood flow is reduced e.g CHF, PE
Overdistended alveoli e.g positive- pressure ventilation
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32. Clinical signs: Hypoxemia. Hypercapnea. Breathlessness.
Tachypnea and RR > 30.
Tachycardia and PR > 110.
Anxious,Restless.
Cyanosed.
Sweating.
Accessory muscles of breathing.
Silent Chest.
Confusion.
Unresponsiveness.
Shallow breathing.
Agitation.
Hypotension.
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33. Basic assessment of a breathless patient:
Quick record of vitals including pulse,BP,RR,Temperature,Oxygen saturation.
Look out for possible drug overdose.
Quick enquiry of prior admission.
Clinical assessment.
Arterial blood gas analysis.
Oxygen supplementation if hypoxemic and IV access.
ECG.
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34. 9PM,breathless,severe pain,Sao2 89%,RR 24,HR 100
Clinical scenario:
40 year old male , BMI 33,underwent emergency upper abdominal surgery under GA , shifted.
9PM,breathless,severe pain,Sao2 89%,RR 24,HR 100
Tried NIV and oxygen , Saturation dropped to 85% and hence he was put on 10 liters O2 and for pain morphine was given.
Oxygen monitored ,> 97%
At about 4AM he was unresponsive ,with shallow breathing ????
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35. Thank you:
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