1. Catherine Jones Practice Educator
Respiratory Failure

2. Have you ever looked after a patient with Respiratory Failure?
Most will – very familiar condition on the wards & most days on ICU – pneumonia, post op chest sepsis, pulm oedema, neoro conditions – reduced drive, asthma …

3. Learning Outcomes Causes of Respiratory Failure
Define the term respiratory failure
Type 1 Respiratory failure
Type 2 Respiratory Failure
Adult Respiratory Distress Syndrome

4. CO2 O2 Major function of airways is to WARM, FILTER & HUMIDIFY AIR
The major function of the lung is to get oxygen into the body and carbon dioxide out. Respiratory Failure occurs when Pulmonary system is unable to achieve this to meet metabolic needs of body.
O2 in – depends on partial pressure of oxygen, diffusing capacity, perfusion & V/Q
CO2 out depends on alveolar ventilation (RR & VT) & deadspace (Anatomical & physiological)

5. RESPIRATORY FAILURE OCCURS WHEN THE RESPIRATORY SYSTEM IS UNABLE TO MAINTAIN GAS EXCHANGE TO MEET METABOLIC DEMANDS OF BODY
CO2 O2
Major function of airways is to WARM, FILTER & HUMIDIFY AIR
The major function of the lung is to get oxygen into the body and carbon dioxide out. Respiratory Failure occurs when Pulmonary system is unable to achieve this to meet metabolic needs of body.
O2 in – depends on partial pressure of oxygen, diffusing capacity, perfusion & V/Q
CO2 out depends on alveolar ventilation (RR & VT) & deadspace (Anatomical & physiological)

6. Types of Respiratory Failure
Oxygenation failure (Type 1)
Acute
Often life threatening
Ventilation failure (Type 2)
Chronic (usually)
Compensation mechanisms

7. Type 1 Respiratory Failure
British Thoracic Society (2002)
Acute Hypoxaemic Respiratory Failure
Pa O2 < 8 KPa HYPOXIA
Pa CO2 < 6 KPa
SaO2 < 92%
Life threatening hypoxaemia
Impairment to gas exchange
normal CO2 can be maintained; CO2 more soluble than oxygen so can perfuse adequately across increased fluid barrier

8. Causes of Type 1 Respiratory (Oxygenation) Failure
Decrease in partial pressure of inspired O2
Ventilation/Perfusion (V/Q) Mismatch
Impaired Diffusion
Alveolar Hypoventilation

9. FIO2
Ventilation without perfusion
(deadspace ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)

10. Dead Space Ventilation
Each breath will have an element of dead space
2 components:
Anatomical:
Volume which never meets alveolar/capillary membrane – conducting airways, ETT tube, ventilator tubing & gubbins
Alveolar:
Volume reaching alveoli which are not perfused so gas exchange cannot occur

11. Type 2 Respiratory Failure
British Thoracic Society (2016)
Acute Hypercapnic Respiratory Failure
Pa O2 < 8 Kpa Hypoxaemia –mild; easily corrected
Pa CO2 > 6.5 Kpa
pH < 7.35
SaO2 < 92%

12. Causes of Type 2 Respiratory (Ventilatory) Failure
Insufficient respiratory drive
Hypoventilation most common cause of hypercapnia
Dead space (wasted ventilation)
Structural abnormalities of chest wall
Neuro- muscular dysfunction
Obesity
COPD

13. Causes of Type 2 Respiratory (Ventilatory) Failure
Capacity, Load & Drive:
For effective ventilation, respiratory muscle pump must have capacity to sustain ventilation against a given load
It also requires a neural drive from central nervous system
Severe derangements of load, drive or capacity can lead to development of ventilatory failure

14. Abnormalities of CAPACITY
Not a constant
Intrinsic weakness of respiratory muscles = reduced capacity
Weakness may be irreversible if due to:
Neuromuscular disease (NMD)
Weakness may be reversible if due to:
Electrolyte disturbance (& malnutrition)
Hypoxia
Hypercapnia
Acidosis 14

15. Abnormalities of LOAD
Load against which the respiratory muscle pump works (& not a constant)
Excessive load due to:
Reduced compliance of chest wall (e.g. scoliosis)
Reduced compliance of lungs (e.g. atelectasis, obstructive airways disease)
Changes to load due to:
Sputum
Fluid retention
Increased airflow obstruction
Normal circadian physiological changes (loss of upper airway muscle tone during sleep leads to increased upper airway resistance) 15

16. Abnormalities of DRIVE
Neural drive reduced by:
Structural & Metabolic abnormalities of respiratory control centre in brain stem
Loss of wakefulness drive
Chronic nocturnal hypoventilation
Sedative drugs 16

17. Ventilatory Failure
Severe derangements of load, drive or capacity (or any combination of these factors) can lead to development of ventilatory failure
Acute asthma:
respiratory muscle pump (capacity) is working against intolerable load (but normal drive)
Sedative drugs:
Apnoea (reduced drive) even though lungs (load) and respiratory muscles (capacity) are normal 17

18. Adult Respiratory Distress syndrome
Direct/Indirect Injury to Lungs:
Pulmonary Oedema
Inflammatory Infiltrates
Surfactant Dysfunction
Risk factors:
Direct: Pneumonia; Aspiration of gastric contents; lung contusion; fat emboli; drowning; inhalational injuries.
Indirect: Non-pulmonary sepsis; multiple trauma; massive transfusion; pancreatitis
Effects:
Hypoxaemia
Decreased Compliance
Collapse/consolidation
Pulmonary hypertension

20. WHAT MIGHT HELP?
Ferguson et al (2012) The Berlin Definition of ARDS an expanded rationale, justification & supplementary material Intensive Care Medicine 38 P

21. Final thoughts
You will all definitely see lots of respiratory failure with varying degrees of severity.
Use your assessment skills to help you understand what has caused… but also what might help…

23. References
British Thoracic Society Standards of Care Committee (2002) Non- invasive ventilation in acure respiratory failure. Thorax; 57: 192 – 211.
O’Driscoll et al (2008) Guideline for emergency oxygen use in adult patients. Thorax; 63: Supp VI.
Coombs et al (2013) Assessment, monitoring & interventions for the respiratory system. In Mallett, Albarron & Richardson Eds: Critical Care Manual of Clinical Procedures & Competencies. (Wiley & Sons, West Sussex)
Intensive Care Foundation (2015) Handbook of Mechanical Ventilation – A Users Guide (Intensive Care Society, London) file:///C:/Users/User/Downloads/Ventilation%20handbook%20(1).p df (downloaded August 2016) 23

24. Ventilation/Perfusion (V/Q) Matching
Distribution of blood flow (Q) and ventilation (V) is closely matched.
This minimises physiological dead space & so optimises gas exchange