Physiology and Treatment of Chronic Ventilatory Failure Flashcards
What two components make up respiratory failure
Oxygenation failure (failure to take in O2)
Ventilatory failure (failure to expel CO2)
Define respiratory failure
Type I
- Hypoxia (PaO2 <8kPa or 60 mmHg)
Type II
- Hypoxia
- Hypercapnia (PaCO2 > 6kPa or 45 mmHg)
What are some causes of respiratory failure
V/Q mismatch
Shunt
Diffusion Issue
Hypoventilation (pump failure)
What is the characteristic finding in ventilatory failure and what is this determined by?
Hypercapnia
Determined by: CO2 production and alveolar ventilation
What is alveolar ventilation determined by (3)
- Tidal Volume
- Respiratory Rate
- Dead space
The amount of air that gets to the alveoli per minute for gas exchange - the amount of air available for gas exchange
What components make up the respiratory pump?
Diaphragm
Intercostal muscles
Controlled by phrenic nerve. Signals come from the medulla.
Alveolar ventilation is a balance between:
Capacity of ventilatory pump and its load
Load can be weight, exercise
Describe the mechanism of ventilatory failure in COPD (capacity vs load)
↓Capacity, ↑Load
- Bronchospasm, airway inflammation, mucus plugging
- ↑Airway Resistance
- ↑Work of breathing
- Respiratory muscle failure
- ↓VT
- Air trapping
- Flattened diaphragm
- Muscle weakness/dystrophy
- Respiratory muscle failure
- ↓VT
- ↑PEEP
- Dyspnoea
- ↑Work of breathing
- ↓VT
- Flattened diaphragm
- ↑Airway Resistance
- All of which increase PaCO2
Describe the mechanism of ventilatory failure in Neuromuscular Disease
↓Capacity, ↔/↑Load
- Inspiratory Muscles
- Weakened diaphragm/intercostals/accessories
- ↓Lung expansion
- ↑Atelectasis
- Compensatory ↑RR and ↓TV
- ↑LOAD
- Upper Airway
- Decreased clearance of secretions
- Obstruction
- ↑LOAD
- Normal central drive and wall compliance
Describe the mechanism of ventilatory failure in Scoliosis
↓Capacity, ↑Load
- Restrictive, small volumes
- Stiff chest walls and high resistance and low compliance
- ↑LOAD
What is breathing governed by and do they increase or decrease in sleep
- Cortical Inputs ↓
- Respiratory centre sensitivity ↓
- Chemosensitivity ↓
- Respiratory muscle contractility ↓
- Airwflow resistance ? depends if person has OSA
Describe how acute hypercapnia can turn into chronic hypercapnia
Acute hypercapnia leads to:
- Acidosis
- Compensatory retention of HCO3- in kidneys
- Compensated Respiratory Acidosis
- Compensation means that youve got high CO2 but being compensated
- So you need higher levels of CO2 to elicit normal response
- Leads to hypoventilation
- Decreased Respiratory Drive
- Daytime alveolar hypoventilation
- Chronic Hypercapnia
Draw a graph showing ventilatory response to CO2 indicating, awake, sleep and blunted response
Describe the factors involved in Chronic Respiratory Failure
Alveolar Hypoventilatoin
- COPD
- ↑Obstruction and resistance
- ↑Work of breathing
- ↑LOAD
- ↑Work of breathing
- Respiratory muscle weakness
- ↓CAPACITY
- ↑Obstruction and resistance
- Obesity
- Restrictive breathing
- ↑Resistance
- ↑LOAD
- ↑Resistance
- Upper Airway Resistance
- Sleep Apnoea
- ↑LOAD
- Sleep Apnoea
- Restrictive breathing
Acute to chronic changes
- Compensated Respiratory Acidosis
- Chronic HCO3- by kidneys
- Blunted chemosensitivity
- ↓ventilatory drive
- Chronic Alveolar Hypoventilation
- Sleep disruption
- ↓QALY
What are some tests used to investigate chronic respiratory failure
- Spirometry
- Respiratory Muscle Testing
- Morning Blood Gases
- Daytime, CO2 will have normalised
- Sleep Studies
How does lung volume change in chronic respiratory failure and describe some implications
In COPD, there is gas trapping
Increased Functional residual volume
No reserve left if there is increase need in ventilation
