Oxygen therapy and sleep apnoea Flashcards
What are the sources of oxygen in a hospital?
- Oxygen Cylinders
- Wall Supply
- Oxygen Concentrators
- Liquid Oxygen
What units is oxygen delivered in?
–litres per minute
–percentage inspired oxygen
What are the features of oxygen cylinders?
- Widely available (home & institutional)
- Various sizes
- Limited length of supply
- Suitable for limited/short duration treatment
- Relatively expensive
- Supply 100% oxygen
What are the features of wall supply oxygen?
- In hospital only
- Central supply piped in to clinical areas
- May not be available in all clinical areas (clinic rooms)
- Supply 100% oxygen
What does the ball show?
Mid-point of ball marks flow rate.
What are the features of oxygen concentrators?
- Mains operated machine
- Molecular sieve- removes nitrogen
- Oxygen predominant gas >90% concentration
- Use in the home or when out
- Regional suppliers with franchise for installation & support
What are the features of liquid oxygen?
- More highly compressed
- Larger gaseous volume per cylinder volume
- Allow higher flow rates
- Well developed in US & parts of Europe
What patient interfaces is there for sponataniously breathing patients?
- Nasal cannulae
- Uncontrolled masks (hudson, non-rebreathe)
- Controlled (fixed percentage - venturi) masks
What are the features of nasal cannulae?
- Usually well tolerated
- Accepts flow rates 1-4L/min
- Delivers 24-40% O2
- % delivered depends on multiple factors
When would nasal cannulae be used?
Uses: mild hypoxaemia, not critically ill
What are the features of simple face masks?
- Simple face mask
- Hudson mask
- Delivers 30-60% O2
- Flow rate 5-10L/min
- Mixing of O2, room air & exhaled air in mask
- Used less often
What are the features of non-rebreathe masks?
- Delivers 85-90% oxygen with 15L flow rate.
- Bag: one-way valve stops:
- mixing with room air
- patient rebreathing expired air
When would a non-rebreathe mask be used?
- Use: acutely unwell patients
- Step down as soon as possible.
What are the features of venturi masks?
- Controlled Oxygen
- Venturi valve allows delivery of a fixed concentration of oxygen
Which mask has these options?
Venturi mask
How should oxygen be prescribed?
Oxygen should be prescribed on drug chart with target oxygen saturations.
What is oxygen a treatment for?
Oxygen is a treatment for hypoxaemia, not breathlessness.
What are the clinical indicators for oxygen?
- Acutely hypoxaemic patients
- Chronically hypoxaemic COPD patients with acute exacerbation
- Chronically hypoxaemic COPD patients who are stable
- Palliative use in advanced malignancy
* Sats <90% and breathless, though often multifactorial
What are the target oxygen saturations?
•Normal young adult average = 96-98%
–Over 70yrs age 94-98%
- Target in most patients = 94-98%
- Target in those at risk of hypercapnic (high PaCO2) respiratory failure = 88-92%
Scenario 1: Acute breathlessness with hypoxaemia in a patient without significant background lung problems
What would be the causes of this?
- acute pulmonary oedema
- acute pneumonia (inclduign Covid-19)
- acute pneumothorax
- acute asthma
- (critical illness: major trauma/MI/sepsis/CO poisoning)
Scenario 1: Acute breathlessness with hypoxaemia in a patient without significant background lung problems
What is the risk and treatment?
Risk
Acute hypoxaemia => acute cardiac dysrhythmia & organ failure
Treatment
Maximal oxygen treatment.
High flow uncontrolled mask- first line
Alter flow and delivery device when stable
Target SpO2 = 94-98%
What else has to be done except oxygen when a patient is hypoxaemic?
Secure and maintain airway patency
Enhance circulation
–(volume, anaemia, cardiac output)
Avoid/reverse respiratory depressants
Establish reason for hypoxaemia and treat
–e.g. bronchospasm (in asthma), pulmonary oedema (in left ventricular failure).
If not improving, may need ventilation
–Invasive or non-invasive
Who is at risk of hypercapnia (CO2 retention) if given high dose oxygen?
Chronic hypoxic lung disease
–COPD
–Bronchiectasis / Cystic fibrosis
Chest wall disease
–Kyphoscoliosis
–Thoracoplasty
Neuromuscular disease
Obesity related hypoventilation
Scenario 2: Chronically hypoxaemic patients with COPD who have an acute exacerbation
What is an exacerbation and what causes it?
- Worsening of breathing in known COPD
- Exacerbation may be viral or bacterial infection or episode of heart failure
Why do COPD patients often tolerate a lower PaO2 than “normal”?
Due to chronic hypoxaemia
They often rely on their hypoxaemic drive - if you over-correct their pO2 you may switch off their respiratory drive
Leading to:
- further CO2 retention
- worsening acidosis
- Narcosis - reduced level of consciousness
- (& death)