Principles of Oxygen Therapy and sleep apnoea

Question 1

Oxygen cylinder

Answer 1

Widely available (home & institutional)
Various sizes
Limited length of supply
Suitable for limited/short duration treatment
Relatively expensive
Supply 100% oxygen

Question 2

Wall supply

Answer 2

In hospital only
Central supply piped in to clinical areas
Not every ward has this
Supply 100% oxygen

Question 3

Oxygen Concentrators

Answer 3

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

Question 4

Liquid oxygen

Answer 4

More highly compressed
Larger gaseous volume per cylinder volume
Well developed in US & parts of Europe

Question 5

Patient interfaces

Answer 5

For spontaneously breathing patients:
Nasal cannulae
Uncontrolled masks (hudson, non-rebreathe)
Controlled (fixed percentage - venturi) masks

Oxygen reaches the patient either as:
litres per minute
percentage inspired oxygen

Question 6

Nasal cannulae

Answer 6

Usually well tolerated

Accepts flow rates 1-4L/min

Delivers 24-40% O2
(= FiO2 of 0.24-0.4)

% delivered depends on multiple factors

Uses: mild hypoxaemia, not critically ill

Question 7

Uncontrolled masks - simple face mask

Answer 7

Hudson mask
Delivers 30-60% O2
Flow rate 5-10L/min
Mixing of O2, room air & exhaled air in mask
Used less often

Question 8

Uncontrolled masks - non rebreathe mask

Answer 8

Delivers 85-90% oxygen with 15L flow rate. 
Bag: one-way valve stops:
mixing with room air 
patient rebreathing expired air
Use: acutely unwell patients 
Step down as soon as possible.

Question 9

Venturi mask

Answer 9

Controlled Oxygen

Venturi valve allows delivery of a fixed concentration of oxygen

Question 10

Clinical indications

Answer 10

Oxygen is a treatment for hypoxaemia, not breathlessness.

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

Question 11

Target oxygen saturation - Normal adult average

Answer 11

96-98%

Minimal reduction with age

Question 12

Target oxygen saturation - Most patients

Answer 12

94-98%

Balance of what is normal and what is safe

Question 13

Target oxygen saturation - Those at risk of hypercapnic

Answer 13

88-92%

May be lower for some

Question 14

Remember not just about oxygen

Answer 14

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

Question 15

Hypercapnia (CO2 retention) risk with high oxygen dose

Answer 15

Chronic hypoxic lung disease 
- COPD 
- Bronchiectasis / Cystic fibrosis 
Chest wall disease 
- Kyphoscoliosis 
- Thoracoplasty 
Neuromuscular disease 
Obesity hypoventilation

Question 16

Aims of treatment

Answer 16

To maintain modest oxygenation whilst preventing CO2 retention & acidosis

Deliver oxygen by fixed percentage venturi oxygen masks starting at 24% (controlled oxygen therapy)

Target saturations 88-92%

Question 17

Assess response to treatment

Answer 17

arterial blood gases, check frequently 
- pO2 <10
- pCO2 falling from peak or maintained <6.0
- pH increasing/maintained >7.35
Adjust dose of oxygen accordingly

If not improving may need non-invasive ventilation

Question 18

Don’t always use nasal cannulae

Answer 18

• potentially dangerous as actual inspired oxygen percentage varies according to the patient’s respiratory characteristics
• Uncontrolled therapy

Question 19

Prescribing Oxygen - British Thoracic Society Guidelines

Answer 19

State:
the target oxygen saturation range
Depends on the clinical scenario
the delivery device
Controlled vs uncontrolled (venturi or nasal cannulae)
the “dose” – flow rate or percentage of inspired oxygen
You may provide a range here to guide ward staff
But may be more important to work to saturation targets

Patients may carry an ‘oxygen treatment card’ with their recommended oxygen saturations/prescription.

Question 20

When to suggest long term oxygen treatment

Answer 20

For some patients with COPD

Specialist assessment:

• In patient’s stable state
• ABGs on 2 occasions at least 3 weeks apart to demonstrate clinical stability
• no sooner than 4 weeks after an exacerbation

Question 21

Long term oxygen treatment indications

Answer 21

COPD patients with pO2 < 7.3 kPa
or
COPD patients with pO2 7.3 < 8 kPa AND:
secondary polycythaemia
nocturnal hypoxaemia
peripheral oedema
 evidence of pulmonary hypertension

Question 22

Long term oxygen treatment

Answer 22

Provided from an oxygen concentrator
Regional concentrator supply service
O2 treatment for ≥15 hours per day

Question 23

Benefits of long term oxygen treatment

Answer 23

Improved long term survival
Prevention of deterioration in pulmonary hypertension
Reduction of polycythaemia (raised Hb)
Improved sleep quality
Increased renal blood flow
Reduction in cardiac arryhthmias
Improved quality of life

Question 24

Portable oxygen

Answer 24

May improve breathlessness in some patients
May extend duration of LTOT

But ….
Most patients breathlessness is not due to low pO2
Weight of cylinders
Duration of supply

Question 25

Apneoa

Answer 25

“Cessation of Airflow” for 10 seconds or longer

Question 26

Obstructiuve

Answer 26

collapse of pharyngeal airway during sleep (continuation of respiratory effort)

Question 27

OSA

Answer 27

5 or more obstructive apnoeas per hour.

Question 28

Hypopneoa

Answer 28

reduction in airflow by 50% accompanied by desaturation of 4% and/or arousal from sleep

Question 29

Apneoa risk factors

Answer 29

Male sex
Obesity
Neck circumference greater than 43 cm (41cm women)
Family history of OSAS
Smoking
Alcohol/sedative use
Craniofacial abnormalities (e.g retrognathia)
Pharyngeal abnormalities (e.g. tonsillar enlargement)
Some medical conditions (hypothryroidism, acromegaly, pregnancy)
Sleeping supine

Question 30

Clinical features of apnoea

Answer 30

Snoring (Hx often from partner)
Nocturnal choking/waking with a “start” 
Unrefreshing/restless sleep
Morning dry mouth
Morning headaches
Excessive daytime sleepiness 

Nocturia

Question 31

Apnoea investigation

Answer 31

Epworth Sleepiness Scale
Sleep Studies
Nocturnal oximetry
Video studies
Polysomnography

Question 32

Consequences of OSA

Answer 32

Increased risk of accidents
Association with:
- Hypertension 
- Type 2 diabetes
- Ischaemic heart disease
- Heart failure
- Cerebrovascular disease/stroke
- Cardiac arrhythmias
- Death

Question 33

Management

Answer 33

Goals
Resolve signs and symptoms of OSA
Improve sleep quality
Normalise:
apnoea-hypopnoea index (AHI) 
oxyhaemoglobin saturation levels

Multi-disciplinary approach needed

Question 34

Mandibular advancement devices

Answer 34

Hold soft tissues of oropharynx forward

Mild-mod OSA, patient preference, failed CPAP

Question 35

Continuous Positive Airway Pressure (CPAP)

Answer 35

Device generates airflow => positive pressure delivered to airway via mask
Intraluminal pharyngeal pressure > surrounding pressure
Pharynx stays open

Question 36

CPAP benefits

Answer 36

Benefits
Symptoms resolve
↓ apnoea/hypopnoea
↓ daytime sleepiness
↓ risk road accidents
↑ quality of life
Normalises BP

Question 37

CPAP problems

Answer 37

Adherence an issue
Airway drying/irritation
Can humidify
Mask problems
Air leak
Comfort
Life long treatment