Oxygen Therapy

Question 1

Sources of Oxygen

Answer 1

Oxygen Cylinders
Wall Supply
Oxygen Concentrators
Liquid Oxygen

Oxygen is delivered from these sources in Litres per minute

Question 2

Oxygen Cylinders

Answer 2

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

Question 3

Wall Supply

Answer 3

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

Question 4

Oxygen Concentrators

Answer 4

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 5

Liquid Oxygen

Answer 5

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

Question 6

Patient interfaces

Answer 6

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 7

Nasal Cannulae

Answer 7

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 8

Uncontrolled masks - simple

Answer 8

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

Question 9

Uncontrolled masks -

Answer 9

Non-rebreathe mask
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 10

Venturi mask

Answer 10

Controlled Oxygen

Venturi valve allows delivery of a fixed concentration of oxygen

Question 11

Target oxygen saturations

Answer 11

Normal adult average = 96-98%
Minimal reduction with age

Target in most patients = 94-98%
Balance of what is normal and what is safe

Target in those at risk of hypercapnic (high PaCO2) respiratory failure = 88-92%
May be lower for some

Question 12

Acute breathlessness with hypoxaemia

Answer 12

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%

Question 13

Risk of hypercapnia

Answer 13

Chronic hypoxic lung disease - COPD, Bronchiectasis & Cystic fibrosis

Chest wall disease - Kyphoscoliosis & Thoracoplasty

Neuromuscular disease
Obesity hypoventilation

Question 14

Chronically hypoxaemic patients with COPD who have an acute exacerbation

Answer 14

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)

Question 15

Assess response to treatment

Answer 15

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

Question 16

Why not use nasal cannulae?

Answer 16

Potentially dangerous as actual inspired oxygen percentage varies according to the patient’s respiratory characteristics

Uncontrolled therapy

Question 17

Prescribe oxygen

Answer 17

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

Question 18

LTOT

Answer 18

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 19

LTOT indications

Answer 19

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 20

Benefits of LTOT

Answer 20

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 21

Remember not just about oxygen

Answer 21

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