Oxygen Therapy Flashcards
Sources of Oxygen
Oxygen Cylinders
Wall Supply
Oxygen Concentrators
Liquid Oxygen
Oxygen is delivered from these sources in Litres per minute
Oxygen Cylinders
Widely available (home & institutional)
Various sizes
Limited length of supply
Suitable for limited/short duration treatment
Relatively expensive
Supply 100% oxygen
Wall Supply
In hospital only
Central supply piped in to clinical areas
Not every ward has this
Supply 100% oxygen
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
Liquid Oxygen
More highly compressed
Larger gaseous volume per cylinder volume
Well developed in US & parts of Europe
Patient interfaces
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
Nasal Cannulae
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
Uncontrolled masks - simple
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
Uncontrolled masks -
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.
Venturi mask
Controlled Oxygen
Venturi valve allows delivery of a fixed concentration of oxygen
Target oxygen saturations
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
Acute breathlessness with hypoxaemia
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%
Risk of hypercapnia
Chronic hypoxic lung disease - COPD, Bronchiectasis & Cystic fibrosis
Chest wall disease - Kyphoscoliosis & Thoracoplasty
Neuromuscular disease
Obesity hypoventilation
Chronically hypoxaemic patients with COPD who have an acute exacerbation
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)
Assess response to treatment
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
Why not use nasal cannulae?
Potentially dangerous as actual inspired oxygen percentage varies according to the patient’s respiratory characteristics
Uncontrolled therapy
Prescribe oxygen
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
LTOT
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
LTOT indications
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
Benefits of LTOT
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
Remember not just about oxygen
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
