Theme 4: Lecture 6 - Principles of oxygen therapy and sleep apnoea Flashcards
What are the sources of oxygen
- Oxygen Cylinders
- Wall Supply
- Oxygen Concentrators
- Liquid Oxygen
Describe oxygen cylinders
- Widely available (home & institutional)
- Various sizes
- Limited length of supply
- Suitable for limited/short duration treatment
- Relatively expensive
- Supply 100% oxygen
Describe oxygen wall supply
- In hospital only
- Central supply piped into clinical areas
- May not be available in all clinical areas (clinic rooms)
- Supply 100% oxygen
Describe oxygen concentrators
- Mains operated machine
- Molecular sieve- removes nitrogen
- Oxygen predominant gas >90% concentration
- Use in the home or when out
- They don’t run out as they concentrate oxygen from the environment
Describe liquid oxygen
- More highly compressed
- Larger gaseous volume per cylinder volume
- Allow higher flow rates
Patient interfaces for oxygen delivery for spontaneously breathing patients
- Nasal cannulae
- Uncontrolled masks
- Controlled masks
Name 2 uncontrolled oxygen masks
- Hudson
- Non rebreathe
Name a controlled oxygen mask
Venturi mask
FiO2 meaning
Fraction of inspired oxygen
Describe 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
When are nasal cannulae used
In mild hypoxaemia, mot critically ill
Describe a hudson mask
- Simple face mask
- Delivers 30-60% O2
- Flow rate 5-10L/min
- Mixing of O2, room air & exhaled air in mask
- Don’t know the exact % of O2 patient is getting
- Used less often
Describe a non rebreathe mask
- Delivers 85-90% oxygen with 15L flow rate.
- Bag: one-way valve stops: mixing with room air and patient rebreathing expired air
- Don’t know the exact % of O2 patient is getting
When are non rebreathe masks used
-In acutely unwell patients (step down as soon as possible)
Describe a venturi mask
- Controlled Oxygen
- Venturi valve allows delivery of a fixed concentration of oxygen
What is oxygen the treatment for
Hypoxaemia (not breathlessness)
What are the clinical indications to give 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)
Target oxygen saturation for a normal young adult
96-98%
Target oxygen saturation for a normal adult > 70 yrs
94-98%
Target oxygen saturation for patients at risk of hypercapnic respiratory failure (ie patients with COPD)
88-92%
What may be the causes of acute breathlessness with hypoxaemia in a patient without significant background lung problems
- acute pulmonary oedema
- acute pneumonia (inclduign Covid-19)
- acute pneumothorax
- acute asthma
- (critical illness: major trauma/MI/sepsis/CO poisoning)
What may acute hypoxaemia cause
Acute cardiac dysrhythmia and organ failure
What is the oxygen treatment for acute breathlessness with hypoxaemia in a patient without significant background lung problems
- Maximal oxygen treatment.
- High flow uncontrolled mask- first line
- Alter flow and delivery device when stable
- Target SpO2 = 94-98%
What is the other treatment, excluding oxygen therapy, for acute breathlessness with hypoxaemia in a patient without significant background lung problems
- 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)
Which patients are at risk of hypercapnia if they are given high dose oxygen
- Chronic hypoxic lung disease (COPD, Bronchiectasis / Cystic fibrosis)
- Chest wall disease (Kyphoscoliosis, Thoracoplasty)
- Neuromuscular disease
- Obesity related hypoventilation
Why shouldn’t you give too much oxygen to chronically hypoxaemic patients
-These patients will often tolerate a lower PaO2 than normal so adjusted to chronic hypoxaemia
-They often rely on their hypoxaemic drive
-If you over-correct their pO2 you may switch off their respiratory drive
This could lead to, further CO2 retention, worsening acidosis, narcosis (reduced level of consciousness) and death
-You can kill the patient with oxygen
Treatment for chronically hypoxaemic patients with COPD who have an acute exacerbation
- 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%
How do you assess response to treatment
With arterial blood gases
What treatment may chronically hypoxaemic patients with COPD who have an acute exacerbation need if they aren’t improving
Non-invasive ventilation
What may untreated chronically hypoxaemic patients develop
- Pulmonary hypertension
- Right ventricular hypertrophy
- Right ventricular failure (cor pulmonale)
- Secondary polycythaemia (raised haemoglobin)
Which patients may be given long term oxygen treatment (LTOT)
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 right ventricular failure -evidence of pulmonary hypertension
Describe long term oxygen treatment (LTOT)
- Provided from an oxygen concentrator
- O2 treatment by more than 15 hrs a day
Benefits of long term oxygen treatment (LTOT) (7)
- 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 arrhythmias
- Improved quality of life
Advantages of portable oxygen
- May improve breathlessness in some patients
- May extend duration of LTOT
Disadvantages of portable oxygen
- Most patient’s breathlessness is not due to low pO2
- Weight of cylinders
- Duration of supply
Definition of apnoea
“Cessation of Airflow” for 10 seconds or longer
Causes of apnoea
- Central: Respiratory Control Centre - no respiratory effort
- Obstructive: collapse of pharyngeal airway during sleep (continuation of respiratory effort)
Definition of obstructive sleep apnoea
5 or more obstructive apnoeas per hour
Definition of hypopnoea
reduction in airflow by 50% accompanied by desaturation of 4% and/or arousal from sleep
Why is the prevalence of sleep apnoea increasing
Due to increasing rates of obesity
Risk factors for sleep apnoea (obstructive sleep apnoea/hypopnoea syndrome OSAHS) (9)
- Male sex
- Obesity
- Neck circumference greater than 43 cm (41cm women)
- Family history of OSAHS
- Smoking
- Alcohol/sedative use
- Craniofacial abnormalities (e.g retrognathia)
- Pharyngeal abnormalities (e.g. tonsillar enlargement)
- Some medical conditions (hypothryroidism, acromegaly, pregnancy)
- Sleeping supine
Name the regions of the pharynx
- Nasopharynx
- Oropharynx
- Laryngopharynx
What happens in sleep apnoea
- Sleep
- Relaxation of muscles/tissues surrounding pharyngeal airway
- Collapse and obstruction of the airway - snoring
- Apnoea
- Arousal
- Muscle tone returns - airway clears
- Resumption of breathing
- Sleep
Clinical features of sleep apnoea (7)
- Snoring (Hx often from partner)
- Nocturnal choking/waking with a “start”
- Unrefreshing/restless sleep
- Morning dry mouth
- Morning headaches
- Excessive daytime sleepiness (Difficulty concentrating, Irritability/Mood changes, Sleeping at inappropriate times)
- Nocturia
Nocturia
Getting up at night because you have to pass urine
Complications of sleep apnoea
- Cor pulmonale (Right heart failure 2ndry respiratory disease)
- Secondary Polycythaemia (Excess of red blood cells)
Definition of obstructive sleep apnoea/hypopnoea syndrome (OSAHS)
Repetitive apnoeas and symptoms of sleep fragmentation with excessive daytime sleepiness
Investigations for sleep apnoea
- Epworth Sleepiness Scale
- Sleep Studies eg Nocturnal oximetry, Video studies, Polysomnography
What is polysomnography
- Also called a sleep study, is a comprehensive test used to diagnose sleep disorders.
- Polysomnography records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study
How is sleep apnoea diagnosed
- Using the apnoea/hypopnea index
- Or oxygen desaturation index
Apnoea/hypopnea index (AHI) equation
AHI = (apnoeas + hypopnoeas) / total hours of sleep
What co morbidities is sleep apnoea associated with (8)
- Increased risk of accidents
- Hypertension
- Type 2 diabetes
- Ischaemic heart disease
- Heart failure
- Cerebrovascular disease/stroke
- Cardiac arrhythmias
- Death
What are the management goals for sleep apnoea
- Resolve signs and symptoms of OSA
- Improve sleep quality
- Normalise apnoea-hypopnoea index (AHI) and oxyhaemoglobin saturation levels
What can patients do to help with sleep apnoea
- Weight loss
- Avoid sleeping supine
- Avoid alcohol
Describe CPAP
- Continuous Positive Airway Pressure (CPAP)
- Device generates airflow => positive pressure delivered to airway via mask
- Intraluminal pharyngeal pressure > surrounding pressure
- Pharynx stays open
When is CPAP used to treat sleep apnoea
- Patients with mild OSAHS AND additional co-morbidities
- Patient with mild OSAHS and high risk profession (e.g. bus driver)
- Patients with moderate/severe OSAHS regardless of symptoms
- But not patients with mild OSAHS, no additional risk factors who aren’t excessive sleepy
Benefits of CPAP
- Symptoms resolve
- ↓ apnoea/hypopnoea
- ↓ daytime sleepiness
- ↓ risk road accidents
- ↑ quality of life
- Normalises BP
Problems with CPAP
- Adherence an issue
- Airway drying/irritation (Can humidify)
- Mask problems (Air leak, Comfort)
- Normally life long treatment
Treatment options for sleep apnoea
- Mandibular advancement devices
- CPAP
- Surgery
How do mandibular advancement devices work to treat sleep apnoea
They hold soft tissues of the oropharynx forward
