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)
Scenario 2: Chronically hypoxaemic patients with COPD who have an acute exacerbation
How would you treat this patient?
- 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%
- If not improving may need non-invasive ventilation
Scenario 2: Chronically hypoxaemic patients with COPD who have an acute exacerbation
How to 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
Scenario 2: Chronically hypoxaemic patients with COPD who have an acute exacerbation
Why not use nasal cannulae?
–potentially dangerous as actual inspired oxygen percentage varies according to the patient’s respiratory characteristics
–Uncontrolled therapy
What are the British Thoracic Society’s guidelines for prescribing oxygen?
In Hospital, oxygen should be prescribed on the drug chart
State:
- the target oxygen saturation range
- the delivery device
- the “dose” – flow rate or percentage of inspired oxygen
When would oxygen be used for chronically hypoxaemic patients?
- Evidence for oxygen therapy only exists for patients with COPD
- Also used in patients with interstitial lung disease and pulmonary hypertension
What do chronically hypoxaemic patients who aren’t treated with oxygen develop?
–pulmonary hypertension
–right ventricular hypertrophy
–right ventricular failure (cor pulmonale)
–Secondary polycythaemia (raised Haemoglobin)
What 2 studies looked at the effects of oxygen therapy of chronically hypoxaemic COPD patients?
–The MRC trial (UK)
•Increased survival in the oxygen group
–Nocturnal oxygen therapy trial - NOTT (US)
•1.96 times the deaths in the 12hour group
When is long term oxygen treatment used?
For some patients with COPD
Specialist assessment:
–In patient’s stable state
–no sooner than 4 weeks after an exacerbation
What are the indications for long term oxygen therapy?
•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
How is long term oxygen therapy provided?
- Provided from an oxygen concentrator
- Regional concentrator supply service
- O2 treatment for ≥15 hours per day
What are the benefits of long term oxygen therapy?
- 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
What are the benefits of portable oxygen?
- May improve breathlessness in some patients
- May extend duration of LTOT
What are the negatives of portable oxygen?
- Most patients breathlessness is not due to low pO2
- Weight of cylinders
- Duration of supply
Define apnoea
Apnoea: “Cessation of Airflow” for 10 seconds or longer
Define central
Central: Respiratory Control Centre - no respiratory effort
Define obstructive
Obstructive: collapse of pharyngeal airway during sleep (continuation of respiratory effort)
Define obstructive sleep apnoea (OSAHS)
Repetitive apnoeas and symptoms of sleep fragmentation with excessive daytime sleepiness.
5 or more apnoeas an hour
Define hypopnoea
Hypopnoea: reduction in airflow by 50% accompanied by desaturation of 4% and/or arousal from sleep
Is sleep apnoea more common in women or men?
Men - 4%
Women - 2%
What are the risk factors for sleep apnoea?
–Male sex
–Obesity
–Neck circumference greater than 43 cm (41cm women)
–Family history of obstructive sleep apnoea
–Smoking
–Alcohol/sedative use
–Craniofacial abnormalities (e.g retrognathia)
–Pharyngeal abnormalities (e.g. tonsillar enlargement)
–Some medical conditions (hypothryroidism, acromegaly, pregnancy)
–Sleeping supine
Why is the prevelance of sleep apnoea increasing?
Increasing prevelance of obesity
Complete the diagram
What is the pathophysiology of sleep apnoea?
Pharynx:
↓ Upper airway (UA) neuromuscular tone
↓ UA caliber,
↑ UA resistance,
↑ pharyngeal compliance
=
Tendency of pharyngeal collapse
Which anatomical features can cause sleep apnoea?
- Nasal pathology: polyps, deviated septum
- Enlarged Tonsils
- Increased soft tissue e.g. obesity, hypothyroidism
- Abnormal chin: micrognathia, retrognathia
- Normal tongue relaxation + any causes of macroglossia
What happens in sleep apnoea?
What are the features of sleep apnoea?
- 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
What are the complications of sleep apnoea?
•Cor pulmonale
–Right heart failure 2ndry respiratory disease
•Secondary Polycythaemia
–Excess of red blood cells
What are the investigations for sleep apnoea?
- Epworth Sleepiness Scale
- Sleep Studies
- Nocturnal oximetry
- Video studies
- Polysomnography
How does the Epworth Sleepiness Scale work?
How likely are you to doze off or fall asleep during the following situations,
in contrast to just feeling tired?
For each of the situations listed below, give yourself a score of 0 to 3, where
0 = Would never doze; 1 = Slight chance; 2 = Moderate chance; 3 = High chance.
What investigation is this?
Polysomnography (PSG)
How is sleep apnoea diagnosed?
•Uses apnoea/hypopnea index (AHI)
–AHI = apnoeas + hypopnoeas / total sleep time in hours
- Mild: AHI 5–14 per hour (+ symptoms/signs).
- Moderate: AHI 15–30 per hour.
- Severe: AHI more than 30 per hour.
•(Or oxygen desaturation index)
What are the consequences of obstructive sleep apnoea?
- Increased risk of accidents
- Association with:
–Hypertension
–Type 2 diabetes
–Ischaemic heart disease
–Heart failure
–Cerebrovascular disease/stroke
–Cardiac arrhythmias
–Death
What are the goals in management of sleep apnoea?
- Resolve signs and symptoms of OSA
- Improve sleep quality
- Normalise:
- apnoea-hypopnoea index (AHI)
- oxyhaemoglobin saturation levels
What is the management of sleep apnoea?
•Patient education – driving
- DVLA website-guidance for medical professional
- Must stop driving if excessive sleepiness
- If moderate/severe OSAHS then DVLA will need medical confirmation of treatment/control/compliance.
•Behavioural change:
- Weight loss
- Avoid sleeping supine
- Avoid alcohol
- Treat contributing problems (e.g hypothyroidism)
- Review medications - Sedating drugs, drugs causing weight gain
What are the treatments for sleep apnoea?
•Mandibular advancement devices
–Hold soft tissues of oropharynx forward
–Mild-mod OSA, patient preference, failed CPAP
•? Surgery
–Most effective if severe, correctable, obstructing lesion
–Tonsillar or adenoid hypertrophy, craniofacial abnormalities
How does CPAP work?
Continuous Positive Airway Pressure (CPAP)
–Device generates airflow => positive pressure delivered to airway via mask
–Intraluminal pharyngeal pressure > surrounding pressure
–Pharynx stays open
What are the clinical indications for CPAP?
- 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
What are the benefits of CPAP?
- Symptoms resolve
- ↓ apnoea/hypopnoea
- ↓ daytime sleepiness
- ↓ risk road accidents
- ↑ quality of life
- Normalises BP
What are the problems associated with CPAP?
- Adherence an issue
- Airway drying/irritation - Can humidify
- Mask problems
- Air leak
- Comfort
•Normally life long treatment
