Sleep Apnoea and Neuromuscular Respiratory Failure Flashcards
What is obstructive sleep apnoea?
Recurrent episodes of upper airway obstruction leading to apnoea (cessation of breathing) during sleep.
What are the common presentations of sleep apnoea?
Heavy snoring
Unrefreshing sleep
Daytime somnolence (sleepiness)
Poor daytime concentration
Where is the obstruction in sleep apnoea?
Between the base of the tongue/soft pallet and posterior pharyngeal wall
What are the causes of sleep apnoea?
Muscle relaxation
Narrow pharynx
Obesity
What is the pathophysiology of sleep apnoea?
Repeated closure of upper airways
What does recurrent closure of the airways lead to?
Oxygen desaturation
Snoring
Apnoea’s and hypopnea’s
What does apnoea’s and hypopnea’s lead to?
Frequent microarousals
What does frequent microarousals lead to?
Daytime hypersomnolence
Poor concentration
What is apnoea and hypopnoea?
Apnoea = obstructed for 10s or more
Hypopnoea = nearly obstructed for 10s or more
What is the importance of sleep apnoea?
Impaired QofL
Marital disharmony
Increased risk of RTA
Increased risk of stroke
Associated with hypertension
Probably increased risk of heart disease
What % of men/women are affected by sleep apnoea?
Men = 2%
Women = 1%
How do you diagnose sleep apnoea?
Clinical examination and history
Epworth questionnaire
Overnight sleep study
What are the 3 types of overnight sleep studies?
Pulse oximetry - basic
Limited sleep studies
Full polysomnography - most sophisticated
What is the Epworth questionnaire?
A questionnaire determining the level of sleepiness a patient experiences
Score of 11 or more = abnormal
What does overnight oximetry measure?
Records O2 sats and pulse rate while asleep
What is an indication of sleep apnoea on an overnight oximetry?
Repetitive desaturations
Pulse rate rises intermittently coinciding with O2 saturation
What does polysomnography measure?
Oronasal airflow
Thoracoabdominal movement
Body position
Oximetry
EEG (brain wave recordings)
Audio-visual recording
EOG (eye muscle movements)
EMG (peripheral muscle movements)
ECG (heart tracing)
How is severity of sleep apnoea measured?
Via desaturation index/apnoea hypopnoea index
0-5 = normal
5-15 = mild
15-30 = moderate
>30 = severe
What are the treatment options for sleep apnoea?
Identify exacerbating factors
Continuous positive airway pressure (CPAP)
Mandibular repositioning splint
What factors can exacerbate sleep apnoea?
Weight (90% of patients with SA are overweight)
Alcohol
Endocrine disorders
What does CPAP do?
Creates positive pressure within the throat and stops the tissue from being sucked together during inspiration.
How does mandibular repositioning splint work and when is it used?
Advances lower jaw forwards bringing base of tongue forwards and creating more space at the back of the throat.
Used if patient cannot tolerate CPAP.
How should patients be advised about driving?
Advice those with excessive daytime somnolence NOT TO DRIVE or RESTRICT driving and inform DVLA of their condition
What is narcolepsy?
A chronic neurological disorder that affects the brain’s ability to control sleep-wake cycles
What are the clinical features of narcolepsy?
Cataplexy
Excessive daytime somnolence
Hypnagogic/hypnopompic hallucination
Sleep paralysis
What is cataplexy?
Where person will suddenly collapse during the day appearing to be asleep but is vaguely aware of what’s going on around them.
What are hypnagogic/hypnopompic hallucinations?
Hallucinations that occur just at the onset of sleep or just at the end of sleep.
They are visual and often quite frightening
What investigations would you perform for narcolepsy?
Polysomnography
MSLT (multi sleep latency test)
Low CSF orexin
What is MSLT?
Patient is asked to try fall asleep in a dark silent room.
Their brain waves and time to fall asleep are recorded.
If time to sleep is less than 6mins then significantly abnormal.
> 1 SOREM and mean sleep latency <8 mins
What does low CSF orexin show?
Orexin = neuropeptide involved in controlling wakefulness.
Typically see low levels in narcolepsy patients
What are the treatment options for narcolepsy?
No cures - have to take drugs to continuously control illness
- Modafinil
- Dexamphetamine
- Venlafaxine
- Sodium Oxybate (Xyrem)
What does modafinil do?
General stimulant taken at morning and lunch
Counteracts excessive somnolence
What does dexamphetamine do?
Is a 2nd line drug used to counteract somnolence
What is venlafaxine for?
Cataplexy
What is sodium oxybate for?
2nd line drug for somnolence and cataplexy
What type of ventilatory failure is chronic ventilatory failure?
Type 2
What are the defining perimeters on ABG for chronic ventilatory failure?
Elevated pCO2
pO2 < 8kPa
Normal blood pH
Elevated bicarbonate in blood
How does chronic ventilatory failure differ from acute?
Acute = rises in pCo2
Acute = Low pH
What is blood pH proportional to?
Concentration of bicarbonate dived by pCO2
What happens in the body when pCO2 rises and how is this managed in chronic situations?
Rise in pCO2 = blood pH falls
In chronic situation body attempts to compensate for this acidity by retaining the week buffer bicarbonate from the kidneys
What is the aetiology of chronic ventilatory failure?
Airway disease
Chest wall abnormalities
Respiratory muscle weakness
Central hypoventilation
What airways diseases can cause chronic ventilatory failure?
COPD
Bronchiectasis
Give an example of a chest wall abnormality causing chronic ventilatory failure?
Kyphoscoliosis
What respiratory muscle weakness can bring about chronic ventilatory failure?
Diaphragm, intercostal, abdominal muscles
Motor neurone disease (ALS)
Muscular dystrophy
Glycogen storage disease (Pompe’s disease)
What can cause central hypoventilation?
Obesity hypoventilation syndrome
Congenital central hypoventilation syndrome (Ondine’s curse)
- Presents in newborns with ventilatory failure
- Used to be fatal but children can now sometimes survive to adulthood
What are the typical symptoms of chronic ventilatory failure?
Breathlessness
Orthopnoea
Ankle swelling
Morning headaches
Recurrent chest infections
Disturbed sleep
What is orthopnoea?
Breathlessness while lying flat
Why do you get ankle swelling in chronic ventilatory failure?
Chronic low pO2 results in hypoxic vasoconstriction within pulmonary vasculature, resulting in elevated pressure within right heart, transferred to venous system, fluid can leak out of veins and cause swelling = cor pulmonale.
Why do you get morning headaches in chronic ventilatory failure?
When pCO2 rises in blood at night, excess CO2 acts a vasodilator in cerebral blood vessels, this can result in headache.
What would you expect to find on examination of a chronic ventilatory failure patient?
Paradoxical abdominal wall motion in suspected neuromuscular disease.
Ankle oedema (hypoxic cor pulmonale).
Why does paradoxical abdominal wall motion come about and what is it?
Due to a weakness of the diaphragm.
Breath in diaphragm descends creating -ve intrathoracic pressure drawing air into the lungs.
When sitting upright it has help of gravity, when lying flat no gravity to help descend.
If significant weakness diaphragm wont contract properly/descend, opposite may happen and diaphragm is drawn up into the chest.
Abdominal wall will move up/out normally, but with diaphragm weakness it moves down during inspiration.
What investigations do you do with chronic ventilatory failure?
Lung function
Assessment of hypoventilation
If suspected weekended diaphragm = fluoroscopic screening of diaphragm
What do you look at with lung function tests and what would you expect to find?
Spirometry when lying and standing = measure VC:
- VC will be lower when lying than sitting/standing
Mouth pressure/SNIP
- Measure pressure person can generate breathing in/out as hard as possible
- SNIP = sniff in/out as hard as possible
What tests are done in assessment of hypoventilation?
Early morning ABG
- Results reflect physiology of what happened during sleep
Overnight oximetry
Transcutaneous CO2 monitoring
- Looking for elevated CO2 during sleep
What would be the expected results of a pulmonary function test for a patient with chronic ventilatory failure?
Reduced FEV1 and FVC
Ratio of FEV1/FVC is high
Characteristic of restrictive ventilatory pattern
Supine FVC is significantly lower than standing FVC
What are the treatment options for someone with chronic ventilatory failure?
Not curable unless the underlying cause is curable.
Non-invasive ventilation (NIV)
Oxygen therapy
Tracheostomy ventilation (t-IPPV)
