Obstructive Sleep Apnoea Flashcards
What percentage of the population snore
40% - not all of these people have obstructive sleep apnoea
Define sleep
Reversible unconsciousness with a characteristic EEG pattern
Why do we sleep
Energy conservation
– oxygen consumption, temperature and heart rate all fall during sleep. Basal Metabolic Rate (BMR) also falls by 5-25 %
Restoration
– anabolism occurs during slow wave sleep (SWS), which is also the time when Growth Hormone (GH) is released. An increased need for growth leads to an increased need for sleep e.g. in pregnancy and after exercise
How can sleep be classified
Non-rapid eye movement (NREM) and Rapid eye movement (REM)
How is NREM divided
Stages 1 - 4
1 - 2: Light sleep
3 - 4: Deep sleep - Slow wave sleep (SWS) - the majority of SWS occurs in the first 1/3 of the night
How is REM classified and when does most REM sleep occur
Tonic and phasic subtypes
Dreaming occurs in REM sleep
Occurs in the last 1/3 of the night
What is a sleep cycle, how long is one sleep cycle and how many occur throughout the night
NREM (1-2) —> NREM (3-4)/SWS –>NREM (1-2) –> REM
±90 minutes per cycle
5 - 6 cycles per night
What is a hypnogram
A graph that plots depth/type/phase of sleep versus time
What is polysomnography
Collection of measurements during sleep including
- EEG
- EMG
- EOG
Describe EEG findings in the different stages
Awake: Beta waves (16 - 25 Hz)
Stage 1: Alpha waves (8 - 12 Hz) Theta waves (3 -7 Hz)
Stage 2: Sleep spindles (higher amplitude, higher frequency bundles) K Complexes (high amplitude low frequency bundles)
Stage 3 - 4 (SWS): Delta waves (0.5 - 3 Hz)
REM:
Mixed frequency + Low voltage
Describe the EMG findings in Stage 1 - 4 NREM sleep
Decreased tone
Describe the EMG findings in REM sleep
Tonic REM - no tone
Phasic REM - increase tone
Describe the EOG findings in STAGE 1 - 4 NREM
Stage 1 -slow rolling
Stage 2 - 4 - none
Describe the EOG findings in REM
Tonic REM - no movement
Phasic REM - increased movement
How do we fall asleep
Reduced sensory input via the ascending RAS to the thalamus
Circadium rhythm
- intrinsic clock with input from extrinsic conditioning (routine of work mealtimes, day-night cycle) keeps accurate 24 hours cycle.
Desire to sleep driven by
- time since last sleep
- quality of last sleep
Describe the physiological changes during sleep relevant to OSA
Pharyngeal muscle tone - decreased in REM and NREM
Airway resistance - increased in REM and NREM
Response to hypoxia - decreased in REM and NREM
Response to hypercapnoea - decreased in REM and NREM
HR and BP increase upon arousal from sleep
During which stage of sleep (REM vs NREM) is Ventilatory response to hypoxia and hypercapnoea most impaired
REM
When awake:
Which muscles hold the tongue forward?
Which muscles hold the soft palate forward?
What happens to these muscles during sleep?
Tongue - genioglossus
Soft palate - Palatine muscles
Loss of muscle tone - negative pressure occurs during inspiration airway collapse occurs at the level of the soft palate and posterior to the tongue
Define apnoea
Cessation of airflow at the mouth and nose for greater then 10 seconds
Classify the causes of apnoea
Central (intermittent loss of respiratory drive)
Obstructive (respiratory drive present but intermittent airway obstruction results in the failure of air to flow
Define Obstructive Sleep Apnoea
Spectrum of disorders ranging from partial to complete airway obstruction during sleep which leads to multiple arousals and disruption of sleep architecture
Describe the spectrum of obstructive sleep apnoea
Snoring - soft palate fluttering with breathing. (40% population, 60% elderly population)
Upper airway resistance syndrome
- small degrees of airway obstruction that do not fulfil the diagnostic criteria described later. However, the patient experiences multiple arousals from sleep, resulting in poor sleep and daytime sleepiness.
Hypopnoea
- Airflow reduced by >50 % for >10 s. Obstructive Sleep Apnoea/Hypopnoea Syndrome diagnosed if they occur >5 times per hour.
No airflow for >10 seconds. Obstructive Sleep Apnoea/Hypopnoea Syndrome (OSAHS) is diagnosed if they occur >5 times per hour. They are usually heavy snorers who experience pauses in breathing followed by a ‘heroic’ snore as arousal reopens the airway.
It is common for there to be 60-80 episodes of obstruction per hour in severe cases. This also blunts the hypoxic and hypercarbic ventilatory reflexes.
How is OSA diagnosed
Screening with home pulse oximetry
If diagnosis remains in doubt - Sleep study (polysomnography)
What are the pathological effects of severe chronic OSA
HPV –> pulmonary hypertension and RHF
Polycythaemia
Raised BP (from multiple arousals)
Daytime sleepiness –> Road Traffic Accidents
–> Untreated OSA: 7 - 20 x more likely to be involved in an accident
What are the adult risk factors for OSA
Middle aged, fat male who smokes ± endocrine disease (acromegaly/hypothyroidism) ± nasal obstruction
Alcohol and sedatives: Reduce pharyngeal tone and may also superimpose upon central apnoeas, worsening hypoxia
What are the adolescent risk factors for OSA
Small jaw Big tongue Craniofacial abnormalities e.g.: - Down's Syndrome - Pierre Robin Syndrome - Treacher Collins Syndrome - Post cleft palate repair
What are the children risk factors for OSA
Age 2-6
Large tonsils with a normally small airway
Sleep with neck extended
25 % have right ventricular abnormalities
Classify the treatment of OSA
Lifestyle
- Lose weight
- Stop smoking
- Avoid EtoH and sedatives
- Sleep on side
Pharmacological
- none
Non-pharmacological
- Airway splinting: CPAP and Mandibular Repositioning device
Surgery
- Tonsillectomy
- Maxillofacial surgery (craniofacial abnormalities)
- Tracheostomy (in life threatening refractory cases)
- UPPP (Uvulopalatopharyngoplasty) -> not recommended - can make CPAP ineffective if needed at later stage
What is the gold standard treatment option for OSA
CPAP - pneumatic airway splinting (7 - 15 cmH2O)
–> Intelligent machines adjust the pressure to maintain airflow
If CPAP is used correctly - how long does it take until improvement is observed
2 - 3 days –> sleepiness resolves. Soft palate oedema resolves
2 - 3 weeks chemoreceptor function improves
The rapid results seen with this treatment contribute to a high compliance rate.
What are the 3 major concerns for OSA patients
- Difficult intubation and difficult BVM
- Anaesthetic drugs and opioids (with decreased V response) -> increased risk of airway obstruction intra and post-operatively –> hypoxic episodes
- Occult CVS disease
Describe some pre-operative considerations in patients with suspected/confirmed OSA
- Cancel if OSA suspected but not confirmed
- ECG/FBC –> RHF/Polycythaemia
- Avoid premeds
- ? RA alone to avoid airway maintenance issues with GA
Describe some intra-operative considerations in patients with OSA
- Prepare for difficult intubation and ventilation
- Anticipate difficulty with extubation due to the residual effects of anaesthetic drugs.
- Use regional anaesthesia and opioid-sparing techniques to limit post-operative sedation.
Describe some post-operative considerations in patients with OSA
- Bring home CPAP machine
- Overnight oximetry
- ? HDU/ICU
- 3rd post op night worst –> increased REM sleep
