Obstructive Sleep Apnoea Flashcards
What is OSA?
- Upper airway obstruction during sleep
- Upper airway narrowing, provoked by sleep causing sufficient sleep fragmentation = daytime symptoms usually excessive sleepiness
Typical OSA patient
- Male
- Upper body obesity (collar size >17 inches)
- Relatively underesized mandible or set back mandible
Pathophysiology of OSA
- Upper airway patency depends on dilator muscles activity - all muscles relax during sleep
- Some narrowing of upper airway is normal
Excessive narrowing can be due: - already small phargyneal size which then narrows a normal amount during sleep but causes critical narrowing
OR - excessive narrowing occuring with relaxation during sleep
Cause of small pharyngeal size
- fatty infiltration of pharyngeal tissues and external pressure from increased neck fat and/or muscle bulk
- Large tonsils
- Craniofacial abnormalities
- Extra submucosal tissue eg myxoedema
Causes of excessive narrowing of airway during sleep
- Obesity may enhance residual muscle dilator action
- Neuromuscular disease with pharyngeal involvement = loss of dilator muscle tone eg stroke, MND, myotonic dystrophy
- Muscle relaxants - sedatives. alcohol
- Increasing age
Clinical effects of OSA
- Repetetive airway collapse with arousal needing to reactivate pharyngeal dilators –> hypoxia or hypercapnia
- Hyperfragmented sleep from arousals = unrefreshing sleep
- Excessive daytime sleepiness
- Every arousal = rise in BP of over 50mmHg, also daytime rise in BP, damage CVS unclear?
- Nocturnal sweating, reduced libido, oesophageal reflux - less common
How is hypoxia and hypercapnia corrected?
- During the inter-apnoeic hyperventilatory period
Who often witnessess OSA?
Partner - witnesses snoring and arousals
What scale is used to measure sleepiness from OSA?
- Epworth sleepiness scale
What is classed as excessive daytime sleepiness?
Epworth score of >9
Epworth sleepiness scale point system
0 - would never dose
1 - slight chance
2 - moderate chance
3 - high chance
What scenarios are asked to be scored in Epworth sleepiness scale?
- Sitting and reading
- Watching TV
- Sitting in public place eg theatre
- Passenger seat in car for 1hr
- Lying down to rest in afternoon
- Sitting and talking
- Sitting quietly after lunch without alcohol
- In a car, whilst stopped in traffic
How is OSA diagnosed?
Sleep study
Types of sleep studies
- Overnight oximetry alone
- Limited sleep study - oximetry, snoring, body movement, HR, oronasal flow, chest/abdo movements, leg movements
- Full polysomnography - limited study plus EEG, EMG
Usual choice of study for diagnosing OSA
Limited sleep study
Management of OSA - what is it based on
- Based on symptoms/QOL and NOT on severity seen on sleep study
- Also consider livelihood eg if driver as occupation
Management of OSA - simple
- Weight loss
- Sleep on side rather than supine
- Avoid/reduce evening alcohol intake
Management of snores/mild OSA
- Mandibular advancement device
- Pharyngeal surgery as last resort
Management for significant OSA
- Nasal CPAP
- Gastroplasty/bypass
- Rarely tracheostomy
Management for severe OSA and CO2 retention
- NIV prior to CPAP if acidotic (BiPAP)
- But compensated CO2 may reverse with CPAP alone
OSA driving advice
- NOT to drive when sleepy
- Stop and nap
- Notify DVLA on diagnosis
- May be advised to stop driving altogether eg HGV driver
CPAP - what is it
- Usually given via nasal mask but can use mouth/nose masks
- Upper airway splinted open with 10cm H2O pressure - prevents airway collapse, sleep fragmentation and daytime sleepines
- Also opens collapsed alveoli and improves V/Q
CPAP vs BiPAP
CPAP
* constant pressure during inspiration and expiration therefore is not a form of ventilatory support
* Can be used to treat OSA and helps oxygenation in some patients with acute resp failure eg pulmonary oedema
BiPAP (NIV)
* provides ventilatory support
* Two levels (bilevel) of pressure, selected inspiratory and expiratory positive pressures (IPAP and EPAP).
* can be set up with back up rates sp machine operates when resp rate drops below a fixed level
