Obstructive Sleep Apnoea Flashcards
What is obstructive sleep apnoea?
Upper airway obstruction during sleep
What is the clinical definition of obstructive sleep apnoea?
Upper airway narrowing, provoked by sleep, causing sufficient sleep fragmentation to result in significant day time symptoms, usually excessive sleepiness
Describe a typical patient with obstructive sleep apnoea
Male
Upper body obesity (collar size >17inches)
Undersized or set back mandible
What is the pathophysiology behind obstructive sleep apnoea?
Upper airway patency depends on dilator muscle activity
All muscles relax during sleep including pharyngeal dilators
Excessive narrowing can be due to either an already small pharyngeal size during awake state which is even smaller at night when there is normal dilatation or excessive narrowing occurring with relaxation during sleep
What are 4 causes of small pharyngeal size?
Fatty infiltration of pharyngeal tissues with external pressure from increased neck fat/muscle
Large tonsils
Craniofacial abnormality
Extra submucosal tissue eg myxoedema
What are 4 causes of excessive narrowing of the airway during sleep?
Obesity enhances residual dilator action
Neuromuscular disease with pharyngeal involvement may lead to greater loss of dilator muscle tone e.g. stroke, MND,
Muscle relaxants like sedatives or alcohol
Increasing age
What is the immediate effect of OSA?
Repetitive upper airway collapse with arousal required to re activate the pharyngeal dilators
There may be associated hypoxia and hypercapnia which are corrected during the inter-apnoeic hyper ventilatory period
What are the impacts of OSA?
Recurrent arousals lead to fragmented and unrefreshing sleep leading to excessive day time sleepiness
How can day time sleepiness be measured?
Epworth Sleepiness Scale
What is a consequence on the body to arousal from sleep?
There is a rise in BP with every arousal - often over 50mmHg This may damage CVS
Rise in daytime BP
Nocturia
What are some less common side effects of OSA?
Nocturnal sweating
Reduced libido
Oesophageal reflux
What types of sleep study can be used to diagnose OSA?
Overnight oximetry alone
Limited sleep study
Full polysomnography
What does a limited sleep study involve?
Oximetry, snoring, body movement, HR, oronasal flow, chest/abdo/leg movements
What is involved in full polysomnography?
Limited sleep study plus ECG and EMG
What is the management of OSA based on?
Quality of life
What are some simple approaches to OSA management?
Weight loss, sleep decubitus not supine, avoid alcohol in the evening
How can mild OSA and snoring be managed?
Mandibular advancement device
?Pharyngeal surgery
How can significant OSA be managed?
Nasal CPAP
Gastric bypass
?Tracheostomy
How can severe OSA with CO2 retention be manages?
NIV then CPAP if acidotic
or CPAP alone
How is CPAP usually delivered?
Given via nasal mask
but can use mouth/nose mask
How does CPAP work?
Upper airways are splinted open with approximately 10mmHg H2O pressure
What is the principle behind CPAP?
It prevents airway collapse, sleep fragmentation and day time sleepiness
Opens collapsed alveoli
Improves V/Q mismatch
Does CPAP provide ventilatory support and why?
It provides a constant positive pressure during inspiration and expiration so is not a form of ventilatory supportt
What is CPAP used for?
It can be used to treat OSA and sometimes in acute respiratory failure e.g. pulmonary oedema
What is NIV and does it provide ventilatory support?
Does provide ventilatory support
Two levels of positive pressure (bilevel) for inspiratory and expiratory
Can also be set up with back up rates so the machine operates when the RR drops below a fixed level
