Sleep reporting Flashcards
Apnoea
- at least 10 secs
- > 90% reduction in airflow
- no desaturation criteria (no min change in spo2)
- can be obstructive, central or mixed
Hypopnea
- at least 10secs
- > 30% reduction in airflow
- minimum 3/4% desaturation (depending on lab)
- can be obstructive or central but difficult to distinguish
Predisposing factors of OSA
There are many predisposing factors to OSA. Being male and over 50, having a large neck circumference, high BMI are some of the more well known. But people can also have OSA when they have a large tongue which can occur in conditions such as acromegaly or Downs Syndrome, Craniofacial abnormalities such as macrognathia (small jaw) or retrognathia (set back jaw). If people have poor nasal patency and so mouth breath this can also promote airway collapse. A crowed airway such as enlarged tonsils or a high Mallampati score are also cause. Alcohol, due to is muscle relaxant properties can aid airway collapse. It also has a negative effect on sleep independent of this airway collapse.
AHI
< 5/hr = normal
5-15 mild
15-30 mod
>30 severe
NAION
NAION (sudden loss of vision in 1 eye due to decreased blood flow to the optic nerve) relative risk of OSA in NAION is 4.9 ie nearly 5 times the risk of these patients having OSA than the general population.
Rf for OSAHS
Who should be prioritised?
- vocational driving job
- construction machinery
- pregnancy
- pre-op patients
- NAION
-unstable cardiovascular disease (poorly controlled arrhythmia, nocturnal angina, treatment resistant HTN)
OSAHS vs OSA
- syndrome distinguishes between symptomatic and non-symptomatic relative to sleepiness symptoms
-oSAHS/OSAS = AHI>5 and daytime symptoms
OSA, SDB = AHI >5 with no excessive sleepiness or tiredness
Central sleep apnoea
10 % of sleep apnoea is central
Central sleep apnoea is a problem of breathing control. It is often associated with cardiac issues: cardiac arrhythmia (AF), congestive HF, stroke, opioid use and can also occur at high altitude.
Unlike obstructive sleep apnea, where the airway is blocked, CSA is a central nervous system issue where the respiratory drive is impaired. This can lead to pauses in breathing, and the person may or may not experience effort to breath
It occurs due to a disturbance in respiratory drive and an increased loop gain such that there is an exaggerated response leading to apnoea then an exaggerated response leading to hyperventilation, giving a pattern of over then under breathing. This is a much rarer type of sleep apnoea compared to obstructive.
When to score an apnoea as central?
If it meets apnoea criteria and is associated with absent inspiratory effort throughout entire period of absent flow
What is cheyne-stokes breathing
- Most common in patients with CHF with LV dysfunction (20-45% of patients with CHF)
- Classic waxing and waning
- Most common in NREM1 & 2
- Cycle time 60-90s (longer than CSA)
- Longer ventilatory phase
- Longer delay to nadir
- Cycle length increases with worsening HF (reducing ejection fraction)
When to score as mixed apnoea
Score an apnoea as mixed if it meets:
apnoea criteria and is associated with absent inspiratory effort in the initial portion of the event, followed by resumption of inspiratory effort in second portion of event
Sleep onset is associated with
Increased upper airways resistance. Chemoreceptor sensitivity decreases during sleep, particularly REM sleep.
In which stages are OSA and CSA worse?
REM sleep makes OSA more likely as there is increased collapsibility of the upper airway causing an obstruction. CSA is more likely to occur in NREM sleep due to the relatively higher chemoreceptor sensitivity compared to REM. CSA is more likely to occur if there is an exaggerated chemoreceptor response
Obesity Hypoventilation syndrom
Definition of OHS – must have no other condition causing hypoventilation. Therefore, an obese person with COPD or neuromuscular condition with hypoventilation cannot have OHS even if obesity is contributing to the hypoventilation.
It causes nocturnal hypoventilation = decreased chemoreceptor sensitivity and loss of waking drive to breathe
