Sleep Apnoea and Respiratory Failure Flashcards
What happens on inspiration?
- rib cage moves up and out
- intercostal muscles contract
- diaphragm contracts and moves down
- pressure in lungs decreases so less than outside and air rushes in
What happens on expiration?
- intercostal muscles relax
- diaphragm relaxes and moves up
- elastic recoil of lungs forces them to contract
- pressure inside lungs greater than outside so air gets pushed out
What are the peripheral chemoreceptors?
- carotid and aortic bodies
Hypoxic pulmonary vasoconstriction
- if alveolus has no oxygen supply = hypoxic
- vasoconstriction occurs = no perfusion = no more oxygen = won’t be inflated
Type 1 respiratory failure
- PaO2 <8 kPa
Type 2 respiratory failure
PaO2<8kPa AND PaCO2 >6.5kPa
Mechanisms of hypoxia
- hypoventilation
- diffusion abnormality
- ventilation/perfusion mismatch
- right to left cardiac shunt bypassing lungs
- low inspired oxygen = high altitude/air flight
Example of ventilation perfusion mismatch
Lobar pneumonia Asthma = mucus plugs so obstructs airflow Lobar collapse PE Pneumothorax
Example of diffusion abnormality
Sarcoidosis
Pulmonary fibrosis
COPD
Example of hypoventilation
Kyphoscoliosis Thoracoplasty for TB COPD Motor Neurone Disease Muscular Dystrophy Morbid obesity
Example of right to left shunt
Eisenmenger syndrome
Types of Resp Failure
Acute and chronic for type 1 and 2
LTOT
- improves survival for COPD with hypoxia
- reduces hypoxia complications = polycythaemia, cor pulmonale
- at least 15 hours per day
Define COPD with hypoxia
PaO2<7.3kPa
Chronic Type 1 Resp Failure Consequences
- Pulmonary hypertension
- Cor pulmonale = peripheral oedema
- 2ndry polycythaemia = stroke
- symptoms from ischaemic heart/peripheral vascular diseases
- poor sleep/fatigue
CPAP
= continuous positive airway pressure
- pushes pressure into airways mainly during exp
- expands collapsed portions of lungs which are under ventilated
- improves hypoxia and V/Q mismatch
- keeps airways open in sleep apnoea
- doesn’t overcome hypoventilation
Cause of type 2 resp failure
ventilation failure
Treatment of acute type 2 resp failure
- oxygen therapy
- 0.5 to 2l/min via nasal cannulae
- 24%-28% masks using venture valves
- keep sats 88-92%
- monitor Co2 levels via ABG regularly
- consider nn invasive ventilation if Ph and Co2 not improving
Causes of hypoventilation
- airways obstruction = COPD< severe asthma
- hyper expanded lungs = COPD
- thoracic cage problems = kypho, thoacoplasty, obesity
- weakness of resp muscles = MND, musc dystrophy
Non invasive ventilation
- improves hypoventilation
- delivers high pressure during insp
- improves oxygenation
- reduces/prevents hypercapnia
- useful in conditions causing hypoventilation and Type 2 resp failure
When to use Non invasive ventilation
- acute type 2 in hospital (COPD exacerbations)
- chronic type 2 at home
Define obstructive sleep apnoea?
- repetitive episodes of partial or complete upper airway obstruction during sleep
Where is the problem anatomically in sleep apnoea?
- between soft palate and tongue base
How to diagnose sleep apnoea?
- home sleep study
Define apnoea?
complete cessation of airflow for at least 10 seconds
Define hypopnoea?
Reduction in airflow to under 50% or by 30% for at least 10 seconds
- with desaturation of at least 4%
Apnoea and Hypopnoea Index
number of apnoeas and hypopnoeas per hour of study
How to measure severity of sleep apnoe
Apnoea and hypopnoea index
RDI
Respiratory Disturbance Index 0-5 = normal 5-15 mild OS 15-30 = moderate 30+ severe
OSA Who?
- 1 in 5 adults
- 24% mild and 9% women
- increases with age until 65
- most undiagnosed
RF of OSA
- obesity! = narrowed airway
- BMI>30
- neck circumference >16.5 inches
- male = longer pharyngeal airway
- Afro-Caribbean
- micrognathia
- tonsillar hypertrophy
Associated conditions with OSA
- micrognathia or retrognathia
- large adenoids and tonsils
- acromegaly
- Downs
- Hypothyroid
- cushings
- T2D
- HTN
Sleep History
- bed partner/family
- heavy snoring
- witnessed apnoeas = prod to start breathing
- arousals = wake up suddenly with snort
- unrefreshed on waking
- daytime tiredness
- planned and unplanned naps
- other CV RF
OSA Diagnosis on history how?
Epworth Sleepiness Scale
out of 24
>10 abnormal
Consequences of OSA
- excessive daytime hypersomnolence
- fall asleep at wheel
- sustained attention required for cognitive function
- 2-3x greater risk of car crash
- inform DVLA of diagnosis
Medical consequences of OSA
RF for
- CV mortality
- systemic HTN
- T2D
- CAD
- Stroke
- Congestive HF
- Pulmonary HTN
- cardiac arryhtmias
Treatment for OSA
- CPAP
- weight loss
- avoiding alcohol and sedatives
- non supine sleep
- tonsillectomy
- mandibular advancement splints
- palatal surgery
- maxillofacial surgery
- treat cause
Indication for mandibular splints
- for simple snorers or mild/mod OSA
- intolerance of CPAP
Indication for CPAP for OSA
- moderate or severe sleep apnoea
