JC16 (Medicine) - Sleep apnea Flashcards
Causes of daytime sleepiness
□ ↓sleep duration: sleep deprivation, disturbance of sleep-wake cycle
□ ↓sleep quality:
→ Respiratory: sleep apnoea (central, obstructive), obesity-hypoventilation syndrome
→ Neurological: periodic limb movement syndrome
□ Normal sleep:
→ Neurological: narcolepsy, fibromyalgia, neurological lesions
→ Others: drugs, idiopathic hypersomnolence (rare)
□ Others: depression, other medical conditions
List night-time symptoms due to sleep apnea
1) Sleep choking, unusual body/limb movements → arousals following apnoeic episodes
2) Snoring → obstructed airflow
3) Witnessed apnoeic episodes: witnessed pausing of breathing
Name of clinical assessment chart for day-time sleepiness
Epworth sleepiness scale
- Assess likelihood to feel sleepy in situations of different activity levels
Risk factors of daytime sleepiness
Nasal obstruction
Obesity
Recurrent tonsillitis in childhood
Medical conditions: acromegaly, hypothyroidism, vocal cord palsy, goitre
Drug Hx: use of hypnotics, alcohol
Complications of chronic sleep deprivation
□ Risk assessment: driving, operation of heavy machinery, any previous accidents
□ Complications: HTN, ischaemic heart disease, DM
List specific P/E for daytime sleepiness
□ Body habitus: weight, height, neck circumference
□ Craniofacial features, eg. short thick neck, receding chin (micronagthia), syndromic facies
□ Oropharyngeal features, eg. macroglossia, enlarged tonsils/uvula, excessive pharyngeal tissue
→ Examination: anterior rhinoscopy, throat examination and nasal endoscopy
□ Thyroid examination: hypothyroidism and goitre
□ BP/P: sleep apnoea is a secondary cause of hypertension
Factors affecting sleep patterns
(1) Age
(2) Prior sleep history
(3) Circadian rhythms
(4) Drug ingestion
(5) Pathological states
Outline the physiological feedback loop that control breathing during sleep
(1) Respiratory centre
(2) Chemical, mechanical and CNS information
(3) Respiratory muscles (upper airways, diaphragm and others)
Describe the normal sleep cycle of REM and NREM sleep
Normal sleep cycle: enter sleep in NREM → alternate between REM and NREM with cycles of 90min
□ REM: ~25% of sleep time, increase in later hours of sleep
□ NREM: Light (stage 1/2) vs deep sleep (stage 3/4, slow wave on EEG)
Compare REM and NREM sleep
- Body movement
- EEG
- Dreaming or non-dreaming
REM:
→ Dreaming
→ Brainstem/motor neurones inhibited, body paralyzed
→ Active vitals/EEG
NREM:
→ Decrease mental activity, regulatory body function only
→ Body movable
Compare breathing patterns between REM and NREM sleep
NREM: Low tidal volume, Normal respiratory rate
REM: erratic, shallow breathing (ataxic)
Explain why ventilation in sleep is decreased
1) Respiratory centre: suppressed arousal response
2) Chemoreceptor reflex: Lower sensitivity to O2 and CO2 → Decrease ventilatory response to hypoxia/hypercarbia
3) Resp apparatus:
- Decrease muscle contraction from intercostal muscles
- Recumbency → diaphragm pushed up → ↓FRC
Explain why hypoxia and hypercapnia does not lead to sleep apnea in normal individual
In normal healthy lungs, there will be
- Mild ↓pO2 but still normal w/o ↓SaO2 (note plateau in HbO2 curve)
- Mild ↑pCO2 but still normal
In diseased lungs, baseline is already abnormal → may have hypoxia/hypercapnia in sleep
Definition of Apnea
Apnoea: complete cessation of airflow at nose/mouth lasting ≥10s
Definition of Hypopnea
Hypopnoea: decrease airflow with ≥3-4% decrease SaO2
and >10s/episode
Metric to measure severity of sleep apnea/ hypopnea
Apnoea-hypopnoea index (AHI): number of apnoeic/hypopnoeic episodes per sleep hour
Normal = <5;
Mild OSA = 5-15;
Moderate OSA = 15-30;
Severe OSA = >30
Differentiate obstructive and central sleep apnea
Obstructive: apnoea due to functional obstruction of upper airways
→ With arousal response
Central: apnoea due to abnormalities of ventilatory drive
→ No arousal response
→ Defect in central (Low ventilatory drive) or peripheral (Low muscle contraction)
→ Causes: central neurological lesions, neuropathies, NMJ disease, muscle diseases
List anatomical abnormalities that cause obstructive sleep apnea
Anatomical abnormalities may predispose to functional obstruction
→ Micronagthia (undersized jaw)
→ Macroglossia (tongue fall back on supine posture)
→ Enlarged tonsils or adenoids: important factor in children (∵small airway)
→ Redundant pharyngeal tissues due to fatty infiltration (obesity)
Describe the pathophysiology of arousal after episodes of sleep apnea
Ventilatory drive drops during sleep
> Decrease responsiveness to changes in blood gas
> Decrease neuromuscular tone of upper airway during sleep
> Increase upper airway obstruction
> Hypoxia and hypercapnia reaches critical point
> Activate chemical receptors
> Activate wakefulness drive and arousal
Risk factors of Obstructive sleep apnea
□ Occurs in all ages but peak at middle age (40-50y)
□ Male gender
□ Obesity (50%) (parapharyngeal fat deposits narrow airway)
□ Anatomical predisposition, eg. nasal obstruction, receding chin
□ Underlying acromegaly and hypothyroidism (submucosal infiltration and narrowing of URT)
□ Alcohol and sedatives (relaxes upper airway dilating muscles)
S/S of obstructive sleep apnea
- Excessive daytime sleepiness
- Snoring
- Apneoic episodes: witness apnea, Nocturnal choking, Restlessness
- Effects of poor sleep: unrefreshing sleep with morning headache, Irritability, Low concentration, Low performance
Others:
- Low libido
- Nocturia, Enuresis
D/dx for sudden arousal with breathing difficulties during sleep
- OSA – ‘choking’ sensation
- PND – may be a/w orthopnoea, does not resolve immediately upon awakening, relieved by sleeping upright
- Asthma – a/w wheezes, Hx of atopy
- Rhinitis with severe nasal blockade
Clinical diagnostic criteria of OSA
Suspect OSA if snoring at night plus either one of
□ Excessive daytime sleepiness (EDS)
→ Mild: activity with little attention needed, eg. public transport
→ Moderate: activity with some attention, eg. conference
→ Severe: activity with much concentration, eg. phone call, conversation
□ Meeting any two out of the following: → Intermittent nocturnal arousal → Nocturnal choking → Unrefreshing sleep at wakening → Daytime fatigue → Impaired daytime concentration
Complications of obstructive sleep apnea
□ Sleep fragmentation
→ Car accidents
→ Neurocognitive impairments
□ Sympathetic activation → ↑BP → Secondary hypertension
□ Oxidative stress + release of mediators (hormones, cytokines, adipokines)
→ atherosclerosis + metabolic disturbances
→ Cardiovascular diseases, eg. CAD, HF, arrhythmia, stroke
□ Chronic hypoxaemia → chronic respiratory failure
→ Cor pulmonale (rare except in presence of other conditions, eg. OHS, COPD)
Indications for Sleep Study (polysomnography)
→ Suspected OSA
→ Unexplained pulmonary hypertension
→ Recurrent CVS events (eg. CVA, angina, CHF) or poorly controlled HT despite adequate medical therapy
List some metrics of polysomnography (what’s measured)
→ EEG, EOG and submental EMG to identify sleep stage and arousal, atonia during REM sleep
→ Lead II ECG for HR and arrhythmias
→ SaO2 for nocturnal desaturations
→ Nasal/oral airflow , thoracic and abdomen belts for respiratory effort
→ Neck microphone for snoring
→ ± leg EMG for leg movement
→ ± body position (by technician)
List characteristic obstructive sleep apnea changes on sleep study
→ SaO2: intermittent hypoxia and reoxygenation
→ HR/rhythm: tachy-brady cycles
→ Thoracic movement: intrathoracic pressure swings, paradoxical movement to abdominal distension
→ Sleep architecture: sleep fragmentation
→ Body position: some people may only get OSA at supine position
→ Leg movements: corresponding to periodic arousals
General management of OSA
→ Weight reduction if overweight
→ Avoid alcohol and hypnotics
→ Sleep hygiene and posture, eg. lying laterally
→ AVOID CAR-DRIVING
→ Mx of predisposing factors, eg. rhinitis, acromegaly, care after sedation/anaesthesia
→ Monitor for obesity-related conditions, eg. metabolic syndrome, DM, HTN
Surgical options for OSA
Surgery for anatomical abnormalities
→ Removal of hypertrophic tonsils/adenoids in children
→ Uvulopalatopharyngoplasty (UPPP):
removal/remodeling of uvula, soft palate and pharynx
→ Faciomaxillary/mandibular surgery
→ Bariatric surgery for obesity-related medical problems
→ Surgical correction of snoring/nasal obstruction
Devices for alleviation of OSA
Nocturnal nasal cPAP: application of positive pressure through nasal mask during sleep
→ Most consistently effective treatment of OSA
Mandibular advancement device
→ Device worn during sleep to advance mandible to enlarge URT and modify muscle collapsibility
Expiratory pressure device, i.e. nasal valve (to exert +ve EEP)
Specific sleep disorder related to obesity
Obesity hypoventilation syndrome (OHS): awake hypoventilation due to gross obesity
Complications of Obesity hypoventilation syndrome
Chronic respiratory failure or CO2 narcosis
Pulmonary HTN and cor pulmonale
Excessive daytime sleepiness
Management of obesity hypoventilation syndrome
□ Weight loss and lifestyle modifications
□ Treatment of comorbidities
□ Non-invasive ventilation: CPAP/ BiPAP
□ Pharmacologic and surgical weight reduction if morbidly obese, eg. Orlistat, bariatric surgery
