OSA is defined by sleep interruption resulting from repetitive upper airway narrowing or collapse leading to airway occlusion. You need both symptoms and evidence on objective testing to meet the diagnosis.

Leads to apneas (no flow for 10+ seconds) or hypopneas (reductions in flow). These events divided by total sleep time comprise the apnea-hypopnea index (AHI) which is the best composite metric of OSA severity. The degree of sleepiness does not exactly correlate to the AHI.

AHI	OSA Severity
5-14	Mild
15-30	Moderate
>30	Severe
# Pathophysiology of OSA
Sleep --> decreased upper airway tone --> decreased patency --> snoring and dynamic upper airway collapse. Worse during REM due to the atonia of pharyngeal muscles.

Brief awakening from sleep due to hypoxia and adrenergic stress --> microarousals --> restored airway patency --> normal ventilation.

Repetitive arousing stimuli and disrupted sleep architecture contribute to excessive daytime sleepiness and neurocognitive symptoms. Desaturations can be profound especially with other lung or heart diseases. The adrenergic stress is causally linked to hypertension, arrhythmias such as atrial fibrillation. OSA is associated with HF, CV death, and diabetes as well.

Risk Factors

1. Obesity is the number 1 risk factor for OSA (BMI typically > 40)
2. Increased age, male sex
3. Alcohol and other sedative medications
4. Anatomic: tonsillar hypertrophy, macroglossia, retrognathia, micrognathia, upper airway mass lesions, increased neck size, other craniofacial abnormalities

Clinical Features and Diagnosis

History and Physical

• The most predictive indicator is whether the patient has nocturnal choking/gasping (LR 3.3).
• Snoring is non-specific. Other symptoms include overnight awakenings, nocturia, morning headaches, and unrefreshing sleep.
• However, no other findings on history and physical are good enough to rule in or out the diagnosis.

Polysomnography (PSG)

• Level I In-lab PSG is the gold standard of diagnosis particularly for people in whom the diagnosis is important (comorbid, drivers, etc)
• Level II full-ambulatory PSG, Level III multichannel CV/R recording devices, and Level IV oximetry can be used to confirm the diagnosis in patients with a moderate to high pretest probability of OSA. Home testing is increasingly used especially in patients with a high pre-test probability.

Management of OSA

Indications for Treatment

1. Daytime symptoms of excessive sleepiness (the strongest indication) or impaired sleep-related QoL (such as mood disturbance, etc) --> all patients should be offered treatment
2. Asymptomatic patients with severe OSA (AHI > 30), critical occupation, or with comorbid HTN or CV disease

Treatment Modalities

1. Positive airway pressure (PAP) therapy splints the airways open and reduces the AHI towards zero.
   1. Fixed-CPAP or auto-CPAP. There is no role for BPAP unless there is a comorbid hypoventilation syndrome.
   2. Oral appliances for mild to moderate OSA. Higher rates of adherence
2. Lifestyle changes such as weight loss (pharm, exercise, diet, surgery) should be offered to all.
3. Surgical referral should be considered for patients with BMI < 40 who are intolerant for PAP (tonsillectomy, uvulopalatopharyngoplasty, maxillomandibular advancement)

Effects of Treatment

• PAP is shown to modestly reduce BP (akin to 1 BP medication)
• PAP is NOT shown to reduce CV outcomes in asymptomatic patients with moderate to severe OSA (based on 2016 NEJM RCT)

Driving and OSA

Severity of OSA alone (i.e. AHI) is not a reliable predictor of collision risk and should not be used in isolation to assess fitness to drive. You need to consider the comorbidities, sleep schedule, and history and awareness of collisions and risk, in addition to the OSA severity.

• Mild OSA without daytime sleepiness without reported driving difficulties: Safe to drive any motor vehicle.
• Moderate to severe OSA:
  • Noncompliant: not safe to drive any vehicle
  • Compliant (≥4 hours ≥70% of nights in the past 30 days, with documented efficacy (i.e. symptom improvement, AHI reduction)): Safe to drive any motor vehicle
  • High AHI: high risk for MVC
• OSA and compliant with therapy with at-fault MVC: do not drive for 1 month, needs reassessment of compliance in that timeframe.

References

1. MKSAP 19
2. 2011 CTS Guidelines on SDB
3. 2019 AASM Guideline on OSA and PAP
4. 2019 CMA Driver's Guide
5. JAMA RCE for PSA