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Sleep Medicine

intermediate

OSA diagnosis, CPAP titration, PSG interpretation, hypoventilation syndromes, and home ventilation.

65 min estimated

Lessons

Obstructive Sleep Apnea: Diagnosis and Severity

Obstructive sleep apnea (OSA) is repetitive upper airway collapse during sleep, causing apneas (≥10 sec cessation), hypopneas (≥30% flow reduction + arousal or desaturation), and arousals.

Diagnosis: polysomnography (PSG) is the gold standard. Home sleep apnea testing (HSAT) acceptable for uncomplicated moderate-to-severe OSA suspicion.

Apnea-Hypopnea Index (AHI) = apneas + hypopneas per hour: - Normal: <5/hr - Mild OSA: 5–14/hr - Moderate OSA: 15–29/hr - Severe OSA: ≥30/hr

Symptoms: loud snoring, witnessed apneas, gasping/choking, EDS (excessive daytime sleepiness), morning headaches, nocturia. STOP-BANG: screening questionnaire (≥3 = high risk).

Complications: hypertension, cardiovascular disease, arrhythmias (AFib), stroke, type 2 diabetes, metabolic syndrome, pulmonary hypertension.

AHI: mild 5–14, moderate 15–29, severe ≥30 events/hr
Gold standard diagnosis: overnight polysomnography (PSG)
HSAT acceptable for uncomplicated moderate–severe OSA screening
OSA complications: HTN, AFib, stroke, pulmonary hypertension, metabolic syndrome
STOP-BANG: ≥3 positive answers = high risk for OSA

Clinical Tip

OSA is the most common sleep disorder in adults and the most common indication for CPAP therapy. Undiagnosed OSA is associated with a 2–3x increased risk of motor vehicle accidents.

CPAP Therapy: Titration and Troubleshooting

Continuous positive airway pressure (CPAP) is first-line treatment for moderate-to-severe OSA. It acts as a pneumatic splint, maintaining upper airway patency through the applied pressure.

Titration: either in-lab CPAP titration (split-night study or full titration night) or auto-titrating CPAP (APAP, adjusts pressure based on flow limitations). Pressure range typically 4–20 cmH2O.

Common CPAP problems and solutions: - Mask leak: refit mask, try different interface - Pressure intolerance: use CPAP with ramp, switch to bilevel (BiPAP) - Aerophagia (air swallowing): reduce pressure or switch to bilevel - Central apneas emerging on CPAP: complex sleep apnea — consider ASV (adaptive servo-ventilation) - Nasal congestion: heated humidifier, nasal steroids

Compliance: defined as ≥4 hr/night on ≥70% of nights. Poor compliance = undertreated OSA.

CPAP: pneumatic splint keeping upper airway open; first-line for OSA ≥15 AHI or ≥5 with symptoms
Auto-CPAP (APAP): adjusts pressure dynamically — used for stable uncomplicated OSA
Compliance: ≥4 hours/night ≥70% of nights
Central apneas on CPAP = complex sleep apnea → consider ASV
BiPAP for CPAP intolerance, hypoventilation, or pressure >15 cmH2O needed

Clinical Tip

If a patient reports CPAP working well but still feeling sleepy, check the device data report — compliance and residual AHI. Consider other causes of EDS (narcolepsy, poor sleep hygiene, insufficient sleep time).

Hypoventilation Syndromes and BiPAP/ASV

Hypoventilation syndromes occur when ventilation is chronically insufficient, leading to hypercapnia (PaCO2 >45 mmHg) during sleep and eventually at rest.

Obesity hypoventilation syndrome (OHS): BMI ≥30 + awake hypercapnia (PaCO2 >45) without other cause. 90% have coexisting OSA. Treatment: BiPAP (IPAP/EPAP), weight loss, CPAP (if pure OSA component).

COPD overlap syndrome (OVS): COPD + OSA — higher risk of hypercapnia, pulmonary HTN, cor pulmonale, worse outcomes than either alone.

Central sleep apnea (CSA): absent respiratory effort during apnea (vs OSA where effort continues). Causes: CHF (Cheyne-Stokes respiration), opioid-induced, idiopathic. Treatment: ASV (adaptive servo-ventilation) — contraindicated in CHF with EF <45%.

Hypoglossal nerve stimulator: surgical option for OSA not tolerating CPAP.

OHS: BMI ≥30 + awake PaCO2 >45 mmHg; BiPAP treatment of choice
OHS almost always has coexisting OSA (90%)
Central sleep apnea: no respiratory effort; treat with ASV (unless CHF EF <45%)
ASV contraindicated in CHF with EF <45% (increased mortality — SERVE-HF trial)
Cheyne-Stokes respiration: waxing-waning ventilation, seen in CHF

Clinical Tip

ASV was thought to be ideal for CHF-related Cheyne-Stokes, but the SERVE-HF trial showed increased mortality in CHF patients with EF <45% on ASV. Now contraindicated in this population.

Key Facts

AHI: mild 5–14, moderate 15–29, severe ≥30 events/hr
OSA gold standard diagnosis: overnight PSG
CPAP compliance: ≥4 hr/night on ≥70% of nights
OHS: BMI ≥30 + awake PaCO2 >45; BiPAP first-line
Central apneas on CPAP = complex sleep apnea → consider ASV
ASV contraindicated: CHF with EF <45% (SERVE-HF trial)
Cheyne-Stokes: crescendo-decrescendo breathing in CHF
STOP-BANG ≥3 = high OSA risk

NBRC Pearls

NBRC tests AHI severity criteria: 5–14 mild, 15–29 moderate, ≥30 severe
ASV is contraindicated in CHF EF <45% — NBRC tests this
OHS = obese + awake hypercapnia — BiPAP, not just CPAP
Cheyne-Stokes in CHF: central sleep apnea pattern

Memory Tricks

💡AHI severity: 'Five to fourteen is mild, fifteen is the moderation line, thirty is severe'
💡OHS: 'Obese + Hypercapnic = Hypoventilating → BiPAP'
💡ASV in CHF: 'SERVE-HF served a warning — avoid ASV in low EF'

Common Mistakes

Using ASV in CHF patient with EF <45% (contraindicated, increased mortality)
Confusing AHI cutoffs for severity — mild starts at 5, not 10
Diagnosing OSA without PSG in patients with complex comorbidities (need full PSG)
Not adding BiPAP for OHS — CPAP alone does not treat hypoventilation component

Clinical Cases

OSA with Insufficient CPAP Response

A 52-year-old male with severe OSA (AHI 42) is on CPAP 10 cmH2O. He reports improvement but still has morning headaches. Download shows AHI 8 with 3 central apneas per hour on CPAP. SpO2 nadir 82%.

What is the most likely diagnosis and appropriate next step?

Complex sleep apnea (treatment-emergent central apneas). Switch to ASV or BiPAP-ST; first rule out CHF (check EF before ASV).

When central apneas emerge on CPAP therapy (treatment-emergent central sleep apnea), this is 'complex sleep apnea.' The residual AHI is driven by centrals, not obstructive events. ASV is most effective but requires EF ≥45% — check echo first. BiPAP-ST (with a backup rate) is an alternative if ASV is contraindicated.

Know This for NBRC

AHI severity cutoffs: mild 5–14, moderate 15–29, severe ≥30
CPAP compliance definition: ≥4 hr/night, ≥70% of nights
OHS: BMI ≥30 + awake hypercapnia — BiPAP not CPAP
ASV contraindicated in CHF EF <45%
Complex sleep apnea: central apneas emerging on CPAP therapy

Sleep Medicine

Lessons

Obstructive Sleep Apnea: Diagnosis and Severity

CPAP Therapy: Titration and Troubleshooting

Hypoventilation Syndromes and BiPAP/ASV

Key Facts

NBRC Pearls

Memory Tricks

Common Mistakes

Clinical Cases

Know This for NBRC

Related Topics

Sleep Medicine

Lessons

Obstructive Sleep Apnea: Diagnosis and Severity

CPAP Therapy: Titration and Troubleshooting

Hypoventilation Syndromes and BiPAP/ASV

Key Facts

NBRC Pearls

Memory Tricks

Common Mistakes

Clinical Cases

Know This for NBRC

Related Topics