POLYsomnography for ent from standard ent text books

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Polysomnography (PSG) - From Standard ENT Textbooks

1. Definition and Overview

Polysomnography (PSG) is the gold standard investigation for the diagnosis of sleep-disordered breathing (SDB), including obstructive sleep apnea (OSA). It involves simultaneous recording of multiple physiological parameters during sleep to characterize sleep architecture, respiratory events, and their consequences.

(Cummings Otolaryngology; K.J. Lee's Essential Otolaryngology; Scott-Brown's Otorhinolaryngology)

2. Parameters Recorded in a Full (Level 1) PSG

A complete polysomnogram records the following:

Category	Parameters Recorded
Sleep staging	Electroencephalography (EEG), Electrooculography (EOG), Electromyography (EMG)
Respiratory effort	Chest and abdominal wall motion (strain gauges / respiratory inductive plethysmography)
Airflow	Nasal-oral thermistor, nasal pressure transducer
Gas exchange	Pulse oximetry (SpO2), end-tidal CO2 or transcutaneous CO2
Cardiac	Electrocardiogram (ECG)
Other	Body position, snoring sound, video monitoring
Optional	Esophageal pressure (Pes) - for UARS detection

Esophageal pressure monitoring (Pes) is the most sensitive method to detect Upper Airway Resistance Syndrome (UARS), but is not routinely performed. (Cummings Otolaryngology)

3. Levels of Sleep Studies (AASM Classification)

(K.J. Lee's Essential Otolaryngology)

Level 1 PSG - The standard, attended, hospital-based overnight study:

Requires at least 6 hours of recording with sleep efficiency ≥70%
A technician hooks up all leads and remains present overnight
Records EEG, ECG, EOG, nasal airflow, SpO2, thoracic and abdominal movements, leg movements, body position, and snoring
Can distinguish central from obstructive apnea
Can be performed as a split-night study: diagnostic first half + CPAP titration second half
Limitation: expensive, resource-intensive; patients often report atypical sleep in the lab

Level 2 PSG - Home-based but with identical recording channels to Level 1; no technician present. Rarely used due to high rate of lost data from displaced leads.

Level 3 PSG (Ambulatory Sleep Study) - Home-based with fewer channels, typically recording SpO2, body motion, snoring, and chest movement. Growing rapidly due to convenience, lower cost, and improved accuracy. Must be part of a comprehensive sleep program and interpreted by a qualified expert.

Level 4 PSG - Home oximetry alone. Simple but insufficient for therapeutic planning; prone to false positives (mild COPD) and false negatives (OSA without major desaturation). Rarely used.

4. Key Definitions Measured on PSG

Obstructive Apnea: Cessation of airflow with continued respiratory effort.

Adults: duration ≥10 seconds
Children: duration ≥2 times the typical breath interval (due to faster respiratory rates)

Obstructive Hypopnea: Partial reduction in airflow with continued respiratory effort (no universally agreed upon definition in children across centers).

Central Apnea: Cessation of airflow due to absent respiratory effort.

Apnea-Hypopnea Index (AHI): Number of apneas + hypopneas per hour of sleep. The primary diagnostic measure.

Respiratory Disturbance Index (RDI): Number of all respiratory events including respiratory effort-related arousals (RERAs) per hour of sleep. RERAs require esophageal pressure monitoring and are seldom routinely measured.

Obstructive Hypoventilation: End-tidal CO2 ≥50 mmHg for more than 8-10% of total sleep time.

5. PSG Tracings - Typical Patterns

Fig. A - Obstructive Apnea (Cummings, Fig. 186.4A): The nasal-oral thermistor and expired CO2 flatten during the apneic episode while chest and abdominal wall movements continue, indicating effort against a closed airway. SpO2 falls shortly after the event.

Obstructive apnea PSG tracing showing flat thermistor with continued chest/abdominal effort and falling SpO2

Fig. B - Obstructive Hypoventilation: Continuous partial airway obstruction results in elevated end-tidal CO2 and a progressive fall in SpO2, with paradoxic inward rib cage motion visible.

Obstructive hypoventilation PSG tracing with elevated end-tidal CO2 and falling SpO2

Real PSG from Scott-Brown's (Fig. 27.3): A multi-channel overnight study showing repeated desaturations (low SpO2) and decreased airflow despite ongoing thoracic and abdominal respiratory effort - confirming OSA.

Multi-channel PSG study showing desaturations and decreased airflow with continued respiratory effort, confirming OSA

6. Severity Classification of OSA on PSG

Adults (Scott-Brown's Otorhinolaryngology)

Severity	AHI (events/hour)
No OSA	AHI <5
Mild OSA	AHI ≥5 and <15
Moderate OSA	AHI ≥15 and <30
Severe OSA	AHI ≥30

Blood pressure is typically at risk when AHI >30. Note: these criteria do not account for desaturation index or duration of individual apneas.

Children (Pediatric PSG - Cummings, Box 186.2)

Box 186.2 - Abnormal Values of Pediatric Polysomnography

Abnormal Pediatric PSG Criteria:

OSA: Obstructive apnea index (AI) >1/hour; AHI >1/hour
- Mild: AHI 1-4 | Moderate: AHI 5-10 | Severe: AHI >10
Minimum SpO2 below 92%
Hypoventilation: Peak end-tidal CO2 >53 mmHg; OR end-tidal CO2 >50 mmHg for >10% of total sleep time
UARS: Esophageal pressure between -10 and -20 cm H2O

In normal children (Marcus et al.), average AI = 0.1 ± 0.5/hr; minimum SpO2 = 96 ± 2%, meaning AI >1/hr is abnormal.

7. When to Use PSG in ENT Practice

Indications

Diagnosis and quantification of OSA (adults and children)
Differentiating OSA from primary (simple) snoring
Detecting UARS
Pre-operative assessment before adenotonsillectomy in high-risk children (per AAO-HNS guidelines):
- Obesity, Down syndrome, craniofacial abnormalities, neuromuscular disorders, sickle cell disease, mucopolysaccharidoses
- Healthy children where clinical picture is uncertain or tonsil size is discordant with SDB severity
Children who remain symptomatic after adenotonsillectomy
Before initiating CPAP/BiPAP in high-risk children or surgical failures
Complex cases: narcolepsy, parasomnias, periodic limb movement disorder (where EEG/EMG are essential)
Neuromuscular disorders requiring nocturnal ventilation
Suspected obesity-hypoventilation syndrome (transcutaneous CO2 monitoring needed)

(Cummings Otolaryngology; Scott-Brown's Vol 1)

8. When is Level 1 (In-Hospital) PSG Needed vs. Home Testing?

(Scott-Brown's Otorhinolaryngology, Vol 1)

In-hospital PSG required for:

Complex OSA (suspected OHS - needs transcutaneous CO2 monitoring)
Neuromuscular disorders (may need assisted ventilation during the study)
Narcolepsy, parasomnias, periodic limb movement syndrome (require full EEG/EOG/EMG)
CPAP titration in complex patients
Unattended studies that previously failed (disconnected leads)

Home (Level 3) ambulatory testing acceptable for:

Straightforward suspected OSA in otherwise healthy adults
Improves diagnostic adherence (patients trust the diagnosis more in their own home)
More convenient and lower cost

9. Limitations of PSG

(Cummings Otolaryngology)

PSG has never been validated to predict risk of adverse outcomes or response to treatment.
A dichotomy often exists between PSG severity and clinical symptom severity - very symptomatic children may have normal PSGs; asymptomatic snorers may have severe findings.
No standardized monitoring method across centers; no universal consensus on what constitutes an "abnormal" study.
First-night effect: Patients frequently report that sleep in the laboratory was atypical - especially in children under 3, where caution is needed in interpreting results (Scott-Brown's Vol 2).
Scoring variability: How hypopneas are scored (AASM vs. Stanford criteria) dramatically changes results - in one study, OSA prevalence varied from 19% to 99% depending on the definition used.
In children, sleep architecture differs with age: preschoolers have more central apneas and are less likely to awaken than school-age children with comparable SDB.
The accuracy of clinical assessment alone vs. PSG in children ranges from 30-88% depending on criteria used - highlighting both the value and the pitfalls of PSG.

10. Alternatives to PSG

Alternative	Method	Notes
Ambulatory device (e.g. ApneaLink Plus)	Nasal airflow + chest movement + SpO2	Comparable to PSG for OSA detection in obese adolescents
Actigraphy	Wrist-worn accelerometer	Good for sleep-wake pattern estimation; no respiratory data
Home oximetry (Level 4)	SpO2 only	Insufficient alone; false positives (COPD) and false negatives (mild OSA)
Clinical scoring tools	PSQ-22 (sensitivity 78%, specificity 72%)	Can predict PSG positivity but does not replace it
	CAS-15	77.3% sensitivity, 60.7% specificity for AHI >2 in children

11. PSG in the Context of UARS

Upper Airway Resistance Syndrome (UARS) is a form of SDB that does not meet standard apnea/hypopnea criteria. On PSG, UARS is characterized by:

A repetitive pattern of increasing negative esophageal pressure culminating in an arousal
Awake esophageal pressure is normally -10 to -5 cm H2O
UARS is diagnosed when pressure repeatedly reaches -10 to -20 cm H2O before arousal

This requires esophageal pressure monitoring (Pes) - not routinely available in most centers. (Cummings Otolaryngology)

Sources:

Cummings Otolaryngology Head and Neck Surgery (9780323612173), Chapter 186 - Polysomnography & Pediatric Sleep
K.J. Lee's Essential Otolaryngology (9781260122237) - Levels of PSG, OSA severity
Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol 2 (9781138094634) - Pediatric PSG
Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol 1 (9781138094642) - Overnight PSG, OSA criteria, CPAP indications

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