Sleep Apnea Overview

Sleep Apnea

Introduction to Sleep-Related Breathing Disorders

  • Sleep-related breathing disorders are characterized by abnormal breathing patterns during sleep, which include:
    • Obstructive sleep apnea syndrome (OSA)
    • Central sleep apnea syndrome (CSA)
    • Mixed sleep apnea (combination of OSA and CSA)
    • Sleep-related hypoventilation and hypoxemia syndromes (SRHHS)

Obstructive Sleep Apnea (OSA)

  • Definition: OSA is a blockage of ventilation due to upper airway obstruction, where there is no airflow despite chest and abdomen movement.

Mechanism of OSA

  • The genioglossus muscle fails to oppose the force that tends to collapse the airway passage during inspiration.
  • As a result, the tongue moves into the oropharyngeal area, obstructing the airway.

Risk Factors for OSA

  • Excessive weight
  • Neck size greater than 17 inches
  • Anatomic narrowing of the upper airway, which can include:
    • Excessive pharyngeal tissue
    • Enlarged tonsils or adenoids
    • Deviated nasal septum
    • Laryngeal stenosis
    • Vocal cord dysfunction
    • Enlarged tongue (macroglossia)
    • Recessed jaw (micrognathia)
  • Age > 65 years
  • Family history of OSA
  • Smoker
  • Use of alcohol or sedatives

Signs and Symptoms of OSA

  • Loud snoring
  • Observed episodes of breathing cessation during sleep
  • Abrupt awakenings accompanied by shortness of breath
  • Insomnia
  • Moodiness and irritability
  • Lack of concentration
  • Memory impairment
  • Awakening with dry mouth or sore throat
  • Morning headache
  • Nausea
  • Excessive daytime sleepiness (hypersomnia)
  • Intellectual and personality changes
  • Depression
  • Nocturnal enuresis
  • Sexual impotence
  • Night sweats

Apnea-Hypopnea Index (AHI)

  • The AHI is a measure that reports the number of apneas and hypopneas per hour of sleep.
  • Additional reported values include:
    • Number of arousals per hour (arousal index)
    • Percentage of each sleep stage
    • Frequency and mean of SaO2 (oxygen saturation)
    • Nadir of SaO2
  • The American Academy of Sleep Medicine (AASM) defines the severity of OSA as follows:
    • Normal AHI < 5
    • Mild AHI = 5 to 15
    • Moderate AHI = 15 to 30
    • Severe AHI > 30

Central Sleep Apnea (CSA)

  • Definition: CSA is characterized by the repetitive stopping or reduction of both airflow and ventilatory effort during sleep.

Types of CSA

  1. Primary CSA: Idiopathic or with an unknown cause.
  2. Secondary CSA: Associated with medical conditions such as:
    • Cheyne-Stokes breathing (often seen in congestive heart failure)
    • Encephalitis
    • Brain stem neoplasm
    • Brain stem infarction
    • Spinal surgery
    • Hypothyroidism
    • Drug or substance abuse
    • High altitude periodic breathing
  3. Subcategories of CSA:
    • Hyperventilation-related CSA
    • Hypoventilation-related CSA

Hyperventilation-Related CSA

  • Most common form, includes:
    • Primary CSA
    • Cheyne-Stokes breathing
    • High-altitude periodic breathing
  • Patients develop alternating cycles of apnea or hypopneas with hyperpnea (increased breathing).

Hypoventilation-Related CSA

  • Usually secondary to underlying conditions, such as:
    • CNS diseases
    • CNS suppressing drugs
    • Neuromuscular diseases
    • Severe pulmonary mechanics disorders (e.g., COPD, pulmonary fibrosis)

Mixed Sleep Apnea

  • Definition: A combination of obstructive and central sleep apnea.
  • Typically begins as CSA, followed by the onset of OSA.

Sleep-Related Hypoventilation/Hypoxemia Syndromes (SRHHS)

  • A broad range of sleep disorders, including common forms like:
    • Obesity hypoventilation syndrome (OHS), also known as Pickwickian syndrome.
    • Crossover syndrome: overlap of COPD and sleep apnea.

Diagnosis of Sleep Apnea

  • Diagnosis is based on:
    • Patient history: presence of snoring, sleep disturbances, and daytime sleepiness.
    • Examination of the upper airway and pulmonary function tests (PFT) to check for upper airway obstruction.
    • Blood evaluation for:
    • Polycythemia
    • Reduced thyroid function
    • Bicarbonate retention
    • Arterial blood gas analysis to assess resting, wakeful oxygenation, and acid-base status.
    • Polysomnography (sleep studies) or in-home portable monitoring.

The Epworth Sleepiness Scale

  • A tool to assess the risk of Obstructive Sleep Apnea using a scoring system for various situations:
    • 0 = would never doze
    • 1 = slight chance of dozing
    • 2 = moderate chance of dozing
    • 3 = high chance of dozing

Situational Examples for Scoring

  • Sitting and reading
  • Watching TV
  • Sitting inactive in a public place (e.g., a theater or meeting)
  • As a passenger in a car for an hour without a break
  • Lying down to rest in the afternoon when circumstances permit
  • Sitting and talking to someone
  • Sitting quietly after lunch without alcohol
  • In a car, while stopped for a few minutes in traffic
Total Score Interpretation
  • 0-10: Normal range
  • 10-12: Borderline
  • 12-24: Abnormal

Mallampati Classification

  • Classification used for evaluating the visibility of parts of the throat:
    1. Class 1: Soft palate, fauces, uvula, and pillars easily seen.
    2. Class 2: Soft palate, fauces, and part of the uvula are visible.
    3. Class 3: Only the base of the uvula is visible.
    4. Class 4: Only the hard palate is visible.

Polysomnography-Monitored Variables

  • Sleep stages measured and recorded via:
    • Electroencephalogram (EEG)
    • Electrooculogram (EOG)
    • Electromyogram (EMG)
  • Monitored variables include:
    • Respiratory efforts (movement of chest/abdomen)
    • Oral and nasal airflow
    • Snoring
    • Pulse oximetry (SpO2)
    • Electrocardiogram
    • Body position
    • Limb movements

Sleep Study Setup

  • Sensors at the nose to measure airflow.
  • Sensors on the face and scalp to monitor eye movement and brain activity.
  • Use of elastic belts around the chest and abdomen to measure respiratory effort.
  • Continuous monitoring by a technician in a nearby room, transmitting data for analysis.

Abnormalities Observed in Sleep Studies

  • Appearance of alpha waves, sawtooth waves, and other EEG patterns.
  • Changes in breathing events and oxygen levels recorded.

Pulmonary Function Tests (PFT)

  • Challenges in evaluating pulmonary function during sleep.
  • Rely on characteristics such as:
    • Findings indicating obstructive patterns, shown as sawtooth on flow-volume loop.

Arterial Blood Gases (ABG)

  • Interpretation of ABG results:
    • Mild to moderate changes are often normal.
    • Severe: chronic ventilatory failure with hypoxemia.
    • Acute on chronic changes may also be observed.

Chest X-rays (CXR)

  • Often normal in OSA patients but may reveal:
    • Enlarged heart due to pulmonary hypertension and polycythemia from persistent apnea leading to right and/or left-sided heart failure.

Treatment for OSA

  • Continuous Positive Airway Pressure (CPAP): Most common treatment method.
  • Lifestyle modifications:
    • Weight reduction
    • Alteration of sleep posture (i.e., head elevation)
  • Oxygen therapy may be administered.
  • Surgical interventions aimed at correcting anatomical defects include:
    • Mandibular advancement surgery
    • Nasal surgery
    • Tracheostomy
    • Uvulopalatoplasty: removing soft palate tissue, including the uvula.

CPAP Mechanism

  • CPAP delivers a constant positive pressure during spontaneous breathing, preventing airway collapse during sleep.

Treatment for CSA

  • For hyperventilation-related CSA, CPAP is the primary therapy.
  • For hypoventilation-related CSA, Bilevel Positive Airway Pressure (BPAP) or Variable Positive Airway Pressure (VPAP) with a backup respiratory rate is the first-line therapy.
  • The backup rate helps to prevent abrupt changes in patient’s PaO2, PaCO2, and pH.

BPAP/VPAP Overview

  • BPAP/VPAP machines provide two differing pressures:
    • Inhalation pressure (IPAP)
    • Exhalation pressure (EPAP)
  • The difference between IPAP and EPAP is usually +/- 4 cm H2O or greater.

Example of BPAP Settings

  • IPAP: +12 cm H₂O
  • EPAP: +5 cm H₂O
  • Pressure support (PS) calculated as IPAP - EPAP = 12 - 5 = 7 cm H₂O.