Upper Airway Obstruction (UAO)
1. Definition
Upper airway obstruction (UAO) is defined as:
Impaired airflow in the airway between the nose/mouth and the trachea, resulting in increased airway resistance and respiratory compromise.
The obstruction may be:
- Partial
- Complete
- Dynamic or fixed
- Intrinsic or extrinsic
2. Anatomy of the Upper Airway
The upper airway extends from the nares to the cricoid cartilage.
Major segments
- Nasal cavity
- Oral cavity
- Pharynx
- Nasopharynx
- Oropharynx
- Hypopharynx
- Larynx
- Epiglottis
- Vocal cords
- Subglottic space
Important features
- Highly compliant and collapsible
- No rigid cartilaginous support in pharynx
- Airway patency maintained by:
- Pharyngeal dilator muscles
- Consciousness
- Neuromuscular tone
Loss of these leads to dynamic obstruction.
3. Epidemiology in ICU
Common ICU situations causing UAO:
- Post-extubation laryngeal edema
- Anaphylaxis
- Angioedema (ACE inhibitor)
- Upper airway tumors
- Trauma
- Foreign body
- Deep neck infections
4. Causes of Upper Airway Obstruction
Classification by mechanism
|
Mechanism |
Examples |
|
Mechanical obstruction |
Foreign body, tumor |
|
Edema |
Anaphylaxis, angioedema |
|
Infection |
Epiglottitis, abscess |
|
Neuromuscular collapse |
OSA, coma |
|
Trauma |
Facial fracture, hematoma |
5. Etiological Classification
A. Infectious Causes
|
Condition |
Key Features |
|
Epiglottitis |
Rapid airway obstruction |
|
Croup |
Subglottic edema |
|
Ludwig angina |
Floor of mouth infection |
|
Peritonsillar abscess |
“Hot potato voice” |
|
Retropharyngeal abscess |
Neck swelling |
B. Allergic / Inflammatory Causes
- Anaphylaxis
- Angioedema
- ACE inhibitor
- Hereditary angioedema
- Post-extubation laryngeal edema
- Radiation-induced edema
C. Structural Causes
|
Cause |
Mechanism |
|
Tumor |
Mechanical narrowing |
|
Vocal cord paralysis |
Inadequate abduction |
|
Subglottic stenosis |
Scar |
|
Laryngomalacia |
Collapse |
D. Traumatic Causes
- Facial fractures
- Neck trauma
- Laryngeal injury
- Expanding hematoma
- Inhalational burns
E. Functional Causes
|
Condition |
Mechanism |
|
Obstructive sleep apnea |
Pharyngeal collapse |
|
Sedation |
Loss of tone |
|
Neuromuscular disease |
Weak airway muscles |
6. Pathophysiology
Upper airway obstruction leads to:
1. Increased airway resistance
Airflow resistance:R∝r41
Small reduction in airway radius → huge increase in resistance
2. Increased work of breathing
Patients generate large negative intrathoracic pressure.
Consequences:
- Increased venous return
- Pulmonary edema
- Respiratory fatigue
3. Negative Pressure Pulmonary Edema (NPPE)
Mechanism:
- Strong inspiratory effort
- Large negative intrathoracic pressure
- Fluid shifts into alveoli
Seen in:
- Laryngospasm
- Post-extubation obstruction
4. Hypoxemia and Hypercapnia
Obstruction leads to:
- Reduced ventilation
- CO₂ retention
- Respiratory acidosis
7. Clinical Features
Early Signs
|
Sign |
Mechanism |
|
Stridor |
Turbulent airflow |
|
Tachypnea |
Increased effort |
|
Accessory muscle use |
Increased work |
|
Voice change |
Laryngeal involvement |
Classic Features
Stridor
|
Type |
Location |
|
Inspiratory |
Supraglottic obstruction |
|
Expiratory |
Tracheal obstruction |
|
Biphasic |
Glottic/subglottic obstruction |
|
Feature |
Stridor |
Grunting |
|
Origin |
Upper airway |
Alveoli / lower respiratory tract |
|
Phase of breathing |
Usually inspiratory |
Expiratory |
|
Sound |
High-pitched, harsh |
Low-pitched, short expiratory sound |
|
Mechanism |
Turbulent airflow through narrowed upper airway |
Partial closure of glottis to maintain PEEP |
|
Clinical significance |
Upper airway obstruction |
Severe lung disease / hypoxemia |
Severe Obstruction Signs
- Silent chest
- Cyanosis
- Altered mental status
- Bradycardia
- Cardiac arrest
8. Special Clinical Signs
1. Hoover sign
Paradoxical chest movement
2. Suprasternal retraction
Severe airway obstruction
3. Tripod position
Patient leaning forward
4. Drooling
Seen in:
- Epiglottitis
- Abscess
9. Investigations in ICU
1. Bedside Assessment
Key priorities:
- Airway patency
- Oxygenation
- Work of breathing
2. Flexible Fiberoptic Laryngoscopy
Gold standard for diagnosis.
Shows:
- Vocal cord mobility
- Edema
- Tumor
- Abscess
3. Imaging
CT Neck
Used for:
- Tumors
- Abscess
- Trauma
4. Flow Volume Loop
Characteristic patterns.
Patterns:
|
Pattern |
Example |
|
Fixed obstruction |
Tracheal stenosis |
|
Variable extrathoracic |
Vocal cord dysfunction |
|
Variable intrathoracic |
Tracheomalacia |
10. Emergency Management (ICU Approach)
First priority = Airway
Stepwise approach
- Oxygen
- Airway positioning
- Pharmacologic therapy
- Definitive airway
11. Initial Stabilization
Airway positioning
- Head tilt chin lift
- Jaw thrust
Used in:
- Sedated patients
Oxygen Therapy
- High flow oxygen
- Non-rebreather mask
Heliox
Helium–oxygen mixture reduces airflow resistance.
Used in:
- Laryngeal obstruction
- Post-extubation edema
12. Pharmacologic Management
|
Drug |
Indication |
|
Epinephrine |
Anaphylaxis |
|
Steroids |
Laryngeal edema |
|
Antihistamines |
Allergic reaction |
|
C1 esterase inhibitor |
Hereditary angioedema |
Nebulized epinephrine
Used in:
- Post-extubation stridor
- Croup
13. Airway Intervention
Indications for intubation
- Severe stridor
- Hypoxemia
- Respiratory fatigue
- Altered consciousness
Preferred Technique
Awake fiberoptic intubation
Used when:
- Anticipated difficult airway
- Tumor
- edema
Rapid sequence intubation (RSI)
Used when:
- Emergency airway
- No predicted difficulty
14. Surgical Airway
If intubation fails:
|
Procedure |
Indication |
|
Cricothyrotomy |
Emergency airway |
|
Tracheostomy |
Long-term airway |
15. Special ICU Scenarios
1. Post-extubation Stridor
Cause:
- Laryngeal edema
Risk factors:
- Prolonged intubation
- Large ETT
- Female patients
Treatment:
- Steroids
- Nebulized epinephrine
- Reintubation if severe
2. Angioedema
Types:
|
Type |
Cause |
|
Histamine mediated |
Allergy |
|
Bradykinin mediated |
ACE inhibitors |
Treatment differs:
- Histamine → epinephrine
- Bradykinin → C1 esterase inhibitor / icatibant
3. Obstructive Sleep Apnea in ICU
Causes obstruction during sedation.
Management:
- CPAP
- Positioning
- Avoid sedatives
16. Complications
Major complications include:
- Hypoxic brain injury
- Cardiac arrest
- Negative pressure pulmonary edema
- Aspiration
- Airway trauma
17. Guideline & Textbook Sources
Major references used in critical care practice:
- Harrison’s Principles of Internal Medicine
- Oh’s Intensive Care Manual
- Irwin & Rippe ICU
- Difficult Airway Society guidelines
- American Society of Anesthesiologists airway guidelines