Laryngeal Mask Airway (LMA) 

4

1. Definition

A laryngeal mask airway is a supraglottic airway device


2. Historical Background

  • Invented by Dr. Archie Brain (1981).
  • Introduced into clinical practice in 1988.
  • Designed as a middle ground between face mask and endotracheal tube.

Advantages:

  • Reduced aspiration risk
  • Higher airway seal pressure
  • Suitable for controlled ventilation

3.Classification of Supraglottic Airway Devices (SADs)

Generation

Characteristic Features

Examples

1st Generation

• Basic supraglottic airway device

• Inflatable cuff present

• No gastric drainage channel

• Lower oropharyngeal seal pressure (~20 cmH₂O)

Classic LMA

Flexible (Reinforced) LMA

LMA Unique (Disposable)

2nd Generation

• Improved airway seal (higher leak pressure ~25–35 cmH₂O)

• Gastric drainage channel present for NG tube insertion

• Allows positive pressure ventilation

• Better protection against gastric insufflation and regurgitation

• May have inflatable cuff or cuffless design

LMA ProSeal

LMA Supreme

LMA Protector

i-gel

3rd Generation

• Advanced aspiration protection systems

• Separate suction channel in addition to gastric drainage port

• Improved pharyngeal sealing and airway stability

• Allows active suctioning of regurgitated material

• Designed for higher safety during controlled ventilation

Baska Mask

Elisha Airway Device


4. Components of LMA

1. Airway Tube

  • Curved tube connecting mask to ventilator circuit.
  • Allows airflow between ventilator and lungs.

2. Mask

  • Elliptical mask that sits over laryngeal inlet.

3. Inflatable Cuff

  • Inflates to form seal around glottis.

4. Aperture Bars

Prevent epiglottis obstruction.

5. Connector

Standard 15 mm connector.

6. Pilot Balloon

Indicates cuff pressure.

7. Gastric Drain Tube (Second Generation LMAs)

Allows:

  • Gastric decompression
  • Reduced aspiration risk


5. Mechanism of Action

LMA sits in hypopharynx with the mask covering:

When cuff inflated:Seal occurs between:

Structure

Role

Base of tongue

Anterior seal

Lateral pharyngeal walls

Lateral seal

Upper esophageal sphincter

Inferior seal

This allows ventilation without entering trachea.


6. Sizes of LMA

Size

Patient Weight

Typical Use

1

<5 kg

Neonates

1.5

5–10 kg

Infants

2

10–20 kg

Children

2.5

20–30 kg

Older children

3

30–50 kg

Small adults

4

50–70 kg

Adults

5

70–100 kg

Large adults

6

>100 kg

Very large adults


7. Indications in Critical Care

1. Difficult Airway Rescue

Important step in failed intubation algorithm.

Used when:

  • Cannot intubate
  • Cannot ventilate

LMA restores oxygenation.


2. Bridge to Definitive Airway

Allows oxygenation while preparing for:

  • Fiberoptic intubation
  • Surgical airway
  • Video laryngoscopy


3. Short Procedures

Used during:

  • ICU bedside procedures
  • Sedation procedures


4. Emergency Airway

In:

  • Cardiac arrest
  • Prehospital airway management


5. Intubation Conduit

Certain LMAs (e.g., Fastrach LMA) allow blind or fiberoptic-guided intubation.


8. Contraindications

Absolute

Condition

Reason

High aspiration risk

Poor airway protection

Full stomach

Regurgitation risk


Relative

Condition

Reason

Severe obesity

Poor seal

Pregnancy

Aspiration risk

Severe GERD

Regurgitation

Bowel obstruction

Gastric distension

Reduced lung compliance

Ventilation difficult


9. LMA Insertion Technique

Step 1: Preparation

  • Select correct size.
  • Deflate cuff completely.
  • Lubricate posterior surface.


Step 2: Patient Position

Sniffing position

Alignment:

  • Oral axis
  • Pharyngeal axis
  • Laryngeal axis


Step 3: Insertion

Device inserted:

Along hard palate → soft palate → hypopharynx

Until resistance felt.


Step 4: Cuff Inflation

Typical volumes:

Size

Max Volume

3

20 ml

4

30 ml

5

40 ml

Target cuff pressure(its not seal pressure ):-<60 cmH₂O


Step 5: Confirmation

Confirm ventilation by:

  • Chest rise
  • Capnography
  • Bilateral breath sounds
  • Absence of gastric insufflation
  • Fiberoptic-goldstandard


 Bubble Test-Used mainly with ProSeal LMA.

Method

  1. Place gel/lubricant over gastric drain tube opening.
  2. Apply positive pressure ventilation.

Interpretation

Finding

Meaning

No bubbles

Correct placement

Bubbles present

Air leak or malposition


 Suprasternal Notch Test (ProSeal LMA)

Apply gentle pressure over suprasternal notch.

Finding

Result

Interpretation

Movement of lubricant in drain tube

Correct positioning

No movement

Malposition



10. LMA Seal Pressure (Oropharyngeal Leak Pressure)

Measured by closing APL valve.

Normal:

Device

Seal Pressure

Classic LMA

20 cmH₂O

ProSeal

30 cmH₂O

i-gel

25–30 cmH₂O

Higher seal pressure = better ventilation.


11. Complications

Minor

  • Sore throat
  • Dysphagia
  • Hoarseness
  • Cough


Major

1. Aspiration

Most serious complication.

Occurs because:

  • Esophagus not sealed completely.


2. Air Leak

Occurs due to:

  • Wrong size
  • Poor positioning
  • High airway pressure


3. Gastric Insufflation

Caused by:

  • Positive pressure ventilation.


4. Laryngospasm

Especially during insertion/removal.


5. Nerve Injury

Rare.

Involves:

Nerve

Mechanism

Lingual nerve

Tongue compression

Hypoglossal nerve

Tongue base compression

Recurrent laryngeal nerve

Excess cuff pressure



12. Advantages

  • Rapid insertion
  • Minimal training needed
  • Less hemodynamic response
  • Useful in difficult airway
  • Less airway trauma


13. Disadvantages

  • Aspiration risk
  • Limited ventilation pressure
  • Not suitable for severe lung pathology
  • Cannot provide full airway protection



14. Troubleshooting LMA

Problem

Cause

Solution

Air leak

Wrong size

Change size

Poor ventilation

Malposition

Reinsert

High airway pressure

Low seal

Use ProSeal

Gastric distension

PPV

Insert NG tube