Classification of LMA (Laryngeal Mask Airway / Supraglottic Airway Devices)

Overview

Classification Systems

1. Cook's Generation-Based Classification (most widely used clinically)

Note: Some sources classify the Baska Mask as 2nd generation (due to gastric drainage ports), while others propose it as 3rd generation due to its dynamic self-sealing cuff.

2. Miller's Sealing Mechanism Classification (used in Miller's Anesthesia)

Per Miller's Anesthesia 10e: "Cuffless anatomically preshaped sealers do not have a cuff; rather, they provide an airway seal by their anatomically preshaped design... The first of these devices, the SLIPA... Other cuffless devices such as the i-gel and the Baska Mask can also be included in this classification."

Short Note: SLIPA (Streamlined Liner of the Pharynx Airway)

Classification

• Miller: Cuffless anatomically preshaped sealer
• Cook: 2nd generation SGA

Design & Features

• Made of medical-grade thermoplastic - stiff at room temperature for easy insertion, softens at body temperature to improve pharyngeal seal
• No inflatable cuff - relies entirely on anatomical shape to conform to the pharynx
• The heel of the SLIPA sits snugly in the nasopharynx, providing a very stable airway
• Contains a unique hollow chamber at its base that acts as a reservoir for regurgitated gastric contents - significantly reduces risk of aspiration pneumonia
• Available in 6 adult sizes (47-57 mm) - size number indicates width at the bridge in millimeters
• Sizing is based on patient height and can be cross-checked against the width of the thyroid cartilage
• Each size is colour-coded for easy identification

Advantages

• Simple, quick insertion (no cuff inflation required)
• Aspiration protection via hollow reservoir chamber
• Softens to body temperature - reduced trauma, improved seal
• No pilot balloon or cuff inflation needed

Disadvantages

• No gastric suction channel (passive reservoir only, not active drainage)
• Limited evidence base compared to LMA Classic or ProSeal
• Cannot be re-sized easily once inserted (rigid initial shape)

Short Note: Baska Mask

Classification

• Miller: Cuffless anatomically preshaped sealer (membranous self-sealing cuff)
• Cook: 2nd generation (or proposed 3rd generation due to dynamic sealing)

Design & Features - What Makes It Unique

1. Self-recoiling thin membranous cuff - no inflatable balloon, no pilot balloon/pilot tube
   • The cuff pressure equals the maximum inspiratory pressure during IPPV - it dynamically adjusts with the ventilator cycle
   • Soft membrane - lower propensity for nerve damage or oropharyngeal trauma
2. Sump area (reservoir) - collects and holds gastric fluid aspirates, similar to ProSeal
3. Two gastric drainage ports - active gastric drainage (unlike SLIPA's passive reservoir):
   • One port can be connected to a 90° suction elbow for active suction
   • The other must be left open to atmosphere (not obstructed)
4. Integrated bite block - protects the airway tube
5. Functions as an intubation conduit in some configurations

Advantages

• Dynamic self-sealing cuff adapts to airway pressures during IPPV
• No cuff inflation required
• Better protection against aspiration than 1st-generation SGAs
• Two gastric drainage channels for active decompression
• Lower trauma risk due to soft membrane cuff

Disadvantages

• Limited large-scale RCT evidence compared to i-gel or ProSeal
• Relatively newer device; fewer practitioners familiar with it
• Mixed comparative evidence vs. i-gel (some studies favour i-gel on certain parameters)

Summary Comparison: SLIPA vs. Baska Mask

Short Note: Intubating Laryngeal Mask Airway (ILMA / LMA Fastrach)

Definition & Introduction

Components of the ILMA kit: the device with rigid metal handle and epiglottic elevating bar (top), wire-reinforced specialized ETT (middle), and standard ETT for comparison (bottom). - Scott-Brown's Otorhinolaryngology

Classification

• Miller: Cuffed perilaryngeal sealer (with intubation capability)
• Cook: 1st generation SGA with intubation conduit function (designated "i" = intubating SGA)
• Considered a 1st generation SGA in terms of aspiration protection (no gastric drainage port in the standard Fastrach)

Differences from Classic LMA

Design Features

1. Rigid, highly curved metal airway tube - enables precise positioning and control
2. Metal handle - allows rapid, one-handed insertion and fine adjustments; enables lifting to improve glottic seal
3. Epiglottic elevating bar (EEB) - a guiding ramp at the mask bowl that lifts the epiglottis as the ETT is advanced, clearing the path to the trachea
4. Wide bore airway shaft - accommodates a standard ETT
5. Dedicated ILMA ETT - straight, wire-reinforced silicone tube with a soft moulded atraumatic tip (novel bevel) that prevents impingement on laryngeal structures; straight design (not curved) to negotiate the ILMA shaft
6. Available as reusable (original) and single-use disposable versions

Sizes

Note: The Fastrach is only available from size 3 upward (not for small children/neonates). Newer ILMAs (Air-Q, i-gel, AuraGain) are available in neonatal sizes.

Indications

• Failed rapid-sequence intubation (RSI)
• Cannot-intubate / cannot-ventilate (CICV) scenario - primary rescue device
• Difficult mask ventilation
• Anticipated or unanticipated difficult intubation
• Refractory hypoxemia despite preoxygenation
• Situations where conventional laryngoscopy is not possible (e.g., limited mouth opening > 2 cm, unstable cervical spine)

Contraindications

• Unable to open mouth (< 2 cm - minimum required)
• Awake/uncooperative patient (relative)
• Known pharyngeal/laryngeal pathology (tumor, abscess, foreign body)
• Latex allergy (earlier models contained latex)

Insertion Technique

1. Head position: neutral (not the sniffing position used for cLMA)
2. Cuff deflated and lubricated
3. ILMA held by its metal handle and rotated into the pharynx in a smooth arc, pressing against the posterior pharynx
4. Cuff inflated with appropriate volume (20 mL for size 4, 30 mL for size 5)
5. Verify ventilation - if resistance encountered, perform the Chandy Maneuver:
   • Step 1: Rotate the ILMA in the sagittal plane until ventilation resistance is minimal
   • Step 2: Gently lift the handle away from the posterior pharyngeal wall just before passing the ETT
6. Pass the specialized ILMA ETT through the shaft, advance slowly without force
7. As the ETT tip exits the bowl, it lifts the epiglottic elevating bar and is directed into the trachea
8. Confirm tracheal placement (capnography, auscultation)
9. Remove the ILMA over the ETT using the dedicated pusher/stabilizer rod (the rigid ILMA causes tissue pressure if left in situ)

Success Rates

The Fastrach has significantly higher blind intubation rates than other ILMAs (Air-Q, i-gel). It is the only ILMA that can reliably facilitate blind intubation without endoscopic guidance. - Roberts and Hedges' Clinical Procedures in Emergency Medicine

Complications

• Laryngeal or esophageal injury from blind intubation attempts
• Aspiration (rare - no gastric drainage port)
• Tissue pressure injury if ILMA left in situ after intubation (due to rigidity)
• Hoarseness, sore throat
• Oropharyngeal mucosal trauma

Advantages

• Rapid insertion with single-hand technique via the metal handle
• Provides ventilation AND acts as intubation conduit
• Allows intubation in neutral head position - valuable in suspected cervical spine injury
• Very high blind intubation success rate (~96.5%)
• Fiberoptic guidance possible through the shaft for 100% success
• Well-studied, most validated rescue airway device in difficult airway algorithms

Limitations

• No gastric drainage channel (aspiration risk remains)
• Only available from size 3 (30 kg) - not usable in small children
• Significant learning curve for insertion vs. classic LMA
• Rigid body - must be removed after intubation; can cause tissue ischemia if left in
• More expensive and bulkier than classic LMA
• Single-use disposable versions add cost

Short Note: i-gel Supraglottic Airway

Introduction

The i-gel: characteristic soft gel cuff (green/colour-coded), clear airway shaft, and integrated bite block - Tintinalli's Emergency Medicine

Classification

Per Miller's Anesthesia 10e: "The i-gel is considered a second-generation SGA considering the presence of a gastric drainage port and higher seal pressure."

Design Features

1. Non-inflatable gel cuff - made from soft thermoplastic elastomer (SEBS); no inflation required; anatomically contoured to the perilaryngeal structures; reduces tissue compression compared to inflated cuffs
2. Gastric channel - present in all sizes except size 1 (neonate); allows:
   • Early warning of regurgitation
   • Passage of a nasogastric tube to empty stomach contents
   • Venting of gastric gases
3. Integral bite block - prevents airway channel occlusion if patient bites down
4. Buccal cavity stabiliser - aids insertion and prevents rotation once placed
5. Epiglottic rest - a notch/rest at the distal end that reduces epiglottic downfolding and subsequent airway obstruction
6. Position guide (adult sizes only) - printed marker on shaft for confirmation of optimal insertion depth; the teeth/lips should align with this marking
7. Standard 15 mm connector - proximal end connects to any standard breathing circuit or BVM
8. Colour-coded packaging cradle/cage - maintains the device in correct anatomical flexion prior to use; also serves as a lubrication base during preparation

Sizes and Colour Coding

Insertion Technique

1. Select appropriate size based on patient weight
2. Apply a thin layer of water-based lubricant to the posterior/dorsal surface of the gel cuff using the cradle/cage as a base - do not over-lubricate the anterior surface (risk of aspiration)
3. Patient in sniffing position (neck flexed, head extended)
4. Hold the i-gel at the bite block with the thumb and index finger; introduce into the mouth aiming toward the hard palate
5. Advance smoothly in a downward-backward arc following the natural curve of the pharynx
6. Continue until definite resistance is felt - this indicates the tip has seated in the hypopharynx
7. Confirm correct placement: teeth/lips align with the position guide marking; satisfactory ventilation; normal capnography waveform; no audible leak

Seal Pressure (Oropharyngeal Leak Pressure - OLP)

Indications

• Routine airway management for elective surgery (spontaneous or controlled ventilation)
• Difficult airway - as a rescue device in failed intubation / cannot-intubate / cannot-ventilate
• Conduit for fibreoptic-guided intubation (sizes 3, 4 and 5 - indication added in 2012)
• Pre-hospital/emergency airway management
• CPR - featured in advanced airway management algorithms (high insertion success rate by non-anaesthetists)
• Patients requiring positive pressure ventilation (laparoscopic surgery, prone position)

Contraindications

• High aspiration risk (full stomach, not fasted, hiatus hernia) - relative
• Known pharyngeal/laryngeal pathology
• Mouth opening < 2 cm
• Morbid obesity with very high airway pressure requirements

Advantages

• No cuff inflation - simpler, faster insertion; no pilot balloon or syringe needed
• Fastest SGA to insert - studies confirm shorter insertion time than LMA ProSeal and Supreme
• Less sore throat than cuffed LMAs - reduced tissue compression
• Gastric channel - aspiration protection and gastric decompression
• Epiglottic rest - reduces epiglottic downfolding
• High seal pressure (~27 cm H₂O) - suitable for PPV and laparoscopic surgery
• Available in 7 sizes from neonate to large adult - widest range of any SGA
• Can be used as intubation conduit (fibreoptic, sizes 3-5)
• Single-use disposable - no sterilisation required; eliminates cross-infection risk
• Suitable for use by non-specialists - high first-attempt success rate

Disadvantages / Limitations

• No dynamic self-sealing (cuff doesn't adapt to airway pressure changes like the Baska Mask)
• Single-use only - higher per-case cost than reusable devices
• Gastric channel not present in size 1 (neonate)
• Intubation conduit use limited to fibreoptic guidance only in sizes 3-5 (no reliable blind intubation capability)
• Aspiration risk still present compared to ETT (2nd gen, not a definitive airway)

Comparison with Classic LMA