What are the components of a second‑generation laryngeal mask airway (LMA) and how does it differ from first‑generation LMAs?

Second-Generation Laryngeal Mask Airways: Components and Modifications

Second-generation LMAs are supraglottic airway devices with design features specifically intended to reduce aspiration risk through higher oropharyngeal seal pressures and integrated gastric drainage tubes, distinguishing them from first-generation devices that lack these safety features. 1

Key Defining Features of Second-Generation LMAs

Second-generation LMAs incorporate two critical modifications that separate them from first-generation devices 1:

• Higher oropharyngeal seal pressures - enabling adequate ventilation of poorly compliant lungs and reducing gastric inflation risk 1
• Gastric drainage tube/oesophageal drain tube - providing separation of gastrointestinal and respiratory tracts, allowing gastric decompression and venting 1

Components of Second-Generation LMAs

The anatomical parts include 2:

• Primary airway tube - the main ventilation channel
• Secondary drainage tube - positioned lateral to the airway tube, ending at the mask tip to access the esophagus 2
• Mask/cuff - the distal sealing component that sits in the hypopharynx
• Posterior/dorsal cuff (in some models) - an additional cuff to improve the seal 2
• Inflatable cuff - should be inflated to minimal pressure required for airway seal, never exceeding 60 cmH₂O 1

Clinical Performance Characteristics

The British Journal of Anaesthesia guidelines specify that second-generation SGAs possess 1:

• Reliable first-time placement capability (including by non-airway experts)
• Ability to ventilate with PEEP (Positive End Expiratory Pressure)
• Compatibility with fiberoptic intubation techniques
• Protection against aspiration through gastric tube passage 1

Specific Second-Generation Devices

The most effective devices ranked by seal pressure 1:

1. ProSeal™ LMA (PLMA) - highest seal pressure of currently available devices; insertion over a bougie may improve placement success 1
2. LMA® Supreme™ (SLMA) - second highest seal pressure, though its narrow airway channel precludes easy use for fiberoptic intubation 1
3. i-gel™ - third in seal pressure ranking 1

Critical Distinction from First-Generation LMAs

First-generation SGAs have inadequate oropharyngeal seal pressures that are unlikely to provide adequate ventilation of poorly compliant lungs and are more likely to lead to gastric inflation - this is why only second-generation SGAs are recommended in current guidelines for airway rescue scenarios 1. The original classic LMA lacks the gastric drainage tube and enhanced sealing features 2.

Clinical Indications

Second-generation LMAs are now recommended for 1:

• Airway rescue after failed intubation in critically ill patients
• Situations requiring maintenance of PEEP
• Patients at risk for aspiration (when tracheal intubation is not achievable)
• Prolonged procedures including laparoscopic surgery 3, 4, 5
• Obese patients 4, 5
• Prone positioning 4, 5

Important Caveats

When using second-generation LMAs 1:

• Cricoid pressure should be released temporarily during insertion, as standard 30-N force impedes placement and adequate ventilation 1
• Maximum of two insertion attempts recommended to avoid trauma 1
• The device must be positioned and fixed correctly to ensure gastric contents are vented through the oesophageal port 1