Supraglottic Airway Devices — LMA, i-gel & Second-Generation Devices

Overview & definition

A supraglottic airway device (SAD) sits in the pharynx and forms a seal around the laryngeal inlet, allowing hands-free ventilation without entering the trachea. It bridges the gap between the bag-valve-mask and endotracheal intubation — faster and less invasive than a tube, with a better seal and less gastric insufflation than a mask. In the difficult-airway algorithm the SAD is the Plan B rescue device; it can also serve as a conduit through which a definitive endotracheal tube is placed.[1][1]

A SAD is not a definitive airway: it sits above the glottis and does not isolate the trachea, so it gives only partial protection against aspiration. For prolonged ICU ventilation, an endotracheal tube remains the standard.[1]

First versus second generation

The distinction matters and drives modern practice.[1][1]

• First-generation devices (classic LMA) — a single lumen with an inflatable cuff, no gastric drainage channel, and a relatively low seal pressure. They provide no protection against aspiration. NAP4 found that first-generation laryngeal masks failed as rescue devices in major airway events (regurgitation, aspiration, displacement). They are no longer recommended for emergency rescue.[1]

• Second-generation devices (i-gel, LMA ProSeal, LMA Supreme, Baska) — add a gastric drainage channel (which vents regurgitated stomach contents away from the airway), a higher seal pressure, and an intubation conduit. They give partial aspiration protection and tolerate higher airway pressures. The DAS 2018 ICU guideline specifies a second-generation device as the Plan B rescue.[1]

The i-gel

The i-gel is the most widely used second-generation SAD in the ICU. Its features:[1]

• A non-inflatable cuff made of a thermoplastic elastomer (gel) that warms to body temperature and moulds to the perilaryngeal anatomy — there is no cuff pressure to manage.
• Very rapid insertion (often a few seconds) and a shallow learning curve.
• A gastric drainage channel and an integrated bite block.
• A wide-bore, short, slightly curved tube that can accept an endotracheal tube (railroaded) or an Aintree airway exchange catheter for fibre-optic-guided intubation through the device.
• Sized 3 to 5 by patient weight.

Other second-generation devices

• LMA ProSeal — an inflatable cuff with a posterior cuff and a drain tube; a high seal pressure, but cuff pressure must be managed.
• LMA Supreme — a disposable double-lumen device with a gastric channel and a fixed curve; easy to insert, single use.
• Baska mask — a non-inflatable cuff with a self-sealing membranous design and gastric channels.[1]

Mechanism of the seal — perilaryngeal anatomy

The SAD works by forming a seal around the laryngeal inlet, not by entering the trachea. Understanding where the device sits explains both its strengths and its failure modes.[1]

• Where it sits. The cuff or bowl of the device lodges in the hypopharynx, with its tip against the upper oesophageal sphincter (cricopharyngeus) and its bowl over the laryngeal inlet. The anterior surface of the cuff faces the base of tongue and vallecula; the posterior surface faces the posterior pharyngeal wall.
• What seals. A first-generation cuff seals anteriorly against the laryngeal inlet with a single inflatable mask; a second-generation device adds a second seal at the upper oesophageal sphincter (the tip of the drain tube), which separates the airway from the gastrointestinal tract and allows venting of regurgitated contents.
• Why seal pressure matters. The oropharyngeal leak pressure (OLP) is the airway pressure at which the seal fails and gas escapes. First-generation devices leak around 15-20 cm H2O; second-generation devices achieve 25-40 cm H2O, tolerating the higher peak pressures of obesity, ARDS, or bronchospasm.
• The gel cuff (i-gel). The thermoplastic elastomer warms from ambient to body temperature over ~3-4 minutes, softening and moulding to the irregular perilaryngeal tissues — seal pressure rises after insertion as the cuff warms. No cuff pressure to monitor is both the advantage (no over-inflation nerve injury) and a limitation (you cannot "tighten" a leaking seal).
• The integrated bite block. A rigid channel through the stem of the i-gel (and others) prevents the patient from occluding the airway by biting, and provides a hand-grip for insertion. In the ICU it is especially valuable in the semi-conscious or post-ictal patient who may clench. [1]

[1]

The recurring theme: every device that survives modern emergency practice has a gastric drainage channel and a higher seal pressure than the classic LMA. The single distinguishing feature that drove the move from first to second generation was the recognition — crystallised in NAP4 — that a rescue airway which cannot vent regurgitated stomach contents is not a rescue airway.[1]

Advantages over bag-valve-mask

• Hands-free ventilation, freeing the operator.
• A better seal and less gastric insufflation (less regurgitation and aspiration).
• Allows continuous waveform capnography through the device.
• Can be used as a conduit for intubation.[1]

Advantages over endotracheal intubation

• Faster, less invasive, requires less skill, less haemodynamic disturbance, and is better tolerated at lighter planes of anaesthesia — but at the cost of tracheal protection.[1]

Indications — where the SAD earns its place

The SAD spans several distinct roles in critical care, each with a different risk/benefit profile.[1][2]

• Rescue airway (Plan B, failed intubation). The defining ICU role. When laryngoscopy fails and oxygenation is threatened, a second-generation SAD is inserted to restore oxygenation; it then either stays as a bridge, is used as a conduit for a definitive tube, or buys time while the patient wakes. The DAS 2018 algorithm specifies the SAD as Plan B after failed Plan A laryngoscopy.[1]
• Difficult-airway conduit. When the airway is anticipated to be difficult (MACOCHA positive, known front-of-neck distortion), a SAD may be placed electively and a fibre-optic scope passed through it to intubate under vision — "intubating through the SAD".[2]
• NIV / CPAP bridge. A second-generation SAD can deliver positive-pressure ventilation short-term while preparations for a definitive airway are made; it is not a durable NIV interface. The gastric drain limits the insufflation that a mask would force into the stomach, and the airway is now "tubed" rather than masked.
• Cardiac arrest. ERC 2021 accepts a SAD as an alternative to bag-valve-mask or endotracheal intubation for providers trained in its use; a second-generation device is preferred because of the gastric channel.[3]
• Procedural sedation / anaesthesia. In theatre and for short ICU procedures (cardioversion, endoscopy) in the fasted patient, the SAD is the standard airway — a role it earns back from intubation by being less invasive and better tolerated at light planes of anaesthesia.
• Pre-hospital airway. Paramedic systems increasingly use a second-generation SAD (or laryngeal tube) as the primary airway when intubation skills are not immediately available; the AIRWAYS-2 and PART trials inform this debate.[4][5]

The SAD inside the difficult-airway algorithm

In both the DAS 2015 (perioperative) and DAS 2018 (ICU) algorithms, the second-generation SAD occupies the same structural slot: it is the Plan B that follows a failed best-effort laryngoscopy (Plan A), and it precedes the front-of-neck-access eFONA (Plan D).[1][2] If the SAD oxygenates, the team stops and thinks: wake the patient, intubate through the device, or continue with the SAD as a temporary airway. If the SAD fails to oxygenate, the team declares CICO and moves to eFONA without further attempts at the upper airway. The SAD is therefore a cognitive hinge — its success or failure determines whether the next step is salvage or scalpel.

Insertion technique — the bedside sequence

The integrated bite block and gastric drain channel — what they do in practice

The two features that separate a second-generation device from a classic LMA both have a specific mechanical job: [1]

• The gastric drainage channel terminates at the upper oesophageal sphincter. When a nasogastric tube or suction catheter passes freely down it, that is confirmation the tip is correctly seated over the oesophageal inlet. If regurgitation occurs, the channel vents liquid away from the larynx and out through the device — turn on suction, place an NG tube, and aspirate. The channel does not actively prevent regurgitation; it manages it after the fact.
• The integrated bite block sits in the stem of the i-gel. It prevents occlusion of the airway by biting (a real risk in the semi-conscious, post-ictal, or emerging patient), stiffens the device for insertion, and gives the operator a hand-grip. It is one reason the i-gel tolerates the lighter planes of anaesthesia common in ICU procedural sedation. [1]

Limitations and contraindications

• Not a definitive airway — no reliable tracheal isolation; aspiration risk remains, especially in the non-fasted or at-risk stomach.
• Limited seal pressure — may leak at the high airway pressures of a stiff lung (obesity, ARDS, asthma), where it cannot ventilate effectively.
• Risk of displacement, malposition (oesophageal placement), and cuff-related nerve injury.
• Contraindications: restricted mouth opening, upper-airway obstruction or trauma, and a high aspiration risk where time allows a definitive airway instead (the RODS assessment: restricted mouth opening, obstruction, disrupted upper airway, stiff lungs).[1][1]

Contraindications in detail — the RODS test

The bedside screen for whether a SAD is the wrong choice is the RODS mnemonic:[1]

• R — Restricted mouth opening. The device must pass between the teeth; an inter-incisor distance <2 cm (trismus, temporomandibular joint ankylosis, facial trauma, post-ictal clenching) precludes insertion. The integrated bite block needs the teeth to clear the stem.
• O — Obstruction. A supraglottic or glottic mass, infection (deep neck space infection, retropharyngeal or peritonsillar abscess, epiglottitis), or foreign body at the laryngeal inlet cannot be bypassed by a device that sits above the glottis. The SAD will seal around, not past, the obstruction.
• D — Disrupted or distorted upper airway. Pharyngeal, laryngeal, or oesophageal surgery or trauma; friable tumour; a large pharyngeal pouch; previous pharyngeal or laryngeal radiotherapy — the seal fails or insertion provokes bleeding.
• S — Stiff lungs / high airway pressure. Obesity, ARDS, severe bronchospasm, pregnancy — the high peak inspiratory pressure exceeds the device seal pressure and the device leaks, failing to ventilate. This is the most common reason a SAD fails in the ICU. [1]

High aspiration risk is a relative contraindication: the non-fasted patient, bowel obstruction, active upper GI bleed, or late pregnancy. The second-generation gastric channel gives partial protection — it is not a licence to abandon tracheal intubation when there is time and skill. In a true cardiac arrest or CICO situation, however, a SAD with a gastric channel is still far better than no airway. [1]

Insertion technique

1. Size the device (i-gel by weight) and lubricate the cuff.
2. Head extension (or neutral in C-spine), jaw thrust if needed.
3. Insert along the hard palate and advance in a smooth curve until resistance is felt; for an inflatable device, inflate the cuff to the recommended volume.
4. Confirm with bilateral chest rise and waveform capnography (a CO2 trace).
5. Secure with tape or a tie; check a chest X-ray if the device is to stay.[1]

The SAD as an intubation conduit (rescue value)

When intubation fails but oxygenation is achieved through a second-generation SAD, the SAD can be converted into a definitive airway: pass an Aintree airway exchange catheter (loaded with a fibre-optic scope) through the SAD into the trachea, railroad an endotracheal tube over the catheter, then remove the SAD. This is the safe way to exchange a rescue SAD for a definitive tube.[1][1]

Why the Aintree catheter is the safe exchange tool

Blindly pushing an endotracheal tube through a SAD has a poor success rate and risks laryngeal trauma, because the SAD lumen rarely aligns perfectly with the glottis. The Aintree intubation catheter solves this: it is a long, hollow, semi-rigid catheter (internal diameter 4.7 mm) that accepts a fibre-optic bronchoscope through its lumen.[7][8]

1. Load the bronchoscope through the Aintree catheter so the scope tip protrudes.
2. Pass the scope–Aintree assembly through the SAD lumen, identify the glottis, and advance into the trachea to the carina.
3. Withdraw the scope, leaving the Aintree catheter in the trachea.
4. Railroad a small endotracheal tube (6.0-7.0 mm) over the Aintree catheter into the trachea, then remove the SAD over the tube.
5. Confirm with capnography and chest rise; secure the definitive airway. [1]

The alternative is a blind intubating LMA (Fastrach), where a specialised curved ETT is railroaded through the device without a scope — faster but less reliable, and not a vision-guided technique. Comparative work on conduit efficiency shows the i-gel and LMA Protector both function well as Aintree conduits, with first-attempt success in the majority when the operator is trained.[7][8] In the ICU, where blood and secretions are common, the fibre-optic/Aintree route is preferred once oxygenation is secured — it converts a blind gamble into a visualised intubation.

Role in cardiac arrest

Resuscitation councils (ILCOR/ERC) accept a supraglottic airway as an alternative to bag-valve-mask or endotracheal intubation for providers trained in its use, with a second-generation device preferred. It does not replace definitive intubation by a skilled operator when available.[1]

Evidence in cardiac arrest — AIRWAYS-2 and PART

Two large pragmatic cluster-randomised trials reshaped the cardiac-arrest airway debate:[3]

• AIRWAYS-2 (Benger, 2018) randomised 9,296 out-of-hospital cardiac arrests to an initial i-gel versus initial endotracheal intubation by UK paramedics. There was no difference in the primary outcome of good functional outcome at 30 days (modified Rankin 0-3): 6.4% (i-gel) vs 6.8% (intubation). Regurgitation and aspiration were more frequent with the i-gel, while first-attempt insertion success was higher with the i-gel.[4]
• PART (Wang, 2018) randomised 3,004 out-of-hospital cardiac arrests to an initial laryngeal tube versus endotracheal intubation by US paramedics and found a survival benefit with the laryngeal tube (18.3% vs 15.4% survival to hospital discharge) — driven partly by higher first-attempt success and fewer chest-compression interruptions with the supraglottic device.[5]
• A 2024 systematic review and meta-analysis (Forestell) reconciled these: across out-of-hospital cardiac arrest trials, an initial supraglottic airway was associated with comparable or improved short-term survival versus intubation, but long-term favourable neurological outcomes did not clearly favour either strategy.[6]

Bottom line for the ICU: in cardiac arrest the airway of the trained operator matters more than the device brand. The SAD is an acceptable primary airway where intubation skills are absent or delayed; it does not replace definitive intubation by an intubation-skilled team once return of spontaneous circulation is achieved and the patient moves to ongoing ICU care. [1]

Complications

• Aspiration (the key risk, especially with a first-generation device or a misplaced/malpositioned device).
• Oesophageal placement (unrecognised without capnography).
• Displacement or failure to seal.
• Sore throat, and nerve injury (recurrent laryngeal, hypoglossal, lingual) from an over-inflated or malpositioned cuff.[1]

Complications in detail

• Aspiration. The cardinal and most feared complication. Risk is highest with a first-generation device (no gastric channel), a malpositioned device, or in the non-fasted or high-risk stomach. Even a second-generation device only vents regurgitated material — it does not prevent it from reaching the airway if the seal is breached or the device is displaced. NAP4 documented aspiration deaths from unrecognised SAD failure.[1]
• Nerve injury. An over-inflated or malpositioned cuff compresses nerves against the pharyngeal mucosa. The recurrent laryngeal and hypoglossal nerves are the classic victims, but lingual and glossopharyngeal injuries are reported — presenting as tongue numbness, weakness, or (if bilateral) upper-airway obstruction. The mechanism is pressure neuropraxia, preventable by using the correct cuff volume (or a non-inflatable i-gel) and avoiding prolonged use.
• Laryngospasm. A stimulatory device sitting at the laryngeal inlet can trigger reflex closure of the cords in the lightly anaesthetised patient — the i-gel is less stimulating than an inflatable cuff, but laryngospasm still occurs. Treat by deepening anaesthesia, 100% oxygen, continuous positive airway pressure, and — if unresponsive — a small dose of suxamethonium.
• Oedema and sore throat. Minor and common (10-40%); usually resolves within 24 hours. Significant pharyngeal or glottic oedema is rare but reported with an oversized cuff or prolonged use.
• Oesophageal / pharyngeal trauma and perforation. Rare but catastrophic; a forced insertion or oversized device can tear the piriform fossa or oesophagus, causing surgical emphysema, mediastinitis, or retropharyngeal abscess.
• Device failure and displacement. The device can rotate, fold, or be pushed too deep (into the oesophagus) or not deep enough (leak). Continuous capnography detects the failure; chest rise alone does not.
• Component allergy. Modern devices are latex-free, but silicone sensitivity and reactions to lubricants are reported.

Special populations

• Obesity. High airway pressure, low functional residual capacity, and difficult mask ventilation make a second-generation SAD an attractive rescue — but the seal may be insufficient at the peak pressures needed. Choose a device with the highest leak pressure (ProSeal, Baska), pass a nasogastric tube down the drain channel, and keep a low threshold to escalate to a definitive airway. Position head-up and ramped.
• Pregnancy. Reduced lower oesophageal sphincter tone and increased intra-abdominal pressure make aspiration the dominant risk — a SAD is a rescue device only, never a planned airway for general anaesthesia in the full-term obstetric patient. The second-generation gastric channel helps but does not negate the need for a cuffed endotracheal tube at induction.
• Paediatrics. SADs are widely used in paediatric anaesthesia and as rescue devices in PICU; size by body weight. The i-gel is available in sizes 1 to 5 (neonate to adult). Children desaturate fast — the SAD is a bridge, not a destination.
• Restricted C-spine. Manual in-line stabilisation is compatible with SAD insertion (the device does not require the cervical extension that laryngoscopy does); jaw thrust opens the hypopharynx. This is one reason the SAD succeeds in the trauma patient where laryngoscopy fails.
• Trismus / clenched jaw (post-ictal, post-ROSC). The i-gel's slim profile and integrated bite block may allow insertion where a laryngoscope blade cannot pass; if the jaw is truly locked, this becomes a front-of-neck-access decision, not a SAD decision. [1]

Comparison with other airway adjuncts

[1] [1]

Clinical pearls

Red flags

Key trials and evidence

[1] [1] [1] [1] [1] [1] [1] [1]

Quick reference — the exam-viva checklist

Before you finish a SAD viva, make sure you have covered: [1]

• Definition: a pharyngeal airway sealing around the laryngeal inlet; not a definitive airway.
• Generations: first (classic LMA, no gastric channel, low seal) vs second (i-gel, ProSeal, Supreme, Protector, Baska — gastric channel, higher seal, conduit). NAP4 retired the first generation from emergency rescue.
• Mechanism: hypopharyngeal bowl over the larynx, tip at the upper oesophageal sphincter; second seal + drain channel = partial aspiration protection.
• Indications: Plan B rescue, difficult-airway conduit, NIV/CPAP bridge, cardiac arrest, procedural sedation, pre-hospital airway.
• Contraindications (RODS): Restricted mouth opening, Obstruction, Disrupted/distorted upper airway, Stiff lungs; plus relative — high aspiration risk.
• Technique: size by weight, sniffing position, slide along the hard palate, seat at the "give", confirm with chest rise + waveform capnography, secure, document.
• Conduit: Aintree catheter over a fibreoptic scope, railroad a 6.0-7.0 ETT, remove the SAD.
• Complications: aspiration, nerve injury (recurrent laryngeal / hypoglossal / lingual), laryngospasm, sore throat, oesophageal trauma, displacement.
• Evidence: NAP4 (retired first generation), DAS 2018 (Plan B), AIRWAYS-2 and PART (cardiac arrest equipoise), ERC 2021 (second-generation SAD accepted). [1]

References

1. [1]Higgs A, McGrath BA, Goddard C, et al.; Difficult Airway Society et al. Guidelines for the management of tracheal intubation in critically ill adults Br J Anaesth, 2018.PMID 29406182
2. [2]Frerk C, Mitchell VS, McNarry AF, et al.; Difficult Airway Society Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults Br J Anaesth, 2015.PMID 26556848
3. [3]Soar J, Bottiger BW, Carli P, et al.; Adult Advanced Life Support Collaborators European Resuscitation Council Guidelines 2021: Adult advanced life support Resuscitation, 2021.PMID 33773825
4. [4]Benger JR, Kirby K, Black S, et al.; AIRWAYS-2 trial collaborators Effect of a Strategy of a Supraglottic Airway Device vs Tracheal Intubation During Out-of-Hospital Cardiac Arrest on Functional Outcome: The AIRWAYS-2 Randomized Clinical Trial JAMA, 2018.PMID 30167701
5. [5]Wang HE, Schmicker RH, Daya MR, et al.; PART investigators Effect of a Strategy of Initial Laryngeal Tube Insertion vs Endotracheal Intubation on 72-Hour Survival in Adults With Out-of-Hospital Cardiac Arrest: A Randomized Clinical Trial JAMA, 2018.PMID 30167699
6. [6]Forestell B, Mancini ME, Coombs HC, et al. Supraglottic Airway Versus Tracheal Intubation for Airway Management in Out-of-Hospital Cardiac Arrest: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis of Randomized Controlled Trials Crit Care Med, 2024.PMID 37962112
7. [7]Michalek P, Hodgkinson P, Donaldson W A comparison of the I-gel supraglottic airway as a conduit for tracheal intubation with the intubating laryngeal mask airway: a manikin study Resuscitation, 2010.PMID 19926388
8. [8]Saracoglu KT, Eris F, Turan AZ, et al. Efficiency of laryngeal mask airway ProtectorTM and i-gel® as a conduit in Aintree catheter-guided fibreoptic tracheal intubation: a randomised clinical trial Anaesthesiol Intensive Ther, 2022.PMID 35413787