Supraglottic airway devices: i-gel and lma variants

How to choose a SAD (rapid framework)

Define the clinical goal: oxygenation/ventilation as a primary airway, rescue after failed intubation, conduit for intubation, or post-extubation bridge
Assess aspiration risk and need for gastric drainage
- Prefer 2nd generation SADs (higher seal pressure + gastric channel) when aspiration risk is not negligible or positive pressure ventilation is anticipated
Assess ventilation requirements: spontaneous vs controlled, peak airway pressure expected (obesity, laparoscopy, Trendelenburg, restrictive lung disease)
- Choose devices with higher oropharyngeal leak pressure (OLP) and better stability for controlled ventilation
Need for intubation through SAD (Aintree catheter/fibreoptic) or as a rescue conduit
- Dedicated intubating LMAs (e.g., LMA Fastrach/ILMA) are designed for blind/fibreoptic intubation, i-gel can be used as a conduit but is not a dedicated intubating device
Patient and airway factors: mouth opening, dentition, pharyngeal pathology, cervical spine precautions, paediatrics
Operator and environment: prehospital/ED, availability of sizes, single-use vs reusable, infection control, familiarity

Insertion and confirmation (standardised approach)

Preparation: correct size, check packaging integrity, lubricate posterior surface only, prepare suction and capnography
Depth and position: advance until definite resistance, ensure midline, avoid folding of epiglottis (especially with some LMAs)
Cuff management (LMAs): inflate to minimal occlusive volume, use manometer, keep intracuff pressure typically ≤60 cmH2O to reduce mucosal injury
Confirm: chest rise, auscultation, capnography, low leak at required airway pressure, adequate tidal volumes, stable waveform
Assess seal (OLP): close APL to ~30–40 cmH2O with fixed flow and listen at mouth/epigastrium, document OLP if relevant (laparoscopy/obesity)
Gastric channel (2nd gen): pass lubricated gastric tube if indicated, confirm easy passage and aspirate

Troubleshooting poor ventilation/leak (stepwise)

Check depth and midline, perform jaw thrust, adjust head/neck position, ensure adequate anaesthetic depth
For LMA: adjust cuff volume/pressure (avoid overinflation), consider repositioning using insertion tools/techniques
For i-gel: reposition (withdraw slightly or advance), ensure correct size, consider gentle chin lift/jaw thrust, avoid excessive lubrication in bowl
If persistent leak at required pressures: change to larger size or different SAD, consider intubation
If obstruction/stridor: suspect malposition, epiglottic downfolding (device-dependent), laryngospasm, biting, treat accordingly

Classification and key concepts

Supraglottic airway device (SAD): sits above the glottis to maintain a patent airway, does not provide a definitive seal of the trachea
1st generation: airway tube + cuff/bowl, no dedicated gastric drainage (e.g., classic LMA)
2nd generation: improved seal + features to reduce aspiration risk (gastric drain channel, higher OLP, bite block, improved stability) (e.g., i-gel, LMA ProSeal, LMA Supreme)
Performance metrics: OLP (seal), ease/success of insertion, fibreoptic view, stability, gastric access, complication profile

i-gel: design and practical points

Single-use 2nd generation SAD with a non-inflatable thermoplastic elastomer cuff designed to mirror perilaryngeal anatomy
Key components: airway tube, integral bite block, epiglottic rest, gastric drain channel, buccal stabiliser
Advantages: rapid insertion (no cuff inflation), reduced risk of cuff overinflation-related mucosal injury, generally good OLP for controlled ventilation, easy gastric tube placement
Limitations: seal depends on size/fit and positioning, may leak at higher airway pressures, can be displaced with movement, not a definitive anti-aspiration device
Sizing: weight-based, choose correct size to optimise seal and reduce trauma (local packaging guidance varies, follow manufacturer and institutional policy)
Insertion: lubricate posterior surface, insert along hard palate into hypopharynx until resistance, avoid pushing tongue posteriorly, confirm ventilation and consider OLP check when PPV required
Use as conduit for intubation: can facilitate fibreoptic intubation, consider Aintree catheter technique, check compatibility of tube size and device size, remove SAD over tube with stabilisation

LMA variants: key differences

Classic LMA (cLMA): reusable (traditionally), inflatable cuff, 1st generation, suitable for spontaneous ventilation and selected controlled ventilation with modest pressures
LMA ProSeal (PLMA): 2nd generation, inflatable cuff with improved seal, gastric drain tube, dorsal cuff to improve seal, better for controlled ventilation and higher airway pressures
LMA Supreme: 2nd generation, single-use, preformed curved tube for easier insertion, gastric drain, generally good seal, convenient for routine cases and rescue
LMA Flexible (reinforced): wire-reinforced flexible tube, useful for head/neck surgery and shared airway, cuff similar to classic, more resistant to kinking but can be harder to insert
Intubating LMA (Fastrach/ILMA): rigid curved airway tube with handle, designed to facilitate blind or fibreoptic tracheal intubation, requires dedicated ETT, no gastric drain (device-dependent and generation-dependent)

Indications and contraindications (i-gel and LMAs)

Indications: routine elective airway for suitable fasting patients, rescue oxygenation in difficult airway algorithms, conduit for fibreoptic intubation, short procedures, day-case surgery
Relative contraindications: high aspiration risk (non-fasted, bowel obstruction, active reflux with symptoms, pregnancy beyond early gestation, upper GI bleed), severe obesity with very high airway pressures anticipated, poor mouth opening, pharyngeal pathology/trauma, need for lung isolation
Caution: laparoscopic surgery and Trendelenburg—often feasible with 2nd generation SADs if seal adequate and aspiration risk acceptable, require careful selection and monitoring

Complications and how to reduce them

Aspiration/regurgitation: risk reduced (not abolished) by 2nd generation SADs and appropriate patient selection, use gastric drain when present, avoid excessive insufflation pressures
Airway trauma: blood on device, sore throat, dysphonia, minimise by correct size, gentle technique, adequate depth, and limiting cuff pressure (LMAs)
Nerve injury (rare): lingual, hypoglossal, recurrent laryngeal—associated with malposition, prolonged use, high cuff pressures, small size
Obstruction: malposition, epiglottic downfolding (device-dependent), biting, laryngospasm, manage with repositioning, deepen anaesthesia, bite block, CPAP, and laryngospasm treatment
Gastric insufflation: occurs with leak and high inspiratory pressures, reduce by optimising seal, limiting pressures, and using gastric drainage where available

Use in difficult airway and rescue algorithms (principles)

After failed intubation with adequate mask ventilation: consider SAD to maintain oxygenation and as a conduit for fibreoptic intubation
After failed intubation with difficult/impossible mask ventilation: immediate insertion of a 2nd generation SAD is a key rescue step, if ventilation achieved, proceed to wake/intubate via SAD depending on context
If SAD fails to ventilate: move promptly to emergency front-of-neck access pathway per local guidelines, avoid repeated traumatic attempts

Test yourself…

Compare i-gel with LMA ProSeal and LMA Supreme. How do their designs affect performance?

Structure your answer by generation, cuff type, seal, gastric access, ease of insertion, and typical use cases.

All are generally considered 2nd generation SADs with gastric drainage capability (device-specific features vary), aiming for higher seal and reduced aspiration risk compared with classic LMA
i-gel: non-inflatable anatomical cuff → fast insertion, no cuff pressure issues, seal is fit-dependent, integral bite block and gastric channel
ProSeal: inflatable cuff with design to improve seal (including dorsal cuff) + gastric drain → often high OLP suitable for controlled ventilation, requires cuff pressure monitoring
Supreme: single-use, preformed curved tube + inflatable cuff + gastric drain → typically easy insertion and stable positioning, cuff pressure monitoring still required
Clinical implication: for controlled ventilation (e.g., laparoscopy) choose a device with reliably high OLP and gastric drainage, confirm seal and limit airway pressures

Describe how you would insert an i-gel and confirm correct placement. What would you do if there is a significant leak?

Preparation: choose correct size, lubricate posterior surface, position head (sniffing if appropriate), ensure adequate depth of anaesthesia
Insertion: open mouth, insert along hard palate into hypopharynx until definite resistance, keep midline, avoid pushing tongue posteriorly
Confirmation: capnography, chest rise, auscultation, adequate tidal volumes, stable waveform, assess OLP if PPV required, pass gastric tube if indicated
Leak management: jaw thrust and reposition (advance/withdraw slightly), optimise head/neck position, deepen anaesthesia, check size (upsizing often improves seal), change device if persistent, proceed to intubation if ventilation inadequate

A common FRCA theme: Explain oropharyngeal leak pressure (OLP). How do you measure it and how does it influence your practice?

Definition: airway pressure at which gas leaks around the SAD seal into the pharynx (audible at mouth) during positive pressure ventilation
Measurement (one method): set fresh gas flow (e.g., 3 L/min), close APL gradually, observe airway pressure at equilibrium when leak heard at mouth/neck, cap maximum pressure to avoid barotrauma (commonly 30–40 cmH2O)
Clinical relevance: higher OLP supports controlled ventilation and reduces gastric insufflation, low OLP suggests malposition, wrong size, inadequate depth, or unsuitable device

Previous FRCA-style viva: Discuss aspiration risk with SADs. How do 2nd generation devices reduce risk and what are the limitations?

SADs do not isolate the trachea, aspiration can still occur despite good seal
2nd generation risk-reduction: higher seal pressures reduce leak, gastric drain channel provides a path for regurgitated material and allows gastric decompression, improved stability reduces displacement
Limitations: regurgitation can still reach larynx, drain can block/malposition, high airway pressures can overcome seal, patient selection remains key
Practical steps: fasting assessment, avoid in high-risk patients, use lowest effective airway pressures, consider RSI/intubation when risk unacceptable, pass gastric tube when available

You are ventilating through an LMA and the patient develops a sore throat and tongue numbness post-op. What device-related factors might contribute and how would you prevent this?

Mechanisms: mucosal pressure/ischemia from high cuff pressure (inflatable LMAs), malposition, oversized device, prolonged duration, traumatic insertion
Nerve injury possibilities: lingual/hypoglossal neuropraxia from compression, recurrent laryngeal injury causing hoarseness
Prevention: correct size, gentle technique, adequate depth, avoid nitrous-related cuff overexpansion, use cuff manometer and keep intracuff pressure typically ≤60 cmH2O, reassess after positioning

Previous FRCA-style scenario: Failed intubation. You insert a 2nd generation SAD and ventilation is now adequate. What are your options and what factors guide your decision?

Immediate priorities: maintain oxygenation, confirm capnography, call for help, optimise anaesthesia and haemodynamics
Options: wake the patient, proceed with surgery using SAD, intubate via SAD with fibreoptic/Aintree, attempt alternative intubation technique after stabilisation
Decision factors: urgency of surgery, aspiration risk, predicted difficulty, adequacy of ventilation and seal, surgical position (e.g., prone), need for paralysis/controlled ventilation, operator skill and equipment availability

How would you use an i-gel as a conduit for fibreoptic intubation? Describe a safe step-by-step plan.

Preconditions: stable oxygenation/ventilation through i-gel, adequate depth, suction ready, capnography and haemodynamic monitoring
Technique: load appropriate ETT onto fibrescope, pass scope through i-gel to visualise cords, advance into trachea, railroad ETT, confirm with capnography
Device removal: consider leaving i-gel in situ if compatible with surgery, if removing, use an exchange/stabilising method (e.g., Aintree catheter or airway exchange catheter) to prevent accidental extubation
Pitfalls: ETT size compatibility, impingement at epiglottis/cuff, loss of airway during device removal, mitigate with planning and assistance

Discuss the effects of nitrous oxide on LMA cuffs and why this matters.

Nitrous oxide diffuses into air-filled cuffs faster than nitrogen diffuses out → increases cuff volume/pressure over time
Consequences: increased pharyngeal mucosal pressure → sore throat, mucosal ischemia, nerve injury, can worsen malposition or leak dynamics
Management: use cuff manometer and adjust, consider filling cuff with saline (device/manufacturer dependent) or avoid N2O when prolonged use/concern

What are the common causes of obstruction with SADs and how do you differentiate them clinically?

Malposition: inadequate depth, rotation, folding, signs include poor chest rise, high airway pressures, leak, abnormal capnography
Laryngospasm: inspiratory stridor, absent/poor capnography, high resistance, often with light anaesthesia or stimulation
Biting: sudden obstruction with patient lightening, bite block helps (i-gel has integral bite block, others may need adjunct)
Secretions/blood: wheeze-like sounds, variable obstruction, suction and optimise depth

A previous FRCA equipment viva theme: Describe checks you would perform before using an LMA and an i-gel.

LMA: inspect cuff for damage, inflate to check symmetry and leaks then fully deflate, check connector patency, ensure correct size, prepare cuff manometer, lubricate posterior surface
i-gel: inspect for damage/deformity, ensure correct size, check gastric channel patency, lubricate posterior surface, no cuff inflation required
Both: ensure availability of suction, capnography, alternative sizes, and a backup plan if ventilation fails