Residency · Residency · Anesthesiology

Supraglottic Airways: Beyond the LMA Classic

Classification of Supraglottic Airways

First-Generation Devices

First-generation supraglottic airways lack a dedicated gastric drainage channel. They provide lower seal pressures (typically below 20 cmH2O), carry a higher aspiration risk, and are limited to lower airway pressure ventilation. Examples include the LMA Classic, LMA Unique, and LMA Flexible.

Second-Generation Devices

Second-generation devices incorporate a gastric drainage channel that separates the alimentary and respiratory tracts. They achieve higher oropharyngeal seal pressures (25-40 cmH2O) and provide improved protection against aspiration, though not equivalent to an ETT. Most include built-in bite blocks. Examples include the LMA ProSeal, LMA Supreme, i-gel, and Ambu AuraGain.

Major Second-Generation Devices

LMA ProSeal

The ProSeal features a dual-lumen design with a ventilation channel and a gastric drainage channel. Its reinforced cuff with a posterior extension provides an improved seal, achieving oropharyngeal leak pressures of 25-35 cmH2O. An orogastric tube can be passed through the drain port. Correct positioning is confirmed by easy gastric tube passage, absence of air leak with positive pressure ventilation, and the suprasternal notch test. It lacks an integrated bite block (instead using a wire-reinforced airway tube) and is reusable up to 40 times after sterilization.

LMA Supreme

The Supreme is a single-use device with a pre-curved rigid airway tube, an integrated bite block, and a gastric drainage channel. It achieves oropharyngeal leak pressures of 24-30 cmH2O. Its rigid curve guides placement, making insertion easier than the ProSeal. It is widely available in most institutions and includes a fixation tab for securing.

i-gel (Intersurgical)

The i-gel features a non-inflatable cuff made of thermoplastic elastomer (a gel-like material) that conforms to the perilaryngeal anatomy as it warms to body temperature. Because no cuff inflation is required, insertion is faster. It includes a gastric drainage channel and an integrated bite block. Oropharyngeal leak pressure is 20-30 cmH2O. Critically, the i-gel has the widest internal diameter for its size among SGAs, making it an excellent conduit for fiberoptic-guided intubation. It is single-use and increasingly popular due to its simplicity and consistent performance.

Ambu AuraGain

The AuraGain is a single-use device with an anatomically curved airway tube, an inflatable cuff, and a gastric drainage channel. It is designed to accommodate intubation, accepting a standard ETT through the ventilation channel. Oropharyngeal leak pressure is 25-30 cmH2O.

SGA as Conduit for Intubation

Technique

After placing the SGA and confirming ventilation, a flexible bronchoscope loaded with an ETT is advanced through the SGA. The vocal cords are visualized and the bronchoscope is advanced into the trachea. The ETT is then railroaded over the bronchoscope into the trachea. The SGA is removed over the ETT (requiring brief circuit disconnection), and ETT position is verified with capnography and auscultation.

Best Conduit SGAs

The i-gel offers the widest internal diameter relative to device size and a smooth non-inflatable cuff that eases ETT passage. The intubating LMA (Fastrach/CTrach) is specifically designed for blind or fiberoptic-guided intubation with a rigid handle for one-handed manipulation. The Ambu AuraGain is designed to accommodate intubation. The Air-Q has a wide-bore lumen designed as an intubation conduit.

ETT Size Through SGAs

As a general guide, a size 3 SGA typically accepts up to a 6.0 mm ETT, a size 4 accepts up to 7.0 mm, and a size 5 accepts up to 8.0 mm. Manufacturer specifications vary by device and should always be checked.

Expanded Indications

Laparoscopic Surgery

While SGAs were traditionally contraindicated due to elevated intraabdominal pressure and aspiration risk, evolving evidence shows that second-generation SGAs with gastric drainage provide adequate ventilation at pneumoperitoneum pressures up to 12-15 cmH2O. Multiple studies demonstrate safe use in laparoscopic cholecystectomy and gynecological procedures. Adequate oropharyngeal seal pressure must exceed insufflation pressure. Patient selection remains important — SGAs should be avoided in morbid obesity, GERD, full stomach, and prolonged steep Trendelenburg.

Prone Surgery

SGA use in the prone position is gaining acceptance for short procedures. The ProSeal and i-gel have been studied in prone position for spinal and orthopedic surgery. Advantages include avoiding intubation, reduced throat soreness, and smoother emergence. The risk is that accidental displacement in the prone position is potentially catastrophic — the device must be secured extremely well with continuous capnography. The rescue plan for SGA failure in prone is emergent supine repositioning.

Obese Patients

Second-generation devices can provide adequate ventilation in patients with a BMI of 30-40, though higher seal pressures may be needed and controlled ventilation may be required rather than spontaneous breathing. Morbid obesity (BMI above 40) remains a relative contraindication for most practitioners. Head-up or ramped positioning improves SGA function in obese patients.

Cesarean Delivery (Rescue)

An SGA serves as a rescue device in failed intubation during general anesthesia for cesarean delivery. A second-generation device is preferred for its gastric drainage and higher seal pressure. DAS/OAA guidelines designate SGA as Plan B after failed intubation in obstetric anesthesia — surgery can proceed through an SGA if oxygenation is maintained and urgency warrants.

Complications

Aspiration

SGAs do not protect the airway as effectively as a cuffed ETT. Second-generation devices reduce but do not eliminate aspiration risk. The gastric drainage channel allows suctioning of regurgitated material. Risk factors include full stomach, obesity, GERD, lithotomy or Trendelenburg position, and prolonged cases.

Airway Trauma

Sore throat occurs in 10-40% of patients (less than ETT in most studies). Rare complications include lingual or hypoglossal nerve injury (from cuff over-inflation or prolonged placement), arytenoid dislocation, and recurrent laryngeal nerve palsy (from high cuff pressures).

Cuff-Related Issues

Over-inflation paradoxically reduces seal pressure by distorting cuff shape, and it increases pharyngeal mucosal pressure and nerve injury risk. Under-inflation produces an inadequate seal and air leak. Recommended cuff pressure is 40-60 cmH2O (device-specific; follow manufacturer guidance). The i-gel avoids this issue entirely because it has no cuff to manage.

Displacement and Obstruction

Partial or complete obstruction can occur from epiglottic downfolding or rotation causing misalignment with the laryngeal inlet. Prevention involves proper sizing, verification with capnography, secure fixation, and a bite block.

Sizing

Sizing is based on patient weight according to manufacturer recommendations: size 3 for 30-50 kg, size 4 for 50-70 kg, and size 5 for 70-100 kg. Clinical judgment may override weight-based selection because anatomy varies.

SGA vs. ETT: When to Choose Each

SGA Preferred

SGAs are preferred for short elective procedures (under 2-4 hours), supine/lateral or limited prone positioning, spontaneous or controlled ventilation with moderate airway pressures, ambulatory surgery (faster emergence, less sore throat), and rescue airway situations in failed intubation.

ETT Required

An ETT is required for full stomach or aspiration risk (unless an SGA is used as rescue), prolonged surgery (beyond 4 hours is a relative indication), high airway pressures (morbid obesity, ARDS, one-lung ventilation), shared airway surgery (head/neck, ENT), steep Trendelenburg for prolonged periods, and neuromuscular blockade with high-pressure ventilation needs.

<image>A comparison diagram of four second-generation supraglottic airways shown in cross-section at the level of the larynx: LMA ProSeal, LMA Supreme, i-gel, and Ambu AuraGain. Each cross-section shows the ventilation channel, gastric drainage channel, and cuff design (inflatable vs. gel). A table below compares oropharyngeal leak pressure, ease of insertion, intubation conduit capability, and cuff type for each device.</image>

<image>An illustrated step-by-step guide for fiberoptic-guided intubation through a supraglottic airway: (1) SGA in place with adequate ventilation confirmed, (2) flexible bronchoscope loaded with appropriate size ETT, (3) bronchoscope advanced through SGA showing view of vocal cords through the SGA aperture, (4) bronchoscope in trachea with carina visible, (5) ETT railroaded over bronchoscope through SGA into trachea, (6) SGA removal over the ETT using the stabilizing rod technique. Inset shows ETT size compatibility chart for common SGAs.</image>

<image>A clinical decision algorithm for selecting between supraglottic airway and endotracheal tube: starting with patient assessment (aspiration risk, BMI, surgical position, expected airway pressures, case duration), branching through decision points, and arriving at recommendations for first-generation SGA, second-generation SGA, or ETT. Special considerations boxes for laparoscopic use, prone position, and obstetric rescue are included.</image>

Clinical Pearls

Second-generation SGAs with gastric drainage channels have significantly expanded the safety envelope for SGA use and are now the standard of care in most institutions. The i-gel is the simplest SGA to insert (no cuff inflation), provides consistent seal pressures, and is the best conduit for fiberoptic intubation due to its wide internal diameter. Over-inflating the SGA cuff actually decreases seal pressure and increases mucosal injury risk — always use the minimum inflation volume that provides an adequate seal. The SGA is a critical rescue device in the difficult airway algorithm, and every anesthesiologist must be proficient with at least one second-generation device. SGAs for laparoscopic surgery are increasingly evidence-supported with second-generation devices, but careful patient selection remains essential. Always pass an orogastric tube through the gastric drainage channel after SGA placement — it confirms correct positioning and decompresses the stomach.

References

• Cook TM, et al. Major complications of airway management in the UK: results of NAP4. Br J Anaesth. 2011;106(5):617-631.
• Timmermann A. Supraglottic airways in difficult airway management: successes, failures, use and misuse. Anaesthesia. 2011;66(Suppl 2):45-56.
• Brimacombe J, Keller C. The ProSeal laryngeal mask airway: a randomized, crossover study. Anesthesiology. 2000;93(1):104-109.
• Theiler L, et al. i-gel supraglottic airway in clinical practice: a prospective observational multicentre study. Br J Anaesth. 2012;109(6):990-995.
• Van Zundert AAJ, et al. The role of the supraglottic airway device in modern anaesthesia. Anaesthesia. 2022;77(Suppl 1):21-28.

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