Supraglottic airways (SGAs) for airway management for anesthesia in adults

INTRODUCTION — 

Supraglottic airways (SGAs) are a group of airway devices that can be inserted into the pharynx to allow ventilation, oxygenation, and administration of anesthetic gases, without the need for endotracheal intubation. For anesthesia, these devices are used for primary airway management, for rescue ventilation when facemask ventilation is difficult, and as a conduit for endotracheal intubation.

The SGAs that are used most commonly in the operating room are the laryngeal mask airways (LMAs) and similar devices. These consist of a hollow shaft or tube connected to a mask-like cuff designed to sit in the hypopharynx facing the glottis, with the tip at the esophageal inlet (figure 1 and picture 1). Other devices used more commonly in the emergency department and for prehospital airway management are referred to as extraglottic devices (eg, Combitube, laryngeal tube, pharyngeal tube).

This topic will discuss SGAs as they are used in anesthesia for adults, including placement and ventilation techniques, endotracheal intubation through the LMA, and use in special clinical situations. Use of other airway devices in anesthesia is discussed separately. (See "Airway management for general anesthesia in adults", section on 'Choice of airway device'.)

Use of SGAs and other extraglottic devices in emergency medicine is discussed separately. (See "Extraglottic devices for emergency airway management in adults".)

ROUTINE USE OF SGAS — 

The supraglottic airway (SGA) is used clinically as an alternative to both mask ventilation and endotracheal intubation. It is usually easily placed and is less stimulating than endotracheal intubation, but it does not provide complete protection against aspiration and does not prevent laryngospasm. Choice of airway device for anesthesia is discussed separately. (See "Airway management for general anesthesia in adults", section on 'Choice of airway device'.)

Choice of SGA — Unless cost is an issue, for most patients we prefer to use the more advanced second-generation devices that include bite blocks and esophageal vents. In addition, when the need for high ventilation pressure is anticipated, we prefer an SGA specifically designed for that purpose (eg, LMA ProSeal).

There are multiple types of reusable and disposable SGAs (picture 2 and picture 3). Although the LMA is the oldest and best known brand, a number of other companies manufacture SGAs.

Classification of SGAs — SGAs are often referred to as first, second, or third generation devices, though second and third generation are variably defined.

●First generation SGAs – The original LMA and similar devices made by other companies are referred to as first-generation SGAs. They include an airway tube with a mask-like inflatable cuff. First-generation SGAs are often used in spontaneously breathing patients undergoing short surgical procedures.

●Second generation SGAs – Second-generation SGAs may include additional features such as bite blocks, cuffs designed to improve the seal, esophageal vents that allow orogastric tube placement, inflatable cuff pressure monitors, or a lumen that allows passage of an upper gastrointestinal endoscope (figure 2). Examples of second-generation products include the LMA ProSeal (picture 4), the LMA Supreme (picture 5) and the LMA Fastrach (picture 6), the i-gel (picture 7), and the Air-Q blocker (picture 8).

●Third generation SGAs – Some experts consider the most recently developed SGAs with video capabilities to be the third generation of SGAs [1-3].

Unique features — Examples of unique features incorporated into various devices include the following:

●A number of SGAs contain aperture bars (a grill) over the laryngeal inlet. This feature serves to prevent the epiglottis from entering the shaft of the SGA (picture 9). The epiglottis can interfere with ventilation and with the visualization of glottic structures with a flexible intubating scope [4], though the clinical significance of this feature has been disputed [5].

●Flexible, reinforced SGAs have wire-reinforced, flexible airway tubes with a smaller diameter than other SGAs. These features allow them to be positioned away from the surgical field without kinking, which is particularly useful for otolaryngologic, dental, and other head and neck procedures in which the surgeon and anesthesiologist share the airway or the surgical field. Examples include the LMA flexible, the Ambu AuraFlex, and the Tru-Cuff Ultra Flex EX (picture 10).

●Some SGAs incorporate a preformed curved airway tube that facilitates placement. Examples include the Ambu AuraOnce, the Ambu Aura Gain, the LMA Supreme, and the LMA Protector (picture 5).

●Some SGAs include features designed to prevent high-pressure overinflation of the cuff. The Tru-Cuff LM inflation syringe has a built-in pressure indicator. After the device is inserted, the cuff is inflated until the indicator is in the green zone on the syringe (40 to 60 mmHg) (picture 11). Another device, the air-Q SP, has a self-inflating, low-pressure cuff (picture 12). (See 'Role of cuff pressure' below.)

●The i-gel differs from other SGAs in that its gel cuff is not inflatable, which may reduce the risk of oropharyngeal trauma. Compared with some other SGAs, use of the i-gel is associated with less postoperative sore throat (picture 7) [6-8]. The i-gel has a gastric vent, an integral bite block, and a flange designed to prevent epiglottic folding.

●A number of SGAs may be used as conduits for endotracheal intubation. Examples include the LMA Fastrach, the air-Q intubating laryngeal airway (ILA), the i-gel, the Ambu Aura Gain, and the LMA protector (picture 6 and picture 13 and picture 7). The LMA Fastrach is designed to be used for intubation and then removed. The other four listed SGAs can be used as primary airway devices. (See 'Supraglottic airways as conduits for intubation' below.)

●The LMA Gastro Airway was developed for use during upper gastrointestinal endoscopy, and allows passage of an endoscope through a dedicated lumen while providing an unobstructed airway (figure 2). In an open label observational study including 292 patients who underwent upper endoscopy with general anesthesia, rates for successful LMA insertion and successful endoscope insertion were both 99 percent [9]. The only notable adverse event was hospital admission for a sore throat with inability to tolerate oral fluids in one patient. In one small study (30 patients), the LMA Gastro was used for endoscopic retrograde cholangiopancreatography without complications [10].

Large diameter endoscopes (eg, ultrasound capable gastroscopes) may not pass easily through the LMA Gastro; before using the LMA Gastro, the intended gastroscope should be tested to make sure it passes easily through the LMA.

Video SGA — Video SGAs are a new type of device that allow vision-guided insertion and confirmation of correct placement (picture 14). These incorporate a dead end channel that accepts a reusable proprietary videoscope, in addition to features of a second generation SGA (eg, a gastric drainage channel). With the videoscope inserted, the lens is within the bowl of the SGA. Video SGAs are placed in the same way as other SGAs, after which the videoscope is removed. (See 'Placement technique for most SGAs' below.)

Video SGAs may reduce or eliminate incorrect SGA placement, and can also be used to facilitate endotracheal intubation if necessary.

Multiple studies using various confirmation techniques have found that blindly inserted SGAs are suboptimally positioned in as many as 80 percent of cases [11-13]. Malpositioning is often unrecognized, and can cause gastric insufflation, aspiration, leak of gas around the cuff and inadequate ventilation, or airway injury. Several studies have reported successful correct SGA placement in >95 percent of video SGA assisted insertions [14,15]. (See 'Supraglottic airway-related complications' below.)

Several models of video SGAs have been introduced into the market. Examples are the UE Medical SaCoVLM, and the SafeLM Video Laryngeal Mask system. The latter allows adjustment of the tip of the videoscope to visualize the entire glottis.

Experience with these devices is limited and their role in routine practice has not been established.

Choice of size — Most SGAs come in full sizes (eg, 3, 4, 5, 6), though some are available in half sizes (eg, 3.5, 4.5). While manufacturers' guidelines recommend weight-based size selection, these guidelines generally assume a typical body habitus (table 1 and table 2). Predicting optimal sizing is complex as an optimal seal depends on a number of factors, including the size of the device, the cuff inflation, and patient anatomy [16-19].

SGA manufacturers provide guidelines for the maximum volume of air to be used for cuff inflation. Suggested cuff volumes are 30 mL for a size-4 SGA and 40 mL for a size-5 SGA, with the caveat that cuff pressures should not exceed 60 cm H₂O. If a high cuff volume is required in order to maintain a seal, we usually replace the device with a larger size, as a better seal may be obtained using a larger size with less air. Using too small a device and overinflating the cuff may result in a poor fit within the oropharyngeal space and may injure the oropharyngeal mucosa. (See 'Role of cuff pressure' below.)

In general, a size-4 SGA will be suitable for most adult females and a size-5 for adult males up to 100 kg. Ultimately, choice of SGA size is as much an art as a science. In many cases, if the initial size chosen does not provide adequate ventilation (eg, large leak at any cuff volume), a different size SGA should be tried, or endotracheal intubation should be performed.

Placement technique for most SGAs — Adequate depth of anesthesia with intravenous (IV) or inhalation anesthetics is generally established before SGA placement in order to avoid coughing, gagging, laryngospasm, breath holding, or straining. Successful placement in awake patients with adequate topical oropharyngeal anesthesia has also been described [20]. In general, SGA placement is less stimulating than endotracheal intubation. Neuromuscular blocking agents are not usually necessary for insertion of an SGA, though they may be. (See 'Use of neuromuscular blocking agents' below.)

Several methods for SGA placement have been described; we generally follow the manufacturer's instructions for placement of the LMA Classic before attempting alternate methods. The technique is summarized as follows (figure 3):

●Lubricate the cuff with a water-based lubricant.

●Hold the device with the index finger of the dominant hand placed at the junction between the cuff and the airway tube.

●Press the cuff upward against the hard palate with the index finger, then backward and downward along the palate in a smooth movement until resistance is encountered. As the index finger is removed, use the nondominant hand to hold the LMA down and prevent dislodgement.

●Inflate the cuff to a target cuff pressure of around 44 mmHg, or to the minimum pressure needed to create an adequate seal [21].

Placement technique for second generation SGAs — Insertion technique varies for second-generation SGAs; for some of them insertion is similar to the technique described above for first generation SGAs. For the stiffer pre-curved SGAs (eg, LMA Supreme, LMA Protector) there is no need to insert a finger into the patient’s mouth when placing the device.

Verification after placement — With correct insertion, the SGA sits over the glottis, with the epiglottis lying within the mask aperture. Clinical confirmation of correct positioning can be established by the following:

●Easy positive pressure ventilation (PPV), requiring low ventilation pressures

●Appropriate chest rise with each breath

●A normal capnogram trace

●No leak with positive pressure breaths under 20 mmHg peak pressure

With correct positioning, the tube may move outward as the cuff is inflated, and a slight swelling in the neck may occur. However, some malpositions may not be clinically apparent and may not be identified unless a flexible intubation scope is used. Common causes of malposition include a down-folded epiglottis or a flipped-over SGA cuff, which may require reinsertion. (See 'Troubleshooting' below.)

Once insertion is complete, cuff pressure can be measured with a manometer designed for this purpose, unless an SGA with a built-in manometer is used (picture 15). (See 'Role of cuff pressure' below.)

Troubleshooting — Although SGAs are usually placed successfully, problems with insertion or ventilation occur. Malpositions can sometimes be managed by repositioning the patient's head, readjusting the SGA position, or adjusting the air in the cuff. When in doubt, we advise removing and reinserting the SGA. When reinserting the SGA, rotating it 90 degrees with or without partially inflating the cuff may be helpful [22,23], or if necessary, a flexible intubation scope or ultrasound can be used to assist placement [24]. Use of neuromuscular blocking agents, including to facilitate insertion, is discussed below. (See 'Use of neuromuscular blocking agents' below.)

●Inadequate anesthesia – Initial difficulty with placement of an SGA may be due to inadequate anesthesia, such that the patient strains, breath holds, or maintains upper airway tone, preventing seating of the device. Insufficient depth of anesthesia may also cause laryngospasm or bronchospasm, resulting in airway obstruction. If clinically appropriate, ventilation may be improved by administration of additional anesthetic (eg, propofol or inhalation agent) without further manipulation of the SGA.

●Down-folded epiglottis – The tip of the epiglottis can be flipped over as the SGA is placed, resulting in noisy ventilation or airway obstruction. The "up-down maneuver" helps correct this by unfolding the epiglottis [25]. With this maneuver, the SGA is withdrawn 2 to 4 cm and reinserted without deflating the cuff. Head extension, slight advancement or withdrawal, or SGA removal and replacement may also improve ineffective ventilation.

●Inadequate seal – Inappropriate sizing may make a seal difficult or impossible. In general, larger sizes create a better seal with lower cuff inflation volumes and pressures compared with smaller sizes [16-18]. The answer to an inadequate seal may be to insert a larger SGA, rather than to add more air to the cuff. In one retrospective review of approximately 19,700 anesthetics involving use of an SGA, use of SGA sizes 2 and 3 was associated with increased incidence of SGA failure [26]. (See 'Choice of size' above.)

Choice of mode of ventilation — SGAs can be used with the patient breathing spontaneously or with positive pressure ventilation (PPV). Since the SGA does not seal the pharynx, the pressure that can be safely used to ventilate is limited by leak around the device, with resultant gastric insufflation and/or hypoventilation. Therefore, pressure-limited ventilation (ie, pressure support or pressure control) is usually used with an SGA in place, rather than volume-control ventilation. (See "Mechanical ventilation during anesthesia in adults", section on 'Choice of mode of ventilation'.)

Use of SGAs with spontaneous breathing offers a number of advantages:

●Opioids can be titrated according to the patient's respiratory rate.

●Gastroesophageal insufflation of air is rarely a problem.

●Air leaks around the SGA are less likely than when using PPV.

●Some malpositions of the SGA are better tolerated.

On the other hand, PPV with SGA devices offers the following advantages:

●PPV allows control of respiratory rate, tidal volume, and minute ventilation.

●Hypoventilation is avoided during deep levels of anesthesia and when high doses of opiates are administered.

Most devices in the LMA family, as well as most other SGAs, were designed for use with peak pressures under 20 cmH₂O, and numerous studies have shown that leak and gastric insufflation are minimal if peak pressures are kept between 15 and 20 cmH₂O [27-31]. The LMA ProSeal was designed for use with higher ventilation pressures (the cuff includes a posterior extension to provide a "double seal") and ordinarily will allow peak airway pressures up to 25 cmH₂O before a leak occurs [31-33] The LMA Protector is another second generation SGA that can be used with higher ventilation pressures. In two randomized trials, the oropharyngeal leak pressure was higher with the LMA Protector than with the LMA Supreme, at the same cuff pressures [27,28].

Use of positive end expiratory pressure (PEEP) with SGAs — PEEP is often used with ventilation during anesthesia to prevent atelectasis. (See "Mechanical ventilation during anesthesia in adults", section on 'Positive end-expiratory pressure'.)

The author uses PEEP (typically at 5 cm H₂O) in most patients when using positive pressure ventilation with an SGA. Similar to the use of PEEP in patients with an endotracheal tube in place, whether PEEP is beneficial during ventilation with an SGA, and optimal levels of PEEP, are unclear. Studies of the effect of PEEP through an SGA have found little if any improvement in oxygenation with the use of PEEP through an SGA [34,35]. There does not seem to be an increase in air leak of gastric insufflation with the use of PEEP, though one trial found an increase in the need to reposition the device in patients who had 8 cm H₂O PEEP with a ProSeal LMA [34].

Pressure-controlled ventilation — Pressure-controlled ventilation (PCV) is a mode of PPV commonly used with SGAs. With PCV, the respiratory rate and peak inspiratory pressure are set, along with other parameters. In contrast to volume-controlled ventilation, PCV prevents high peak pressures that can lead to airway gas leaks and gastric insufflation. With an SGA in place, peak pressure is set between 15 and 20 cmH₂O, with the rate adjusted to achieve adequate minute ventilation. (See "Mechanical ventilation during anesthesia in adults", section on 'Pressure-controlled ventilation'.)

Pressure support ventilation — We routinely use pressure support ventilation (PSV) with SGAs, though not all anesthesia ventilators allow PSV mode. In PSV mode, the patient initiates each breath, and the ventilator delivers additional support with a preset pressure value. A minimum number of breaths is also set. In this mode, the patient controls his or her own respiratory rate and tidal volume, but if the resultant minute ventilation is too low, the minimum rate or the degree of pressure support can be increased. (See "Mechanical ventilation during anesthesia in adults", section on 'Pressure support'.)

In a randomized crossover study comparing PSV with continuous positive airway pressure (CPAP) using an LMA, PSV at 5 cmH₂O above positive end-expiratory pressure (PEEP) resulted in more effective gas exchange compared with spontaneous ventilation with CPAP at 5 cmH₂O [36].

Use of neuromuscular blocking agents — Neuromuscular blocking agents (NMBAs) are not usually necessary for insertion of an SGA. NMBAs may reduce the incidence of gagging, coughing and laryngospasm, though these adverse effects are unusual if the patient is adequately anesthetized. Reported first attempt success rates without NMBAs are from 90 to 97 percent [37,38]. The literature on the use of NMBAs during SGA placement is conflicting, with some studies finding that NMBAs improved first pass success or reduced complications [38,39], and others finding no beneficial effect [40,41].

NMBAs may be used with an SGA along with mechanical ventilation when relaxation is necessary for surgery. The author’s most common use of an NMBA with an SGA is to avoid laryngospasm during bronchoscopy.

NMBAs can also be used to facilitate endotracheal intubation through an SGA. One study that evaluated the administration of an NMBA during intubation through an intubating LMA reported less coughing and movement during intubation and less difficulty removing the LMA with use of NMBA [42].

SUPRAGLOTTIC AIRWAYS AND THE DIFFICULT AIRWAY — 

The SGA can serve as an airway rescue device by establishing ventilation and/or by allowing intubation through the device. Case reports have demonstrated that SGAs can be lifesaving in re-establishing an airway when ventilation by facemask and endotracheal intubation is impossible, situations in which a surgical airway would otherwise be required [43]. (See "Management of the anatomically difficult airway for general anesthesia in adults".)

If an SGA is used as a rescue device for ventilation after induction of anesthesia, depending on the clinical situation, the decision must be made to either continue the procedure using the SGA, to attempt endotracheal intubation using the SGA as a conduit, or to awaken the patient.

SGAs appear in multiple society guidelines for management of the difficult airway, as options for rescue ventilation after failed intubation or as conduits for endotracheal intubation (algorithm 1 and figure 4) [44-47].

SUPRAGLOTTIC AIRWAYS AS CONDUITS FOR INTUBATION — 

Once an SGA has been placed, it can act as a conduit for tracheal intubation using one of a number of techniques. Some SGAs (eg, i-gel, LMA Fastrach, air-Q, LMA Protector) permit direct passage of an endotracheal tube (ETT). Standard laryngeal mask airways (LMAs) are too narrow to permit passage of standard-size ETTs.

When an SGA is used for tracheal intubation, the ETT must slide through the SGA without difficulty and the SGA must be easily removed. Dimensional compatibility was investigated in an in vitro study of over 1000 combinations of various SGAs and ETTs, lubricated with medical silicone spray [48]. Failure to slide the ETT through the SGA occurred most commonly with first generation SGAs, almost always because the connector was too narrow. Removal of the SGA was impossible for most wire reinforced ETTs, and successful for all standard ETTs.

Intubating SGAs include features designed to facilitate or improve the success rate of endotracheal intubation. For example, the LMA Fastrach includes a bar that elevates the epiglottis as the ETT passes through the aperture. In addition, a ramp in the LMA Fastrach's intubating tube channel directs the tube centrally and anteriorly in order to minimize the risk of esophageal placement or damage to glottic structures (picture 6).

We prefer to intubate with a flexible intubation scope (FIS) through the SGA, though intubation is possible using a blind technique. The reported first attempt success rate is higher using an FIS than with a blind technique (95 to 100 percent [49] versus 40 to 75 percent [50]).

Use of flexible intubation scope — Use of flexible scope for intubation through an SGA is discussed in detail separately. (See "Flexible scope intubation for anesthesia", section on 'Intubation through a supraglottic airway' and "Flexible scope intubation for anesthesia", section on 'Aintree catheter-aided intubation through a supraglottic airway'.)

Blind technique — Studies of blind ETT placement through an SGA with or without the use of an intubating stylet, or bougie, have reported variable success rates. Examples of studies of the success rates of blind techniques for endotracheal intubation through an SGA include the following:

●In a prospective trial evaluating blind intubation through the i-gel and the LMA Fastrach devices, overall successful intubation rates were relatively high (82 and 96 percent), with first-attempt success rates of 66 and 74 percent, respectively [51].

●In a study comparing the LMA Fastrach and the air-Q, successful blind intubation after two attempts was achieved in 75 out of 76 (99 percent) patients in the LMA Fastrach group versus 60 out of 78 (77 percent) patients in the air-Q group [52]. In another study comparing blind tracheal intubation using the i-gel versus the LMA Fastrach, success was obtained on the first attempt in 69 percent of patients with the i-gel and in 74 percent of patients with the LMA Fastrach [53].

●In another study, 120 anesthetized patients were randomly assigned to neck extension or a neutral neck position for blind intubation through the Ambu AuraGain [54]. Overall intubation success rates were 71 percent with neck extension versus 50 percent with neutral neck position. First pass success rates were 68 and 47 percent, respectively.

SPECIAL POPULATIONS AND SCENARIOS — 

Use of SGAs in infants and children, and in obstetric patients is discussed separately. (See "Airway management for pediatric anesthesia", section on 'Choice of airway device' and "Airway management for the pregnant patient", section on 'Choice of airway device'.)

Patients with gastroesophageal reflux disease — Since SGAs likely do not offer protection against the aspiration of gastric contents to the same degree as cuffed tracheal tubes, their use for patients at high risk for aspiration under general anesthesia is contraindicated, other than during airway rescue. We routinely choose tracheal intubation rather than SGA placement for patients with significant gastroesophageal reflux disease (GERD). However, SGAs are commonly used in patients with mild GERD that is well controlled with medication, such as proton-pump inhibitors (PPIs).

SGAs with esophageal vents were initially developed to decompress esophageal pressure and allow drainage of gastric contents, and they may be preferred when used for patients with GERD [55-59]. (See 'Aspiration' below.)

Patients with obesity — Patients with obesity are at higher risk for difficult airway management, including difficulty with SGA use. Patients with obesity often require higher peak inspiratory pressures and may therefore be at higher risk for inadequate ventilation with an SGA, leak around the device, and gastric insufflation. (See "Anesthesia for the patient with obesity", section on 'Airway management'.)

There is insufficient literature to assess the safety of SGA use in patients with obesity. A 2013 systematic review that included 232 patients enrolled in two randomized trials compared the use of the LMA ProSeal versus placement of an endotracheal tube (ETT) for patients with obesity (body mass index [BMI] >30 kg/m²) [60]. Leaks were more likely around the laryngeal mask airway (LMA), and the LMA was changed to an ETT in approximately 4 percent of patients because of unsatisfactory placement. No serious complications or cases of aspiration occurred, and postoperative hypoxemia (O₂ saturation <92 percent) was less common with LMA use.

Obesity-specific criteria for the use of SGAs have not been established, and practice varies. The author typically avoids use of SGAs for patients with BMI >35 kg/m², for patients with obesity having surgery that will last longer than 90 minutes, who will be placed in the lithotomy position, and when access to the airway will be limited during the procedure.

Prone position — SGAs have been used for patients having surgery in the prone position, both for planned airway management and as rescue devices [61]. In many cases, patients position themselves prone prior to the induction of anesthesia and placement of the SGA. We place SGAs while the patient is in the prone position in a very select population (eg, patients with no risk factors for difficult airway management) having short procedures that do not require paralysis (eg, rectal surgeries).

Advantages of prone SGA placement include the following [62]:

●Induction-to-incision time is shortened, less manpower is needed for positioning, and time to extubation at the conclusion of surgery is usually shorter than when an ETT is placed.

●With self-positioning, the patient can confirm that the neck and head positions are comfortable. There may be less chance of injury to the patient or to operating room personnel and less chance of dislodging intravenous (IV) lines or the airway device than with prone positioning after induction.

●Hemodynamic changes associated with the prone position may be less with self-positioning.

Disadvantages of the prone SGA include the following:

●Higher airway pressures may be required for positive pressure ventilation (PPV) in the prone position, increasing the potential for inadequate ventilation, leak, and/or gastric insufflation.

●The SGA provides a less secure airway than an ETT, and manipulation or replacement may be more difficult in the prone position.

A number of studies have evaluated the use of SGAs in the prone position:

●A prospective study of 50 patients compared prone positioning before and after induction and LMA placement [62]. There were no complications or cases of airway loss, and induction after positioning resulted in shorter induction-to-incision time and fewer hemodynamic changes after induction.

●A retrospective review of 245 cases in which the LMA ProSeal was placed prone reported successful use of the LMA in all patients without complications [63]. In eight patients, the LMA was placed using laryngoscope-guided bougie insertion after one unsuccessful blind insertion, per the institution protocol.

●A prospective study compared the i-gel SGA with the LMA Supreme in patients undergoing back surgery [64]. The devices were inserted while the patient was supine. While the i-gel required more attempts at insertion, it provided a higher airway seal pressure. No difference was observed in the fiberoptic views of the vocal cords. The authors concluded that both devices may also be used safely in airway management of patients undergoing lumbar surgery in the prone position.

●A prospective audit of 73 patients who positioned themselves prone, followed by induction and LMA placement, reported that one patient developed laryngospasm and that nine required deepening of anesthesia before the LMA could be inserted [65]. LMA malpositioning was encountered in four cases, and in one edentulous patient, it was necessary to hold the LMA for the entire procedure.

For prone SGA placement, we use the following strategy:

●We limit prone SGAs to those patients without risk factors for difficult airway management, without limitations in neck movement, and who will undergo short procedures that do not require paralysis (eg, hemorrhoidectomy, rectal fistulotomy). (See "Airway management for general anesthesia in adults", section on 'Airway assessment'.)

●We help the patient self-position with the head turned to the side and with the cheek on the edge of the pillow or head support, allowing free access to the face and mouth.

●The stretcher is kept in the operating room throughout and after induction of anesthesia, until the anesthesiologist specifically agrees that it can be removed, in order to allow a rapid return to the supine position if necessary for airway management.

●We preoxygenate as for routine airway management, induce anesthesia, and prove the ability to mask ventilate prior to SGA placement. (See "Airway management for general anesthesia in adults", section on 'Preoxygenation'.)

●We place the SGA and confirm the ability to ventilate as usual.

SUPRAGLOTTIC AIRWAY-RELATED COMPLICATIONS — 

A number of complications of supraglottic airway (SGA) use have been reported.

Aspiration — SGAs do not fully protect against aspiration of regurgitated stomach contents. The incidence of aspiration with the use of an SGA is unknown, but it is likely low in patients without risk factors for regurgitation. A review of approximately 100 observational studies, abstracts, and studies that were presented in letter form included 12,900 anesthetics with a first-generation laryngeal mask airway (LMA) [66]. There were three cases of aspiration, for an incidence of 1 in 5000, which is similar to the estimated risk of aspiration with the use of a facemask or endotracheal tube (ETT) for airway management [67].

A review of the literature on aspiration with SGAs found that most reported cases occurred in patients with risk factors (ie, upper gastrointestinal disease, full stomach, obesity, multiple trauma), surgical factors (ie, lithotomy position, intraabdominal surgery), and/or anesthesia factors (ie, inadequate depth of anesthesia, SGA cuff deflation) [68].

Esophageal reflux with SGAs — SGA placement may predispose to regurgitation by relaxing the lower esophageal sphincter via a reflex mechanism similar to that which occurs with swallowing a bolus of food. A study including 40 patients under general anesthesia reported that laryngeal mask placement was associated with a 15 percent decrease in lower esophageal sphincter barrier pressure [69]. Studies using pH electrodes have reported that LMAs result in an increase in reflux of stomach acid to the mid to upper esophagus compared with facemask airway management [70,71].

Positioning may influence the degree of reflux with SGA use. Studies using pH electrodes [72] and dye swallowed preoperatively [73] have reported an increase in the incidence of reflux with SGAs when patients are placed in the lithotomy and Trendelenburg positions.

Prevention of aspiration — While reflux into the esophagus can occur with SGAs, the device may act as a plug to prevent aspiration of esophageal contents into the lungs. Vomiting or increase in abdominal pressure can overcome the capacity of the SGA to prevent pharyngeal reflux. Both cadaver and live-patient methodologies have been used to study this issue.

●Cadaver studies – Fresh cadaver preparations have been used to study the ability of SGAs to withstand an increase in esophageal pressure [74-77]. Resting intragastric pressure and esophageal pressure during reflux in a fasted patient are usually between 10 and 30 cmH₂O [78] and can reach more than 60 cmH₂O during vomiting [79]. Cadaver studies have reported that the LMA Classic can prevent regurgitation of esophageal fluid into the pharynx up to 40 to 48 cmH₂O [74,75,77] and that the LMA ProSeal with the esophageal vent clamped can seal the esophagus up to 70 cmH₂O [74]. With the esophageal vent open, the LMA ProSeal can prevent any increase in esophageal pressure and can drain fluid away from the pharynx [76].

With a similar cadaver preparation, the i-gel SGA with its esophageal lumen clamped was less effective than the LMA Classic or the LMA ProSeal at sealing the esophagus, leaking at 13 cmH₂O [59].

●Anesthetized patients – In a prospective study of 102 patients under general anesthesia with an LMA ProSeal, dyed saline was introduced down the esophageal vent of the LMA [80]. Fiberoptic laryngoscopy showed no transfer of the dye into the bowl of the LMA in 100 patients; in two patients, dye appeared in the bowl after increased intra-abdominal pressure, one with cough, and one with laryngospasm.

Our approach to minimizing the chance of aspiration with SGAs is as follows:

●Carefully select the patient and surgical procedure, considering risk factors for aspiration, expected duration of surgery, surgical site, and positioning. (See "Airway management for general anesthesia in adults", section on 'Supraglottic airway versus endotracheal tube'.)

●Maintain an adequate depth of anesthesia for insertion of the SGA and during surgery.

●Ensure adequate reversal of neuromuscular blockade prior to emergence from anesthesia.

●Minimize peak airway pressure during positive pressure ventilation (PPV) in order to avoid gastric insufflation and distention.

Airway complications — Airway complications with SGA insertion are unusual, with an airway-related critical incident rate of 0.15 percent in one survey study [81]. Potential airway complications include:

●Irritation of the oropharyngeal mucosa (especially with excessive cuff pressures).

●Injury to teeth, tongue, and lips at the time of insertion.

●Injury to the glottic structures (eg, epiglottis, arytenoids).

●Injury to the lingual, hypoglossal, recurrent laryngeal, and inferior alveolar nerves (rare) [82-86].

●Aspiration of gastric contents. (See 'Aspiration' above.)

●Negative pressure pulmonary edema (eg, following vigorous biting of the SGA shaft on emergence from anesthesia, causing airway obstruction) [81].

●Pharyngolaryngeal rupture and pneumomediastinum (very rare complications of LMA placement described in case reports) [87].

●Laryngospasm (less common at extubation with SGAs than with ETTs, but unlike ETTs, SGAs do not protect against intraoperative laryngospasm) [88].

Role of cuff pressure — The following studies have evaluated the role of increased cuff pressure (beyond 44 mmHg) in the development of SGA-related complications:

●In a randomized trial that compared the use of manometry to maintain cuff pressure below 44 mmHg versus standard cuff inflation, the use of manometry resulted in a lower incidence of pharyngolaryngeal adverse events (13.4 versus 45.6 percent) [21]. Significant differences were seen in rates of early dysphonia, early and late dysphagia, and early and late sore throat.

●In another randomized trial that compared the use of a built-in cuff pressure monitor versus standard cuff inflation, monitoring resulted in lower combined rates of sore throat, dysphonia, and dysphagia at 1, 2, and 24 hours postoperatively (26 versus 49 percent) [89].

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

●Uses of supraglottic airways (SGAs) – SGAs are used for airway management for anesthesia, for primary airway management, as conduits for endotracheal intubation, and for rescue ventilation (algorithm 1). (See 'Routine use of SGAs' above.)

●Types of SGAs – SGAs are available in a range of sizes and a variety of styles; some are designed to allow placement of an orogastric tube, while others are designed to allow tracheal intubation through the device. The optimal SGA size for a given patient is one that minimizes leak without excessive cuff inflation (table 1 and table 2). (See 'Choice of SGA' above and 'Choice of size' above.)

●SGA placement technique

•The method for insertion of most SGAs is described above and is shown in a figure (figure 3) (see 'Placement technique for most SGAs' above)

•Insertion of some second generation SGA differs somewhat. For the stiffer pre-curved SGAs (eg, LMA Supreme, LMA Protector) there is no need ot insert a finger into the patient’s mouth when placing the device. (See 'Placement technique for second generation SGAs' above.)

●Ventilation through SGAs – SGAs can be used with the patient breathing spontaneously or with positive pressure ventilation. Pressure-limited ventilation (ie, pressure support or pressure control) is usually used with an SGA in place, rather than volume-control ventilation. Peak pressures should be kept below 20 cmH₂O to minimize leak and gastric insufflation. (See 'Choice of mode of ventilation' above.)

The use of positive end expiratory pressure (PEEP) with an SGA has not been shown to be beneficial. (See 'Use of positive end expiratory pressure (PEEP) with SGAs' above.)

●Airway rescue – An SGA can be used as an airway rescue device when mask ventilation is difficult or impossible. It can also be used as a conduit for endotracheal intubation (algorithm 1). (See 'Supraglottic airways and the difficult airway' above and 'Supraglottic airways as conduits for intubation' above.)

●Patients with obesity – Use of SGAs in patients with obesity is limited by the potential need for higher peak inspiratory pressures and the possibility of difficult seating of the device. (See 'Patients with obesity' above and "Anesthesia for the patient with obesity", section on 'Choice of airway device'.)

●Patients in the prone position – SGAs can be used for airway management in the prone position, as the primary airway device in selected patients, and for airway rescue. We limit prone SGAs to those patients without risk factors for difficult airway management, without limitations in neck movement, and who will undergo short procedures that do not require paralysis (eg, hemorrhoidectomy, rectal fistulotomy). (See 'Prone position' above.)

●Complications

•SGAs do not provide complete protection against aspiration of stomach contents. (See 'Patients with gastroesophageal reflux disease' above and 'Aspiration' above.)

•Other complications of SGA use include failed placement and airway complications, including airway trauma. Sore throat, dysphonia, and dysphagia may be related to high SGA cuff pressures. The cuff inflation should be limited to approximately 44 cmH₂O or the minimum volume required for an adequate seal. (See 'Supraglottic airway-related complications' above.)