INVENTION AND DEVELOPMENT
In 1878, Dr William Macewan, a surgeon in Glasgow, first described the use of endotracheal tubes (ETTs) instead of performing tracheostomies. However, performing endotracheal intubations did not become common practice until Dr Ivan Magill introduced blind nasotracheal intubations during the First World War. Today, endotracheal intubations have become routine in the anesthesia and critical care settings. Indeed, an ETT is the most effective and safe method of securing an airway. However, the realization that other less invasive devices can be used in a wide number of situations prompted a search for a suitable alternative. Such a device should be supraglottic in order to be less invasive and at the same time, be able to produce an airtight seal over the glottic opening to make gas exchange effective. The most important and widely used supraglottic device today is the laryngeal mask airway (LMA).
The inventor of the LMA is Dr Archie Brain, an anesthesiologist from the United Kingdom. Development started on the LMA in 1981 and was available for commercial use, in the United States, by 1992. Since its introduction, several modifications, additions, and variations have been developed, and are currently in use.
The classic LMA consists of a tube with an inflatable mask (Fig. 1). The entire apparatus is latex free with a silicone rim. The mask is a flattened, pear-shaped, inflatable cuff with an open front. If properly positioned, the opening overlies the glottis and the proximal end opposes the base of the tongue and the distal rim wedges against the upper esophageal sphincter, making a seal. The classic LMA is autoclavable and reusable. Its total usage has been estimated to be approximately 200 million patient uses since its introduction to clinical practice.1
The ProSeal LMA was released in the year 2000 and is a modified version of the classic LMA.2 In addition to the silicone rim intended to obtain a seal around the larynx, the distal tip has an esophageal drainage port designed to communicate with the gastrointestinal tract. The port permits suctioning, potentially decreasing the risk of gastric content aspiration. Its insertion time is slightly longer when compared with the classic LMA, but shows a 50% improvement in obtaining a proper seal.3 If the device is placed too proximal or there is a leak, air is detected from the esophageal port. Many nonconventional techniques for insertion of the ProSeal LMA have been described,4–6 offering options for the operator when confronted with a difficult airway in the adult or pediatric population.7 Potential problems may include malpositioning,8 laryngeal edema,9 and airway obstruction. Complications regarding LMAs in general are discussed later.
Intubating LMA, Fastrach
The Intubating LMA (iLMA) is a modified version of the classic LMA with the upper part of the tube removed. The remaining tube has a metallic core with a handle used for positioning at its proximal end (Fig. 2). After establishing an airway with the iLMA, an ETT can be introduced through the metallic channel. It has been incorporated into the difficult airway management algorithms.10,11 It is easy to use and may be life-saving. In a study using manikin models, both experienced and nonexperienced operators were able to achieve high intubation success rates on the first attempt after having a 60-second demonstration.12
Last year, a modified iLMA incorporating fiberoptics to provide a real-time view of the glottis was developed.13 It is intended for the difficult airway, and a study looking at its utility in intubating obese patients demonstrated initial favorable success rates.14
There are 3 main types of disposable LMAs. These include the LMA-Unique, the Portex Soft-Seal, and the Ambu laryngeal mask (now called the AuraOnce). The LMA unique is very similar to the Classic reusable LMA (Fig. 3). The Portex Soft Seal does not have the silicone rim. The Ambu-laryngeal mask (Fig. 4) has a rigid curve in the main tube in order to better conform to the oropharyngeal anatomy. Most studies of these devices are small and investigate the time of insertion and safety. Brimacombe et al15 compared the LMA-unique and the Soft-Seal, and found that the LMA-unique is easier to insert and allows for better glottic positioning. All 3 were compared recently by Francksen et al.16 All were fairly similar in clinical use, ease of insertion, and success rate; the Ambu laryngeal mask having the shortest insertion time.16
GUIDE TO USE
All LMAs consist of 2 parts, a hollow tube continuous with a hollow mask. The pear-shaped mask has an open front and closed back. An aperture bar extends across the open front to prevent obstruction of the tube by the epiglottis. The backside is lubricated and makes contact with the palate and pharynx during insertion.
Standing above the supine patient's flexed neck and extended head; the tube is grasped with the dominant hand as near to the mask as possible, as you would hold a pen. The deflated flattened mask is inserted against the hard palate downward into the mouth following the contour of the back of the pharynx to get behind and under the tongue to finally seat at the entrance to the larynx. The index finger follows the tube into the mouth to keep pressing “back” and “down” until the apparatus is properly seated in the pyriform fossa (Fig. 5). An alternative to intraoral manipulation is to allow the dominant hand to guide the tube when the mouth is reached and use the nondominant hand to push the tube with or without an introducer.17–19 Several manuals and videotapes demonstrating the proper techniques are available.20–23
It is important to quickly assess proper placement of the airway. Cuff inflation pressure should not exceed 60 mm Hg and adequate tidal volumes should be achieved with minimal leak. If the mask is malpositioned, the mask may have to be replaced and other maneuvers tried. Using a partially or fully inflated cuff may facilitate insertion.24–26 Wakeling et al24 claims that insertion with a fully inflated cuff causes less mucosal trauma and hence fewer postoperative sore throats. Brimacombe26 refutes this assertion. These maneuvers may not only aid in insertion but also increase morbidity. If available, a second operator can apply a jaw thrust maneuver. This moves the tongue forward and out of the way and also prevents compression of the epiglottis.27 If a second operator is unavailable, then a tongue depressor or even laryngoscopy can be used to reposition the tongue.28
Another maneuver for difficult placement is to stand facing the patient. This may facilitate placement because the action of the dominant hand is now “forward” rather than “backward.” This technique can be used if the patient is in the sitting or semi-reclining positions or when neck flexion and head extension is undesirable.
The mask fit is also dependent on the size of the cuff and the volume of air used to fill it. The maximum volume of air, which can be used for cuff inflation, is written on the LMA with inflation pressure not to exceed 60 mm Hg (Table 1). Dr Brain, in his 1991 manual,29 asserts that a better seal is obtained by using the largest size cuff possible. If the mask is too small, the cuff will have to be overinflated to form a seal, which may lead to malposition. There is controversy whether the larger mask with less inflation decreases30 or increases31 postoperative morbidity such as sore throat.
Weight-based selection has given way to sex-based selection, especially in adults (Table 1). Asai and Brimacombe32 have summarized many studies that have looked at this issue. The consensus seems to be that using a size 3 for most adult women and size 4 for most adult men is inadequate. The correct size would be a size 4 for most adult women and a size 5 for most adult men. Whatever the initial size selected, if malposition or an inadequate seal is present, a larger size LMA should be considered.
A priori identification of a difficult LMA insertion may be problematic. A smaller than desired LMA may be used because of a small mouth opening. Mallampati class, used to identify difficult intubations, may or may not herald difficult LMA placement. A study by Brimacombe and Berry33 indicated that LMA placement does not correlate with Mallampati class whereas a study by McCrory and Moriarty34 indicates that there is a positive correlation.
We suggest that if repeated attempts with one type of LMA are unsuccessful, changing to another type or even a third type, may work. No studies looking at this phenomenon have been conducted.
One of the reasons that laryngeal masks have gained in popularity is because successful placement is easily learned. However, we caution its routine use by personnel untrained in airway management. None of the studies claim 100% successful placement and alternate airway management maneuvers may be necessary.
Many studies have looked at the ease of training with medical providers who have little experience with airway management.35–40 It seems clear that training using a manikin is sufficient to master the basics of LMA use. Further, studies have demonstrated that these basics only need a brief training period.
However, not all manikins are the same. Silsby et al41 evaluated 4 different manikins for teaching LMA use. They concluded that 3 (ie, Bill 1, Airsim, and Airway Trainer) of the 4 manikins offered an acceptable training experience whereas the Airway Management Trainer was rated as not acceptable. Hesselfeldt et al42 evaluated Simman, a full patient simulator, and it was judged acceptable for training with a LMA. Parry and Owen43 tested many manikins and found that most would be acceptable or good for training with a LMA.
Tiah et al44 advocate that airway management training should be emphasized in medical school. They found that medical students were able to place the LMA the quickest, with reproducibility, when compared with other airway devices including the Combitube and the ETT.
Effect on Physiologic Response
Another reason the LMA has gained in popularity is because of its diminished physiologic response as compared with insertion of an ETT. Many studies have shown that the changes in heart rate and blood pressure are significantly lessened with insertion of a laryngeal mask as compared with insertion of an ETT or comparable invasive device.45–48 The hemodynamic changes are similar if a LMA and a less invasive device (eg, cuffed oropharyngeal airway) are compared.49
Insertion of a LMA minimizes other effects as well. Insertion does not cause an increase in intraocular pressure50–52 and Agarwal and Shobhana53 imply that insertion does not raise ICP.
To an untrained observer, the insertion of the LMA may seem to be a simple procedure. However, incorrect insertion techniques account for many of the problems associated with its use.
Optimal position of the mask at the laryngeal inlet allows gas exchange to take place without hindrance and may also allow ventilation using positive pressure. An improperly placed LMA causes leakage of gas around the cuff especially when using positive pressure. Malposition of the LMA may not always be apparent54 and a flexible bronchoscope may be needed to check the position of the aperture.28
The risk of gastric distension, gastroesophageal reflux, and tracheal soiling may be increased with incorrect positioning especially if positive pressure is used. Several studies, however, have showed that if an LMA was placed properly, the risks of gastric distention55,56 and gastroesophageal reflux57 were not increased compared with an ETT. Cassu et al58 showed that the use of an LMA in ventilated cats may cause reflux but no aspiration.
Haslam et al59 reported a case of gastric rupture during cardiopulmonary resuscitation attributed to LMA use. Nolan et al60 refute this.
Trauma to the soft tissues during placement of the LMA is not an uncommon occurrence and blood may frequently be noticed on removing the LMA. Folding of the tip of the LMA over itself, use of undue force, wrong technique, or inadequate depth of anesthesia is often to blame for these mishaps. Trauma to the uvula and the posterior pharyngeal wall have been reported.61 Several instances of nerve paralyses including paralysis of the lingual nerve, hypoglossal nerve, glossopharyngeal nerve, and recurrent laryngeal nerve have been reported. Brimacombe et al62 review many of these cases. Swelling of the tongue, cyanosis of the tongue, arytenoid cartilage dislocation, temporomandibular joint dislocation, and vocal cord dysfunction have all been reported. At least some of these complications may be attributed to high cuff pressures or prolonged duration of use of the LMA.
Bronchospasm, laryngospasm, stridor, and partial or total airway obstruction may be encountered and may be related to depth of anesthesia or the noxiousness of the surgical stimulus. Though many of these complications may be amenable to deepening of anesthesia or the use of a muscle relaxant, occasionally, replacement of the LMA with an ETT may be necessary. Coughing, bucking, and biting down on the LMA are also seen often during emergence from anesthesia. However, for the most part the LMA is fairly well tolerated even during emergence and removal is accomplished after simply asking the patient to open his or her mouth.
USES OF LMA FOR AIRWAY MANAGEMENT
The LMA may be used in the spontaneously breathing patient with adequate sedation and topical anesthesia, or the paralyzed, anesthetized patient with assisted mechanical ventilation. It can be used in many situations, such as bronchoscopic procedures performed in the endoscopy setting, elective surgeries in the ambulatory clinics, procedures in the critical care units, as well as in the field outside of the hospital with emergency care providers and first responders.
As a Substitute for a Facemask
Anesthesiologists have viewed the LMA as a substitute for a facemask in many situations. LMAs are especially useful when mask fit is difficult as in edentulous or bearded patients. They also serve to free up the anesthesiologist's hands so that one can attend to other essential tasks simultaneously.
Diagnostic and interventional procedures of the airway are becoming common among pediatric pulmonologists. Flexible bronchoscopies comprise the major airway procedures performed including bronchoalveolar lavage, transbronchial biopsies, and foreign body removal.63 Complications are rare but include hypoxemia, laryngospasm, bronchospasm, and local trauma.64 A laryngeal mask is a preferred technique for controlling the airway in the pediatric population compared with the adult population owing to the difference in body size, airway diameter, and lesser tolerance to conscious sedation.65 When bronchoscopy is performed, LMAs provide a safe alternative with minimal complication as compared with nasal route or endotracheal intubation.64,66–68 LMA use during pediatric bronchscopies is associated with ease of insertion, patient comfort during general anesthesia with spontaneous or assisted ventilation, as well as a net decrease in procedure time.67 As a laryngeal mask is a supraglottic device, its utility in aiding the diagnosis of subglottic pathologies has been demonstrated.69
The majority of adult diagnostic bronchoscopies are performed on spontaneously breathing patients under conscious sedation. Therefore, general anesthesia is not usually required. However, certain patients who cannot tolerate the procedure even with conscious sedation (ie, excessive gag response or discomfort) may require general anesthesia. A laryngeal mask is an ideal device to establish an airway. It is fairly noninvasive and its proper positioning can be easily ensured with the flexible bronchoscope. Additionally, new technologies in diagnostic bronchoscopy may, under specific circumstances, benefit from a deeply sedated or even generally anesthetized patient. For example, electromagnetic navigation bronchoscopy is a technology used to sample small peripheral lesions, such as solitary pulmonary nodules. The technology is safe with improved accuracy over conventional bronchoscopy70 but its precision has not been compared between the moderately sedated, spontaneously breathing patient and the deeply sedated or anesthetized patient. Using the LMA in this outpatient procedure would facilitate navigation to the periphery as well as during actual acquirement of tissue. Further, the anesthesiologist may be able to manipulate the respiratory cycle to improve the diagnostic accuracy. However, the use of a laryngeal airway has not been investigated and may obviate the intended benefit of the minimal invasive nature of the procedure.
Therapeutic bronchoscopies are becoming common place in the armamentarium of interventional pulmonologists. Tools such as self-expanding metallic stents,71 photoablation techniques for tumor ablation or hemoptysis, and foreign body retrieval can be life-saving. The anesthesia for these procedures is also evolving, as they are traditionally performed with general anesthesia and rigid bronchoscopies.72 In proximal central airway lesions, LMAs as supraglottic devices can be used for therapeutic intervention, while providing a secure airway in the anesthetized patient.
Bedside percutaneous tracheostomies are performed increasingly in the intensive care setting. The majority of percutaneous tracheostomies are indicated in patients who are dependent on mechanical ventilation owing to acute illnesses, or if duration of endotracheal intubation is anticipated to be more than 2 weeks.73 The recommended technique is performed with the bronchoscope at the proximal end of the ETT, and withdrawing it to above the first tracheal ring. The bronchoscope assists in visualizing the needle and guidewire being introduced into the lumen of the trachea, with subsequent dilatation with a conic dilator for the creation of the stoma. Once the proper placement of the tracheostomy tube is confirmed, the ETT can then be safely removed. A retrospective study by Cattano et al74 reviewed patients who underwent percutaneous tracheostomy with a dilating forceps approach after the ETT was replaced by a LMA. They felt that the supraglottic device offered a superior view of the proximal trachea without the risk of needle puncturing equipment such as the bronchoscope or the ETT. The study did not demonstrate increased risks such as bleeding. An earlier prospective study comparing LMA versus ETT for percutaneous tracheostomies found less hypercarbia with the LMA.75 However, concerns of aspiration of gastric contents and other potential complications remain. A study by Ambesh et al76 found significantly more complications with the LMA as compared with an ETT. Therefore, more studies are needed to address both efficacy and safety of this approach before recommendations can be made for LMA-assisted airway management for percutaneous tracheostomies.
Aiding Endotracheal Intubation by Flexible Bronchoscopy
Alternative and contingent options are needed when facing a difficult airway. As mentioned, the iLMA has provided an important option for the clinician. Although LMAs are designed as blind intubating devices, newer approaches have been reported to incorporate the flexible bronchoscope for airway management (Fig. 6). For example, the Aintree catheter has been incorporated with the ProSeal LMA in facilitating the endotracheal intubation. After the placement of the LMA, a bronchoscope fitted with the Aintree catheter is directed into the LMA and through the glottis, and subsequent placement of the ETT using the catheter as the guidewire.4 In the pediatric literature, combining the flexible bronchoscope with the LMA for intubating the difficult airway has also been described.65,77
Pre or Outside the Hospital Airway
In the field, securing an airway may be paramount. In the “can't ventilate, can't intubate” situation, the LMA may be lifesaving. A LMA can be used for transport until a definitive airway can be obtained.78 An iLMA can also be used, as a 6-mm internal diameter ETT may be easily inserted. As stated before, the basics of LMA placement is easily mastered with limited training.
Case reports of infants with laryngotracheoesophageal clefts and an infected neonate showed the ability to use the LMA for interhospital transport.79
During CPR, the first part of the secondary survey includes securing an airway device as soon as possible.80 In the event that the patient cannot be ventilated or intubated easily, or if the patient is in a difficult position where there is limited space to perform direct laryngoscopy, then the LMA can be a backup device for securing the airway. Keller et al81 demonstrated increased vertebral pressures in a cadaver study using an LMA as compared with an ETT. They suggest that an LMA should be used with caution in an unstable neck. Todd and Traynelis82 question the clinical validity of the study.
Since its introduction, the LMA has offered anesthesiologists and other physicians who manage airways as an important option in their armamentarium. Different designs give specific advantages for different clinical scenarios. Insertion can be learned with ease, and nonphysicians are capable of securing an airway with adequate training. Knowing the indications and contraindications of using a LMA is paramount to its appropriate usage, as complications are distinct from endotracheal intubations owing to its inherent design and position as a supraglottic airway. Its applications are growing with its recognized advantages, in outpatient, inpatient, and the critical care environment. Increasing recognition of a LMA's applications should expand its role in airway management for the anesthesiologist and the bronchoscopist.
The authors thank Dr Alexey Amchentsev for his technical assistance during the preparation of this manuscript.
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