Airway Equipment







Overview


Of all the equipment in the toolbox of the anesthesiologist, airway devices may be the most commonly used as well as the most varied in design and function. The last decade has witnessed a remarkable expansion of the airway armamentarium, necessitating a review of traditional and modern devices. The anesthesia face mask and tracheal tube once comprised the bulk of airway management apparatus; supraglottic airways, video laryngoscopes, and minimally invasive devices have now captured a significant share of both routine and rescue tools. In an attempt to be clinically relevant, this chapter focuses little on historic devices and the forces guiding instrument evolution; that is, the causes, pressure, and findings that led to device development. The exception to this is a historic discussion of the origins of airway management, including tracheal intubation. Although we recognize the importance of historic perspective of all the devices in use today, more authoritative reviews exist.




Anesthesia Face Mask


The anesthesia face mask was invented in 1917. Prior to that, inhalational anesthesia was administered by an open-drop ether technique. The face mask allowed the administration of gases to the patient without instrumentation of the airway. The face mask may be considered the original supraglottic device; it comes in both adult and pediatric sizes. The face mask is held over the patient’s face to encompass the patient’s nose and mouth. Two fingers are placed over the body of the mask to firmly hold it in place, and three fingers are placed along the bony mandible to complete a tight seal. In edentulous patients, it may be necessary to include the chin of the patient in the mask to compensate for the lack of dentition.


Anesthesia masks are made either of silicone or rubber. In the past, anesthesia masks were opaque, but most modern anesthesia masks are clear to allow the provider to view the patient’s lip color, condensation from expiration, secretions, vomitus, and any expelled blood. In some practices, the rubber mask is reusable.


When positioning the mask, the clinician must be careful not to compress the facial nerve and artery, the eyes, or the lips. Face mask fit can be engaged with the help of a head strap ( Fig. 16-1 ) attached to a four-prong ring that encircles the circuit fitting. The head strap is helpful for the clinician with small hands, when the patient is edentulous or has a large face or beard, or to allow providers to have their hands free when the patient is breathing spontaneously.




FIGURE 16-1


Mask headstrap.




Oral and Nasopharyngeal Airways


An oral airway prevents the base of tongue and the epiglottis from obstructing the pathway to the larynx. With a few exceptions, oral airways are made from a hard plastic and are inserted into the mouth with their concave surface facing cephalad. Once well within the oral cavity, the airway is rotated 180 degrees so that the preformed concavity comes to its final position following the contour of the tongue. The proximal end of the airway has a flange to prevent the entire device from falling into the mouth; the distal tip sits just above the epiglottis. Because of the position against the base of tongue and posterior pharyngeal wall, oral airways are poorly tolerated in the awake or inadequately anesthetized patient. Nasal airways are made from soft, flexible materials and are tolerated better in awake patients than are oropharyngeal airways ( Fig. 16-2 ). Appropriate nasal airway sizing is determined by measuring the distance from the patient’s bony mandible or nostril to the meatus of the ear. Some of the commonly available oral airways include the Berman-Guedel, the split Berman, and the Ovassapian and Williams airways used in fiberoptic laryngoscopy ( Fig. 16-3 ).




FIGURE 16-2


Nasal airways.



FIGURE 16-3


Williams, Ovassapian, and Split Berman oral airways.


Supraglottic Airways


Obstruction of the airway was a poorly understood phenomenon prior to 1874. Opening the mouth with a wooden screw and drawing out the tongue with a forceps or steel-gloved fingers was the height of airway management. Recognition that the base of the tongue falling against the posterior pharyngeal wall accounted for most airway obstruction did not occur until 1880. Credit for the first use of a true supraglottic airway is given to Joseph Thomas Clover (1825–1882), although it is possible that similar devices were used toward the end of the second millennium. Clover used a nasopharyngeal tube for the delivery of chloroform anesthesia. The O’Dwyer tube was introduced in 1884, a device that consisted of a curved metal tube with a conical end that could seal the laryngeal inlet when placed into the oropharynx. Although designed for the treatment of narcotic overdose, it was later modified to be used with volatile anesthetics. Over the next 50 years, several modifications of the basic oropharyngeal airway were described. In the 1930s, Ralph Waters introduced the now familiar flattened-tube oral airway. Guedel modified Waters’ concept by fitting his airway within a stiff rubber envelope in an attempt to reduce mucosal trauma.


Tracheal intubation was first described in 1788 as a means of resuscitation of the “apparently dead” but was not used for the delivery of anesthesia until almost 100 years later. The forerunner of the modern tracheal tube was designed by the German otolaryngologist, Dr. Franz Kuhn (1866–1929), who developed a flexible metallic tube that resisted kinking and could be shaped to the patient’s upper airway anatomy. The tube was inserted using a rigid stylet, and the hypopharynx was sealed with oiled gauze packing. Sir Ivan Magill and Stanley Rowbotham are credited with the initial development of modern tracheal intubation. Performing anesthesia for reconstructive facial surgery during World War I, they developed a two-tube nasal system. One narrow tube of a gum elastic design was passed through the nares and guided into the larynx using a surgical laryngoscope. The other tube was blindly passed into the pharynx to provide for the escape of gases. During use of this “Magill” tube, the exhaust lumen would occasionally pass into the larynx, leading Sir Ivan to describe blind nasal intubation.


Cuffed supralaryngeal airways were initially described in the early part of the twentieth century. The impetus for the development of these devices was threefold. First, the introduction of cyclopropane, an explosive agent, required an airtight circuit for appropriate evacuation. Second, blind and laryngoscope-guided tracheal intubation remained a difficult task. Third, protection of the lower airway from blood and surgical debris in the upper airway was an important concern. The Primrose cuffed oropharyngeal tube, the Shipway airway—which was a Guedel oropharygeal airway fitted with a cuff and circuit connector designed by Sir Ivan Magill—and the Lessinger airway were predecessors of the modern supralaryngeal devices. In 1937 Leech introduced a “pharyngeal bulb gasway” with a noninflatable cuff that fit snugly into the hypopharynx. The use of supralaryngeal airways remained dominant until the introduction of curare in 1942 and the mass training of anesthetists in tracheal intubation in anticipation of and during World War II. Mendelson’s description of gastric contents aspiration in obstetric cases (66 of 44,016 patients, with 2 deaths) further pushed the move toward tracheal intubation in most surgical procedures. Within a few years, proficiency in direct laryngoscopy and tracheal intubation became a mark of professionalism. The advent of succinylcholine in 1951 furthered the dominance of tracheal intubation by providing rapid and profound muscle relaxation.


By 1981, two types of airway management prevailed: tracheal intubation and the anesthesia face mask/Guedel airway. Although both were time-tested devices, each had its failings (apart from airway failure in a small number of patients). Tracheal intubation was associated with both dental and soft tissue injury and cardiovascular stimulation, and mask ventilation often required a hands-on-the-airway technique. These difficulties led to the reconsideration of supralaryngeal airways.


Laryngeal Mask Airway


The laryngeal mask airway (LMA) was developed by Dr. Archie Brain in 1982. An exhaustive review of the history of the LMA and its inventor can be found in the text by Joseph Brimacombe. The “classic” LMA (LMA Classic; LMA North America, San Diego, CA) became commercially available in 1988 in England (1992 in the United States). At the time of this writing, the LMA had been used in an estimated 200 million patients. Its components are 100% silicone rubber (no latex), except for a metal spring and a polypropylene component in the inflation valve. It is a reusable device that has a lifespan of 40 uses or cleanings. The mask consists of three components: an inflatable cuff, an airway barrel, and an inflation line ( Fig. 16-4 ). The airway tube is semirigid and semitransparent. Proximally, a standard 15-mm circuit adaptor is permanently fused to the barrel; distally, the barrel is fused to the inflatable cuff. Two flexible aperture bars cross the junction between the barrel and the mask and prevent obstruction by the epiglottis. The aperture bars are flexible enough to allow instrumentation (e.g., intubation) without their removal. The mask is oblong and based on plaster casts of cadavers. The distal aspect is narrow (over the esophageal inlet), whereas the proximal cuff is broad (upper hypopharynx). With the pilot cuff and syringe tip–activated air valve, the inflation line emerges from the most proximal aspect of the cuff, just behind the barrel-cuff junction. The LMA Classic comes in sizes 1 through 6, with smaller half sizes (1.5 and 2.5); cuff length changes approximately 15% between sizes. The LMA Classic was released in 1998 in a single-use version made of polyvinyl chloride (PVC). Although the LMA Unique has identical dimensions to the LMA Classic, the barrel is more rigid. A rerelease of this device, the LMA Unique in 2000, had a softer barrel and cuff backplate. The LMA has been used in a wide variety of surgical and resuscitative procedures, including spontaneous and controlled ventilation cases, laparoscopy, otolaryngology, and cardiothoracic surgery, in all body positions, in morbidly obese patients, and in other applications. The most feared complication of supraglottic airway (SGA) use, an increased rate of aspiration of gastric contents, has not been realized when the LMA has been used correctly in appropriate patients.




FIGURE 16-4


Single-use version of the classic Laryngeal Mask Airway, the LMA Unique (LMA North America, San Diego, CA).


Other versions of the LMA, which were never commercially available, include the nasal LMA, with the barrel and mask assembled in the pharynx; the double-lumen LMA, in which the second lumen is used for instrumentation; the malleable LMA, with a malleable external stylet that allows shaping; the split LMA, to facilitate fiberoptic-aided tracheal intubation; the short-tube LMA, to facilitate through-LMA tracheal intubation; the wide-barrel LMA, to accept a 9-mm tracheal tube; and the gastroscope LMA, to allow passage of an endoscope. Descriptions and citations for these devices can be found in exhaustive reviews by Brimacombe.


A number of accessory devices have been developed by Brain, independent clinicians, and researchers. Two devices have been introduced by Brain to facilitate deflation of the LMA cuff—the block deflation tool and the spring-loaded shoehorn deflation tool. A wide range of insertion aids include an artificial palate, intralumenal devices, extralumenal devices, and laryngoscope-like blades. Commonly available airway devices have been used to facilitate both tracheal intubation via the classic LMA and its removal after intubation, including the gum elastic bougie, fiberscopes, gastric tubes, and guidewires. Likewise, many different devices have been used to verify the position of the in situ LMA, including light wands, fiberscopes, and the Patil intubation guide (Anesthesia Associates, San Marcos, CA).


Although the LMA shows some resistance to low-power laser strikes, these devices are generally considered non–laser compatible. Details on resistance to a variety of laser sources are available. The metallic spring in the pilot cuff of the LMA Classic and some other LMAs is not MRI compatible; however, no morbidities have been associated with its use, although there have been reports of the spring interfering with the quality of the magnetic resonance image (MRI). An MRI-compatible LMA is available that uses a plastic spring. The metal reinforcement in the LMA Flexible and LMA ProSeal is non–MRI compatible, as is the barrel of the reusable Fastrach and Ctrach LMAs. The silicone cuff of the LMA is permeable to nitrous oxide (N 2 O), and intracuff pressure will increase during N 2 O anesthesia. The LMA contains no natural latex.


Cleaning and sterilization are important steps in the use of any reusable device, and appropriate cleaning improves the safety and longevity of LMA products. Manual cleaning is done with sodium bicarbonate, soapy water, or a mild enzymatic cleaner. Other chemical agents should be avoided, and a soft brush should be used to remove secretions. During cleaning, every attempt should be made to keep the inflation valve dry because water may cause malfunction. After cleaning, the device should be reinspected for soiling or damage. Sterilization is by steam autoclave, and the cuff of all LMAs should be emptied of air immediately before autoclaving (spontaneous reinflation will occur if the device is left for hours prior to sterilization). Immediate spontaneous reinflation may indicate a faulty inflation valve; if this happens, the device should be discarded. Small amounts of gas in the cuff may cause rupture during autoclaving, and autoclave temperature should not exceed 135° C. The duration of the autoclave cycle can be from 3 to 15 minutes depending on the autoclave mechanism. The manufacturer suggests that all reusable LMAs be discarded after 40 uses.


Although a number of LMA modifications have been made, only a handful have found widespread acceptance and commercial success. The following devices are based on the classic LMA but incorporate changes in the barrel or mask design that facilitate usability or improve safety.


The flexible LMA (FLMA; LMA Flexible, LMA North America) was designed to be used in surgical cases where the area in and around the airway must be shared with the surgical team. The barrel of the FLMA is longer and narrower than the classic LMA and is wire reinforced. It may be deflected away from the surgical field without kinking or placing torque on the cuff. When the surgical field includes the head or neck and heavy drapes cover the airway, the drapes can fall on the FLMA barrel with impunity. The FLMA is available in sizes 2 to 6, including a size 2.5. Neither the LMA Classic nor the FLMA is laser resistant, nor are they MRI compatible because of the reinforced barrel. The FLMA has been used for a wide variety of otolaryngeal surgeries, including adenotonsillectomy, uvulopalatoplasty, and dental, intranasal, ear, and eye procedures. The narrow barrel of the FLMA is not compressed by a surgical mouth gag, but placement requires cooperation between the anesthesiologist and surgeon. The barrel is placed midline under the grooved blade of the Dingman (or similar) mouth gag. Outward tension is applied on the FLMA barrel as the mouth gag is placed; this maneuver prevents redundancy of the barrel in the pharynx, which occurs as the blade shortens the distance over the tongue. During the mouth gag placement, care must be taken to ensure the FLMA inflation line is not trapped and occluded. The blade of the mouth gag must be appropriately sized; too large a blade can crush the proximal FLMA cuff, and too small a blade can pull the cuff out of position.


The principal concern among clinicians contemplating otolaryngeal procedures with the laryngeal mask has been airway protection from surgical blood and debris. Studies have shown superior airway protection compared with the use of a tracheal tube (or nasal mask in dental surgery) by virtue of the supraglottic seal.


The cleaning procedure and life expectancy of the FLMA are identical to those of the LMA Classic. A single-use FLMA is also available.


ProSeal LMA


The ProSeal LMA (PLMA) was introduced in 2001 as an improved version of the LMA Classic. The PLMA is a relatively complex device compared with other laryngeal masks ( Fig. 16-5 , A and B ). Differences in the ProSeal, compared with the LMA Classic, are listed in Table 16-1 .




FIGURE 16-5


A, ProSeal Larygneal Mask Airway (LMA North America, San Diego, CA). B, With insertion handle attached.


TABLE 16-1

Unique ProSeal Laryngeal Mask Airway Features







































Gastric drain lumen (secondary lumen) Diagnostic position testingPassive gastric drain
Active gastric emptying (gastric tube)
Pressure pop-off valve
No mask aperture bars Drain tube prevents obstruction by epiglottis
Introducer tool Creates Fastrach-like insertion
Insertion strap Fixing of introducer tool
Placement of index finger
Wire-reinforced airway tube Reduces diameter, improves flexibility
Dorsal cuff Increased seal pressure
Ventral cuff larger in proximal end Improved seal
Deeper bowl Improved fit
Integrated bite block Accessory bite block not required
Hard silicone drain tube rings Prevents drain tube collapse
Accessory vent (within bowl, under drain tube) Prevents pooling of secretions

LMA North America, San Diego, CA.



There are three primary improvements of the PLMA: 1) diagnosis of device position, 2) access to the alimentary track, and 3) higher airway pressures. Although the incidence of complications during LMA anesthesia is similar to that of the tracheal tube, it is believed that poor positioning contributes to most of these events. In one well-described case report, aspiration of gastric contents occurred because of PLMA misplacement. Importantly, the clinician did not perform any confirmatory test to ensure the device’s correct position. Several techniques have been described to determine whether the PLMA is correctly inserted ( Table 16-2 ).



TABLE 16-2

Tests to Ensure Proper Positioning of ProSeal Laryngeal Mask Airway
























Test Observation Reference
Bite block test Depth of bite block adequate 32
Suprasternal notch test Pressing on suprasternal notch moves bubble placed on gastric drain 33
Leak test No gas leak from drain tube 34
Gastric tube placement Tube placed into stomach ensures patency 35

LMA North America, San Diego, CA.



Because of the upper esophageal positioning of the PLMA’s nonairway lumen, access to the alimentary tract is possible. Gastric emptying may occur that may be passive, via regurgitation, or active, via Salem sump placement. Table 16-3 lists the maximum gastric tube diameter for each PLMA size. Brain suggests that the gastric tube not be left in situ during the maintenance phase of the anesthetic because the lumen of the gastric drain should be left unobstructed (see Table 16-3 ).



TABLE 16-3

Maximum Gastric Tube Diameters for ProSeal Laryngeal Mask Airways

























Airway Size OG Tube Size
10 Fr
2 10 Fr
14 Fr
3 16 Fr
4 16 Fr
5 18 Fr

OG, orogastric.

LMA North America, San Diego, CA.



Although the LMA Classic typically achieves a seal pressure of 20 to 25 cm H 2 O, some patients, such as the morbidly obese, may require positive airway pressure beyond this. Because of its deep bowl, and possibly the back cuff, the PLMA seals the airway to 40 to 45 cm H 2 O or more.


LMA Supreme


The LMA Supreme may first be considered a disposable ProSeal LMA because of a similarly configured drain tube. The LMA Supreme also has a fixed-curve airway tube, like the Fastrach LMA. The LMA Supreme consists of a preformed airway tube, integrated bite block, gastric drain for placement confirmation and gastric decompression, and fixation tabs that help maintain the correct insertion depth. The LMA Supreme is available in adult sizes 3 to 5 ( Fig. 16-6 ).




FIGURE 16-6


LMA Supreme (LMA North America, San Diego, CA).


Fastrach LMA


The Fastrach (LMA North America), or intubating LMA (ILMA), was introduced in 1995 to improve the technique of tracheal intubation through the LMA. Several intubation techniques have been described through the LMA Classic, including blind, retrograde wire-assisted, flexible fiberoptic, light wand, bougie, and tracheal tube exchange catheter placements. Table 16-4 examines the problems with tracheal intubation via the LMA Classic and how the ILMA corrects these problems.



TABLE 16-4

Problems with Tracheal Intubation

























LMA Classic Intubating LMA
22 cm in length, requires long tracheal tube 14 cm in length
Diameter accepts up to size 7.0 tracheal tube Size 8.0 ID tracheal tube
Obstruction by epiglottis Lifting bar raises epiglottis away from tracheal tube path
Difficult removal of LMA while leaving the tracheal tube in situ Removal facilitated by large diameter and short length
Flexible barrel hinders readjustment Stainless steel barrel
Fingers must be placed in the mouth during placement Stainless steel handle facilitates insertion

ID, inner diameter; LMA, laryngeal mask airway.


The stainless steel, silicone-coated barrel of the ILMA is anatomically shaped to fit the oral cavity–pharynx-hypopharynx axis, when the head is in the neutral position. This curve was based on the analysis of 60 sagittal MRI sections of patients with normal airways. The barrels of the three available sizes—3, 4, and 5—are identical. The masks vary in the size of the cuff and the placement of the epiglottic lifting bar (ELB). The ELB is a vertically oriented semirigid bar fixed at the proximal end of the bowl aperture and positioned to sit beneath the epiglottis in situ. As a tracheal tube is passed through the barrel, the EBL lifts the epiglottis out of its path to the larynx. A handle at the proximal end of the barrel is used for insertion, repositioning, and removal. A secondary advantage of the handle is that the operator does not need to place fingers into the patient’s mouth ( Fig. 16-7 ).




FIGURE 16-7


A, Fastrach (LMA North America, San Diego, CA). B, Fastrach with plunger.


The Fastrach is designed to be used with a straight, armored, silicone tracheal tube (Euromedics, Malaysia), although standard or Parker Flex-tip (Parker Medical, Englewood, CO) PVC tracheal tubes have been used. The Fastrach is indicated for routine, elective intubation and for anticipated and unanticipated difficult intubation. Because it was designed to facilitate blind tracheal intubation, the presence of airway secretions, blood, or edema, such as from previous intubation attempts or trauma, has not hindered its usefulness as a ventilating and intubating device after failed rapid-sequence intubation.


Paraesophageal Devices


King Laryngeal Tracheal Tube


The King laryngeal tube (LT; King Systems, Noblesville, IN), is a latex-free, single-use, single-lumen silicone tube that consists of a 130-degree angled airway tube, an average barrel diameter of 1.5 cm, esophageal and oropharyngeal low-pressure cuffs, and two ventilation ports. The distal esophageal tube seals the esophagus and protects against regurgitation, while the proximal oropharyngeal tube sits in the oropharynx and seals both the oral and nasal cavities. During ventilation through the two ventilation ports, the trachea is oxygenated. The King LT is available in sizes 3 to 5 in the United States and in sizes 0 to 2 outside the United States. A double-lumen version of the King LT suction (LTS) also is available. One lumen is available for ventilation, and the other lumen is used for decompression of the stomach, suctioning, and placement verification. Both the King LT and King LTS are available in disposable versions ( Fig. 16-8 ). Cuff pressures in supraglottic airways should never exceed 60 cm H 2 O. Devices are available to easily measure intra-cuff pressures ( Fig. 16-9 ).




FIGURE 16-8


A and B, King laryngeal tube (King Systems, Noblesville, IN).



FIGURE 16-9


Cuff pressure gauge.


I-Gel


The I-Gel (Intersurgical, Liverpool, NY) is a single-use cuffless supraglottic device made from a thermoplastic elastomer that helps create a seal of the pharyngeal, laryngeal, and perilaryngeal structures. Compression trauma is limited with the use of this material. The I-Gel has a gastric lumen and a built-in bite block along with a buccal cavity stabilizer that aids insertion and eliminates rotation within the oropharynx. The device is available in adult sizes 3 to 5 and accommodates nasogastric tube sizes 12 to 14 ( Fig. 16-10 ).




FIGURE 16-10


The I-Gel (Intersurgical, Liverpool, NY) cuffless supraglottic device.


SLIPA Pharyngeal Liner


The SLIPA streamlined pharyngeal liner (CurveAir Limited, London, UK) is a hollow, cuffless, preformed pharyngeal liner. No cuff is needed for the device to seal the pharynx. The SLIPA was named because it is shaped like a slipper, with a “toe,” “bridge,” and “heel.” During insertion, the jaw is lifted forward “to negotiate the toe of the chamber past the bend in the pharynx at the base of the tongue.” The bridge fits into the piriform fossa, sealing the upward outlet at the base of the tongue. The heel anchors the SLIPA into position, sealing off the nasopharynx. The hollow bowl acts as a reservoir for secretions and aids in preventing aspiration as a result of regurgitation. The nonlatex SLIPA is available in six sizes related to patient height and the dimension across the thyroid cartilage. Preformed indentations in the SLIPA help spare the hypoglossal nerve from compression, and the stem aids in placement without the need for fingers to be inserted in the mouth. This is a single-use device ( Fig. 16-11 ).




FIGURE 16-11


SLIPA streamlined pharyngeal liners (CurveAir Limited, London, UK).


Cobra Plus


The Cobra Plus (Engineered Medical Systems, Memphis, TN) is a single-use, nonlatex supraglottic device designed positioned in the hypopharynx. The device has an airway tube, standard 15-mm connector, and a distal ventilation port surrounded by a slotted port cover that helps prevent the soft tissue and the epiglottis from obstructing the ventilation port. In addition, the Cobra Plus has the ability to monitor the patient’s core temperature, has a distal carbon dioxide sampling port, and is available in pediatric sizes. Fiberoptic intubation can be facilitated by this device, which is available in adult and pediatric sizes, ½ to 6 ( Fig.16-12 ).




FIGURE 16-12


The Cobra Plus (Engineered Medical Systems, Memphis, TN).

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Aug 12, 2019 | Posted by in ANESTHESIA | Comments Off on Airway Equipment
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