SUPRAGLOTTIC AIRWAY DEVICES
Supraglottic airway devices (SADs) are used with both spontaneously and ventilated patients dur-ing anesthesia. They have also been employed as conduits to aid endotracheal intubation when both BMV and endotracheal intubation have failed. All SADs consist of a tube that is connected to a respira-tory circuit or breathing bag, which is attached to a hypopharyngeal device that seals and directs air-flow to the glottis, trachea, and lungs. Additionally, these airway devices occlude the esophagus with varying degrees of effectiveness, reducing gas dis-tension of the stomach. Different sealing devices to prevent airflow from exiting through the mouth are also available. Some are equipped with a port to suc-tion gastric contents. None offer the protection from aspiration pneumonitis offered by a properly sited, cuffed endotracheal tube.
A laryngeal mask airway (LMA) consists of a wide-bore tube whose proximal end connects to a breath-ing circuit with a standard 15-mm connector, and whose distal end is attached to an elliptical cuff that can be inflated through a pilot tube. The deflated cuff is lubricated and inserted blindly into the hypophar-ynx so that, once inflated, the cuff forms a low-pres-sure seal around the entrance to the larynx. This requires anesthetic depth and muscle relaxation slightly greater than that required for the insertion of an oral airway. Although insertion is relatively simple (Figure 19–11), attention to detail will improve the success rate (Table 19–2). An ideally positioned cuff is bordered by the base of the tongue superiorly, the pyriform sinuses laterally, and the upper esophageal sphincter inferiorly. If the esophagus lies within the rim of the cuff, gastric dis-tention and regurgitation become possible. Anatomic variations prevent adequate functioning in some patients. However, if an LMA is not func-tioning properly after attempts to improve the “fit” of the LMA have failed, most practitioners will try another LMA one size larger or smaller. The shaft can be secured with tape to the skin of the face.The LMA partially protects the larynx from pharyngeal secretions (but not gastric regurgitation), and it should remain in place until the patient has regained airway reflexes. This is usually signaled by coughing and mouth opening on command. The LMA is available in many sizes (Table 19–3).
The LMA provides an alternative to ventila-tion through a face mask or TT (Table 19–4). Relative contraindications for the LMA include patients with pharyngeal pathology (eg, abscess), pharyngeal obstruction, full stomachs (eg, preg-nancy, hiatal hernia), or low pulmonary compli-ance (eg, restrictive airways disease) requiring peak inspiratory pressures greater than 30 cm H2O. Traditionally, the LMA has been avoided in patients
with bronchospasm or high airway resistance, but new evidence suggests that because it is not placed in the trachea, use of an LMA is associated with less bronchospasm than a TT. Although it is clearly not a substitute for tracheal intubation, the LMA has proven particularly helpful as a life-saving temporiz-ing measure in patients with difficult airways (those who cannot be ventilated or intubated) because of
its ease of insertion and relatively high success rate (95% to 99%). It has been used as a conduit for an intubating stylet (eg, gum-elastic bougie), ven-tilating jet stylet, flexible FOB, or small-diameter (6.0-mm) TT. Several LMAs are available that have been modified to facilitate placement of a larger TT, with or without the use of a FOB. Insertion can be performed under topical anesthesia and bilateral superior laryngeal nerve blocks, if the airway must be secured while the patient is awake.
The ProSeal LMA, which permits passage of a gastric tube to decompress the stomachThe I-Gel, which uses a gel occluder rather than inflatable cuffThe Fastrach intubation LMA, which is designed to facilitate endotracheal intubation through the LMA deviceThe LMA CTrach, which incorporates a camera to facilitate passage of an endotracheal tube Sore throat is a common side ef fect follow-ing SAD use. Injuries to the lingual, hypoglossal, and recurrent laryngeal nerve have been reported. Correct device sizing, avoidance of cuff hyperinfla-tion, and gentle movement of the jaw during place-ment may reduce the likelihood of such injuries.
The esophageal–tracheal Combitube consists of two fused tubes, each with a 15-mm connector on its proximal end (Figure 19–12). The longer blue tube has an occluded distal tip that forces gas to exit through a series of side perforations. The shorter clear tube has an open tip and no side perforations. The Combitube is usually inserted blindly through the mouth and advanced until the two black rings on the shaft lie between the upper and lower teeth. The Combitube has two inflatable cuffs, a 100-mL proximal cuff and a 15-mL distal cuff, both of which should be fully inflated after placement. The distal lumen of the Combitube usually comes to lie in the esophagus approximately 95% of the time so that ventilation through the longer blue tube will force gas out of the side perforations and into the lar-ynx. The shorter, clear tube can be used for gastric
decompression. Alternatively, if the Combitube enters the trachea, ventilation through the clear tube will direct gas into the trachea.
King laryngeal tubes (LTs) consist of tube with a small esophageal balloon and a larger balloon for placement in the hypopharynx (Figure 19–13). Both tubes inflate through one inflation line. The lungs are inflated from air that exits between the two balloons. A suction port distal to the esophageal balloon is present, permitting decompression of the stomach. The LT is inserted and the cuffs inflated. Should ventilation prove difficult, the LT is likely inserted too deep. Slightly withdrawing the device until compliance improves ameliorates the situation.