ALS Airway Adjuncts
A tracheal tube (ET) is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide. Most endotracheal tubes today are constructed of polyvinyl chloride, but specialty tubes constructed of silicone rubber, latex rubber, or stainless steel are also widely available. Most tubes have an inflatable cuff to seal the trachea and bronchial tree against air leakage and aspiration of gastric contents, blood, secretions, and other fluids. Uncuffed tubes are also available, though their use is limited mostly to pediatric patients.
The ET maintains a paten airway, facilitates suctioning of airway secretions, enables delivery of oxygen in higher concentrations than ambient air, permits delivery of a prescribed tidal volume, and provides an alternate route for delivery of some medications. Cuffed ET may also protect the airway from aspiration. Use of an ET is indicated in when providers are unable to ventilate effectively with a BVM and when the airway protective reflexes are absent. Although placement of an ET tube can be accomplished during on-going chest compressions during CPR, intubation is generally associated with considerable interruption of chest compressions. The interruption of chest compressions from ET placement can minimized when ALS providers prepare in advance to begin placement as soon the provider performing compressions pauses during normal CPR protocol. Compressions should resume as soon as the ET passes through the vocal cords. The ALS provider with a preference for ET intubation should plan to be able to complete ET intubation in less than 10 seconds, or consider airway management using a supraglottic devices or deferring advanced airway placement until the patient fails to respond to initial CPR attempts.1
ET use is associated with a 6%-25% incident of misplacement or displacement. In addition, the risk of a properly placed ET becoming displaced is considerable, particularly during movement of the patient. Therefore, ALS providers should always plan to use a combination of clinical assessment and CO2 monitoring, such as waveform capnography or an exhaled CO2 esophageal detector device, to verify initial placement and ensure that the ET does not become displaced during care. 1
Laryngoscopy is endoscopy of the larynx, a part of the throat. It is a medical procedure that is used to obtain a view, for example, of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during general anaesthesia or cardiopulmonary resuscitation or for surgical procedures on the larynx or other parts of the upper tracheobronchial tree.
Direct laryngoscopy is typically carried out with the patient lying on his or her back; the laryngoscope is inserted into the mouth on the right side and flipped to the left to trap and move the tongue out of the line of sight. Depending on the type of blade used, the laryngoscope is inserted either anterior or posterior to the epiglottis and then lifted with an upwards and forward motion, away from the provider and towards the roof of the patient’s mouth. This move makes a view of the glottis possible.
Indirect laryngoscopy is performed whenever the provider visualizes the patient’s vocal cords by a means other than obtaining a direct line of sight. For the purpose of intubation, this is facilitated by fiberoptic bronchoscopes, video laryngoscopes, fiberoptic stylets and mirror or prism optically-enhanced laryngoscopes.
The vast majority of tracheal intubations involve the use of a viewing instrument of one type or another. Since its introduction by Kirstein in 1895, the conventional laryngoscope has been the most popular device used for this purpose. Today, the conventional laryngoscope consists of a handle containing batteries with a light source, and a set of interchangeable blades.
Early laryngoscopes used a straight “Magill Blade”, and this design is still the standard pattern veterinary laryngoscopes are based upon; however the blade is difficult to control in adult humans and can cause pressure on the vagus nerve, which can cause unexpected cardiac arrhythmias to spontaneously occur in adults.
Two basic styles of laryngoscope blade are currently commercially available: the curved blade and the straight blade. The Macintosh blade is the most widely used of the curved laryngoscope blades, while the Miller blade is the most popular style of straight blade. Both Miller and Macintosh laryngoscope blades are available in sizes 0 (neonatal) through 4 (large adult). There are many other styles of curved and straight blades (e.g., Phillips, Robertshaw, Sykes, Wisconsin, Wis-Hipple, etc.) with accessories such as mirrors for enlarging the field of view and even ports for the administration of oxygen. These specialty blades are primarily designed for use by anesthetists, most commonly in the operating room. Additionally, paramedics are trained to use direct laryngoscopy to assist with intubation in the field.
The Macintosh blade is positioned in the vallecula, anterior to the epiglottis, lifting it out of the visual pathway, while the Miller blade is positioned posterior to the epiglottis, trapping it while exposing the glottis and vocal folds. Incorrect usage can cause trauma to the front incisors; the correct technique is to displace the chin upwards and forward at the same time, not to use the blade as a lever with the teeth serving as the fulcrum.
The Miller, Wisconsin, Wis-Hipple, and Robertshaw blades are commonly used for infants. It is easier to visualize the glottis using these blades than the Macintosh blade in infants, due to the larger size of the epiglottis relative to that of the glottis.
Besides the conventional laryngoscopes, many other devices have been developed as alternatives to direct laryngoscopy. These include a number of indirect fiberoptic viewing laryngoscopes such as the flexible fiberoptic bronchoscope. The flexible fiberoptic bronchoscope or rhinoscope can be used for office-based diagnostics or for tracheal intubation. The patient can remain conscious during the procedure, so that thevocal folds can be observed during phonation. Surgical instruments passed through the scope can be used for performing procedures such as biopsies of suspicious masses. These instruments have become indispensable within the otolaryngology, pulmonology and anesthesia communities.
Other available fiberoptic devices include the Bullard scope, UpsherScope, and the WuScope. These devices are widely employed for tracheal intubation, especially in the setting of the difficult intubation.
The conventional direct laryngoscope uses a line of sight provided by a rigid viewing instrument with a light on the blade or intra-oral portion which requires a direct view of the target larynx; this view is clearly seen in 80-90% of attempts. The frequent failure of direct laryngoscopy to provide an adequate view for tracheal intubation led to the development of alternative devices such as the lighted stylet, and several indirect fiberoptic viewing laryngoscopes, such as the fiberscope, Bullard scope, Upsher scope, and the WuScope. Though these devices can be effective alternatives to direct laryngoscopy, they each have certain limitations, and none of them is effective under all circumstances. One important limitation commonly associated with these devices is fogging of the lens. To address some of these limitations, Dr. Jon Berall, a New York City internist and emergency medicine physician, designed the camera screen straight video laryngoscope in 1998. The first true video laryngoscope glidescope was produced in 1999 and a production version with 60-degree angle, an onboard heater, and a custom screen was first sold in 2000. The true video laryngoscope has a camera on the blade with no intervening fiberoptic components. The concept is important because it is simpler to produce and handle the resultant images from CMOS cameras. The integrated camera leads to a series of low cost variants that are not possible with the hybrid Fiberoptic units.
Several manufacturers have developed video laryngoscopes which employ digital technology to generate a view of the glottis so that the trachea may be intubated. The KARL STORZ C-MAC Video Laryngoscope and the Glidescope video laryngoscope are examples of such devices. Other examples include the McGrath laryngoscope, Daiken Medical Coopdech C-scope vlp-100, the Storz V-MAC DCI Video Laryngoscope and the Pentax AWS laryngoscopes.
Use of a supraglottic airway device (SGD)is an acceptable alternative to an ET, particularly during CPR as SGD may be placed without interrupting chest compressions.1
The esophageal-tracheal tube (ETT or Combitube), is a blind insertion double-lumen airway (BIAD) used in the pre-hospital and emergency setting to facilitate the mechanical ventilation of a patient in respiratory distress.
The Combitube consists of a cuffed, double-lumen tube that is inserted through the patient’s mouth to secure an airway and enable ventilation. Generally, the distal tube (tube #2), enters the esophagus, where the cuff is inflated. Ventilation is provided through the proximal tube (tube #1) which opens at the level of the larynx. In the rare instance where the distal tube intubates the trachea, ventilation is provided through the distal tube. Inflation of the cuff in the esophagus allows a level of protection against aspiration of gastric content. The Combitube is available in two sizes. A size 37 Fr is used for patients 4 to 6 ft or 122 to 183 cm tall while a 41 Fr is used for patients more than 5 ft or 152 cm tall. 1,11,12,13
The simplicity of placement is the main advantage of the Combitube over endotracheal intubation. When intubating with a traditional endotracheal tube, care must be taken to visually ensure that the tube has been placed in the trachea while the dual-lumen design of the Combitube allows for ventilation to proceed regardless of esophageal or tracheal placement.1, 11, 12,13
A device called the Positube allows for esophageal intubation detection. The Postitube can be used on tube #2 to rule out the intubation of the Combitube in the trachea. The Positube checks for air flow resistance on tube #2 and is very helpful in checking proper Combitube placement when intubation is performed in noisy environment’s.
The Combitube’s ease of use makes it an option for use in the pre-hospital, emergency setting when advanced level providers capable of placing an endotracheal tube are not immediately available. The drawbacks of Combitubes are evidenced by reports of serious complications such as aspiration, esophagus perforation and facial nerve dysfunction associated with their use. Ventilation and oxygenation with the Combitube are favorable to the ET.1
While it has been suggested as an option by the American Heart Association and European Resuscitation Council for situations where intubation attempts are unsuccessful since the year 2000, it is seldom used outside of the pre-hospital, emergency setting, as it does not allow for long term airway control. SGD alternatives to the Combitube include the laryngeal mask airway and the laryngeal tube.
Laryngeal Mask Airway
A laryngeal mask airway, or LMA, is a supraglottic airway management device composed of an airway tube that connects to an elliptical mask with a cuff which is inserted through the patient’s mouth to form an airtight seal on top the glottis. Unlike endotracheal tubes which pass through the glottis, the LMA forms an airtight seal as it sits atop the glottis. The LMA cuff can be either self-sealing or inflatable. Once correctly placed the mask conforms to the anatomy with the bowl of the mask facing the space between the vocal cords. After correct placement, the tip of the laryngeal mask sits in the throat against the muscular valve that is located at the upper portion of the esophagus. LMA devices may be particularly advantageous when there is the possibility of unstable cervical spine injury as these devices are blind inserted airway devices (BIAD) that can be placed without the movement associated with intubation. 1,11,12,13
The laryngeal tube, or King LT, is an airway management device that can be inserted blindly through the oropharynx into the hypopharynx to create and maintain a patent airway. In its standard version, the laryngeal tube is made up of a tube with a larger balloon cuff in the middle (oropharyngeal cuff) and a smaller balloon cuff at the end (oesophageal cuff). The tube is kinked at an angle of 30-45° in the middle; the kink is located in the larger cuff. There are two apertures, located between the two cuffs, through which ventilation takes place. Both cuffs are inflated through a single small lumen line and pilot balloon. The cuffs are high-volume, low-pressure cuffs with inflating volume ranging from 10 ml (size 0) to 90 ml (size 5). A large bore syringe, which is marked with the required volume for each size, is used to inflate the cuffs. A cuff inflator can also be used, in which case the cuffs should be inflated to a pressure of 60 cm H2O. Three black lines on the tube indicate the depth of insertion when aligned with the teeth. 1, 11,12,13
Various studies have shown that insertion and use of the standard tracheal tube is easy, providing a clear airway in most cases. Comparative studies indicate that the standard laryngeal tube is generally as effective as the LMA, while some studies indicate that an inflatable LMA may be more effective than the standard laryngeal tube under controlled ventilation conditions in general anaesthesia.4,5 Several studies describe the usefulness of the device in securing a difficult airway, even in cases where insertion of the LMA had failed. The laryngeal tube is also recommended for medical personnel not experienced in tracheal intubation, and as a rescue device when intubation has failed in adults. According to the manufacturer the use of Laryngeal tubes is contraindicated in people with an intact gag reflex, known oesophageal disease, and people who have ingested caustic substances.
|Combitube Demonstration||LMA Demonstration||King LT Demonstration|