Airway management is in a constant state of improvement and change. As might be expected, surgical tracheostomy, albeit not under the best conditions, was the first attempt to manipulate the airway in the presence of trauma or obstruction. The first recorded use of an artificial airway was described in 2000 B.C.E. in India, with a description of the healing of a post-tracheostomy wound [1]. Further descriptions came in the period of 400 to 300 B.C.E. from the Greek physician Hippocrates and Greek "first responder" and conqueror Alexander the Great, who reportedly performed a field-expedient tracheostomy with his sword on a fellow soldier who was suffocating on an aspirated bone around 320 B.C.E. [1]. Tracheostomy continued as the technique of choice, though the insertion of a hollow reed in the trachea of a newborn is described as early as 400 C.E. [1]. A lack of understanding that air needed to be pumped through the trachea limited the usefulness of tracheostomy, except in those patients already able to breathe. This limited usefulness is despite the fact that as early as 200 C.E., the Greek physician Galen used bellows attached to the trachea to mechanically move air into and out of the lungs. One author notes that between the years of 1546, when the Italian surgeon Brassavola first published an account of surgical tracheostomy, and 1825, only 28 cases of recovery from the underlying illness or trauma were reported [1,2]. The Renaissance brought new and innovative techniques and ideas relating to patient care, especially in the areas of airway management and ventilatory support. Andreas Vesalius, noted anatomist and physician of the 16th century, described the insertion of a reed into the tracheae of animals he was dissecting to better understand the physiologic interactions between the heart and lungs [3]. Work such as this led the Italian physician Fabricius of Acquapendente to write the following [3]:

Of all the surgical operations which are performed in man . . . the foremost [is] that by which man is recalled from a quick death to a sudden repossession of life . . . the operation is the opening of the aspera arteria ["artery of air" or trachea], by which patients, from a condition of almost suffocating obstruction to respiration, suddenly regain consciousness, and draw that vital ether, the air, so necessary to life, and again resume an existence which had been all but annihilated.

To manage the airway, healthcare providers require a good working knowledge of the anatomy of the mouth, oropharynx, nose, nasopharynx, and glottic opening. Further, while emergency airway management "opens the door" to saving the patient's life, a knowledge of the conducting and respiratory airways of the lungs, as well as the ability to adequately ventilate the lungs, is a crucial part of saving the patient's life. The following section will work using a "top-to-bottom" approach, beginning with the mouth and nose and ending in the alveoli.

Figure 1 is a representation of the open mouth. This seems basic, yet, in many instances, the basics are overlooked. Note the presence of the tongue, one of the biggest culprits when it comes to obstructing the airways. In many instances, simply displacing the tongue from the posterior of the oral airway is sufficient to allow the patient to breathe. Air enters the mouth and nose first and then descends down the conducting airways to the respiratory airways. One of the primary purposes of the nose and mouth and other upper airway structures is to warm and humidify the air the patient breathes before it enters the trachea and other conducting airways. As this is the case, these upper airway structures are both highly innervated and highly vascular. The mouth is innervated by branches V2 and V3 of cranial nerve (CN) V, the trigeminal nerve [9]. The high degree of innervation means that any manipulation of the upper airway in the mouth, no matter how slight, can precipitate gagging, retching, and in the worst case, vomiting. This is an adaptive mechanism, as objects entering the airway may occlude it, resulting in asphyxiation. The presence of high vascularity means that failure to use care in manipulating the upper airway may result in bleeding, further compromising a patient with airway management problems. One should always engage the minimum amount of intervention needed to open the patient's airway in an effort to decrease the potential for traumatization of the airway. More about the nervous innervation of the airway will be presented later in this course.

Figure 1 is a representation of the open mouth. This seems basic, yet, in many instances, the basics are overlooked. Note the presence of the tongue, one of the biggest culprits when it comes to obstructing the airways. In many instances, simply displacing the tongue from the posterior of the oral airway is sufficient to allow the patient to breathe. Air enters the mouth and nose first and then descends down the conducting airways to the respiratory airways. One of the primary purposes of the nose and mouth and other upper airway structures is to warm and humidify the air the patient breathes before it enters the trachea and other conducting airways. As this is the case, these upper airway structures are both highly innervated and highly vascular. The mouth is innervated by branches V2 and V3 of cranial nerve (CN) V, the trigeminal nerve [9]. The high degree of innervation means that any manipulation of the upper airway in the mouth, no matter how slight, can precipitate gagging, retching, and in the worst case, vomiting. This is an adaptive mechanism, as objects entering the airway may occlude it, resulting in asphyxiation. The presence of high vascularity means that failure to use care in manipulating the upper airway may result in bleeding, further compromising a patient with airway management problems. One should always engage the minimum amount of intervention needed to open the patient's airway in an effort to decrease the potential for traumatization of the airway. More about the nervous innervation of the airway will be presented later in this course.

Children may develop an infection of the epiglottis called epiglottitis that results in extreme swelling and partial occlusion of the airway. Children with this disorder typically have fever and lean forward to breathe while drooling heavily. A patient with these symptoms is experiencing a true airway emergency, and endotracheal intubation is ordinarily required. This should not be done except in the presence of an experienced laryngoscopist, usually an anesthetist, and preferably in the operating room with a surgeon present to gain a surgical airway if intubation fails.

Though frequently confused by novice practitioners and students of health care, dead space and shunt are crucially important concepts when managing a patient's airway and ventilation. In areas of dead space, the tissue is ventilated, but not perfused. The inhaled gases flow over and around these anatomic structures, but due to a lack of specialized capillary bed and the absence of alveoli, no gas exchange occurs. This concept is important, as inadequate amounts of air provided to the patient during artificial or mechanical ventilation will only move air in these dead space areas. Air can rush into and out of the trachea, but if the volume is not sufficient to get to the capillary beds in the lungs, no exchange of gases will take place—the patient will become hypoxic and eventually expire. In areas of shunt, the tissue is perfused, but not ventilated. Once again, inadequate volumes of artificial ventilation or a blockage of an airway will result in ventilatory gases not reaching the capillary beds. This means no oxygen is able to get to the alveoli, so no oxygen will get into the bloodstream. Further, the blood entering these capillaries, filled with carbon dioxide, is not able to unload this gas into fresh alveolar ventilation, resulting in its build up systemically. Carbon dioxide is a volatile acid, and its retention results in respiratory acidosis (Figure 9).

Each patient has approximately 8% physiologic shunt, as some of the blood that enters the lungs is not used for gas exchange but rather to oxygenate lung tissues themselves. This small volume of blood is perfused (comes in contact with the tissue to oxygenate the tissue and carry away waste and carbon dioxide) but not ventilated (does not enter the alveolar capillary membrane to load oxygen and unload carbon dioxide). Patients may have illnesses or pathologic conditions that lead to increased shunt levels. For example, a patient with an asthma or bronchitis may occlude an airway, which causes a section of the lung not to be ventilated, due to either severe airway narrowing (asthma) or the creation of a mucous plug (bronchitis). As a result, alveoli distal to the site of occlusion will be perfused but not ventilated. The heart will continue to pump blood to this region of the lung, but no exchange of gases can take place.

These observations will help to determine the difficulty that may be involved in manipulating the airway. To begin, ask conscious patients to look straight at you and open their mouth as widely as possible without sticking out their tongue. This will provide a Mallampati score (Figure 10), which indicates prospective difficulty in airway maintenance and intubation [16]. The ability to see tonsillar pillars, the soft palate, and the uvula indicate an airway that will be comparatively easily manipulated [16]. Conversely, the ability to see only teeth and tongue is prognostic for a difficult intubation, should one be required [16]. Next, patients should be asked to open their mouths. Does the patient have teeth? What is the general condition of the teeth? Missing and carious teeth are indicators of overall health, and poor dentition may be an indicator of poor health overall. How far can the patient open his or her mouth? Patients should be able to open their mouths to provide a space two to three fingerbreadths wide [17]. Is the patient obese? This does not require a body mass index (BMI) calculation, just a simple observation. Obesity correlates positively with airway obstruction and increased difficulty in airway management [18]. The upper lip bite test is a rapid and effective way to determine jaw movement and opening. Ask patients to place their bottom teeth on their upper lip. An inability to do so may portend problems with airway management, especially in mandibular manipulation. Absent teeth result in better intubating conditions, as the mouth opening tends to be wider, but the absence of structure provided by the teeth may result in more difficulty in obtaining a tight seal with a device. Head and neck movement provides the rescuer an idea of how flexible the patient's neck is and may demonstrate that a head-tilt initial technique will be useless and possibly dangerous if there is limited extension of the neck.

The purpose of the head-tilt, chin-lift, and jaw-thrust maneuvers is the same: to displace the tongue from the posterior airway. Patients who have decreased levels of consciousness, either from some pathologic state (e.g., syncope) or after receiving sedative or narcotic medications, may relax their head and neck and allow their tongue to slip to the back of the airway. This is usually accompanied by loud, stertorous breathing sounds, such as snoring. A key point to remember is that noisy breathing is obstructed breathing until proven otherwise. The first step is to determine if the patient is truly unconscious or in need of airway manipulation. This can be accomplished by grasping the patient's shoulder firmly and gently agitating the patient, calling his or her name to see if there is any response to these stimuli. Avoid both shouting and whispering; use a conversational tone such as you might employ speaking to a friend in a crowded room—a voice just a bit louder than usual. If the patient fails to respond, the rescuer is free to proceed with noninvasive airway maneuvers.

The head-tilt method is generally preferred and considered the easiest. With this maneuver, the patient is placed supine, and the rescuer places one hand on the patient's forehead and another on the patient's chin. The rescuer then gently tilts the patient's head back until the chin points up. If the rescuer suspects the patient may have a cervical spine injury, this technique is not recommended. The chin-lift technique is also quite simple. The provider moves beside or to the head end of the patient and places her/his thumb beneath the patient's chin and lift upwards (Figure 11). With either technique, one of the following results will be evident:

The oropharyngeal airway (Figure 14) is designed to be used for patients with both airway problems and diminished consciousness. This latter condition is extraordinarily important, as oropharyngeal airways should not be used for patients who have a gag reflex. Their insertion may result in causing the patient to vomit, placing her or him at risk for pulmonary aspiration.

The King airway has been described as being both easy to insert (with an 86% first-time success rate) and effective (Figure 17) [20]. The device is inserted in the mouth and passed midline. The device may be slightly rotated before insertion if the tip is getting caught on the tongue. It is important that the tube is first lubricated with the packet of water-soluble lubricant (packaged with the device) and that both the balloons are fully deflated. The use of a tongue depressor or the thumb of the non-insertion hand to hold the tongue away from the back of the airway will facilitate the insertion of this device. The device will pass down the oropharynx into the larynx. Once seated, the balloons are inflated using a provided 30-mL syringe. There is only one port for the syringe, and both balloons will inflate from this single port. If properly inserted, the lower balloon enters the esophagus, partially to fully occluding it and decreasing the likelihood of aspiration of vomitus into the airway. The upper balloon inflates above the glottic opening. The time required for the correct insertion of the airway is quite short, an average of 26 seconds in one study [21]. Using a BVM device, the pressure created by squeezing the bag causes air to exit the openings distal to the bag and enter the respiratory tract. The King airway comes in various sizes, and care should be taken to match the correct size airway for the patient according to manufacturer guidelines (provided with the device).

The LMA was developed in 1981 and is now widely used as to maintain airway patency during anesthesia [22]. The LMA comes in numerous sizes and permutations, but essentially, it is designed to maintain the airway by placing an inflatable cuff around the glottic opening. It differs from the King airway in that no part of the device enters the esophagus. When it first appeared on the market, the LMA was hailed as a breakthrough rescue device when endotracheal intubation failed. Now, these devices are routinely inserted for all types of surgeries. The ability to place the device without visualizing the airway, as with the King, is one of the keys to its popularity. The practitioner first selects the correct size for the patient and then uses the water-soluble lubricant (included with the device) to thoroughly lubricate the cuff. Some practitioners advocate the complete deflation of the LMA cuff for insertion, while others find insertion easier if the cuff is partially inflated. In either event, the device is somewhat wide, and it may easily become caught on the tongue (especially if inadequately lubricated) or on the posterior wall of the oropharynx. Therefore, when inserting the LMA, the patient should be obtunded, as this large airway device will provoke gagging, with his/her head tilted slightly back. The LMA should slide smoothly over the tongue and seat securely in the larynx. At this point, the practitioner can finish inflating the balloon, thus securing the airway. In one study, insertion of this device was successful 98% of the time [23].

The straight or Miller blade (Figure 19) also comes in various sizes, but a 2 or 3 blade is ordinarily used in the average adult patient. The Miller blade is used to physically raise the epiglottis away from the glottic opening by lifting the epiglottis with the tip of the blade.

The straight or Miller blade is used somewhat differently (Figure 22). After the patient is correctly placed and prepared, inspect the tongue to identify a faint midline. Align the straight blade marginally to the right of this line, so 40% of the blade is on the left side of the line and 60% is on the right side. Advance the blade to the back of the tongue, watching the tip of the blade at all times. When the epiglottis is in view, gently place the tip of the straight blade on the epiglottis itself and, just as with the curved blade, push the handle straight toward the imaginary point on the ceiling, as described in the section on the MacIntosh blade. The patient's glottic opening should be clearly visible. There is a groove in the straight blade that allows the operator to view the glottic opening, not to guide the endotracheal tube. The endotracheal tube should be placed into the oropharynx to the right of the straight blade, while continuing to visualize its entry through the glottic opening and disappearance below the vocal cords. The laryngoscope blade is then gently removed from the patient's mouth, while maintaining a firm grip on the endotracheal tube to ensure it is not inadvertently removed from the trachea. The cuff of the endotracheal tube is inflated with the insertion of 5–7 mL of air; the amount of air placed in the cuff should be just enough to prevent back flow of air into the laryngopharynx. Backflow can be heard by placing a stethoscope over the neck and listening for a leak (air "whooshing" or rustling). When the noise stops, there is sufficient air in the cuff. A BVM device is then attached, with continued monitoring of breath sounds and end-tidal carbon dioxide. The end-tidal carbon dioxide monitor is the criterion standard for monitoring and confirming correct tube placement and will work in all situations unless cardiac output is either absent or so low that the lungs are not being perfused. The final step is securing the endotracheal tube. In a non-operating-room environment (e.g., the emergency department or intensive care unit), it is prudent to obtain a portable chest x-ray as soon as possible after tube insertion to confirm its correct position.

The straight or Miller blade is used somewhat differently (Figure 22). After the patient is correctly placed and prepared, inspect the tongue to identify a faint midline. Align the straight blade marginally to the right of this line, so 40% of the blade is on the left side of the line and 60% is on the right side. Advance the blade to the back of the tongue, watching the tip of the blade at all times. When the epiglottis is in view, gently place the tip of the straight blade on the epiglottis itself and, just as with the curved blade, push the handle straight toward the imaginary point on the ceiling, as described in the section on the MacIntosh blade. The patient's glottic opening should be clearly visible. There is a groove in the straight blade that allows the operator to view the glottic opening, not to guide the endotracheal tube. The endotracheal tube should be placed into the oropharynx to the right of the straight blade, while continuing to visualize its entry through the glottic opening and disappearance below the vocal cords. The laryngoscope blade is then gently removed from the patient's mouth, while maintaining a firm grip on the endotracheal tube to ensure it is not inadvertently removed from the trachea. The cuff of the endotracheal tube is inflated with the insertion of 5–7 mL of air; the amount of air placed in the cuff should be just enough to prevent back flow of air into the laryngopharynx. Backflow can be heard by placing a stethoscope over the neck and listening for a leak (air "whooshing" or rustling). When the noise stops, there is sufficient air in the cuff. A BVM device is then attached, with continued monitoring of breath sounds and end-tidal carbon dioxide. The end-tidal carbon dioxide monitor is the criterion standard for monitoring and confirming correct tube placement and will work in all situations unless cardiac output is either absent or so low that the lungs are not being perfused. The final step is securing the endotracheal tube. In a non-operating-room environment (e.g., the emergency department or intensive care unit), it is prudent to obtain a portable chest x-ray as soon as possible after tube insertion to confirm its correct position.

The straight or Miller blade is used somewhat differently (Figure 22). After the patient is correctly placed and prepared, inspect the tongue to identify a faint midline. Align the straight blade marginally to the right of this line, so 40% of the blade is on the left side of the line and 60% is on the right side. Advance the blade to the back of the tongue, watching the tip of the blade at all times. When the epiglottis is in view, gently place the tip of the straight blade on the epiglottis itself and, just as with the curved blade, push the handle straight toward the imaginary point on the ceiling, as described in the section on the MacIntosh blade. The patient's glottic opening should be clearly visible. There is a groove in the straight blade that allows the operator to view the glottic opening, not to guide the endotracheal tube. The endotracheal tube should be placed into the oropharynx to the right of the straight blade, while continuing to visualize its entry through the glottic opening and disappearance below the vocal cords. The laryngoscope blade is then gently removed from the patient's mouth, while maintaining a firm grip on the endotracheal tube to ensure it is not inadvertently removed from the trachea. The cuff of the endotracheal tube is inflated with the insertion of 5–7 mL of air; the amount of air placed in the cuff should be just enough to prevent back flow of air into the laryngopharynx. Backflow can be heard by placing a stethoscope over the neck and listening for a leak (air "whooshing" or rustling). When the noise stops, there is sufficient air in the cuff. A BVM device is then attached, with continued monitoring of breath sounds and end-tidal carbon dioxide. The end-tidal carbon dioxide monitor is the criterion standard for monitoring and confirming correct tube placement and will work in all situations unless cardiac output is either absent or so low that the lungs are not being perfused. The final step is securing the endotracheal tube. In a non-operating-room environment (e.g., the emergency department or intensive care unit), it is prudent to obtain a portable chest x-ray as soon as possible after tube insertion to confirm its correct position.

The endotracheal tube has markings indicating the depth of the tube opening. For the average adult patient, the tube is correctly placed at a distance three times the tube diameter. For example, a 7.5-mm tube can be secured in such a fashion that the tube line indicating 22 or 23 centimeters is shown at the level of the patient's teeth. Most modern tubes have markings indicating correct oral and nasal depth.

Video laryngoscopy systems are a modification of the direct laryngoscopy systems discussed. The primary advantage of these systems is that the fiber-optic camera is located near the end of the blade, thus decreasing the force required to bring the glottic opening into view. These systems all use curved blades, which are inserted in a manner similar to the Macintosh blade. The main difference is that this blade need not be maneuvered into the vallecula; indeed, doing so would occlude the user's visual field. The video laryngoscope either has a small video screen mounted on a rolling platform, or a smaller screen connected directly to the handle of the laryngoscope. In the case of the former, the screen should be placed in such a position that the practitioner can see both the screen and the patient, usually somewhere near the patient's left shoulder. In either case, immediately after the insertion of the blade into the patient's mouth, the practitioner should watch the screen and identify the anatomic landmarks of the upper airway. It is not necessary to employ the degree of force needed to expose the glottic opening with direct laryngoscope; merely instead, the practitioner can gently lift the laryngoscope, while being careful not to damage the patient's teeth, until the glottic opening is in view [28]. These devices come with endotracheal tubes with specially designed stylets. The tubes are inserted into the mouth to the right of the device and carefully passed toward the oropharynx until the tip of the tube is also seen on the video screen. The tube can then be advanced through the glottic opening under video observation, confirming its placement. It is likely that these devices will soon replace direct laryngoscopy almost entirely. The technique is easier and associated with greater first-time success rates, particularly in patients with difficult airways [28,29]. Video laryngoscopy has also been suggested as a rescue technique to be used in the case of failed direct laryngoscopy [18]. Other uses include difficult airways in patients with obesity, cervical spine disorders (e.g., arthritis, osteoporosis), or traumatic cervical spine injuries. Perhaps the best reason to use video laryngoscopy is its increased success rate when used by novice practitioners when compared with direct laryngoscopy [30].

Gases surround all people as they walk through the sea of air that blankets the earth. Air is composed of approximately 21% oxygen and 78% nitrogen, along with numerous trace gases. At sea level, the pressure of the air, measured in millimeters of mercury (sometimes referred to as torr), is the sum of the pressures of all of the gases surrounding us. For example, 21% oxygen times 760 mm Hg of pressure means that almost 160 mm Hg of the pressure is from oxygen. The remaining pressure comes from the nitrogen and other trace gases. When we breathe, oxygen enters conducting airways in the nose and mouth at this pressure of 160 mm Hg but is quickly reduced as the water vapor excreted from our tissues moistens these gases. This water pressure is about 47 mm Hg, so the partial pressure of oxygen is now reduced to 113 mm Hg [13]. Gases are carried in the bloodstream after passing through the alveolar membrane and associated structures into the blood in the capillary. When the 113 mm Hg of oxygen moves through the conducting airways, it is somewhat diluted by gases already present, until the oxygen entering the alveolus has a pressure of approximately 104 mm Hg. Normal arterial blood gas values for oxygen are 80–100 mm Hg, and one can quickly see that in times of normal health, the diffusion of oxygen into the bloodstream has little hindrance.

However, altitude can affect these values significantly. At 15,000 feet above sea level, the pressure is just 429 mm Hg; the composition of the air remains 21% oxygen, 78% nitrogen, and trace gases. Inhaled oxygen is now just 91 mm Hg. This level is saturated with 47 mm Hg of water, and now only 44 mm Hg of oxygen is left, far below the normal partial pressure of 80–100 mm Hg at sea level. The shortness of breath and feeling of exhaustion at even the slightest exertion at this altitude is easily understood, as individuals have less than half the oxygen in their blood as would be present at sea level.