EMS Airway Management in Adverse Conditions

Anatomy and Physiology

The airway comprises all anatomical spaces from the nares and oral aperture down to the end of the alveolar tree in the lungs. It includes the nose, mouth, pharynx, larynx, trachea, and bronchi, all of which are lined internally with mucous membranes. The vocal cords in the larynx mark the transition point between the upper airway and the lower airway.

The nose consists of the external nose and the nasal cavity. The external nose is the most superficial part, made up of cartilage and bone. It continues posteriorly into the nasal cavity, which is divided in two by a septum in the midline. Each half of the cavity is bounded by a roof (formed of nasal, frontal, ethmoid, and sphenoid bones), a floor (formed of palatine and maxilla bones), and the nasal septum (formed of ethmoid and vomer bones as well as cartilage). The nose may be used as a conduit for delivering oxygen to the patient via a nasal cannula; alternatively, tracheal tubes or nasopharyngeal airways may be passed through the nares.

The mouth consists of the mouth cavity and the vestibule. The mouth cavity is bounded by the maxilla, mandible, and teeth anteriorly; the hard and soft palate superiorly; the mandible and anterior tongue inferiorly; and the oropharyngeal isthmus posteriorly. The vestibule is the space surrounding this between the lips and cheeks on the outside and the teeth and gums on the inside.

From superior to inferior, the pharynx consists of the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is directly posterior to the nasal cavity, starting at the level of the base of the skull and continuing down to the soft palate; it contains the adenoids (nasopharyngeal tonsils). The oropharynx extends from the level of the soft palate down to the level of the tip of the epiglottis, lying behind the oropharyngeal isthmus; it contains the palatine tonsils at the sides. The laryngopharynx continues from the epiglottis down to the inferior border of the cricoid cartilage at the level of the sixth cervical vertebra. The prevertebral fascia and the cervical vertebrae lie directly behind the pharynx along its whole length. Its walls are made of several layers of muscles with a complex neurovascular supply. Supraglottic devices such as laryngeal mask airways terminate at this level, resting at the level of the epiglottis.

The larynx is a tightly interlocked structure made up of cartilages, ligaments, and muscles. The largest structure at the front is the thyroid cartilage; its notch forms the prominent “Adam’s apple.” The ring-shaped cricoid cartilage is below this. The narrow space between them is spanned in the front by the cricothyroid ligament. The thyrohyoid ligament stretches from the upper border of the thyroid cartilage superiorly to the hyoid bone, deep in the neck. Posterior to the thyroid cartilage is the laryngeal cavity, a space that contains the upper (false) and lower (true) vocal cords. Definitive airway management requires passage of an airway device below the level of the vocal cords with a good seal, protecting the respiratory exchange zone in the lower airways from vomitus or other debris while allowing goal-directed oxygenation and positive-pressure ventilation if required.

Indications

Airway management is widely indicated in the prehospital setting, commonly where a patient has become unable to maintain adequate oxygenation and ventilation or where they have become unable to protect their airway due to intercurrent illness or injury.

In choosing a primary method for advanced airway management, circumstances must allow time for appropriate visualization, suctioning, and gentle placement of the device. Hypoxia should not occur, and a physiologic “cushion” should allow for apneic time without desaturation. Techniques to provide this cushion, such as apneic oxygenation and nitrogen washout, should be explored separately. If the primary method fails, a backup method should be implemented; this should allow for promptly securing the airway but without the comfort of a cushion to maintain oxygenation during the apneic period. Examples of a backup device include video or bougie-assisted laryngoscopy or a laryngeal mask airway (LMA). Rescue methods are used in sequence when the above methods fail, or as the initial method when the patient is too ill and iatrogenic injury will be caused by further delays in oxygenation and ventilation. The rescue method of choice should allow for rapid placement and should be familiar to the practitioner.

Contraindications

Given the essential nature of adequate oxygenation and ventilation to patient survival, there are no absolute contraindications, but there may be relative contraindications to some techniques in certain clinical contexts. Advanced maneuvers such as intubation should only be performed by adequately trained providers and if the potential benefits in that clinical context outweigh the risks. Airway manipulation should be minimized in certain scenarios when aggressive prehospital interventions may lead to sudden deterioration, such as suspected epiglottitis in children, or where a patient has risk factors for difficult intubation and basic maneuvers are proving sufficient.

Equipment

A wide variety of airway procedures and adjuncts are in use, each requiring varying degrees of skill and posing benefits and risks in different clinical contexts. They include:[1]

• Manual airway management maneuvers, using the head-tilt-chin-lift method or the jaw-thrust method
• Oxygen devices, including high-flow nasal oxygen
• Insertion of oropharyngeal or nasopharyngeal airways
• Bag-valve-mask device
• Supraglottic airways
• Continuous positive airway pressure (CPAP) devices and non-invasive ventilation
• Direct laryngoscopy with endotracheal intubation
• Nasal intubation
• Rapid sequence intubation (RSI), with sedatives and paralytics
• Drug-assisted or facilitated intubation without paralytics
• Airway intubation adjuncts, such as bougies, styles, or video laryngoscopes
• Front of neck access, such as needle cricothyrotomy or surgical cricothyrotomy

Personnel

All personnel working in EMS should have at least basic levels of knowledge and training in airway management. Those expected to provide advanced interventions such as intubation should have adequate background training and experience and ongoing mentoring and maintenance of skills. Advanced techniques generally require the presence of more than one trained responder and should not be undertaken solo if possible due to the need to provide multiple interventions to such patients simultaneously.

Preparation

Formulating a clear treatment plan is crucial, and the responding team should consider patient, personnel, and environmental factors.

• Patient factors include predictors of a difficult airway (such as facial trauma or vomitus), patient positioning, and physiological and psychological status, including whether these can be optimized prior to the proceeding.
• Personnel factors include the relative training and experience of the clinicians who are present, the availability of backup, fatigue and stress, and familiarity with the available equipment.
• Environmental factors include the time of day, ambient light, temperature, altitude, weather conditions, proximity to other healthcare resources (such as travel time to the nearest hospital), and safety of the immediate environment (particularly in tactical or military settings). Monitoring of airway adjunct balloon turgor is an important aspect in relation to atmospheric pressure changes in flight. Video laryngoscopy equipment may malfunction in extremes of temperature, and backup methods should be available in case of malfunction.

Technique or Treatment

Poor Ambient Light

Lighting is often suboptimal in the prehospital environment. Inadequate ambient light interferes with proper preparation of airway equipment and impairs good communication and situational awareness among team members during the procedure itself, and has obvious implications for airway procedures themselves (particularly for intubation which relies on direct visualization of tube position). An excess of ambient light may cause problems due to glare blinding the airway operator, particularly where light sources are in the operator’s line of sight (such as the low-lying sun at dusk or dawn).

In low light settings, bystanders or team members can be tasked with positioning artificial light sources to illuminate the immediate surroundings, and responders should consider using head-mounted lamps.

If excessive light is interfering with airway management, bystanders and team members may similarly facilitate the procedure by using a sheet or tarpaulin to reduce glare. Video laryngoscopy, as opposed to direct laryngoscopy, may be of benefit, but video laryngoscope screens may be difficult to view in broad daylight compared to artificial indoor lighting conditions.[2]

The illumination of the airway during intubation generally relies on light emitted from the laryngoscope itself. Batteries and light bulbs should be charged and checked ahead of time, and it is good practice to have a second laryngoscope immediately available in case of last-minute equipment problems.

In the absence of a functioning light source, blind digital intubation guided only by the rescuer’s fingers has been described.[3] A flexible, lighted stylet (which should transilluminate across the trachea if the tube has been correctly placed) may increase first-pass success.[4] However, digital intubation is unfamiliar to most clinicians and carries a significant risk of tube malposition and failure. One study looking at night vision goggles in the tactical setting found that this strategy did allow for successful intubation but required significantly more time.[5] In such cases, it may be preferable to use alternative airway devices that do not require direct airway visualization, such as supraglottic airways, as a first-line.

Atypical Patient Position

Patients in the prehospital setting are often found on the ground rather than on a waist-high surface which is more ergonomic for responders. They are often not lying in the optimal supine ramped position. Space creation around the patient, or (in extremis) a snatch-and-grab strategy moving the patient to adjacent flat terrain for emergent airway management, is often desirable but may not always be possible due to entrapment or restricted patient access.

Various techniques can be employed, which may need to be tailored to specific circumstances. Basic techniques such as the head-tilt-chin-lift maneuver, jaw thrust maneuver, or insertion of an oropharyngeal or nasopharyngeal airway may be sufficient to improve the patient’s condition until good access is possible. Second-generation supraglottic airway devices have become more widely available over the last decade and may provide a more secure airway and improved oxygenation in the obtunded patient, with the advantage that they can be inserted without requiring line-of-site of the patient’s vocal cords. Insertion can be aided by using small judicious doses of sedative medication – this technique is referred to as pharmacologically assisted laryngeal mask insertion (PALM).[6]

If tracheal intubation is judged essential while the patient is on the ground, the responder can adopt various postures. If the patient is supine, the simplest approach is often for the rescuer to lie prone, kneel or sit on the ground at the patient’s head; the responder can alternatively take a lateral decubitus position; this may be easier when lying on the left, as the responder’s right arm movements will be less restricted for tube insertion, and the left arm is stabilized on the ground during laryngoscopy.[7][8]

For patients who may require intubation while in an upright position (such as those entrapped while sitting in a car), or where there is an absolute restriction of access at the patient’s head, it may be possible for the rescuer to adopt a face-to-face approach using inverse direct laryngoscopy, with the laryngoscope held upside down in the right hand and the tracheal tube in the left. This may require the rescuer to straddle the patient. Video laryngoscopy may facilitate this; one study found significant differences in success when using different designs of video laryngoscope.[9] Given that most responders will have limited experience with the unnatural ergonomics of face-to-face intubation, it may be preferable to rely instead on other techniques to improve oxygenation and ventilation until extrication or better patient access is possible for conventional laryngoscopy.

Obesity

Obesity is associated with a significantly increased risk of airway complications.[10] Increased soft tissue mass results in increased weight, and the volume of soft tissue can distort the airway in a supine obese patient, making visualization of vital structures harder. Increased pressure on the diaphragm from the obese abdomen prevents normal diaphragmatic excursion. This effect is dramatically exacerbated when the patient is supine, leading to lower tidal volumes in spontaneously breathing patients, faster desaturation once sedated or paralyzed, and more difficult bag-valve-mask ventilation. The increased pressure required to bag these patients sometimes results in gastric inflation, which exerts more upward pressure on the diaphragm. A dangerous downward spiral can result from this scenario. Desaturation happens more quickly in obese patients due to the poor mechanics of their airway and their increased metabolic demands/oxygen consumption, as well as their underlying hypoxia-inducing pathology. Patient positioning and preparation remain the key to the management of the airway in the bariatric patient. Manual airway manipulation via jaw thrust, oropharyngeal, or nasopharyngeal airway may help to alleviate the effects of habitus-related airway obstruction. Practitioners should ensure alignment of the airway axis by attempts to align the patient’s earlobe with the sternal notch in the horizontal plane.

Minimal Backup and Limited Equipment

The number of trained clinicians present at a prehospital incident is invariably lower than the in-hospital setting, and skilled backup is generally not immediately available. Advanced airway interventions are complex, and their success relies on having a well-trained team of skilled providers. If inadequate providers are present, the priority must be to maintain oxygenation and ventilation, even if this means using only basic adjuncts and techniques.[11] In the tactical or military setting, it may be necessary to institute only basic interventions at the site of illness or injury, delaying definitive airway management until the patient has been removed to a location of relative safety.

The use of standardized equipment sets and protocolized checklists may reduce the rate of errors by reducing superfluous decision-making during the incident, freeing up cognitive “bandwidth.”[12] The increasing availability and reduced costs of handheld telecommunications with internet connectivity have made telemedicine more feasible. Some studies have explored the use of real-time video transmission during airway management, allowing senior clinicians at a distant location to aid in the decision-making process.[13]

Complications

The vast majority of patients do not have anatomically difficult airways. However, in the emergency setting and particularly in the prehospital environment, even patients whose airways are physically normal may still present with “physiologically difficult” airways due to inadequate preoxygenation and serious intercurrent illness or “situationally difficult” airways due to lack of skilled assistance, time pressures, poor patient positioning or other adverse conditions.[14] Complications of airway management can include aspiration, esophageal intubation, hypoxia, and physiological derangement.[10] Before performing advanced procedures such as intubation, EMS clinicians should actively plan for how they will troubleshoot any immediate complications that arise. These may include removing the device and swapping it for another or proceeding down a failed airway algorithm towards the front of neck access.

Clinical Significance

Airway management is not a benign procedure. Retrospective and observational studies have demonstrated that complications relating to airway management occur more frequently when tracheal intubation is deemed to be difficult.[15] In recent decades, evidence has become more equivocal as to whether prehospital tracheal intubation confers a significant enough benefit in many clinical conditions when balanced from the harm arising from potential airway complications.[16] Critical decision making, restricting advanced airway management where a patient’s condition or co-morbidities are not favorable, may be associated with low rates of adverse outcomes.[17]

Enhancing Healthcare Team Outcomes

A number of interprofessional teams, organizational and environmental factors have a bearing on airway management and have previously been identified in level 5 evidence in the human factors literature, including time and resource limitations; teamwork and communication; equipment location and storage; experience and learning; insufficient backup planning; and equipment preparation.[18] Developing robust protocols with good clinical governance and ongoing medical oversight will affect the ability of an EMS organization to deliver safe airway management reliably.[16] Focused team-based simulation training may have a role, particularly for adverse airway management scenarios that rarely occur in everyday practice.[19]