Definition of airway management

Airway management may be defined as the provision of a free and clear passageway for airflow. Obstruction of the airway may be partial or complete and may occur at any level from the nose to the trachea. In the unconscious patient, the most common site of airway obstruction is at the level of the pharynx² and this obstruction has usually been attributed to posterior displacement of the tongue caused by reduced muscle tone. However, the cause of airway obstruction is often the soft palate and the epiglottis rather than the tongue.^3,4 Obstruction may also be caused by vomit or blood, swelling of the airway (e.g. anaphylaxis), a foreign body, or laryngeal spasm.

Concept of a stepwise approach

Basic anatomy of the airway

See Figure 1.1.

Safe airway management requires sound knowledge of the relevant anatomy. This section provides an overview of the nose, pharynx, larynx, trachea and main bronchi; the practitioner is advised to refer to an appropriate anatomy text book for a deeper description of the airway.

Nose

The nose can be divided into external and internal portions. The external portion provides a supporting structure of bone and cartilage for the overlying muscle and skin; it is lined with a mucous membrane. The bony framework of the external nose is formed by the frontal bone, nasal bones and maxillae.

The internal portion lies inferior to the nasal bone and superior to the mouth and contains both muscle and a mucous membrane. It is worth remembering that the internal nares extend in an anterior-posterior direction, especially when inserting a nasopharyngeal airway.

Mouth

The mouth is not strictly a part of the airway, but as many airway management interventions involve the mouth, it is worth reviewing basic anatomy. The mouth is formed by the cheeks, hard and soft palates, and the tongue.⁵ The lips surround the opening to the mouth and each lip is attached to its respective gum by the labial frenulum. The vestibule is the space between the cheeks or lips, and the teeth. The roof is formed by the hard and soft palates, whilst the tongue dominates the floor. The anterior portion of the tongue is free but connected to the underlying epithelium by the lingual frenulum. The border between the mouth and the oropharynx extends from the dangling uvula to the base of the tongue.⁶

Figure 1.1 Lateral wall of nasal cavity. Reproduced from Faiz, O. and Moffat, D. Anatomy at a Glance, 2nd edn, copyright 2006, with permission of Blackwell Publishing.

Pharynx

The pharynx is divided into three anatomical sections; the nasopharynx (extending from the internal nares to the posterior edge of the soft palate), the oropharynx (extending to the base of the tongue at the level of the hyoid bone) and the laryngopharynx (extending to the opening of the oesophagus).

Larynx

See Figures 1.2 and 1.3.

This is a very important structure in terms of airway management and it is essential to know the anatomy in depth. Basic anatomy is outlined here but it is recommended that revision should be undertaken with an appropriate anatomy text (see reference 5).

Figure 1.2 Cartilages of the larynx. Reproduced from Faiz, O. and Moffat, D. Anatomy at a Glance, 2nd edn, copyright 2006, with permission of Blackwell Publishing.

Figure 1.3 Larynx as viewed through a laryngoscope. Reproduced from Faiz, O. and Moffat, D. Anatomy at a Glance, 2nd edn, copyright 2006, with permission of Blackwell Publishing.

The larynx consists of nine cartilages; three paired and three single, as described below.

The epiglottis projects above the glottis and protects the larynx during swallowing. The thyroid cartilage forms most of the anterior and lateral surfaces of the larynx and tends to be more prominent in men. The cricoid cartilage is the ring-shaped cartilage that connects the larynx to the trachea. The three paired cartilages are found within the interior structure of the larynx and are the arytenoids, corniculate and cuneiform cartilages.

Trachea

See Figure 1.4.

The trachea is approximately 11–12 cm long and 2.5 cm in diameter. It is held open by ‘C’ shape cartilage, which is open posteriorly to allow for extension of the oesophagus during swallowing. The trachea bifurcates into the left and right main bronchi around the level of the 5th thoracic vertebra. The right main bronchus is larger in diameter than the left and extends at a steeper angle – an endotracheal tube that has been inserted too far is most likely to locate itself in the right side, as are foreign body obstructions.

Figure 1.4 Trachea and main bronchi. Reproduced from Faiz, O. and Moffat, D., Anatomy at a Glance 2nd edn, copyright 2006, with permission of Blackwell Publishing.

Basic airway management manoeuvres

This manoeuvre has been the mainstay of basic airway management for nearly 50 years with few changes advocated since the early 1960s. The rescuer’s hand is placed on the patient’s forehead and the head gently tilted back; the fingertips of the other hand are placed under the point of the patient’s chin, which is gently lifted to stretch the anterior neck structures (Figure 1.5).

Jaw thrust

The jaw thrust is recommended where there is a risk of cervical spine injury but it may be used electively on any patient. Where there is no risk of spinal injury, the manoeuvre may be applied on its own or in conjunction with a head tilt manoeuvre.

The jaw thrust brings the mandible forwards and relieves obstruction by the soft palate and epiglottis. The practitioner places their index and other fingers behind the angle of the mandible and their thumbs on the mandible itself (Figure 1.6). The thumbs gently open the mouth whilst the fingers are used to apply pressure upwards and forwards. This movement causes the condyles of the mandible to sublux anteriorly in the temporomandibular joints. This displaces the mandible and tongue anteriorly, thereby clearing the airway.⁷

Figure 1.5 Head-tilt, chin-lift.

Figure 1.6 Jaw thrust.

Basic airway adjuncts

See Figure 1.7.

The nasopharyngeal airway (NPA) is a simple airway adjunct that is used by a number of different healthcare disciplines. It has advantages over the oropharyngeal airway (OPA) in that it can be used in the presence of trismus, an intact gag reflex, or oral trauma.⁸ Despite these advantages, the NPA is used less frequently than the OPA.^9,10

Figure 1.7 Nasopharyngeal airways.

Figure 1.8 Bevel of NPA against the septum.

The NPA is designed to relieve soft tissue upper airway obstruction in a patient requiring airway support. The tube follows the natural curvature of the nasopharynx and extends to the posterior pharynx below the base of the tongue where it separates the soft palate from the pharynx. The distal end is bevelled to facilitate placing of the tube; the bevel should be placed against the nasal septum (Figure 1.8).

Sizing of an NPA

Traditional methods of sizing have tended to compare the NPA with the patients little finger or the size of their external nares; these methods are based on anecdote rather than evidence and are likely to be flawed. Both methods place emphasis on the diameter of the tube rather than the length despite an earlier study clearly showing that the length of the tube was more important than the diameter.¹¹ This study suggested that the tube should lie within 1 cm of the epiglottis. If too short the airway would not separate the soft palate from the posterior wall of the pharynx and if too long would enter either the larynx and stimulate laryngeal reflexes, or enter the vallecula with the inherent risk of obstructing the airway.

One small study has shown that neither of the traditional methods for measuring the NPA correlated with the nasal anatomy of the subject, so are unreliable.¹² A clear correlation between patient height and their nares-epiglottis length has been demonstrated¹¹ so it is perhaps more sensible to base NPA size on the patient’s height and sex. In the absence of a more accurate measurement, it is recommended that a size 6 (130 mm length) be used for an average female and a size 7 (150 mm length) for an average male.^8,12 Longer or shorter lengths may be considered for patients who are taller or shorter than average.

Once the initial choice has been made the NPA should be measured to ensure that only the correct length is inserted. A reasonable way of ascertaining this is to measure from the tip of the nose to the tragus of the ear. There is sufficient anatomical correlation for this to prove reliable although checks to ensure correct placement should be undertaken afterwards. When the length has been ascertained, the safety pin should be inserted into the proximal end of the NPA at the maximum point of insertion; this will prevent the NPA from being inserted too far into the pharynx and possibly into the oesophagus. For example, if a size 7 (150 mm) had been selected and the measure from the tip of the nose to the tragus was 145 mm, the pin should be placed 5 mm distal to the flange of the NPA. The safety pin is not there to prevent loss of the NPA into the external nares. When inserting the safety pin, place to the side of the NPA to allow free passage for suction catheters if required.

Contraindications

A commonly taught contraindication to the use of an NPA is a potential or known basal skull fracture. Two published case reports of an NPA being inserted through a fractured cribriform plate into the cranial vault^13,14 may have been responsible for the development of this contraindication and it has been propagated by the Advanced Trauma Life Support Manual and courses. It is difficult to know whether these were isolated occurrences or whether further reports are less likely as it is no longer a novel complication, plus there may be a tendency to under report clinical errors.¹⁵ The consensus appears to be that NPA placement may be necessary, even where relative contraindications exist, to avoid sub-standard airway management in patients with suspected or apparent base of skull fracture.

Complications

The most common complication is bleeding, which may cause serious airway obstruction if not managed. Blood tends to coagulate in the trachea and will form a solid occlusion to the passage of air. Patient positioning may help if bleeding does occur and suctioning will also be of benefit, although it is possible that suctioning may not be sufficient to maintain a clear airway.

If the bleeding is in the anterior portion of the nose, consider use of a tampon to stem the flow. If in the posterior portion of the nose, it may be necessary to insert a device such as a urinary catheter so that the balloon can be inflated to prevent aspiration of blood. Any practitioner who inserts an NPA must have a contingency plan for managing haemorrhage should it occur.

Necrosis of the anterior aspect of the nose may also occur if the diameter of the NPA is too large. If there is evidence of blanching around the external nares the NPA should be removed and a smaller one inserted. Necrosis will commence within about 20 minutes of the occlusion of blood supply and it is very difficult to cosmetically alter any damage.

Equipment required

• Range of nasopharyngeal airways
  
• Water-based lubricant
  
• Devices to arrest haemorrhage in both anterior and posterior portion of nose should it occur.

Technique for insertion

Oropharyngeal airway

See Figure 1.9.

Oropharyngeal airways (OPA) are available in sizes suitable for neonate (00) to large adult (4). It is a curved plastic device designed to follow the curvature of the palate. It works to keep the tongue away from the posterior pharynx and to separate the soft palate from the pharyngeal wall. The OPA is designed to be used in unconscious patients requiring airway support and should only be inserted in those patients who have absent laryngeal and glossopharyngeal reflexes.¹⁶ Use of an OPA in patients with these reflexes intact may cause vomiting or laryngospasm.

The oropharyngeal airway can become obstructed at three possible sites:¹⁷ part of the tongue can occlude the end of the airway; the airway can lodge in the vallecula; and the airway can be obstructed by the epiglottis.

Sizing of an OPA

There is little evidence to support or contradict the traditional methods of sizing an OPA. Current teaching suggests that the length of the OPA should correspond with the vertical distance between the patient’s incisors and the angle of the jaw (Figure 1.10).¹⁶ This measurement is achieved by placing the flange of the OPA against the patient’s cheek, parallel to the front of the incisors and viewing the tip at the angle of the jaw.¹⁸ If the airway is too long it may occlude the airway by locating within the vallecula and displacing the epiglottis; if too short it will not separate the soft palate or tongue from the posterior wall of the pharynx.

Figure 1.9 Oropharyngeal airways.

Figure 1.10 Measuring an OP airway.

Contraindications

The OPA should not be used in any patient with an intact gag reflex.

Equipment required

Range of oropharyngeal airways.

Techniques for insertion

See also Figures 1.11–1.14.

In small children the above technique should not be used due to the friable nature of the hard palate. Instead a tongue depressor should be employed and the OPA should be inserted ‘right side up’ with the tip pointing towards the tongue rather than the roof of the mouth.¹⁹ This technique may also be utilised for adult patients where a tongue depressor is available.¹⁸

Figure 1.11 Insertion of an OPA.

Figure 1.12 Insertion of an OPA.

Figure 1.13 Insertion of an OPA.

Figure 1.14 Insertion of an OPA.

Advanced airway adjuncts and cricothyroidotomy

See Figure 1.15.

The laryngeal mask airway (LMA) comprises a wide-bore tube with an elliptical inflatable cuff designed to seal around the laryngeal inlet.¹⁶ The proximal end of the tube is fitted with a standard 15/22 mm connector. The LMA can be placed blind, requires less skill and is easier to insert than a tracheal tube.^20–26 The LMA provides for more efficient ventilation than with a bag-valve-mask (BVM) alone,²⁷ and when an LMA can be inserted without delay, it is recommended that bag-mask ventilation be avoided altogether.¹⁶

Figure 1.15 Laryngeal mask airway.

The LMA has been studied during cardiopulmonary resuscitation (CPR) but no studies have made a direct comparison with endotracheal intubation. The literature suggests that during CPR successful ventilation is achieved with an LMA in 72–98% of cases^28–34 and there is a reduction in the number of cases of regurgitation.³⁵ The perceived disadvantages of the LMA over endotracheal intubation surround the increased risk of aspiration and the inability to provide adequate ventilation for those with low lung or chest compliance.¹⁶ There is currently no evidence demonstrating whether it is possible to perform continuous chest compressions with an LMA in situ; this may be one of the main benefits of endotracheal intubation.

A case series suggests that the LMA may have a use in the prehospital management of critically ill patients with inaccessible airways following trauma,³⁶ a contention supported by a manikin-based study comparing LMA with endotracheal intubation or Combitube in a simulation of restricted access to the patient’s airway.³⁷ Times to ventilation with the LMA were much more rapid than with either of the other options but further research is required before a categorical recommendation can be made. Given the current level of evidence it is reasonable to suggest that where basic airway adjuncts do not provide the level of airway support required and endotracheal intubation is constrained by poor access to the patient’s airway, the LMA should be considered as an alternative.

There are significant concerns regarding the intubation success of paramedics (mainly from literature in the USA [see later in this chapter]) and the LMA may be a reasonable alternative where endotracheal intubation has failed, or electively as part of a stepwise approach to airway management.

Sizing of a laryngeal mask airway

Sizing of the LMA is based upon the weight of the patient and this information can normally be found on the sterile packet and the LMA device itself. Table 1.1 gives typical ranges, but these values may change depending upon the brand of LMA used.

Contraindications

The LMA cannot be used in a patient with an intact gag reflex.

As the LMA is less effective at preventing aspiration, consideration needs to be given to alternative methods in patients at higher risk of regurgitation; for example, patients who are pregnant or who have a hiatus hernia.³⁸

Table 1.1 Typical values for LMA

Equipment required

• LMA – range of sizes
  
• 50 mL syringe
  
• Tie
  
• Lubrication
  
• Stethoscope.

Procedure

Note: this describes the ‘classic’ technique; modified techniques exist for specific situations and LMA devices.

Complications

Complications from LMA use can be categorised into mechanical, traumatic and pathophysiological.⁴⁰ Mechanical complications relate to the technical performance as an airway device and include failed insertion (0.3–4%), ineffective seal (>5%), and malposition (20–35%).⁴⁰ Traumatic complications relate to local tissue damage and include sore throat (10% with ranges between 0–70%), dysphagia (4–24%), and dysarthria (4–47%).⁴⁰ Pathophysiological complications relate to the LMA’s effects on the body and include coughing (<2%), vomiting (0.02–5%) detectable regurgitation (0–80%), and clinical regurgitation (0.1%).⁴⁰

There is little evidence available from prehospital studies so the figures presented above are derived largely from studies in the operating department. It has been stated that prehospital LMA success rates are lower than those seen in the hospital cardiac arrest or elective surgical patient but the data are old and may not reflect current trends.⁴¹

An incident of gastric rupture associated with paramedic use of the LMA during CPR has been reported although there appears to be only one published report of such an occurrence;⁴² healthcare professionals should not discount the use of the LMA on the basis of one case report.

Endotracheal intubation

Endotracheal intubation (ETI) is considered to be the ‘gold standard’ of airway management⁴³ and involves the introduction of a cuff-sealed tube into the trachea. The cuffed tube seals the trachea up to peak pressures of approximately 50 mbar and prevents aspiration of solid or liquid foreign material.⁴⁴ Endotracheal intubation confers numerous advantages over the bag-valve-mask:⁴⁴

• Secure ventilation with patient-adjusted airway pressures
  
• Optimum protection against aspiration
  
• Option of administering medication (e.g. epinephrine, lidocaine, atropine, naloxone)
  
• Bronchial suction.

The indications for prehospital ETI may be dependent upon the availability of sedatives or neuromuscular-blocking agents to facilitate endotracheal intubation; without pharmacological adjuncts, the practitioner may be unable to intubate unless the patient has a severely reduced level of consciousness.

There are numerous concerns surrounding out-of-hospital intubation by paramedics as studies evaluating either survival or neurological outcome following out-of-hospital ETI have failed to show any significant benefits.^45–59 It is acknowledged that there are weaknesses in many of these studies in that they were mainly retrospective analyses of trauma patients involving a single centre or countrywide trauma register. Studies tended to evaluate survival to discharge only rather than long-term follow-up, and often inferred neurological outcome based on discharge destination, e.g. to home, to rehabilitation centre; none used formal neurological scales to measure outcomes. Not all studies took into account the confounding factors that may have affected patient outcome, which is a major factor in retrospective studies, and some did not adjust outcomes for severity of injury or illness.

Although there are inherent weaknesses in the studies, it has to be recognised that multiple studies have arrived at similar conclusions.

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