‘Difficult airway management is one of the most challenging tasks for anaesthesia care providers.’ (Carin A. Hagberg) 
In most cases where anaesthesia is required, mask ventilation, classic intubation and adequate oxygenation are easily established. However, management of the difficult airway is a challenge for the anaesthesiologist even if the problem of the difficult airway is anticipated and if not, it may turn out to be a threat . Hypoxia can lead to severe consequences and in worst cases to irreversible brain damage. Oxygen delivery requires an intact circulation and relies in particular on adequate ventilation and maintenance of a patent airway. The anaesthesiologist should therefore be trained properly to deal with ventilation and airway problems .
During the last decade many experts [3,4] in the field have set the trend towards a more realistic and practical approach of difficult airway management. In addition, the American Society of Anesthesiologists (ASA) published a report on practical guidelines for management of the difficult airway . The ASA difficult airway algorithm is most helpful in decision-making. The emergence on the market of a huge number of airway devices and techniques might cause confusion and become counterproductive if not categorized in a decision algorithm.
The most important factor in dictating success or failure in airway management is the anaesthesiologist. He or she should be familiar with a carefully composed array of airway instruments and should be able to select and use them appropriately. This means that a well-structured formal training programme in intubation and extubation techniques is needed, substantiating the view of Mason , who stated that: ‘Resuscitation training is already well established within hospitals. There is even more reason to provide similar facilities for airway management training.’
In 1996 a structured airway management training course was developed at the University Hospital of Groningen (The Netherlands) in close collaboration with colleagues of the University Hospital of Maastricht (The Netherlands). The training courses seem to have had a significant impact on clinical practice . Lecturers and trainers from adjacent specialities participate together in a multifaceted programme. Over the last 5 years approximately one-third of the anaesthesiologists and residents in anaesthesiology in the Netherlands have attended these courses, which may illustrate the need for training as experienced by the professionals. In addition co-operation with and therefore training of the anaesthetic nurse is essential; they have also been encouraged to attend. In general there are a well-selected, and thus restricted number of airway devices available for routine use. The armamentarium should depend on the characteristics of the patient population, the local circumstances and the experience of the anaesthesiologists. Skills as well as the budget available may be a limiting factor, influencing the choice of the equipment to deal with problems associated with the airway.
Some index numbers on airway management
Data from the Closed Claims Project of the ASA indicate that the most important source of anaesthesia-related injury is the occurrence of adverse respiratory events [2,8,9]. Three types of adverse respiratory events resulted in the majority of claims, i.e. inadequate ventilation (38%), oesophageal intubation (18%) and difficult intubation (17%). Three-quarters of these adverse events were judged to be preventable and could be attributed to substandard care. According to the literature difficult intubation will occur in 1–3% of patients and intubation will fail in 0.1–0.4% [10–12]. A ‘cannot intubate cannot ventilate’ situation will occur in about one in 10 000 patients. These numbers have been derived from data obtained from elective patients and should therefore be indicative only for patients undergoing this type of scheduled intervention.
Predicting and managing the difficult airway
The likelihood of the encountering a difficult airway should be investigated before any anaesthetic procedure by obtaining an airway history, examining the airway for specific physical signs and using particular diagnostic tests [13,14]. ‘Numerical’ physical features, measurements and scores have been advocated as useful tools in identifying an airway management problem, although none have been shown to be failsafe in predicting intubation failure [2,4,15].
Special emphasis must be placed on techniques for emergency situations outside the hospital [16–18]. However, basic strategies and techniques, such as rapid sequence induction and crash intubation, do not differ under these conditions.
One particular protocol for assessing difficult airway management is the LEMON law, which is applicable in emergencies. Ron M. Walls described the LEMON law in his book entitled Manual of Emergency Airway Management . This commonsense approach also seems useful outside the emergency department. The basic principals of the LEMON law are outlined in Table 1, and a more detailed description of its salient features is listed below.
Explanation of the LEMON law
Presence of a beard, a particular shape of the face, traumatic disruption of the lower part of the face or presence of buck or large teeth, a high-arching palate, a receding mandible or a short bull-neck, factors, which may make adequate mask seal and/or intubation difficult, should alert the clinician. Obesity may make both intubation and ventilation difficult.
Evaluation of the 3-3-2 rule.
The geometry of oral intubation requires alignment of the oral, the pharyngeal and the laryngeal axes to permit access to the trachea. The 3-3-2 rule evaluates these relationships. The first three items in the 3-3-2 rule mean that a three-fingers mouth opening may permit easy introduction and manipulation of a laryngoscope. The second three involve measurement of the space from the mentum to the hyoid bone. If three fingers can be placed this means that there are adequate mandibular dimensions to permit access to the airway. The two in the 3-3-2 rule means that two fingers can be placed between the thyroid notch and the floor of the mouth (i.e. the hyoid bone). This indicates that the larynx is sufficiently low-positioned within the neck to permit access by the oral route.TABLE
The Mallampati score may indicate whether the oral space is sufficient to accommodate and manipulate the laryngoscope and the endotracheal tube . In classes I and II intubation is expected to be reasonably easy, while in classes III and IV intubation is likely to be (very) difficult.
Obstruction of the upper airway will lead to difficulty both with ventilation and intubation. Hoarseness or stridor may indicate the presence of a tumour, an infectious process with oedema, a haematoma or a foreign body in the airway that may complicate the intubation. If the patient has a known laryngeal tumour, a known or suspected epiglottitis or a peritonsillar abscess, both laryngoscopy and (assisted) ventilation may be difficult.
An important factor in successful intubation is adequate positioning of the patient's head, and may play a crucial role in successful intubation. Neck mobility is reduced in the elderly, in patients with systemic arthritis or cervical-spine immobilization after trauma or in patients with Bechterew disease. It is important to test the mobility of the neck of the patient by asking to flex and extend the neck, starting from a neutral position while seated. The immobilized trauma patient will always present a difficult airway.
Heidegger and colleagues have described recently a simple, very successful, algorithm for tracheal intubation in clinical practice . The authors state that: ‘only methods that are practised daily can be used successfully in emergencies’. As a consequence, fibreoptic intubation is used frequently in their practice. We agree fully with Heidegger that fibreoptic intubation, in a well-prepared and locally anaesthetized patient, is in most cases the gold standard in a predicted difficult airway. Even in an unpredicted difficult airway, when oxygen saturation can be kept adequate and the operator is skilled, fibreoptic intubation can be very useful. However, fibreoptic intubation may be very difficult or impossible in trauma care or emergency situations. For this reason anaesthesiologists should be familiar with alternative approaches to secure the airway.
Explanation of instrument types and their indications
As stated earlier, the management of a difficult airway has benefited from the enormous number of new instruments and techniques that have been developed. The choice of instrument and technique employed should be based on the ASA recommendations, the patient population, and should also take into account the various parts of the airway: (a) supraglottic, (b) glottic, (c) infraglottic and (d) emergency situations. Details of the different types and the indications for which they are specified are listed below. The instruments selected for use in our institution are summarized in Table 3.
Multiple laryngoscope blades.
For laryngoscopy various instruments have been developed that differ basically in the shape (and length) of their blades. The Macintosh blade is useful in the case of space limitations such as occur in a small and narrow mouth opening and limited oropharyngeal space. The Miller blade in particular may be applied successfully in the case of a small mandibular space (anterior larynx), or the presence of large incisor teeth and/or a long floppy epiglottis, etc. A left-handed Macintosh blade can be used in patients with a large tumour or swelling at the right side of the tongue.
These are used for protection of the fibreoptic intubation scope in oral intubation.
The nasal airway might be helpful in mask ventilation in a patient with macroglossia or to accommodate oropharyngeal intubation in an anaesthetized patient spontaneously breathing through a nasal airway.
Gum elastic bougie.
The gum elastic bougie, or Eschmann stylet (adult and paediatric sizes), is the first choice of intubation aids particularly in patients with an anterior larynx and in those with limited mouth opening. The device can also be used for tube exchange or as an extubation tool.
Laryngeal mask airway.
The laryngeal mask airway (multiple sizes) is used widely in routine clinical practice as an airway or as a (fibreoptic bronchoscope) conduit for tracheal intubation. In our institution the laryngeal mask airway is the first intubation tool in an unanticipated difficult airway if the mouth opening is larger than 2 cm. If a sealed airway is necessary the intubating laryngeal mask airway (I-LMA™) is indicated. The patient can be intubated through the I-LMA™ with or without the fibreoptic bronchoscope [19–21]. The head of the patient must be maintained in a neutral position during insertion, which might be advantageous to patients with cervical spine injury.
Fibreoptic intubation bronchoscope (FOB).
The fibreoptic intubation bronchoscope (adult and paediatric sizes) is the instrument of choice if a difficult airway is predicted . In a ‘cannot intubate, can ventilate’ situation an endotracheal tube can be inserted with the fibreoptic bronchoscope, via the facemask, while using a mask-connector with a membrane (Mainzer-adapter). As described previously the FOB can be used to intubate the patient if a sealed airway is necessary via a laryngeal mask airway or an I-LMA™. One of the disadvantages of the fibreoptic intubation is that the technique is ‘partially blind’, i.e. that introduction of the fibrescope is performed by direct visualization of the anatomical structures. Advancement of the tube over the FOB, however, is not visualized directly, so a successful introduction of the FOB into the trachea does not necessarily mean that it will be followed by a successful introduction of the tube into the trachea. This means that in many cases one should preferably not anaesthetize the patient before the endotracheal tube is properly positioned.
Various tools may be helpful and cost-saving in FOB intubation. The so-called Mainzer adapter can be mounted on a facemask to allow FOB intubation via the nasal or oral route during mask breathing or ventilation. The Ovassapian airway may be used to facilitate oral FOB intubation. Finally, the Aintree intubation catheter (Cook Critical Care) can be used as a to guide to introduce the FOB and to exchange an LMA™ or a tracheal tube. The lumen of this catheter allows oxygen administration (Rapi-Fit® connector).
In skilled hands this instrument is useful in case of an unexpected difficult intubation, for example in obstetric patients when a secure airway is needed and mouth opening is small (< 2 cm), or slightly bigger than the tube diameter, to introduce a laryngeal mask airway. In emergency (trauma-care) situations with possible cervical-spine injury, when the head and neck must be fixed with a rigid neck collar, using this instrument can also be advantageous. The Trachlight® can also be applied if a Sellick manoeuvre has to be carried out. In small children there is little experience in emergency situations with the Trachlight®.
Indirect rigid laryngoscope.
The specially designed indirect rigid laryngoscope is used by the ENT-physician to intubate, e.g. in case of a narrowed glottic aperture (tumour), when the anaesthesiologist cannot introduce a tube alongside a laryngeal mass. A side port enables (jet) ventilation. This instrument should always be close at hand in cases of epiglottitis if classic intubation fails.
Emergency cricothyrotomy set.
In the case of an emergency, e.g. a ‘cannot intubate, cannot ventilate’ situation, when all appropriate intubation methods have failed, the Melker set (Cook Critical Care, two sizes), introduced through the cricothyroid membrane should be life-saving. All anaesthesiologists and anaesthesia residents are usually familiar with the Seldinger technique, therefore the Melker set should be preferred in anaesthetic practice.
Needle cricothyrotomy set.
The needle cricothyrotomy set should be used with a jet device only in the case of an emergency as a final solution. Experience in children is negligible.
When dealing with the airway, some essential rules must be obeyed:
- • Adequate oxygenation prior to any intubation is of major importance [23,24].
- • Consider the relative merits of preservation of spontaneous ventilation vs. the use of muscle relaxants in a patient with an anticipated difficult airway. Preferably the ‘respiratory bridge’ should be preserved by letting the patient breathe spontaneously.
- • Fibreoptic intubation (while maintaining spontaneous ventilation) is the gold standard in a predicted difficult airway.
- • In every anticipated difficult airway a surgical airway (tracheotomy) has to be considered. An experienced surgeon should perform this technique.
- • The laryngeal mask airway is the first instrument to be used in case of an unanticipated difficult airway; when repositioning and additive measures fail (different laryngoscope blades, sniffing position and adequate cricoid pressure), assuming that the mouth opening exceeds 2 cm (adequate cricoid pressure by OELM: optimal external laryngeal manipulation; pressing the thyroid cartilage (and hyoid and cricoid) in a posterior and cephalad direction. In other words, a ‘BURP-manoeuvre’: backward, upward and rightwards pressure .)
- • The Trachlight® is the first instrument to be used in case of an unanticipated difficult airway, when repositioning and additive measures fail (see above) when the mouth opening (>1 cm, or slightly bigger than the tube diameter) is limited and a sealed airway is obligatory.
- • Every difficult intubation needs also a carefully prepared extubation procedure.
- • The use of regional anaesthesia in a patient with a known difficult airway does not solve the airway problem.
Successful management of the difficult airway requires development of protocols, algorithms and a well-considered collection of airway instruments. The ASA has outlined excellent ‘basic’ algorithms and strategies for airway management awareness and recognition of the difficult airway. In the future a carefully designed training schedule should be developed for all anaesthetic personnel, so that all basic techniques and strategies should be used in elective cases to enable the anaesthesiologist to deal with airway problems. Airway management requires teamwork to ensure that in the most complex emergency situations even the most complex procedures can be carried out to secure the airway and so to save the patient's life.
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