Introduction
Difficult airway (DA) is a clinical situation where a conventionally trained anaesthesiologist encounters difficulty in different aspects of management of the airway which include mask ventilation, laryngoscopy, video laryngoscopy, insertion of supraglottic airway device (SAD) and endotracheal intubation. At the core of this whole range of issues lies the patient safety which depends on ensuring continuous oxygen supply and prevention of pulmonary aspiration of gastric contents. Step wise and systematic approach to difficult airway is essential to provide optimal management in patients with DA.
Some basics
- Difficult airway is a common term, the use which alone doesn’t describe neither the nature nor the details of the difficulty.
- Difficult airway can manifest in different forms and severity. Pathology/defect can be supraglottic or infraglottic.
- DA can be anticipated or unanticipated, surgery elective or emergency
- Presence of DA in a patient can be complicated by several other factors such as age, obesity, pregnancy, co morbidity ( ASA 3or more PS, bronchial asthma, poor respiratory function etc) and risk of aspiration .Presence of obstructive sleep apnoea(OSA) is an independent risk factor complicating DA management.
- Further, DA can be associated with obstructed or compromised airway, wherein the patient is already at risk of hypoxia and aspiration.
- Difficulty in mask ventilation (DMV), DA due to infra glottic pathology and the pathology obscuring the anterior part of neck represent potentially most dangerous situations.
- It is the failure to plan and prepare for different possible scenarios and complications which is most often responsible for airway disasters.
- A past history of normal airway management doesn’t rule out DA in subsequent general anaesthetics.
- Decision making, skills, anticipation and having a help are the important human aspects of DA management.
- Waking up and rescheduling are among the options to be kept in mind while managing DA.
- Extubation plan is as important as intubation in DA
Approach to difficult airway
A. Identify the presence of DA and its nature and severity
Presence of DA is suspected and confirmed by clinical assessment using appropriate history, clinical examination, relevant investigations and review of records. Different clinical criteria for assessment of DA include mouth opening, temporomandibular joint movement, modified Mallampati classification, Wilsons Criteria, Upper lip bite test, thyromental and sternomental distances, neck extension, neck circumference etc. A combination of different parameters and tests increases specificity and sensitivity compared to single test.
While a majority of difficult airway conditions are diagnosed relatively easily, more subtle forms may be missed unless carefully looked for History of snoring, strider, day time sleepiness, patient assuming specific positions for sleeping etc point to the possibility of underlying airway pathology.
Once a patient is diagnosed to have a DA, clinical features are analysed for
- Difficult mask ventilation: obesity, males, beard, edentulous, OSA, micrognathia, age more than 55years, previous surgery on mandible or maxilla, radiotherapy etc. A beard may be hiding the scar of previous surgery
- Difficult supraglottic airway insertion due to reduced mouth opening or intra oral pathology
- Difficult laryngoscopy, including video laryngoscopy (DL) and intubation (DI) :Mouth opening less than 3 fingers, Mallampati 3 and 4,Lehane and Cormack grade 3 and above, short neck, neck circumference more than 40cm in females and 43 cm in males are predictors of potential DL and DI.
- Difficulty in patient positioning: ankylosing spondylosis, severe rheumatoid disease, morbid obesity, trauma patients, restricted neck movement and cervical spine injury or disease cause problems in patient positioning and result in DMV, DL or DI.
- Difficulty in patient co operation: elderly, mentally challenged, emergency surgery, CNS disorders etc
- Difficulty in procedures in front of the neck i.e. altered or distorted anatomy of cricothyroid membrane. This precludes ability to perform the rescue procedures such as cricothyroidotomy, transtracheal jet ventilation or surgical tracheostomy.
- Risk of aspiration
B. Preparation and planning
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Patient preparation
- Discussion and counselling
- Anxiolysis with drugs like midazolam and dexmeditomedine
- Antisialogogue : Intramuscular glycopyrolate preferred
- Sedation, in patients without OSA or risk of aspiration. Key is to avoid polypharmacy, give the drug in titrated doses and to carefully monitor the patient
- Intravenous access
- Monitors : ECG, NIBP and SpO2
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Planning
There should be a primary plan and a backup plan for airway management in every patient with DA which should be based on the individual situation (see above). The plan should be as per the guidelines and include consideration for appropriate equipment, drugs, monitoring and help as required. Important is to have a plan for continuous oxygen administration irrespective of technique. Primary plan is the initial plan for achieving endotracheal intubation and involves direct laryngoscopy. In situations where endotracheal intubation is not absolutely necessary for the proposed surgery use of SAD can be considered if appropriate. Back up plan is the secondary or alternate plan to secure intubation which may involve use of SAD, airway adjuncts and aids and change in device, person or patient position.
In severe difficulty, a rescue plan also should be in place where in case of difficulty in oxygenation despite use of different techniques for intubation, SAD or mask ventilation, patient is at risk of developing hypoxia. The techniques for rescue are cricothyroidotomy, transtracheal jet ventilation and surgical airway.
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According to ASA guidelines (2007), consider the different options as follows
1) Awake techniques or Intubation after anaesthesia?
2) Non invasive or Invasive technique?
3) Video assisted laryngoscopy as in the initial choice?
4) Preservation or ablation of spontaneous ventilation?
Planning also should include consideration for appropriate equipment and availability of help[/su_note]
C. Execution: Different techniques
Awake techniques for endotracheal intubation
- A) Fibrotic guided nasotracheal intubation, considered as gold standard of DA management: useful in all anticipated difficult airway such as Ludwig’s angina, TMJ ankylosis, ankylosing spondylosis, cervical spine injury etc. Where DMV is anticipated or patient is at risk of aspiration or both. Patient cooperation, anaesthesiologist’s experience, appropriate equipment, preparation, dry airway (Antisialogogue), airway anaesthesia with or without sedation are keys to success. Any fibrotic assisted or guided technique should be attempted before other techniques. It is not ideal for emergency airway management except in expert’s hands. Secretions and blood are the important barriers for success.
- B) Retrograde intubation, suitable where fiberscope is not available or has failed and patients mouth opening is restricted. The technique is limited to elective situation and is safe, simple and inexpensive. Steps are
- C) Blind or auditory guided nasotracheal intubation: This is a safe technique requiring expertise and guided by constant listening of breath sounds. External manipulation of larynx is usually required and tube is passed into the trachea during maximum inspiration. Airway anaesthesia required. Indicated in patients with anticipated DA with restricted mouth opening.
- C) Intubation through SAD, most commonly LMA, after insertion of the same awake and subsequent induction of anaesthesia. Here, LMA or other SAD is introduced into the mouth under local anaesthesia and once it is in proper position, anaesthesia is induced with LMA as a ventilating device. Subsequently, intubation is performed through LMA.
- D) Surgical tracheostomy under local anaesthesia is performed when there is a significant distortion of airway is present along with difficult mask ventilation. It is also indicated if the patient has preoperative compromised airway, as indicated by strider. Common causes are growth at the laryngeal inlet, advanced malignancy of pharynx or larynx etc and airway trauma. Lastly, awake preoperative tracheostomy can be performed for complex craniofacial reconstruction procedures requiring post operative ventilation.
Airway anaesthesia
Anesthetizing the airway is crucial for success of airway techniques. Lignocaine is the most commonly used drug and the total dose should be less than 7mg/Kg The aim is to anesthetize supraglottic and infraglottic regions of the airway and tracheal mucus membrane by surface anaesthesia (nebulisation) or nerve blocks and transtracheal injection. Nerve blocks include superior laryngeal nerve block and glossopharyngeal nerve block (not very commonly used). In addition, lignocaine spray can be used for nasal mucosa and for the oral cavity..Airway blocks may increase risk of aspiration in a patient with full stomach.
Techniques for endotracheal intubation after induction of anaesthesia
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Indications and prerequisites
- Anticipated difficult airway without predictors of difficult mask ventilation
- Un-cooperative patient
- Adequate mouth opening
- Lack of risk of aspiration
- Adequate cardiopulmonary reserve
- Normal cervical spine
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Induction of anaesthesia abolishes protective reflexes which results in need for mask ventilation. To facilitate mask ventilation, use of oral or nasal airway may be required. If mouth opening is adequate, another option for managing DMV becomes available in terms of insertion of SAD. Intubation after induction of anaesthesia can be performed with or without muscle relaxant. Preserving spontaneous ventilation helps to wake up the patient faster should the decision be made, in case of failed intubation. However, intubation under spontaneous ventilation is technically more difficult and can precipitate coughing and bronchospasm. Muscle relaxant helps to prevent these problems and provides ideal intubating conditions. The risk of administration of relaxant is potential loss of airway and progress into “cannot intubate, cannot ventilate cannot oxygenate” scenario which can be rapidly fatal. Among the muscle relaxants, both succinyl choline and non depolarizing drugs like rocuronium or atracurium can be used depending on ability to mask ventilate.
Direct laryngoscopy with Macintosh blade is standard approach for endotracheal intubation. However, in anticipated DA, alternate blades and laryngoscopes, optical stylets and video laryngoscopes may be required. Video laryngoscope, when available, should be considered as initial technique for laryngoscopy in DA. Intubation aids such as Gum elastic bougie, airway exchange catheter, Aintree catheter etc should be available and the anaesthesiologist should be familiar with their use.
Another technique of intubation after induction of anaesthesia is through SAD where patient is ventilated initially with SAD. After adequate relaxation and/or depth of anaesthesia, intubation is performed through the LMA. Direct intubation is possible only through the intubating LMA, Air Q mask and Ambu Aura. For other SAD, alternate technique can be used where an AEC can be passed through the SAD followed by the removal of SAD and subsequent railroading of the endotracheal tube over AEC. This is indirect and twp stage technique.
Irrespective of the technique(s) chosen or the drugs used certain basic rules should be strictly adhered to in intubating a DA patient. They are
- Oxygenation takes priority over intubation. Patients with DA rarely die or develop hypoxic damage because they could not be intubated, but interruption of oxygen supply due to failure ventilate can kill a patient.
- Number of attempts should be limited to 3, at the most. Each subsequent attempt after the first, should consider changing the patient position, changing the blade or laryngoscope, using intubation aids or video laryngoscope and changing the person. Help should be called for at the earliest.
- Failure to plan for failure can lead to life threatening events.
- In a patient with DA, sometimes airway management can altogether be avoided, if the surgery can be safely under regional anaesthesia. Even then, plan and facilities for airway management should be kept ready.
Confirmation of endotracheal tube placement should be by clinical signs of bilateral and equal air entry and a normal capnographic wave form for more than 6 waves continuously. If further confirmation required, use of intubating fiberscope provides the definitive answer. In the absence of both fiberscope and ETCO2 monitoring, it’s safer to remove the endotracheal tube when in doubt. Hypoxia is a late sign in case of oesophageal intubation.
Extubation
Extubation in patients with DA should be an integral part of overall airway management. Occasionally, an airway which was normal before the surgery can become a difficult airway after the procedure, as in cases of extensive resection for head and neck malignancies. Decision has to be made regarding
a) immediate reversal and Extubation
b) delayed extubation in the recovery or postoperative ward with the patient spontaneously breathing after reversal
c) extubation in ICU after a period of ventilation in ICU
Details of the above are shown in the table
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| Extubation | Indication and Remarks |
| immediate | Awake patient, no airway edema, bleeding,Non airway surgery, hemodynamically stable,easy re intubation (if required)can be extubated over airway exchange catheter (AEC) |
| Delayed,spontaneously breathing,in recovery | Drowsy patient, but fully reversed, facial or intra oral oedema (facial osteotomy, posterior cranial fossa or prone position),prolonged surgery,re intubation likely to be difficult.Oxygen supplementation, sedation, steroids, watch for tube block. Use of AEC suggested during extubation |
| Extubation in ICU | Co existing injuries, need for prolonged ventilation, unstable patient, extensive resection of head and neck structures, need for re exploration |
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Before extubation, always ensure
- Complete reversal and recovery
- Inspection of the airway for bleeding and oedema
- Gentle and thorough suction
- Availability of airway exchange catheter
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A different approach to extubation involves removing the endotracheal tube in deep planes of anaesthesia and replacing it with a SAD which is kept in place till patient is fully awake. This may not be suitable for most of the DA situations.
Role of Supraglottic Airway Device
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SAD can be used as
- elective ventilation device
- elective intubating device
- emergency ventilating device
- rescue device and
- extubation device.[/su_note]
Most commonly used SAD is LMA. Selection is based on a) surgical procedure b) purpose of using LMA (intubation, ventilation, rescue etc) c) risk of aspiration d) need for positive pressure ventilation e) availability and f) familiarity. In general, SAD with gastric drainage channels is preferred for patients with full stomach and those in whom positive pressure ventilation is likely to be required.
Complications during difficult airway management
- DMV: Progressive difficulty varies from simple need for triple manoeuvre to inability to maintain oxygenation with optimal manoeuvres. Different techniques for management of DMV include jaw thrust, chin lift, head tilt, insertion of oral or nasal airway, two hand ventilation and two person ventilation. In two hand ventilation, anaesthesiologist’s both hands are used for optimal mask fit whereas second person assists in ventilation. In two person technique, the second person can provide additional chin lift as well. If DMV persists, insertion of SAD and/or paralysing the patient should be considered depending on the clinical situation. Consequences of DMV include gastric distension, hypoxia and risk of aspiration.
- Difficult laryngoscopy or intubation : Different options to manage DL and DI include a)VL as the first choice or after the first failed attempt with DL b) change in patient position ( Ramped position) c)Change in type of blade and laryngoscope d) use of optical stylets like Bonfills intubation scope d) use of intubation aids like bougie, AEC or Frova introducer.
- Failed intubation: if intubation is not possible within 3 attempts, further action should aim at preserving adequate ventilation. Use of SAD can be considered either for ventilation or for ventilation and subsequent intubation. If surgery is not urgent, waking up and rescheduling the surgery or surgery under regional anaesthesia should also be considered.
- “Cannot intubate cannot ventilate” situation: is usually preventable and is a result of multiple attempts or improper planning leading to wrong choice of techniques. The underlying mechanisms could be airway obstruction due to oedema or unrecognized infraglottic pathology. If the cause is suspected to be supraglottic, SAD may be life saving and if it is infraglottic, it is mandatory to go for rescue technique immediately.
Exit strategy
If endotracheal intubation fails in three attempts and patients oxygenation is stable, four options can be considered
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(Canadian Airway Focus Group guidelines)
- Wake up and reschedule the surgery
- Proceed with the surgery with a SAD or face mask. This is particularly relevant in trauma and obstetric patients
- Another attempt at intubation with a different person or equipment, if it is appropriate and
- establishing a surgical airway under stable conditions.[/su_note]
Role of guidelines and algorithms
Guidelines and algorithms help the anaesthesiologist to develop a proper plan which incorporates all possible scenarios in a given situation.
ASA guidelines, Anesthesiology, 118 No 2 Feb 2013.
It is an update over previous 2003 guidelines and includes definitions of components of DA. The guidelines are accompanied by recommendations. Guidelines are for 1) evaluation of airway with history, examination and additional evaluation. 2) Basic preparation foe DA management which includes discussion with the patient, proper equipment, help, preoxygenation and administration of supplemental oxygen throughout the airway management 3) Strategies for intubation ;awake intubation, video assisted laryngoscopy, intubating stylet or tube changers and SAD for ventilation or intubation 4) strategy for extubation of DA and 5) follow up care.
ASA guidelines do not focus on any patient subgroup nor include special recommendation for emergency surgery.
Difficult Airway Society UK has published guidelines for management of obstetric difficult airway, paediatric difficult airway, Fiberoptic guided intubation through SAD with Aintree catheter, extubation guidelines, guidelines for management of CICV, guidelines for rapid sequence intubation(RSI) and guidelines for default strategy for intubation.
Update on DAS guidelines 2015 has proposed following changes
Plan A is now Mask ventilation and intubation: includes a)Ramping position b) Videolaryngoscope and c) monitoring of neuromuscular blockade
Plan B is now Maintenance of oxygenation using 2 nd generation of SAD insertion of which is limited to 2 attempts
Plan C is now Pause and Think : about proceeding with Plan D below or return to face mask ventilation or wake up or continue surgery with SAD
Plan D Front of Neck Access : needle or surgical cricothyroidotomy or tracheostomy
Changes proposed for RSI include use of maintenance breaths during RSI, preference to rocuronium over succinylcholine, removal of cricoids pressure during SAD insertion and nasal oxygen supplementation
CAFG guidelines includes definitions of different components similar to ASA and provides guidelines to management of DMV, primary and alternate intubation strategies in different scenarios, exit strategies, confirmation of endotracheal tube and management of obstetric and pediatric airways.
Special situations
Trauma: Cervical spine injury and airway injury should be kept mind. The effect of co existing injuries also should be considered. Waking up the patient may not be a feasible exit strategy for failed intubation. Early surgical access can be considered in facial trauma or in severe injuries.
Obstetric patients: Changes in the airway during pregnancy and superimposed effect of pregnancy induced hypertension on the airway necessitate selection of equipment carefully and detailed planning of airway strategies. Failed intubation is more common. Early use of video laryngoscope may be considered. Intubation aids like bougie, or Aintree catheter can be very useful.RSI is routinely recommended and fetal conditions should be included in decision making. In addition, parturients can desaturate very rapidly and are prone for aspiration.
Obesity: Head up position during airway management facilitates mask ventilation, improves functional residual capacity and facilitates laryngoscopy and intubation. Associated OSA can complicate airway management. Front of the neck procedures may be technically difficult. Intubation aids can be very useful.
Summary
DA management is both an art and science. Though guidelines are available for different DA scenarios, importance of step wise approach with pre anaesthetic airway assessment, planning, proper execution and anticipation and management of complications cannot be underestimated.All DA management are prone for complications.
Facility for continuous oxygen supplementation, availability of help, proper equipment , decision making and prevention of CICV are important.