The difficult airway algorithm has been outlined by the American Society of Anesthesiology and provides a basic pathway for difficult intubation. It is vital that all practitioners who attempt intubation be familiar with the equipment and techniques necessary for a successful intubation. In the Closed Claims Analysis performed by the American Society of Anesthesiology, failed intubation remains a major cause of morbidity and mortality.
Evaluation of the airway for signs of potential difficulty should be performed as soon as possible on any patient in respiratory distress. A quick assessment of congenital or acquired anatomic defects should be performed initially. Particular attention should be paid to patients who have suffered facial, head, or neck trauma, or who have oral bleeding, regurgitated gastric contents, or frothing of the mouth.
In patients who are cooperative, a Mallampati evaluation should be performed. The practitioner asks the patient to open their mouth and views the oral cavity. This examination reveals the size of the tongue, adequacy of mouth opening, and condition and presence of the teeth and uvula. The more uvula that is visible behind the tongue, the easier the intubation should be. Externally, one should examine the thyromental distance. The closer the chin is to the chest wall with the head in mid-position, the more difficult the intubation may be. Similarly, a drastic overbite can cause difficulty with laryngoscope positioning. Neck trauma may result in the inability to move the head safely, and difficult intubation may be secondary to non-optimized positioning. In all patients with neck instability, in-line stabilization should be performed during every intubation attempt. Obesity can also contribute to a difficult airway. Redundant skin folds in the buccal cavity, and increased fatty tissue around the posterior pharynx can make visualization of the vocal cords difficult. However, even with a careful assessment of these findings, occasionally, patients will be surprisingly difficult.
The indications for intubation are respiratory distress and moderate to deep sedation required for a procedure.
A patient with a difficult airway does not preclude any procedures which are medically necessary. Obviously, any patient in respiratory distress must be intubated to ensure adequate oxygenation. It is prudent to allow the most experienced personnel present to manage the suspected difficult airway.
The standard equipment required for any intubation should be available. These include a self-inflating bag with attached mask, an oxygen source, a laryngoscope and blade, a properly sized endotracheal tube, end-tidal carbon dioxide measurement device, a suction, a ventilator for post-intubation, and standard induction medications. Having both propofol and etomidate available for induction is useful. Succinylcholine, rocuronium, and cisatracurium should also be available for paralysis.
Additional equipment necessary for intubating a difficult airway should be located at the bedside as well. This equipment will be dictated by the clinician who is performing the procedure and what is available. It is prudent to have a 'Difficult Airway Cart' in any unit where intubations are frequently performed (i.e., emergency room [ER], intensive care unit [ICU], operating room [OR]). Options include a video laryngoscope, Combitube, intubating Laryngeal Mask Airway, intubating stylet, fiber-optic bronchoscope, assorted laryngoscope blades (i.e., Miller and Macintosh), and an articulating laryngoscope.
The personnel necessary include the proceduralist, a respiratory tech, and a nurse. In the case of a suspected difficult airway, it is vital that an anesthesiologist or nurse anesthetist be consulted early.
As for any procedure, the patient should be prepared adequately. The first step is to have the patient positioned ideally on the bed. The body should be located just at the head of the bed so that the occiput is supported on edge. The head is placed in neutral alignment with the vertebral axis and, if the cervical spine is stable, the head is slightly extended to achieve the so-called 'sniffing' position. The bed is then raised or lowered to the proper height required by the proceduralist.
If time allows, denitrogenation of the lungs should be performed. This is accomplished with 100% oxygen via a facemask for 5 minutes before administration of an induction dose of either propofol or etomidate. This will allow apneic ventilation of the patient during a potentially prolonged intubation attempt. Other than for patients with mechanical obstruction of the trachea, this step should be performed before any intubation. Patients who are obtunded should be mask ventilated with 100% oxygen before any intubation attempt to achieve the same denitrogenation. In the obtunded patient, it should be confirmed before mask ventilation that no obstruction is present, and the mouth and posterior pharynx can be examined and suctioned to accomplish this.
All required equipment should be immediately available at the bedside, and all necessary medications should be drawn up in syringes. Reliable intravenous access should be confirmed.
Distinguishing difficult intubation from difficult ventilation is important. If the patient is difficult to intubate, adequacy of bag-mask ventilation becomes paramount, especially if the patient is already paralyzed or not breathing on their own. This technique requires a mask attached to a self-inflating bag with an oxygen source. The bag is placed over the nose and mouth, and the non-dominant hand is used to create a seal with the face and provide chin lift. The thumb and forefinger are used to seal the mask to the face. The other three fingers should be positioned on the bone, with the fifth finger under the angle of the mandible providing lift. It is vital that the fingers do not press in on the soft tissue under the chin as this can easily occlude the airway. The dominant hand is used to squeeze the bag and provide positive pressure ventilation. In some cases, both hands must be used to provide an adequate seal on the mask and to provide enough chin lift. A second person is then required to squeeze the bag. This tends to be more common in patients with large heads or edentulous patients who don't have internal support for the buccal skin which allows air to escape. A skilled practitioner can support a patient for prolonged periods of time with bag-mask ventilation alone. If the unanticipated difficult airway arises, bag-mask ventilation can provide a bridge to the patient while equipment is retrieved or more skilled hands arrive for intubation.
Practitioners who are not regularly performing intubations should not attempt a difficult airway unless it is an emergency. Failed intubation attempts lead to increased intragastric air, trauma to the posterior pharynx, increased blood and secretions in the airway, and edema to the subglottic structures which can make subsequent intubation impossible and completely obstruct the airway. In this instance, a surgical airway must be obtained immediately.
After a difficult airway is identified, one needs to determine what equipment is available to make informed decisions about how to proceed. Preferably, this is done before there is an immediate threat of desaturation. For each practitioner, the difficult airway tools used will be those which they are most familiar with and have achieved the best results with anecdotally. The options include the intubating laryngeal mask airway, fiberoptic bronchoscope, intubating stylet, articulating laryngoscope, video laryngoscope, and cricothyrotomy.
If the patient is breathing on their own, consideration should be made to holding off on the administration of neuromuscular blocking drugs. Often, in traumatic airways, the only way to identify the tracheal opening is to watch the subglottic area for spontaneous respiration. In elective intubations, the patient with a history of difficult intubation can be intubated awake. The airway is prepped with nebulized viscous lidocaine 4% 10 cc to 15 cc for 15 minutes to achieve topicalization of the buccal, subglottic structures and trachea. A fiber-optic bronchoscope with a preloaded endotracheal tube is introduced through the nares, which leads to a less acute angle on approaching the vocal cords. The vocal cords are identified, and the scope is passed through the true cords. After visualization of the tracheal rings, an endotracheal tube is passed over the bronchoscope, and position is confirmed through direct visualization. The bronchoscope is removed, and the patient is sedated immediately and ventilated. Fiberoptic bronchoscopy has the disadvantages of being operator dependent, and considerable experience is necessary. It can also be difficult to visualize laryngeal structures when the airway is bloody or full of secretions since the aspiration port on the scope is small, and it can be difficult to suction large volumes or thick mucus.
In an emergency situation, the patient should have the buccal cavity suctioned completely, and bag-mask ventilation should be attempted. If bag-mask ventilation is successful, direct laryngoscopy can be performed. If direct laryngoscopy fails because the vocal cords cannot be visualized due to an anterior larynx, an articulating laryngoscope blade may provide a better view. This blade has a lever attached to the tip which allows the tip greater range of anterior motion, thus elevating the epiglottis and allowing visualization of the vocal cords. If direct laryngoscopy fails, a glidescope may make the visualization of the cords easier. The endotracheal tube can then be placed under direct video guidance using the specialized, rigid stylet. If a glidescope is not available, placement of an intubating LMA may be done. This device is placed in the posterior pharynx, and the patient can be ventilated through the device. It should be noted that LMAs do not protect the airway from large volume aspiration and are easily displaced by struggling patients or inadvertently by healthcare personnel. The iLMA is designed to accept a specific endotracheal tube that should be kept in the same package which passes through the LMA and may blindly enter the trachea based on the appropriate positioning of the tip of the device in the esophagus. The Combitube functions similarly to this in that it is placed blindly. The tip is placed into the esophagus, and the distal balloon inflated, sealing the esophagus. A proximal balloon is then inflated, and the result is the lumen of the ventilatory circuit isolated around the larynx. Positive pressure can then be applied to ventilate the patient. This device also is easily displaced, and other difficulties with cuff pressures can disrupt the mucosal membranes in which they come into contact. A Combitube should not be considered a long-term solution; it does not protect from aspiration.
Another option is the intubating stylet. This small diameter plastic tube is hollow and has an adapter that allows ventilation. The benefit to this device is that it is more flexible than an ETT and can be passed through small openings when tracheal intubation is impossible with a regular ETT. It can also accept a pre-applied curvature to allow access to an anterior vocal cord position. A standard ETT can be passed over the intubating stylet if long-term ventilation is necessary.
If all else fails, and the patient cannot be ventilated or intubated, a surgical airway is necessary. If a potentially difficult airway is identified, a surgeon should be made aware early. There are also kits available using a Seldinger technique, with a needle inserted through the cricothyroid membrane. On successful aspiration of air, a wire is passed into the trachea, and the needle removed. A small incision is made in the skin, and a dilator is passed over the wire. This should produce a large air leak on positive ventilation, confirming the placement. Then a cricothyrotomy tube is passed through the opening and the patient ventilated. Proper placement of an airway device should always be confirmed with an end-tidal carbon dioxide (CO2) device immediately, and radiographically later to document the placement of the tube tip proximal to the carina.
The most common complication of endotracheal intubation is esophageal intubation. This may present in a delayed fashion if adequate pre-oxygenation is performed. It can be difficult in obese patients to recognize distension of the abdomen from gastric expansion and initial end-tidal CO2 monitors may show a color change or some quantitative end-tidal CO2. Auscultation of breath sounds is notoriously ineffective in definitively determining esophageal intubation due to the proximity of the stomach to the diaphragm. The obvious sign then becomes desaturation despite the external appearance of adequate ventilation. In this case, the endotracheal tube should be removed immediately and mask ventilation resumed to provide oxygenation. It may be necessary to decompress the abdomen to allow effective mask ventilation.
Placing the endotracheal tube too deep may lead to single lung ventilation. Most often, because of the anatomical angle that the right mainstem bronchus comes off the trachea, the right mainstem bronchus is most often where a deep intubation occurs. Auscultation of right-sided breath sounds and absent left sided sounds can confirm this. It may also become evident when the post-intubation chest x-ray is examined. The ETT may be pulled back carefully until bilateral breath sounds are auscultated and another chest x-ray can be performed to confirm placement in the trachea, ideally 2 cm to 3 cm above the carina.
Displaced vocal cords are another complication, especially in difficult patients. The presence of a displaced vocal cord may not be apparent until extubation. The patient may have persistent hoarseness, stridor, or fail extubation completely due to airway obstruction. This occurs if the ETT lumen catches on an arytenoid and the tube is forced. An ETT which does not pass easily should never be forced into the trachea. Consultation with otolaryngology should be sought immediately if this is identified.
As with any intubation, there is always a risk to the teeth. Care needs to be taken that proper laryngoscope technique is used and the top of the blade does not break a tooth. The fragments may be aspirated, and bronchoscopy is then necessary to retrieve them. Extremely loose teeth should be removed before intubation to avoid this complication. Poor dentition is also a harbor for pathogenic bacteria, and significant pneumonia may arise from aspiration of bacteria or obstruction to the airways.
Other less common complications can arise, such as mediastinal intubation, tracheoesophageal fistula, and tracheal stenosis. The endotracheal tube should never be forced if resistance is felt once the tube passes below the cords. If the tube meets resistance that cannot be overcome with rotation, consideration should be made to using a smaller ETT size.
A difficult airway can become a life-threatening condition very quickly if care is not taken to identify and prepare for this eventuality properly. All practitioners responsible for intubating patients should be familiar with three or four of the above techniques. If the primary attempt at intubation fails, a clear plan that addresses the reason for failure should exist for subsequent attempts. Few medical emergencies will result in death faster than the inability to oxygenate a patient.
In summary, many airway devices exist to assist in the successful management of the difficult airway. Proper identification is paramount to avoiding an airway disaster, and the feared "cannot intubate, cannot ventilate" scenario. Any difficult airway should be left to the best-trained personnel available. Each practitioner should have a number of intubation techniques and tools with which they are most comfortable with and know when to call for help. When a difficult airway is encountered, healthcare workers should refrain from repeated attempts at intubation, but instead call the anesthesiologist.