Aspects of airway management that may prove to be difficult include:
Ventilation
Laryngoscopy
Endotracheal tube placement
Laryngeal mask airway (LMA) placement
The most dangerous situation in airway management is the "cannot ventilate, cannot intubate" scenario.
Airway evaluation is important in predicting a difficult airway; most difficult or emergent airways are associated with preoperative anatomic or pathologic risk factors.
The ASA American Society of Anesthesiologists (ASA) Difficult Airway Algorithm provides a useful approach to difficult airway management in the event that laryngoscopy or ventilation becomes impossible (1).
Skilled help, alternative airway tools, and surgical airway equipment may be necessary to secure the airway.
Epidemiology
Incidence
Difficult mask ventilation occurs in 5% of the adult population.
Morbidity
Most adverse outcomes relating to airway management occur at the time of induction.
Mortality
30% of deaths attributed to anesthesia involve airway management.
Etiology/Risk Factors
Components of the airway evaluation that are associated with a difficult laryngoscopy include the following (2,3):
Mallampati score >2
Thyromental distance <6 cm
Mouth opening <4 cm
Limited neck mobility
Neck circumference >45 cm
Abnormal upper teeth
Obstructive sleep apnea
Large tongue
A history of difficult intubation makes repeat intubation very likely to be difficult.
Pathologic processes:
Distortion of the airway (submandibular abscess, anaphylaxis) may make visualization of the vocal cords difficult or impossible
Hoarseness may indicate a vocal cord lesion
The inability to breathe while lying flat may be the result of mass compression on the trachea or a bronchus, which could make ventilation difficult or impossible while under anesthesia
Anatomic defects found in some congenital syndromes are associated with a difficult airway. The conditions most characteristically associated with difficult airway management include Pierre Robin Syndrome, Treacher Collins Syndrome, Menkes Disease, and acromegaly.
Patients with Pierre Robin Syndrome have mandibular hypoplasia, micrognathia, cleft palate, and glossoptosis. Patients will occasionally have a cleft uvula, macroglossia, or laryngomalacia.
Treacher Collins Syndrome is associated with hypoplasia of the maxilla and mandible, micrognathia, and cleft palate. Airway management becomes more challenging as the patient ages.
Menkes Disease is a copper metabolism disease that results in micrognathia, poor bone strength, and easily damaged teeth.
Acromegaly is caused by excessive growth hormone, resulting in characteristic facies, macroglossia, prognathism, and hypertrophy of laryngeal soft tissue, the epiglottis, and the aryepiglottic folds.
External devices may make positioning for direct laryngoscopy difficult or impossible. The halo device is not only associated with difficult laryngoscopy, but also hinders LMA placement and seating.
Pregnancy Considerations
Pregnancy is associated with oropharyngeal edema, engorgement of vessels making bleeding more likely, a full stomach, and large breasts impeding direct laryngoscopy.
Physiology/Pathophysiology
In an anesthetized patient, oropharyngeal muscle tone is lost and the soft palate, epiglottis, and tongue can obstruct the airway. Positioning and the use of oropharyngeal or nasopharyngeal airways may assist in adequate mask ventilation of the anesthetized patient.
for direct visualization of the vocal cords to be possible, the tracheal and pharyngeal axes must be in-line. This is most often accomplished by placing the patient's head in the "sniffing position," a combination of flexion of the neck (usually accomplished by elevating the head) and extension of the head.
Care should be taken when positioning the obese patient. The use of a special ramp-shaped pillow or series of stacked sheets will bring the tracheal and pharyngeal axes in line. External landmarks that aid in this process are the external auditory meatus and sternum, which should be in a straight line parallel with the ground.
Prevantative Measures
To create an appropriate airway management plan, one must perform a detailed history, including prior difficult intubation, hoarseness, breathing difficulty, and obstructive sleep apnea. A thorough airway evaluation, including examination of relevant anatomy, will aid in the prediction of a difficult airway.
When a difficult airway is suspected, alternative airway tools and skilled assistants should be made readily available.
When adequate ventilation seems unlikely, an awake intubation with maintenance of spontaneous ventilation should be performed.
Awake intubation may be via the nasal or oral routes. It involves patient cooperation and local anesthesia of the airway, with or without intravenous sedation.
Diagnosis⬆⬇
A successful intubation is typically characterized by vocal cord visualization on laryngoscopy, a view of the endotracheal tube passing through the cords, condensation in the tube, bilateral breath sounds on auscultation, and confirmed end-tidal carbon dioxide. When the vocal cords are not visualized and the usual methods to confirm endotracheal intubation are not positive, the intubation is unsuccessful. A change in patient position or use of an alternative laryngoscopy blade may facilitate a repeat attempt at intubation. However, excessive repetitive attempts at laryngoscopy should be avoided to minimize airway trauma and edema.
When intubation fails, consider calling for help. Determine whether mask ventilation is possible by visualizing chest rise, end-tidal carbon dioxide, bilateral breath sounds, and maintenance of oxygen saturation.
If mask ventilation is adequate, continue on the non-emergency pathway of the ASA Difficult Airway Algorithm. Alternative airway equipment can be used to reattempt intubation. If intubation proves to be impossible, the patient can be awakened or a surgical airway can be performed.
If mask ventilation is impossible after failure to intubate, call for help and insert an LMA. If the LMA provides adequate ventilation, continue on the non-emergency pathway. If ventilation is still inadequate, follow the emergency pathway. This is a "cannot intubate, cannot ventilate" scenario.
When a "cannot intubate, cannot ventilate" situation arises, call for help. Attempt emergency noninvasive methods of ventilation, including transtracheal jet ventilation, Combitube, or rigid bronchoscope. If these methods are unsuccessful, perform a cricothyroidotomy or tracheostomy (4).
Differential Diagnosis
The absence of bilateral breath sounds could be caused by an esophageal intubation, pneumothorax, foreign body in the trachea or bronchus, large body habitus impeding auscultation, or mainstem intubation.
The absence of end-tidal carbon dioxide could be caused by esophageal intubation, low cardiac output, severe bronchospasm, kinking or dislodgement of the end-tidal carbon dioxide line, or machine failure.
Treatment⬆⬇
Optimize patient positioning with a shoulder roll or stacked sheets.
Attempt direct visualization with different blades. The Macintosh blade is useful for patients with an anterior airway. Because the Macintosh blade indirectly lifts the epiglottis and the Miller blade directly lifts it, the Miller blade is optimal for patients with a large epiglottis.
Supraglottic devices
The LMA is a supraglottic device that is inserted blindly. It is useful to facilitate ventilation in a "cannot ventilate, cannot intubate" situation. Many LMAs can also facilitate tracheal intubation (aperture is positioned over the glottic opening) via fiberoptic techniques (see below).
The Combitube is a double-lumen device that is inserted blindly into the trachea or esophagus, and can ventilate the trachea based on which balloon is inflated and which lumen is used for ventilation.
Fiberoptic bronchoscopy (FOB)
Awake FOB: The known or suspected difficult airway can be secured by performing an awake fiberoptic intubation. Spontaneous ventilation is maintained and topical anesthesia is applied to the oropharynx, hypopharynx, and larynx to blunt the response to airway instrumentation.
Asleep FOB: In patients where ventilation appears feasible, an asleep approach can be utilized.
The LMA-Aintree technique begins with insertion of the LMA and confirmation of ventilation. An Aintree Intubation Catheter (AIC) is fiberoptically guided through the LMA into the trachea. The LMA and fiberoptic scope are removed while the AIC is left in place. The endotracheal tube is passed over the AIC and the AIC is removed.
Bougie catheter: If the vocal cords are not visualized, a Bougie catheter may be placed into the trachea with laryngoscopy guidance or blindly. The tracheal rings can be felt and the endotracheal tube is then passed over the Bougie.
Video laryngoscopes include the CMAC and GlideScope. These devices provide a view of the vocal cords that may not be possible with direct laryngoscopy, especially in the anterior airway.
Surgical airway
A cricothyroidotomy can be performed by an experienced provider in less than a minute. It can provide a stable airway for 24 hours before being converted to a tracheostomy.
A tracheostomy is a surgical airway that takes longer to perform as compared with a cricothyroidotomy. Given its more inferior position, risks include damage to the recurrent laryngeal nerves, nearby vascular structures, and the thyroid gland.
Follow-Up⬆⬇
When a difficult intubation occurs, inform the patient in writing. Emphasize the importance of alerting the surgical and anesthesia teams for future procedures.
Document the details regarding the airway and how it was secured and maintain this information in the patient's medical record.
Closed Claims Data
The time periods 1985–1992 and 1993–1999 were most recently compared. Death/brain death occurred most often at the time of induction, but there was a decrease in the incidence at induction during the later time period. This improvement is likely a result of widespread adoption of the 1993 Difficult Airway Guidelines (5).
Claims during maintenance, extubation, and recovery remained the same for both time periods.
The odds of death/brain death increased with airway emergency and multiple attempts at laryngoscopy.
A delay in alternative emergency airway management or surgical airway placement led to worse outcomes.
Since 1993, the airway guidelines were used in 8% of cases to defend anesthetic care and in 3% of cases to criticize care.
References⬆⬇
American Society of Anesthesiologists. Practice guidelines for management of the difficult airway: An updated report by the American Society of Anesthesiologists Task force on Management of the Difficult Airway. Anesthesiology. 2003;98(5):1269–1277.
LangeronO, MassoE, HurauxC, et al.Prediction of difficult mask ventilation. Anesthesiology. 2000;92(5):1229–1236.
EzriT, GewurtzG, SesslerD, et al.Prediction of difficult laryngoscopy in obese patients by ultrasound quantification of anterior neck soft tissue. Anaesthesia. 2003;58(11):1111–1114.
BenumofJL, SchellerMS.The importance of transtracheal jet ventilation in the management of the difficult airway. Anesthesiology. 1989;71(5):769–778.
PetersonGN, DominoKB, CaplanRA, et al.Management of the difficult airway: A closed claims analysis. Anesthesiology. 2005;103(1):33–39.
A thorough history and physical exam prior to induction will help the anesthesia care team plan an appropriate airway management strategy.
When an airway cannot be easily secured, call for help early and follow the ASA Difficult Airway Algorithm. Avoid repetitive intubation attempts, which may cause airway trauma.