How to handle the difficult airway, part 1
How to handle the difficult airway, part 1
Airway management is one of the most crucial skill sets needed in the care of critically ill patients and of those requiring surgery. The timely and definitive approach to airway management leaves little margin for error. Indeed, the price of failure includes hypoxic brain injury and death.
One study estimated that 30% of deaths attributable to anesthesia are caused by the inability to successfully manage the difficult airway.1 Fortunately, the incidence of this problem is relatively low. Various studies have demonstrated the incidence of significant complications to be 0.05% to 0.4% in the more controlled setting of the operating room and 6% in the more chaotic setting of the emergency department.2-7
There are many underlying causes of difficult airway management, including facial deformity, cervical spine injury, airway hemorrhage, and uncooperativeness or combativeness on the part of the patient.8 To minimize the risks of poor outcomes, astute physicians must recognize the potential for difficulty and have an array of options for intervention.
In part 1 of this article, we will address factors that help clinicians predict difficult airway situations. We also will discuss management techniques, such as bag-valve mask ventilation, direct laryngoscopy, and use of light wands. In a coming issue of The Journal of Respiratory Diseases, we will continue our discussion of management techniques, including laryngeal mask airways and surgical techniques.
PREDICTING THE DIFFICULT AIRWAY
The American Society of Anesthesiologists (ASA) Task Force on Management of the Difficult Airway defines the difficult airway as a clinical situation in which an anesthesiologist has difficulty with face mask ventilation of the upper airway and/or difficulty with tracheal intubation.9 In difficult mask ventilation, the anesthesiologist cannot provide adequate face mask ventilation. Difficult tracheal intubation may result either from problematic direct laryngoscopy, in which it is not possible to visualize any portion of the vocal cords after multiple attempts, or from difficulty in inserting the endotracheal tube (ETT). Earlier ASA guidelines also considered a difficult intubation as a circumstance in which proper ETT insertion required more than 3 attempts or took longer than 10 minutes.10
Several scoring systems and anatomic landmarks can be helpful in the assessment of the airway and in determining whether intubation may be difficult. Mallampati11 and others4,12 devised a classification system to predict risk by correlating ease of laryngeal exposure with visibility of posterior pharyngeal structures. The Mallampati classification scheme has 4 classes based on which posterior pharyngeal structures can be visualized when a patient is seated with his or her head in a neutral position with the mouth open and tongue protruding. In class I, the soft palate, uvula, and pillars of fauces are observed; in class II, the soft palate and pillars of fauces are revealed; in class III, only the soft palate is seen; and, in class IV, only the hard palate is visible (Figure). Class III and IV airway views correlate with more difficult intubations.
While Mallampati scores are routinely ascertained in intubations for elective surgeries, they may be more difficult to assess in emergent situations. However, additional clinical features and measurements may be more useful to alert the practitioner to a potentially problematic airway.
The ASA describes several such findings, including relatively long length of upper incisors; prominent overbite; mandibular incisors anterior to maxillary incisors; less than 3 cm or 3 of the patient's finger breadths between upper and lower incisors on mouth opening; nar-row palate; edematous mandibular space; thyromental distance of less than 3 finger breadths; thick neck; and limited flexion of the neck, as in patients with cervical spine immobilization.9 Furthermore, trauma patients with facial distortion, secretions and blood in the airway, and mandibular injury, or those with possible cervical spine injuries can pose challenging airway management issues.13,14
Walls and colleagues,15 developers of the National Emergency Management Airway Course, created the mnemonic "LEMON" to help practitioners remember the features that should be used to assess the potentially difficult airway:
Look at the patient's external features, such as buckteeth, prominent mandible, obesity, and odd facial shape.
Evaluate the 3-3-2 rule that describes facial and neck relationships and allows the practitioner to place 3 of the patient's finger breadths between the upper and lower teeth, 3 finger breadths between the tip of the mandible and the hyoid bone, and 2 finger breadths between the notch of the thyroid cartilage and the floor of the mandible or the mouth.
Mallampati score: determine the class by checking the appearance of the oral pharynx.
Obstruction: consider the presence of a foreign body, illness, or injury in the posterior larynx or upper larynx that could impede airflow and the ability to intubate the larynx.
Neck mobility (or lack thereof in cervical spine immobilization): mobility is necessary to align the airway axes to facilitate intubation.
CONFIRMING ACCURATE ETT PLACEMENT
One of the last but most critical components of airway management is confirming that the ETT has been successfully placed in the trachea. It is no longer acceptable to use indirect methods to do this. Visualizing the tube passing between the vocal cords is the best way to confirm ETT placement.
Listening for breath sounds, auscultation over the stomach, or watching the tube "fog and clear" are unreliable techniques. Acceptable methods include detection of end-tidal carbon dioxide combined with monitoring of the oxygen saturation trend and/or use of an esophageal detector device. The most commonly used end-tidal carbon dioxide detector is a device that attaches to the end of the ETT and uses a qualitative sensor that changes color in the presence of carbon dioxide.
The esophageal detector device is a large syringe that attaches to the end of the ETT. To begin testing, suction is applied to the syringe. When the tube is correctly positioned, 30 to 40 mL of air is easily aspirated into the syringe. If the tube is in the esophagus, resistance will be felt during aspiration.
These devices are reasonably sensitive and specific, but false- positive results can occur if a large amount of air had been forced into the patient's stomach (as when there is a large quantity of carbonated beverage in the stomach). False-positive results also can occur in low-flow states. A false- negative result can occur if a large amount of mucus in the trachea obstructs airflow into the syringe or if the ETT was placed in the trachea or bronchus with the beveled side against the mucosa.
MANAGING THE PROBLEMATIC AIRWAY
Practitioners who expect airway difficulties can requisition equipment and appropriate personnel for definitive airway management and, thus, optimize patient outcome. A variety of methods are available, each with its own particular challenges.