Airway Assessment and Prediction of the Difficult Airway

KEY POINTS

Poor airway assessment may contribute to poor patient outcomes.
An airway history and physical examination should be performed in all patients undergoing airway management. Relevant diagnostic studies should be reviewed.
No single test reliably predicts difficult mask ventilation (DMV), difficulty with a supraglottic airway (SGA), difficult laryngoscopy, or difficult intubation (DI).
A greater number of airway abnormalities imply increasing difficulty.
Proposed predictors of impossible face-mask ventilation include neck radiation changes, beard, male gender, obstructive sleep apnea (OSA), and modified Mallampati class of III or IV.
Proposed predictors of SGA airway failure include male sex, high BMI, poor dentition, and surgical table rotation.
Some factors that predict a DI include a history of a difficult airway (DA), interincisor distance <3 cm, failed temporomandibular joint (TMJ) translation, small mandibular space, limited cervical spine mobility, temporomandibular distance translation <6 cm, modified Mallampati class of III or IV, and a short, thick neck.
Because most DAs are not expected, clinicians should develop a comprehensive airway strategy rather than a single airway plan for every patient even if the airway assessment is normal.

Introduction

An airway evaluation, including history, physical examination, and other diagnostic tests, should be performed for all patients who are undergoing anesthesia or have a need for airway management. When the 2013 American Society of Anesthesiologists (ASA) Guidelines for Management of the Difficult Airway (DA) were developed, 100% of consultants and ASA members agreed that a preanesthetic examination should include an airway assessment. The Fourth National Audit Project (NAP4) of the United Kingdom, one of the largest population-based studies of complications of airway management, concluded that lack of airway assessment was correlated with poor planning and patient morbidity and mortality.

An assessment of the airway focuses on medical history and physical features that impact the patient’s risk for difficult mask ventilation (DMV), difficult intubation (DI), supraglottic airway (SGA) failure, challenging surgical airway, increased risk for aspiration of gastric contents, or poor tolerance of apnea. Variations or abnormalities are found by reviewing records, taking an anesthetic- and airway-focused history, examining the patient, and reviewing relevant laboratory and radiologic studies.

Patient History

History of a Difficult Airway

A history of a DA is a strong predictor of future airway problems. ^, The inverse is not necessarily true; a history of problem-free airway management suggests straightforward airway management but does not guarantee it. Factors such as weight, age, dental issues, or pathology may have altered the airway after previous procedures. If a patient reports a history of DMV or DI, additional investigation is warranted. If possible, medical records from those procedures should be obtained. Questions are then asked regarding the nature and context of the event. Noting the year an event occurred may be helpful, especially if newer airway devices were not available at the time. History of severe sore throat, trauma to the airway, unanticipated postoperative intubation, or reintubation also may indicate that providers experienced difficulty. Disease processes such as obstructive sleep apnea (OSA) or respiratory illness may have influenced extubation.

Medical Conditions

Diabetes

The incidence of DI in patients with long-standing diabetes is 21% to 41%. Nonenzymatic glycosylation of collagen may lead to limited joint mobility. Poor glycemic control in long-standing disease increases the likelihood of developing joint problems. If the atlanto-occipital joint or laryngeal joints become involved, then neck extension and laryngeal mobility may become limited, making laryngoscopy or intubation difficult. Collagen glycosylation starts in the fourth and fifth interphalangeal joints, preventing the patient from approximating the palms and fingers of the hands; therefore, limited phalangeal extension may be used as a predictor of DA management caused by neck and larynx stiffness. The prayer sign and palm print test have been suggested as tests of phalangeal joint immobility. For the prayer sign, the patient is asked to place his hands in the prayer position with the palms approximated as much as possible; the ability of the interphalangeal joints to oppose one another so that the fingers lie flat against each other can be assessed. Difficulty with intubation is considered more likely in patients with less ability to oppose the joints successfully. To perform the palm print test, the patient’s hand is painted with black ink and pressed against a piece of paper. The fraction of the palm print present in ink is deemed inversely proportional to intubation difficulty. Several studies of the predictive value of these tests found sensitivity ranged from 13% to 75%, and specificity from 69% to 96%. ^, Although these individual tests have poor predictive value, the palm print test or prayer sign may give additional information about difficulty of intubation in patients with diabetes.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that affects joints throughout the body. It can cause immobility or hypermobility of the joints of the jaw, larynx, and neck. The temporomandibular joint (TMJ), cricoarytenoid joint, cricothyroid joint, atlantoaxial joint, and cervical spine may be involved. ^,

Some manifestations of the disease are laryngeal nodules, mucosal edema, and swelling of the arytenoids or surrounding tissue. Dysphonia, dysphagia, sore throat, and poor exercise tolerance can occur. Cricoarytenoid arthritis can cause voice changes, hoarseness, pain on swallowing, dyspnea, stridor, and tenderness over the larynx. If the vocal cords move poorly as a result of arytenoid edema, the larynx may be more difficult to identify during laryngoscopy. Swelling may be so severe that the glottis is obscured. Not only can arthritis influence airway management, but instrumenting the airway can also exacerbate the condition. Worsening of laryngeal symptoms after tracheal intubation or SGA placement in patients with RA has been reported. Postextubation stridor in patients may indicate aggravation of the arthritis. The patient with RA should be asked about symptoms, length of diagnosis, and steroid use. Cervical spine disease is correlated with duration of arthritis, significant peripheral joint erosion, long-standing steroid use, older age, and neck symptoms. ^, Depending on symptoms, surgical plan, or other factors, additional diagnostic work-up such as radiographs, laryngoscopy, or even pulmonary function tests (PFTs) may be warranted.

Ankylosing Spondylitis

Ankylosing spondylitis is a seronegative spondyloarthropathy affecting the bony insertion points of ligaments. The disease can lead to fusion and rigidity of joints including the spine, the TMJ, and, in some cases, the cricoarytenoid joint. The disease is progressive, leading to spinal immobility and the characteristic “bamboo spine” on radiograph. Osteoporosis also develops, causing bones to be more fragile. Preoperative evaluation is guided by the severity of the disease and procedure to be performed. Disease duration can indicate severity. Cervical fractures and spinal nerve root compression can occur. During the airway assessment, any related neurologic deficits should be documented. Atlantoaxial subluxation occurs in 21% of patients with the condition. Care with airway instrumentation is of utmost importance in these patients, as the lower cervical spine can fracture with improper neck extension. Neurologic injury, including quadriplegia after cervical spine injury during intubation, has been reported. ^,

Temporomandibular Disorders

Temporomandibular disorders can arise from joint problems (articular) or nonarticular causes. Articular disorders can be associated with RA, ankylosing spondylitis, gout, infectious arthritis, or osteoarthritis. Nonarticular causes include fibromyalgia, muscle spasm, and acute muscle sprain. Patients with muscle disorders, disc condyle disorders, joint inflammation, or hypermobility will likely display normal mouth opening after the induction of general anesthesia. Synovitis of the TMJ leads to reduced mandibular motion, causing a reduced oral aperture. Severe forms of juvenile RA (Still’s disease) can involve the TMJ, leading to poor mandibular development (micrognathia).

TMJ disease or dysfunction should be noted in the patient’s medical history. Patients with TMJ disease may be more difficult to intubate, and many experience worsening of symptoms postoperatively. The patient should be asked about any clicking or grinding with mandibular movement, periauricular pain, pain that radiates to the head or neck, pain with chewing, restricted movement, and joint hypermobility. The presence of symptoms should prompt the practitioner to discuss the possibility that symptoms may worsen postoperatively. Patients with or without preexisting signs and symptoms may develop TMJ dysfunction or dislocation even after uneventful laryngoscopy and intubation. Absence of symptoms or a diagnosis does not preclude disease or provide immunity to postoperative symptoms.

Bleeding Risk

Bleeding in the airway during instrumentation can obscure the view of the glottis. Bleeding can be especially problematic during flexible scope intubation (FSI) or video-assisted laryngoscopy (VAL). The patient with an inherited or acquired clotting factor deficiency may develop severe epistaxis with nasal intubation, and some consider nasal intubation to be contraindicated in these patients. Patients taking anticoagulants that have been discontinued pose only a relative contraindication to nasal intubation. Nasal intubation is not contraindicated in patients taking antiplatelet medication. Patients with severe coagulation abnormalities may be at risk of developing a tongue hematoma, which can cause partial or complete airway obstruction that may not manifest until the airway device is removed.

Cardiopulmonary Illness

Although time to oxyhemoglobin desaturation after preoxygenation is not a predictor of DA management, it is an important consideration when developing an airway management strategy. The longer the time available to secure the airway, the greater the likelihood of successful intubation. Patients with a reduced functional residual capacity (FRC), decreased diffusion of oxygen across the lung parenchyma, or increased oxygen consumption tolerate less apneic time before desaturation begins. Restrictive lung disease, advanced pregnancy, and morbid obesity are common causes of reduced FRC.

Airway manipulation in patients with obstructive airway disease such as asthma or chronic obstructive pulmonary dysfunction (COPD) may lead to severe bronchospasm, hypoxia, and even death. The National Asthma Education and Prevention Program (NAEPP) Expert Panel Report and the GOLD Guidelines provide stepwise approaches to the assessment and treatment of patients with asthma and COPD, respectively. Clinicians can refer to these guidelines when optimizing the medical status of patients preoperatively. Cardiac illness should also be assessed. The patient with severe cardiac disease may not be able to withstand a long apneic period or the sympathetic responses to intubation and extubation.

Congenital Abnormalities

Developmental abnormalities of the first and second pharyngeal arches can lead to craniofacial abnormalities, including cleft lip, cleft palate, and micrognathia. Specific syndromes include Treacher-Collins syndrome, Pierre Robin syndrome, and Goldenhar syndrome. In some severe cases of micrognathia, airway obstruction can occur even during normal wakefulness. Macroglossia, an abnormally large tongue, can also lead to difficulty with airway management. Macroglossia is associated with Down syndrome and the mucopolysaccharidoses. It is not important to remember each syndrome and its accompanying features. Rather, practitioners should educate themselves on the syndrome preoperatively and, if appropriate, refer the patient to a tertiary center for care.

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