Airway Management

Although the role of the supraglottic airway (SGA) is firmly established in routine anesthetic care as well as airway rescue, the adoption of video and optical laryngoscopy promises to remove many of the failings of direct laryngoscopy, a technique that has been in use for more than 200 years (Rosenblatt WH, Sukhupragarn WA. Airway management. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds. Clinical Anesthesia. Philadelphia: Lippincott Williams & Wilkins; 2013:762–802). Management of the airway is paramount to safe perioperative care (difficult and failed management account for 2.3% of anesthetic deaths in the United States), and specific steps are necessary to favorably affect outcome (Table 27-1).

I. Review of Airway Anatomy

The term “airway” refers to the upper airway, consisting of the nasal and oral cavities, pharynx, larynx, trachea, and principal bronchi. The anatomically complex airway undergoes growth and development and significant changes in its size, shape, and relationship to the cervical spine between infancy and childhood (Table 27-2).
The laryngeal skeleton consists of nine cartilages (three paired and three unpaired) that together house the vocal folds that extend in the anterior–posterior plane from the thyroid cartilage to the laryngeal cartilages.
- The larynx is innervated by two branches of the vagus nerve, superior laryngeal nerve, and recurrent laryngeal nerve.
  - The recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx with the exception of the cricothyroid muscle.
  - Vocal cord dysfunction accompanies trauma to these nerves.
- Unilateral nerve injury is unlikely to impair airway function, but the protective role of the larynx in preventing aspiration may be compromised.

The cricothyroid membrane joins the superior aspect of the cricoid cartilage and the inferior edge of the thyroid
cartilage (8–12 mm in width). It can be identified 1 to 1.5 fingerbreadths below the laryngeal prominence (thyroid notch). It is suggested that any incisions or needle punctures to the cricothyroid membrane be made in its inferior third and be directed posteriorly (vocal folds may be 0.9 cm above the ligament’s upper border).

Table 27-1 Steps to Favorably Affect Outcome as Related to Airway Management

Airway history and physical examination
Consideration of the ease of rapid tracheal intubation (direct or indirect laryngoscopy)
Formulation of management plans for use of supraglottic means of ventilation
Weighing the risk of aspiration of gastric contents
Estimating the relative risk to the patient of failed airway maneuvers

The trachea in adults measures about 15 cm and is supported circumferentially by 17 to 18 C-shaped cartilages with a posterior membranous aspect overlying the esophagus.

The first tracheal ring is anterior to the sixth cervical vertebra.
The trachea ends at the fifth thoracic vertebra (carina), where it bifurcates into the right and left bronchi. The right mainstem bronchus is larger than the left and deviates from the plane of the trachea at a less acute angle.
Aspirated materials as well as deeply placed tracheal tubes are more likely to enter the right than the left bronchus.

Table 27-2 Anatomic Differences Between Pediatric and Adult Airways

Proportionately smaller infant/child larynx
Narrowest portion: Cricoid cartilage in infant/child; vocal folds in adults
Relative vertical location: C3, C4, C5 in infant/child; C4, C5, C6 in adult
Epiglottis: Longer, narrower, and stiffer in infant/child
Aryepiglottic folds closer to midline in infant/child
Vocal folds: Anterior angle with respect to perpendicular axis of larynx in infant/child
Pliable laryngeal cartilage in infant/child
Mucosa more vulnerable to trauma in infant/child

Limitations of Patient History and Physical Examination. In the absence of a difficult airway “note” or a “difficult airway letter” given to the patient, it is useful to review, when possible, prior anesthetic records. Signs and symptoms related to the airway should be sought (Table 27-3).
- When interpreted as individual tests, currently used techniques of evaluation have only modest discriminative powers (Tables 27-4 and 27-5).
- Five attributes can be used to predict difficult laryngoscopy (Table 27-6).
- Ultrasonography has limited application in airway evaluation.
- Predicting difficult direct laryngoscopy remains an enigma because commonly used indexes may not only be less predictive than originally thought but may be misleading. The advent of video laryngoscopy may make these deficits irrelevant.

II. Clinical Management of the Airway

Preoxygenation (denitrogenation) should be practiced in all cases when time allows. This procedure entails the replacement of the lung’s nitrogen volume with oxygen to provide a reservoir for diffusion of oxygen into the alveolar capillary bed after the onset of apnea (as associated with direct laryngoscopy for tracheal intubation).
- Breathing room air results in desaturation to below 90% after approximately 1 to 2 minutes of apnea.
- An alternative to breathing oxygen for 5 minutes is to use a series of four vital capacity breaths of 100% oxygen over a 30-second period.

Support of the Airway with the Induction of Anesthesia. With the induction of anesthesia and the onset of apnea, ventilation and oxygenation are supported by the anesthesiologist using traditional methods (face mask, tracheal tube) or a newer SGA device (laryngeal mask airway [LMA]).

The anesthesia face mask is the most ubiquitous device used to deliver anesthetic gases and oxygen as well as to ventilate a patient who has been rendered apneic. Appropriate positioning of the patient’s head and neck (“sniffing position”) is paramount to successful mask ventilation.

Table 27-3 Signs, Symptoms and Disorders with Airway Management Implications

History Related to Airway Problems
Aspiration risk

History of voice changes
History of vocal cord polyps
History of frequent pneumonias
Coughing after eating/drinking
Acute opioid therapy
Acute trauma
Intensive care unit admission (current)
Pregnancy (gestational age ≥12 weeks)
Immediate postpartum period (before second postpartum day)
Systemic disease associated gastroparesis: Diabetes mellitus, postvagotomy, collagen vascular disease, Parkinson disease, thyroid dysfunction, liver disease, CNS tumors, chronic renal insufficiency

Difficult Laryngoscopy/SGA Ventilation

History of surgical manipulation in or around the airway
History of radiation therapy of the head/neck
Various congenital and acquired syndromes

Obstructive Sleep Apnea

Ody mass index >35 kg/m² (indicative)
Loud snoring
Pauses in breathing during normal sleep
Sleep interruption (with choking)
Daytime somnolence/napping
Airway-affecting craniofacial abnormalities

Lingual Tonsil Hyperplasia/Supraglottic Cyst or Tumors

Chronic sore throat
Globus sensation
Voice change
Dysphagia
Obstructive sleep apnea
History of tonsillectomy (controversial)

Thyroglossal Duct Cyst

Asymptomatic anterior cervical mass that moves with deglutination
Complications: cysts infection, fistula, spontaneous rupture, voice change, dysphagia, dyspnea, and snoring

Signs and Symptoms Related to the Airway

Snoring
Changes in voice
Dysphagia
Stridor
Bleeding
Cervical spine pain or limited range of motion
Upper extremity neuropathy
Temporomandibular joint pain or dysfunction

Sequelae of Previous Intubation

Chipped teeth
Significant prolonged sore throat/mandible after a previous anesthetic

CNS = central nervous system; SGA = supraglottic airway.

Table 27-4 Summary of Pooled Sensitivity and Specificity of Commonly used Methods of Airway Evaluation

Examination	Sensitivity (%)	Specificity (%)
Mallampati classification	49	86
Thyromental distance	20	94
Sternomental distance	62	82
Mouth opening	46	89

Table 27-5 Techniques of Common Airway Indexes Measurement

Thyromental distance: Measured along a straight line from tip of mentum to thyroid notch in neck-extended position
Mouth opening: Interincisor distance (or interalveolus distance when edentulous) with the mouth fully opened
Mallampati score (see legend, Fig. 27-3)
Head and neck movement: The range of motion from full extension to full flexion
Ability to prognath: Capacity to bring the lower incisors in front of the upper incisors

Only gold members can continue reading. Log In or Register to continue