Section Editor
1.2 Airway Assessment and Management
All forms of surgery in the head and neck region require consideration of airway management, maintenance of ventilation with an adequate form of anesthesia, and prevention of concentrated oxygen in the operative field in the presence of cautery or laser. Various forms of airway management are discussed below, considering anatomy, innervation, indications, instru- mentation and equipment, and clinical context. The specific situation of the difficult airway is then discussed.
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Airway Anatomy
There are two physiologic entry points to the airway: the nose and the mouth. The epiglottis, located at the base of the tongue, separates the oropharynx from the hypopharynx. The larynx is made up of a cartilaginous structure supported by muscles and ligaments.
Innervation
The sensory innervation above the epiglottis is provided by the trigeminal nerve (cranial nerve V [CN V]) and the glossopharyngeal nerve (CN IX);
below the epiglottis, by the superior laryngeal and recurrent laryngeal branches of the vagus nerve (CN X). For more information on the cranial nerves, see Appendix B.
● Nasal mucosa: by the sphenopalatine ganglion branch of the middle divi- sion of the trigeminal nerve
Table 1.4 American Society of Anesthesiologists (ASA) Physical Status Classification System
ASA Class Definition
1 Patient has no organic, physiologic, biochemical, or psychiatric disturbance.
The pathologic process for which the procedure is to be performed is localized and does not entail systemic disturbance.
2 Mild to moderate systemic disturbance caused either by the condi- tion to be treated surgically or by other pathophysiologic processes.
3 Severe systemic disturbance or disease; variable degree of disability.
4 Severe systemic disorders that may be life threatening, not always correctable by operation.
5 Seriously ill patient who has little chance of survival, but is submitted to the operation in desperation.
6 Patients who have met brain death criteria and are undergoing organ procurement.
● Posterior pharynx (including uvula and tonsils): by the continued branches from the sphenopalatine ganglion
● Oropharynx and supraglottic area: by the glossopharyngeal nerve; branches of this nerve include the lingual, pharyngeal, and tonsillar nerves
● Trachea: by the recurrent laryngeal nerve
● Larynx: sensory and motor innervation from the vagus nerve
● Sensory: above the vocal folds, innervation is supplied by the internal branch of the superior laryngeal nerve; below the vocal folds, by the recurrent laryngeal nerve.
● Motor: all muscles are supplied by the recurrent laryngeal nerve except for the cricothyroid muscle, which is supplied by the external branch of the superior laryngeal nerve.
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Airway Equipment
Oral and Nasal AirwaysIn anesthetized patients, loss of airway tone allows the tongue and epiglottis to contact the posterior pharyngeal tissue leading to obstruction. Artificial airway devices can be placed in the nose or mouth to provide an air passage.
Nasal airways carry a risk of epistaxis and should be avoided in anticoagu- lated patients. These devices should also be avoided in patients with basilar skull fractures to avoid intracranial penetration of the airway device. If an airway device is indicated in a lightly anesthetized patient, the nasal route is generally tolerated better.
Face Masks
The face mask is designed to contour and conform to a variety of facial features with the intention of creating an airtight seal capable of delivering gasses from the anesthesia equipment.
Laryngoscopes
The most commonly used intubating laryngoscopes by the anesthesiology team have curved (Macintosh) or straight (Miller) blades and an open-blade design. Newer fiberoptic video rigid laryngoscopes are useful, such as the GlideScope (Diagnostic Ultrasound Corporation, Bothell, WA). There are a variety of operative laryngoscopes that may be useful for intubation, such as the Holinger or Dedo laryngoscope.
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Airway Assessment
A complete airway examination looks at several aspects of the airway. How- ever, the first priority is to identify patients who may be difficult to ventilate or intubate. This is critically important: induction of general anesthesia with the subsequent inability to adequately ventilate the patient is an acute life- threatening emergency. Thus identification of a patient with a potentially
difficult airway before induction will enable the operative and anesthetic team to institute an appropriate plan, backup plans, and assemble and test airway equipment ahead of time.
● Mallampati classification : used to predict the ease of intubation by looking at the anatomy of the oral cavity while the patient is sitting upright in the neutral position ( Fig. 1.1 )
● Thyromental distance : measured from the upper edge of the thyroid
cartilage to the chin with head in full extension. A short thyromental distance (⬍6 cm) equates with an anterior (superior) laryngeal posi- tion that is at a more acute angle, which makes the larynx difficult to visualize via direct laryngoscopy. It is a relatively unreliable test unless combined with other tests.
● Mouth opening : less than two finger-widths of mouth opening (trismus) suggest difficulty with intubation.
● Cervical spine movements : mobility of the atlantooccipital and atlan- toaxial joints may be assessed by asking the patient to extend the head while the neck is in flexion. Extension of the head with atlantoaxial joint immobility results in greater cervical spine convexity, which pushes the larynx anteriorly and impairs laryngoscopic view.
● Temporomandibular joint (TMJ) mobility : assessed by asking the patient to protrude the jaw while sitting up in the neutral position. De- creased mobility suggests greater difficulty with intubation.
● Grade A – lower incisors in front of upper incisors (good mobility)
● Grade B – lower incisors up to upper incisors
● Grade C – lower incisors cannot be protruded to touch upper incisors (poor mobility)
Fig. 1.1 The Mallampati classification of oral opening. Class 1: visualization of soft palate, hard palate, uvula, and tonsillar pillars. Class 2: visualization of soft palate, hard palate, and portion of uvula. Class 3: visualization of soft palate, hard palate, and base of uvula. Class 4: visualization of hard palate only. (From Goldenberg D, ed.
Acute surgical management of the airway. Oper Tech Otolaryngol Head Neck Surg 2007;18(2):73. Reprinted with permission.)
● Cormack and Lehane grade : used to classify the view on direct laryn- goscopy. Previous documentation of laryngoscopy should include the grade of glottic view ( Fig. 1.2 ).
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Preoperative Medication
Medications are often administered preoperatively to alleviate anxiety, to provide analgesia, or as aspiration prophylaxis ( Table 1.5 ).
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Airway Management
Endotracheal IntubationIndications for Endotracheal Intubation
● Protection from aspiration
● Altered level of consciousness (Glasgow Coma Score [GCS] score ⬍8)
● Respiratory distress
● Severe pulmonary or multiorgan failure
● Facilitation of positive pressure ventilation
● Operative position other than supine
● Operative site involving the upper airway
Table 1.5 Common Preoperative Medications
Anxiolysis Analgesia Aspiration Prophylaxis
Diazepam Midazolam Lorazepam
Narcotics: fentanyl, morphine, meperidine Nonsteroidal antiinflamma- tory drugs
COX II inhibitors Acetaminophen Gabapentin
Bicitra Metoclopramide Famotidine
Fig. 1.2 Cormack & Lehane grades. Grade I: visualization of entire laryngeal aperture. Grade II: visualization of posterior part of the laryngeal aperture. Grade III: visualization of epiglottis only. Grade IV: not even the epiglottis is visible.
(From Goldenberg D, ed. Acute surgical management of the airway. Oper Tech Otolaryngol Head Neck Surg 2007;18(2):73. Reprinted with permission.)
● Disease involving the upper airway
● One-lung ventilation
Confirmation of Endotracheal Intubation
● Direct visualization of endotracheal tube passing through the vocal folds
● Carbon dioxide present in exhaled gasses in at least four consecutive breaths (positive end-tidal CO 2 )
● Bilateral breath sounds
● Absence of air entry during epigastric auscultation
● Condensation of water vapor in endotracheal tube (ETT) during exhalation
● Maintenance of arterial oxygenation
● Chest x-ray with tip of ETT between the carina and thoracic inlet Endotracheal Tube Size Recommendations
● Endotracheal tube size (mm): Age/4 ⫹ 4 for patients ⬎2 years old.
● Length of insertion: 12 ⫹ Age/2. Add 2 to 3 cm for nasal intubation.
● Pediatrics: Uncuffed ETTs are generally used in patients ⬍8 years old.
Types of Endotracheal Tube
● Ring-Adair-Elwyn Endotracheal Tubes. Ring-Adair-Elwyn (RAE) endotracheal tubes are preformed to fit in the nose or mouth and are commonly used in oral or pharyngeal surgery, particularly adenoidectomy or tonsillectomy.
The shape prevents obstruction of the surgical field and fits surgical retrac- tors such as the Crow–Davis retractor.
● Armored Endotracheal Tubes. These tubes are commonly used in head and neck surgery. They prevent kinking of the tube when the head is manipulated.
This tube works well through a tracheotomy as it can be curved inferiorly out of the surgical field without kinking and sutured in place temporarily.
● Laser-Resistant Endotracheal Tubes. Laser-resistant endotracheal tubes are used in laser surgery, particularly treatment of laryngeal lesions. By preventing an interaction of inhaled oxygen and the laser, these tubes help prevent airway fires.
● Nerve-Monitoring Endotracheal Tubes. For thyroid surgery, a tube with con- tact electromyographic electrodes positioned at the level of the vocal folds permits intraoperative monitoring of recurrent laryngeal nerve integrity.
Endotracheal Intubation Procedure
● Preoperative evaluation will help determine the route (oral vs. nasal) and method (awake vs. anesthetized) for tracheal intubation.
● Equipment: laryngoscope with working light, appropriate-sized endo- tracheal tubes, oxygen supply, functioning suction catheter, functioning intravenous (IV) line, and anesthetic medications.
● Cricoid pressure: an assistant’s thumb and forefinger depress the cricoid cartilage downward, compressing the esophagus against the underly- ing vertebral body. This prevents spillage of gastric contents into the pharynx during the period of time from induction of unconsciousness to placement of the endotracheal tube in the trachea.
● Induction of anesthesia can be achieved by using IV or inhaled agents.
Endotracheal Intubation Complications
During intubation, possible complications include aspiration, dental damage, laceration of lips/gingiva/palate, laryngeal injury, esophageal intubation, endobronchial intubation, bronchospasm, and activation of sympathetic nervous system (elevated heart rate [HR] and blood pressure [BP]).
After intubation, possible complications include aspiration, laryngospasm, transient vocal fold incompetence, pharyngitis, or tracheitis.
Orotracheal Intubation (Fig 1.3)
If there is no history of cervical spine instability, the patient’s head is extended into a “sniffing” position. This position aligns the oral, pharyngeal, and laryn- geal axes such that the passage from the lips to the glottic opening is a straight line. The height of the operating room (OR) table should be manipulated so that the patient’s head is at the level of the clinician’s xiphoid cartilage.
The laryngoscope is introduced into the right side of the mouth. Advanc- ing the blade posteriorly and toward the midline, the tongue is displaced to
Fig. 1.3 Intubation. (A) Necessary instruments. 1, Mcintosh laryngoscope; 2, stylette; 3, tube with cuff; 4, Guedel tube. (B) Introduction of the tube. (From Becker W, Naumann HH, Pfaltz CR. Ear, Nose, and Throat Diseases: A Pocket Reference. 2nd ed. Stuttgart/New York: Thieme; 1994:450.)
the left. Check that the lower lip is not pinched between the blade and the incisors. Placement of blade depends on which style has been selected:
● Macintosh (curved) blade: the tip of the blade is advanced until the tip enters the vallecula (the space between the epiglottis and the base of the tongue).
● Miller (straight) blade: the tip of the blade is passed below the laryngeal surface of the epiglottis, which is then lifted to expose the vocal folds.
Regardless of the blade selected, the laryngoscope is lifted upward and forward in the direction of the long axis of the handle. The upper incisors should not be used as a fulcrum for leverage as this may damage teeth.
The vocal folds should be visualized prior to advancement of the endo- tracheal tube. Passing the endotracheal tube from the right, little resistance should be encountered. The balloon cuff of the endotracheal tube should pass 1 to 2 cm past the vocal folds. Once the proper position of the endotra- cheal tube is confirmed, it should be secured in place.
Nasotracheal Intubation
Prior to instrumentation, a vasoconstrictor (i.e., oxymetazoline) should be applied to nasal mucosa. After induction of anesthesia and mask ventilation is established the endotracheal tube can be placed.
The naris and endotracheal tube should be generously lubricated. The tube can be softened by placing it in warm water prior to induction. The tube is placed in the nose parallel to the palate, aiming inferiorly to avoid skull base injury, until a loss of resistance is encountered consistent with entrance into the pharynx.
Placement under direct visualization can be performed using a laryngo- scope and McGill forceps to direct the endotracheal tube past the glottic opening. Alternately, a fiberoptic bronchoscope can be placed through the tube and directed past the vocal folds.
Rapid-Sequence Intubation
Indications include aspiration risk (full stomach, history of gastroesophageal reflux disease [GERD], pregnancy, trauma) in a patient who does not appear to be a difficult intubation on physical examination.
Nonparticulate antacids, H2 blockers, and metoclopramide can be admin- istered to decrease the acidity and volume of gastric contents. As with a standard intubation described above, instrumentation should be prepared and available. Preoxygenation with 100% O 2 by mask for 3 to 5 minutes or 4 maximal breaths over 30 seconds is sufficient. Once the paralytic and induction agents are administered, no further ventilation is given.
Induction is accomplished with any induction agent, and the procedure is followed immediately with the administration of a paralytic agent. As the medications are being delivered, cricoid pressure should be applied. Suc- cinylcholine (1–1.5 mg/kg) because of its speed of onset is the drug of choice for rapid sequence induction. As soon as jaw relaxation is present, intuba- tion should be performed. Cricoid pressure should continue until tracheal placement of the endotracheal tube is verified.
Conscious Intubation
Indications include history of difficult intubation, acute infectious/inflam- matory process that may involve the airway, mandibular fractures or other facial deformities, morbid obesity, and certain neoplasms involving the upper aerodigestive tract.
The indications and plan should be discussed with the patient. As with a standard intubation all necessary equipment should be available and checked prior to induction. A backup plan should be formulated should intubation be difficult, such as the creation of a surgical airway.
Preparing the airway by decreasing secretions with an antisialagogue (gly- copyrrolate 0.2 mg 30 minutes before intubation) will help with visualization.
If the nasal route is desired, administer 4 drops of 0.25% Neo-Synephrine to each naris to reduce bleeding. After standard monitors are placed, sedation with fentanyl, midazolam, or dexmedetomidine should be considered.
Topical anesthesia can be achieved using topical agents or nerve blocks.
Topical agents include lidocaine jelly, nebulized lidocaine, nasal cocaine, or Cetacaine (Cetylite Industries, Pennshauken, NJ) spray. Regional anesthesia, either alone or in combination with topical agents, is useful in awake intu- bations. Each major nerve should be approached as described above.
Fiberoptic-Assisted Tracheal Intubation
Indications for a fiberoptic-assisted tracheal intubation include upper airway obstruction, mediastinal mass, subglottic edema, congenital upper airway abnormalities, immobile cervical vertebrae, and confirmation of proper double lumen ETT placement.
Nasal Technique
After vasoconstricting and anesthetizing the airway (see above), the ETT is advanced through the naris into the nasopharynx. The bronchoscope is then inserted into the ETT until the epiglottis and glottic opening are visualized.
The scope is then passed through the opening until the carina is in view.
While maintaining the carina in sight, the ETT is passed over the scope.
Oral Technique
A bite block should be inserted to protect the fiberoptic scope after anes- thetizing the airway (see above). The tracheal tube is inserted into the oropharynx (8–10 cm) and the bronchoscope is inserted through the ETT.
The epiglottis and glottic opening should be in view. The ETT is advanced over the scope as the carina is kept in view.
Transtracheal Ventilation
Transtracheal ventilation serves as a temporizing measure if mask ventila- tion and oxygenation become inadequate or impossible. A catheter (12- or 14-gauge) is inserted into the trachea through the cricothyroid membrane and connected to a jet-type ventilator capable of delivering gas at a pres- sure of 50 psi. The gas is then delivered using the hand-held jet ventilator.
Ventilation is best assessed by observing chest rise and fall. It is advised that an inspiration:expiration (I:E) ratio of 1:4 is utilized.
Complications include catheter displacement (caused by high pressure), pneumothorax, and pneumomediastinum.
Laryngeal Mask Airway (LMA) Indications for the LMA
● Can be used in place of a face mask or ETT
● Can be used in place of an ETT for controlled ventilation as long as the peak pressure does not exceed 30 cm H 2 O
● Can aid in the management of difficult airways by providing ventilation or as a guide for fiberoptic intubation
Contraindications for the LMA
● Does not protect against gastric regurgitation and aspiration because it does not provide an airtight seal of the airway
Insertion of the LMA
● The backside of the LMA should be lubricated with a water-soluble lubricant.
● Unconsciousness is rendered with an induction agent of choice. Typically, propofol at doses of 2 to 3 mg/kg produces reliable jaw and pharyngeal muscle relaxation.
● With the LMA held like a pencil, it is placed into the midline of the mouth and advanced with pressure against the hard palate as it slides into the hypopharynx. When the upper esophageal sphincter is encountered resistance is felt. The LMA is then inflated.
● When placed properly, the black vertical line on the back of the LMA faces backward toward the head of the patient.
● The LMA is then removed upon emergence when the patient can follow commands.
Complications of the LMA
● Possible regurgitation/aspiration
● Negative pressure pulmonary edema can result when placed improperly in a spontaneously breathing patient.
● LMA malfunction in patients with pharyngeal or esophageal disease.
● Placement requires neck extension, which is often contraindicated with cervical spine disease.
The GlideScope
The GlideScope is a video laryngoscope that can be a useful alternative to the fiberoptic scope for placement of an endotracheal tube if a difficult airway is expected. The blade is curved like the Macintosh blade with a 60-degree
curvature to match the anatomic alignment. The GlideScope has a digital camera incorporated in the blade, which displays a view of the vocal folds on a monitor. Under visualization on the monitor, an endotracheal tube is passed between the vocal folds.
Surgical Laryngoscopes
Closed cylinder-style rigid laryngoscopes with bright fiberoptic light guides such as the Dedo or Holinger are used by the otolaryngologist and have advantages that permit visualization of the glottis and intubation.
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The Difficult Airway
Among otolaryngology–head and neck surgery patients, a high percentage presents with a difficult airway ( Table 1.6 ). By definition, a patient with a
Table 1.6 Conditions Associated with Difficult Airway and Intubation
Condition Examples
Tumors Cystic hygroma
Hemangiomas Hematoma
Infections Submandibular abscess
Peritonsillar abscess Epiglottitis
Congenital anomalies Pierre Robin syndrome Treacher Collins syndrome Laryngeal atresia Goldenhar syndrome Craniofacial dystocias
Trauma Laryngeal fracture
Mandibular/maxillary fracture Inhalational burn
Cervical spine injury Inadequate neck extension Rheumatoid arthritis
Ankylosing spondylitis Halo traction Anatomic variations Micrognathia Prognathism Large tongue Arched palate Short neck
Prominent upper incisors Obesity
Airway foreign body
difficult airway potentially poses difficulty with ventilation or endotracheal tube placement. The goal of history, physical exam, and chart review is to identify patients with difficult airway before they arrive in the OR. Evaluation by the otolaryngologist and review of diagnostic studies can provide invalu- able information to the anesthesiologist when a difficult airway is suspected.
Conditions associated with difficult airway are discussed below.
The induction of anesthesia in otolaryngology patients should not be initiated until a plan is formulated between the surgical and anesthesia teams. As outlined in the Difficult Airway Algorithm of the American Society of Anesthesiologists ( Fig. 1.4 ), the plan should address basic management choices: surgical versus nonsurgical approach, awake versus asleep, and spontaneous versus nonspontaneous ventilation. The discussion should address backup plans should the initial attempt to secure the airway fails or inability to ventilate ensues. A surgical airway is indicated when ventilation becomes inadequate despite utilization of a nonsurgical airway ventilation device [jet ventilation, LMA, Combitube (Tyco-Kendall, Mansfield, MA)] in a patient under general anesthesia.
If a difficult airway is suspected, instrumentation and plans for possible sur- gical airway should be available. Cricothyroidotomy is the preferred method in adults. Briefly, the neck is extended, and the cricothyroid membrane is palpated and incised with a scalpel. The airway is entered and an endotracheal or tracheotomy tube is placed to ventilate the patient. Details on cricothy- roidotomy are below.
Clinical situations involving a patient with a difficult airway can be divided into two categories. The first is the acute or urgent problem and the second, an elective situation with a suspected or known difficult airway. Both of these scenarios are to be handled differently. A logical, strict approach can prevent a disastrous outcome in what is often a stressful situation. The otolaryngologist–head and neck surgeon should have particular expertise in ensuring an adequate airway and should be skilled in the use of laryngos- copy, bronchoscopy, and surgical approaches to the airway.
Specific techniques to be discussed here include cricothyroidotomy and awake tracheotomy.
Cricothyroidotomy
For a patient with impending or complete obstruction, rapid establishment of an airway is required — the OR is the safest place for this airway control though this is not always possible. If the situation requires establishment of an emergency surgical airway, a cricothyroidotomy is generally the preferred procedure ( Fig. 1.5 ). This is because it is simpler and faster than a trache- otomy and has a lower complication rate, especially in less- experienced hands. If it is impossible to mask ventilate, intubate, or control the airway by any other technique such as a laryngeal mask or jet ventilation, or if these are not readily available, cricothyroidotomy should be performed by the most trained and skilled physician in attendance.
Contraindications to cricothyroidotomy include subglottic stenosis or mass, laryngeal trauma, with an inability to identify landmarks; in general, it should be avoided in the pediatric population. A cricothyroidotomy