Key WordsAirway anatomy, Difficult airway management, Difficult pediatric airway management, Pre-anesthestic airway assessment, Pediatric airway management, Supraglottic airway devices, Videolaryngoscopy
The editors and publisher would like to thank Dr. Robin A. Stackhouse for contributing to this chapter in the previous edition of this work. It has served as the foundation for the current chapter.
Expertise in airway management is critical for administering anesthesia safely. Difficult airway management is defined as the clinical situation in which conventionally trained anesthesia personnel experience difficulty with ventilation via a face mask or endotracheal intubation or both. Difficult or failed airway management is a major factor in anesthesia-related morbidity (dental damage, aspiration of gastric contents, airway trauma, unanticipated surgical airway, anoxic brain injury, cardiopulmonary arrest) and fatality. Competence in airway management requires (1) knowledge of the anatomy and physiology of the airway, (2) ability to evaluate the patient’s history that is relevant to airway management, (3) physical examination of anatomic features correlating with difficult airway management, (4) skill with the many devices for airway management, and (5) appropriate application of the American Society of Anesthesiologists (ASA) algorithm for difficult airway management ( Fig. 16.1 ).
Anatomy and Physiology of the Upper Airway
Air is warmed and humidified as it passes through the nares during normal breathing. Resistance to airflow through the nasal passages is twice that through the mouth and accounts for approximately 50% to 75% of total airway resistance. The majority of the sensory innervation of the nasal cavity is derived from the ethmoidal branch of the ophthalmic nerve and branches of the maxillary division of the trigeminal nerve from the sphenopalatine ganglion ( Fig. 16.2 ).
Mouth and Pharynx
Branches of the maxillary division of the trigeminal nerve that innervate the mouth include the greater and lesser palatine nerves and the lingual nerve. The greater and lesser palatine nerves provide most of the sensation to the hard palate, soft palate, and the tonsils, and the lingual nerve provides sensation to the anterior two thirds of the tongue. The posterior third of the tongue, the soft palate, and the oropharynx are innervated by the glossopharyngeal nerve (cranial nerve IX) ( Figs. 16.3 and 16.4 ).
The pharynx connects the nasal and oral cavities to the larynx and esophagus. The pharynx is composed of the nasopharynx, oropharynx, and hypopharynx. The nasopharynx is separated from the oropharynx by the soft palate. The epiglottis demarcates the border between the oropharynx and the hypopharynx. The internal branch of the superior laryngeal nerve, which is a branch of cranial nerve X (vagus), provides sensory innervation to the hypopharynx, including the base of the tongue, posterior surface of the epiglottis, aryepiglottic folds, and arytenoids ( Fig. 16.5 ).
Airway resistance may be increased by prominent lymphoid tissue in the nasopharynx. The tongue is the predominant cause of airway resistance in the oropharynx. Obstruction by the tongue is increased by relaxation of the genioglossus muscle during anesthesia.
The adult larynx is located at the level of the third to sixth cervical vertebrae. One of its primary functions is to protect the distal airways by closing when stimulated to prevent aspiration. This protective mechanism, when exaggerated, becomes laryngospasm. The larynx is composed of a cartilaginous framework connected by fascia, muscles, and ligaments. There are three unpaired and three paired cartilages. The unpaired cartilages are the epiglottis, thyroid, and cricoid, and the paired cartilages are the arytenoids, corniculates, and cuneiforms. The cricoid cartilage is shaped like a signet ring, wider in the cephalocaudal dimension posteriorly, and is the only cartilage that is a full ring structure. The vocal cords are formed by the thyroarytenoid ligaments and are the narrowest portion of the adult airway. An understanding of the motor and sensory innervation of the laryngeal structures is important for performing anesthesia of the upper airway ( Table 16.1 ).
|Superior laryngeal, internal division||Epiglottis |
Base of tongue
|Superior laryngeal, external division||Anterior subglottic mucosa||Cricothyroid membrane|
|Recurrent laryngeal||Subglottic mucosa |
|Thyroarytenoid membrane |
Lateral cricoarytenoid membrane. Interarytenoid membrane
Posterior cricoarytenoid membrane
The trachea extends from the larynx to the carina, which overlies the fifth thoracic vertebra. An adult trachea is 10 to 15 cm long and supported by 16 to 20 horseshoe-shaped cartilages. The sensory innervation of the trachea is from the recurrent laryngeal nerve, a branch of cranial nerve X (vagus).
History and Anatomic Examination
A comprehensive assessment of the airway should consist of a history of the patient’s airway experiences, review of previous anesthetic and medical records, physical examination, and additional evaluations when necessary. The airway history should be evaluated to determine whether there are any medical, surgical, or anesthetic factors that have implications for airway management, including the risk of aspiration of gastric contents. Various congenital and acquired disease states have a correlation with difficult airway management ( Tables 16.2 and 16.3 ). Patients who have had a previous problem with airway management should have been informed of the problem. Patients’ difficult airway specifics can be documented by a written letter, an alert or note in the medical record, a notification bracelet such as the medical alert system or equivalent device, or by discussion with the patient’s surgeon, primary care physician, family member, or patient representative. The previous anesthetic record should contain a description of the airway difficulties (i.e., difficult laryngeal mask, supraglottic airway or intubation, or both), what airway management techniques were used, and whether they were successful.
|Trisomy 21||Large tongue, small mouth make laryngoscopy difficult |
Small subglottic diameter possible
Laryngospasm is common
|Goldenhar (oculoauriculovertebral anomalies)||Mandibular hypoplasia and cervical spine abnormality make laryngoscopy difficult|
|Klippel-Feil||Neck rigidity because of cervical vertebral fusion|
|Pierre Robin||Small mouth, large tongue, mandibular anomaly|
|Treacher Collins (mandibular dysostosis)||Laryngoscopy is difficult|
|Turner||High likelihood of difficult endotracheal intubation|
|Epiglottitis (infectious)||Laryngoscopy may worsen obstruction|
|Abscess (submandibular, retropharyngeal, Ludwig’s angina)||Distortion of the airway renders face mask ventilation or endotracheal intubation extremely difficult|
|Croup, bronchitis, pneumonia||Airway irritability with a tendency for cough, laryngospasm, bronchospasm|
|Tetanus||Trismus renders oral endotracheal intubation impossible|
|Traumatic foreign body||Airway obstruction|
|Cervical spine injury||Neck manipulation may traumatize the spinal cord|
|Basilar skull fracture||Nasotracheal intubation attempts may result in intracranial tube placement|
|Maxillary or mandibular injury||Airway obstruction, difficult face mask ventilation and endotracheal intubation |
Cricothyroidotomy may be necessary with combined injuries
|Laryngeal fracture||Airway obstruction may worsen during instrumentation |
Endotracheal tube may be misplaced outside the larynx and worsen the injury
|Laryngeal edema (after intubation)||Irritable airway |
Narrowed laryngeal inlet
|Soft tissue neck injury (edema, bleeding, subcutaneous emphysema)||Anatomic distortion of the upper airway |
|Neoplastic upper airway tumors (pharynx, larynx)||Inspiratory obstruction with spontaneous ventilation|
|Lower airway tumors (trachea, bronchi, mediastinum)||Airway obstruction may not be relieved by endotracheal intubation |
Lower airway is distorted
|Radiation therapy||Fibrosis may distort the airway or make manipulation difficult|
|Inflammatory rheumatoid arthritis||Mandibular hypoplasia, temporomandibular joint arthritis, immobile cervical vertebrae, laryngeal rotation, and cricoarytenoid arthritis make endotracheal intubation difficult|
|Ankylosing spondylitis||Fusion of the cervical spine may render direct laryngoscopy impossible|
|Temporomandibular joint syndrome||Severe impairment of mouth opening|
|Scleroderma||Tight skin and temporomandibular joint involvement make mouth opening difficult|
|Sarcoidosis||Airway obstruction (lymphoid tissue)|
|Angioedema||Obstructive swelling renders ventilation and endotracheal intubation difficult|
|Endocrine or metabolic acromegaly||Large tongue |
|Diabetes mellitus||May have decreased mobility of the atlanto-occipital joint|
|Hypothyroidism||Large tongue and abnormal soft tissue (myxedema) make ventilation and endotracheal intubation difficult|
|Thyromegaly||Goiter may produce extrinsic airway compression or deviation|
|Obesity||Upper airway obstruction with loss of consciousness |
Tissue mass makes successful face mask ventilation difficult
Physical Examination Findings
Physical examination of the airway should evaluate multiple features to detect predictors of a difficult airway ( Table 16.4 ). Physical examination features and other bedside tests have a low sensitivity and specificity for any single test and its implications for difficult airway management. Combining tests and other risk factors correlates with some improvement in the accuracy of predicting a difficult airway. Examination of the oropharyngeal space, submandibular space and compliance, and cervical spine mobility as well as evaluation of patients’ body habitus can help to identify increased risk of difficult airway management. Recognition of patients who may be a difficult laryngoscopy and intubation as well as difficult mask, supraglottic airway placement, or surgical airway can highlight the need for further evaluation and preparation.
|Airway Examination Component||Nonreassuring Findings|
|Length of upper incisors||Relatively long|
|Relationship of the maxillary and mandibular incisors during normal jaw closure||Prominent overbite (maxillary incisors anterior to the mandibular incisors)|
|Relationship of the maxillary and mandibular incisors during voluntary protrusion of the mandible||Patient cannot bring the mandibular incisors anterior to (in front of) the maxillary incisors|
|Interincisor distance||Less than 3 cm|
|Visibility of the uvula||Not visible when the tongue is protruded with the patient in a sitting position (Mallampati class higher than II)|
|Shape of the palate||Highly arched or very narrow|
|Compliance of the mandibular space||Stiff, indurated, occupied by a mass, or nonresilient|
|Thyromental distance||Less than three fingerbreadths|
|Length of the neck||Short|
|Thickness of the neck||Thick|
|Range of motion of the head and neck||Patient cannot touch the tip of the chin to the chest or cannot extend the neck|
The Mallampati test is used to evaluate the oropharyngeal space and its predicted effect on ease of direct laryngoscopy and endotracheal intubation. There is a correlation between a modified Mallampati score of 3 and 4 with difficult laryngoscopy. The airway is classified according to what structures are visible. For the modified Mallampati score, the observer should be at eye level with the patient holding the head in a neutral position, opening the mouth maximally, and protruding the tongue without phonating ( Fig. 16.6 ).
Class I: The soft palate, fauces, uvula, and tonsillar pillars are visible.
Class II: The soft palate, fauces, and uvula are visible.
Class III: The soft palate and base of the uvula are visible.
Class IV: The soft palate is not visible.
In conjunction with the Mallampati examination, the interincisor gap, the size and position of the maxillary and mandibular teeth, and the conformation of the palate can be assessed. An interincisor gap of less than 3 to 4.5 cm correlates with difficulty achieving a line of view on direct laryngoscopy. Maxillary prominence or a receding mandible also correlate with a poor laryngoscopic view. Overbite results in a reduction in the effective interincisor gap when the patient’s head and neck are optimally positioned for direct laryngoscopy. A narrow or highly arched palate is another airway examination finding that is associated with a potential difficult airway.
The submandibular space is the area into which the soft tissues of the pharynx must be displaced to obtain a line of vision during direct laryngoscopy. Anything that limits the submandibular space or compliance of the tissue will decrease the amount of anterior displacement that can be achieved. Micrognathia limits the pharyngeal space (tongue positioned more posterior) and the space in which the soft tissues need to be displaced. This causes the glottic structures to be anterior to the line of vision during direct laryngoscopy.
The extent of an individuals’ ability to prognath the mandible is another correlate of the visualization of glottic structures on direct laryngoscopy. The upper lip bite test (ULBT) classification system is as follows (class III is associated with a difficult intubation):
Class I: Lower incisors can bite above the vermilion border of the upper lip.
Class II: Lower incisors cannot reach vermilion border.
Class III: Lower incisors cannot bite upper lip.
Ludwig’s angina, tumors or masses, radiation scarring, burns, and previous neck surgery are conditions that can decrease submandibular compliance.
A thyromental distance (mentum to thyroid cartilage) less than 6 to 7 cm correlates with a poor laryngoscopic view. This is typically seen in patients with a receding mandible or a short neck, which creates a more acute angle between the oral and pharyngeal axes and limits the ability to bring them into alignment. This distance is often estimated in fingerbreadths. Three ordinary fingerbreadths approximate this distance. If the sternomental distance is used, it should measure more than 12.5 to 13.5 cm.
Atlanto-Occipital Extension/Cervical Spine Mobility
Extension of the head on the atlanto-occipital joint is important for aligning the oral and pharyngeal axes to obtain a line of vision during direct laryngoscopy ( Fig. 16.7 ). Flexion of the lower neck, by elevating the head approximately 10 cm, aligns the laryngeal and pharyngeal axes. These maneuvers place the head in the “sniffing” position and bring the three axes into optimal alignment. Atlanto-occipital extension is quantified by the angle traversed by the occlusal surface of the maxillary teeth when the head is fully extended from the neutral position. More than 30% limitation of atlanto-occipital joint extension from a norm of 35 degrees, or less than 80 degrees of extension/flexion, is associated with an increased incidence of difficult endotracheal intubation.
Body Habitus/Other Examination Findings
Obesity, with a body mass index (BMI) greater than 30, is associated with an increased incidence of difficult airway management. Proper positioning with a wedge-shaped bolster behind the patient’s back results in a more optimal sniffing position. However, the problem of decreased functional residual capacity (FRC) with subsequent decreased time to arterial oxygen desaturation still persists. Other factors that are associated with difficult airway include increased neck circumference and the presence of a beard.
Assessing the ease of performing invasive airway procedures before airway instrumentation has been advocated and is especially important with predicted difficult airway management. When routine airway management techniques have failed, ventilation is not adequate, and endotracheal intubation is unsuccessful, invasive airway control through the cricothyroid membrane is indicated; therefore, correctly identifying the cricothyroid membrane can be crucial (see Fig. 16.1 ). It can be identified by first locating the thyroid cartilage, then sliding the fingers down the neck to the membrane, which lies just below. Alternatively, in patients who do not have a prominent thyroid cartilage, identification of the cricoid cartilage can be achieved by beginning palpation of the neck at the sternal notch and sliding the fingers up the neck until a cartilage that is wider and higher (cricoid cartilage) than those below is felt. The superior border of the cricoid cartilage demarcates the inferior border of the cricothyroid membrane. Predictors of difficulty identifying the cricothyroid membrane include female sex, age less than 8 years, presence of large neck circumference, a displaced airway, and overlying neck malformation.
Airway Management Techniques
Ventilation Via a Face Mask
Ventilation via a face mask is a vital airway management tool. Prospectively identifying patients at risk for difficult ventilation via a mask, ensuring the ability to ventilate the patient’s lungs before administering neuromuscular blocking drugs, and developing proficient face mask ventilation skills are fundamental to the practice of anesthesia.
Independent variables associated with difficult face mask ventilation are (1) age older than 55 years, (2) BMI higher than 30 kg/m , (3) a beard, (4) lack of teeth, (5) a history of snoring or obstructive sleep apnea, (6) Mallampati class III to IV, (7) history of neck radiation, (8) male sex, (9) limited ability to protrude the mandible, and (10) history of an airway mass or tumor. In addition, difficult ventilation via mask can develop after multiple laryngoscopy attempts. The incidence of difficult face mask ventilation ranges from 0.9% to 7.8% and may be due to one or more of the following problems: inadequate mask or supraglottic airway seal, excessive gas leak, or excessive resistance to the ingress or egress of gas. Severe adverse outcomes related to difficult ventilation via a mask include inability to oxygenate, ventilate, prevent aspiration of gastric contents, or a combination of these factors, which can result in hypoxic brain damage or death.
Face Mask Characteristics
Face masks are available in a variety of sizes. A properly sized face mask should have the top of mask fit over the bridge of the nose, with the upper border aligned with the pupils and the bottom of the mask should sit between the lower lip and the chin. Most face masks come with a hooked rim around the 15- to 22-mm fitting that attaches to the anesthesia breathing circuit. This rim allows straps to be used to hold the face mask in place when a patient is breathing spontaneously or to improve the seal during face mask ventilation.
Prior to induction of anesthesia, breathing 100% O 2 allows for a longer duration of apnea without desaturation by increasing oxygen reserves (denitrogenation). A healthy adult, who is not obese, can be apneic for approximately 9 minutes before significant desaturation occurs. This time is primarily dependent on oxygen consumption and the FRC. Obesity, pregnancy, and other conditions that significantly decrease FRC or factors that increase oxygen consumption decrease the time to desaturation ( Fig. 16.8 ) (also see Chapter 29, Chapter 33 ).
Several techniques of preoxygenation exist with the goal of achieving an end-tidal oxygen level above 90%. Three minutes of tidal volume breathing of 100% O 2 is superior to four deep breaths in 30 seconds. Eight deep breaths in 60 seconds are equivalent to breathing 100% oxygen for 3 minutes. Preoxygenation in a 25-degree head-up position in obese patients can increase the time to desaturation by decreasing atelectasis and improving ventilation/perfusion matching. In addition, preoxygenation with noninvasive positive-pressure ventilation followed by a recruitment maneuver immediately after endotracheal intubation in obese patients can preserve lung volumes and oxygenation better than preoxygenation alone (also see Chapter 29 ).
After induction of anesthesia, the face mask should be held to the patient’s face with the fingers of the anesthesia provider’s left hand lifting the mandible (chin lift, jaw thrust) to the face mask. Pressure on the submandibular soft tissue should be avoided because it can cause airway obstruction. The anesthesia provider’s left thumb and index finger apply counterpressure on the face mask. Anterior pressure on the angle of the mandible (jaw thrust), atlanto-occipital joint extension, and chin lift combine to maximize the pharyngeal space. Differential application of pressure with individual fingers can improve the seal attained with the face mask. The anesthesia provider’s right hand is used to generate positive pressure by squeezing the reservoir bag of the anesthesia breathing circuit. Ventilating pressure should be less than 20 cm H 2 O to avoid insufflation of the stomach.
Managing Inadequate Ventilation Via a Mask
Signs of inadequate mask ventilation include absent or minimal chest rise, absent or inadequate breath sounds, cyanosis, gastric air entry, decreasing or inadequate oxygen saturation, absent or inadequate exhaled carbon dioxide, and hemodynamic changes associated with hypoxemia or hypercarbia, or both.
Inadequate face mask ventilation is usually due to decreased compliance and increased resistance. An oral or nasal airway may help to generate sufficient positive pressure for adequate ventilation with the anesthesia breathing circuit. Oral and nasal airways are designed to create an air passage by displacing the tongue from the posterior pharyngeal wall. Aligning the airway device with the patient’s profile and approximating the anatomic path that it will take can be used to estimate the appropriate size. The distal tip of the oral and nasal airway should be at the angle of the mandible when the proximal end is aligned with the mouth or the nose, respectively. An oral airway may generate a gag reflex or cause laryngospasm in an awake or lightly anesthetized patient. Nasal airways are better tolerated during lighter levels of anesthesia, but are relatively contraindicated in patients who have coagulation or platelet abnormalities, are pregnant, or have basilar skull fractures.
Presence of a beard or lack of teeth may result in inadequate seal between the patient’s face and the mask making it difficult to deliver positive pressure. If the patient is amenable, shaving or trimming a beard can improve face mask seal. If a patient’s dentures are well adhered, allowing them to be left in place or use of an oral airway can improve face mask seal in edentulous patients.
If oral and nasal airways do not optimize ventilation with a face mask, a two-handed face mask technique should be utilized. The anesthesia provider uses the right hand to mirror the hand position of the left to improve face mask seal and jaw thrust. A second person can assist by ventilating the patient with the reservoir bag. In spite of corrective measures, if difficult or impossible face mask ventilation continues, intubation or placement of a supraglottic airway should be attempted.
Supraglottic Airway Devices
Supraglottic airway devices have become invaluable for routine and difficult airway management. For elective airway management, advantages over endotracheal intubation include the following: placement quickly and without the use of laryngoscope, less hemodynamic changes with insertion and removal, less coughing and bucking with removal, no need for muscle relaxants, preserved laryngeal competence and mucociliary function, and less laryngeal trauma. In the difficult airway scenario, they can be a lifesaving tool for oxygenation and ventilation as well as a conduit for intubation. Many of the factors that result in difficult mask ventilation and intubation do not overlap with those that influence supraglottic airway success. Therefore, when other oxygenation or ventilation techniques have failed, a supraglottic airway device may still succeed. Difficult supraglottic airway placement or failure has been associated with small mouth opening, supra- or extraglottic disease, fixed cervical spine deformity, use of cricoid pressure, poor dentition or large incisors, male sex, surgical table rotation, and increased BMI. The incidence of difficult supraglottic airway placement, indicated by inability of an anesthesiologist to provide adequate ventilation is 1.1%.
Some contraindications for using supraglottic airway devices are as follows: patients at risk for regurgitation of gastric contents, nonsupine position, obesity, pregnant patients, long surgical time, and intra-abdominal or airway procedures. Although there have been numerous studies of patients in these categories in which supraglottic airways have been successfully used, one must consider the risk versus benefit of use in these situations. After placement of a supraglottic airway device, it is important to confirm correct positioning by observing end-tidal CO 2 and auscultation of breath sounds.
Reported complications of laryngeal mask airway (LMA) use in difficult airway patients include bronchospasm, postoperative swallowing difficulties, respiratory obstruction, laryngeal nerve injury, edema, and hypoglossal nerve paralysis. Aspiration remains a concern with supraglottic airway placement and its risk increases with gastric inflation, high airway pressures, and poor supraglottic airway positioning over the glottis. There are many different types of supraglottic airway devices in single-use and reusable forms, including intubating supraglottic airways and supraglottic airways allowing gastric decompression. Supraglottic airway devices are sized according to the patient’s weight, and sizes vary by manufacturer. Selected devices are detailed next.
Laryngeal Mask Airway
LMA Classic and Unique
The original LMA, the LMA Classic, is reusable, and the LMA Unique is the comparable single-use device. These LMAs consist of a flexible shaft connected to a silicone rubber mask (Classic) or polyvinylchloride (Unique) that seals with the airway in the hypopharynx ( Fig. 16.9 ). The distal tip of the cuff should be against the upper esophageal sphincter (cricopharyngeus muscle), the lateral edges rest in the piriform sinuses, and the proximal end seats under the base of the tongue. Before placement, the cuff should be deflated, the device should be lubricated, and the head should be positioned in the sniffing position. These LMAs are designed to be inserted by holding the shaft between the index finger and thumb with the tip of the index finger at the junction of the mask and the tube. Upward pressure against the hard palate is applied as they are advanced toward the larynx until resistance is felt. Intubation through these devices can be facilitated by use of an intubation catheter and a fiberoptic bronchoscope (see later section regarding Aintree Intubation Catheter [AIC] ). The LMA Classic and LMA Unique are available in sizes for infant, pediatric, and adult patients.
The LMA Fastrach (intubating LMA, ILMA) was designed to obviate the problems encountered when attempting to blindly intubate the trachea through the LMA Classic. The ILMA is used with a specialized endotracheal tube that exits the laryngeal mask at a different angle than a standard endotracheal tube and results in better alignment with the airway. It is also available in a single-use version.
LMA ProSeal/LMA Supreme
The reusable LMA ProSeal and single-use LMA Supreme are modifications of the LMA Classic ( Fig. 16.10 ). Their cuffs are modified to extend onto the posterior surface of the mask, which results in an improved airway seal without increasing mucosal pressure. This allows for ventilation with higher airway pressures. They both contain a second lumen that opens at the distal tip of the mask to act as an esophageal vent to keep gases and fluid separate from the airway and facilitate placement of an orogastric tube. This is designed to decrease the risk of regurgitation and aspiration of gastric contents. In addition, placement of an orogastric tube can help confirm proper placement of these devices. The LMA ProSeal and Supreme also have built in bite blocks to decrease the chance of obstruction of the airway tube. The LMA Supreme may be more rapid and easier to insert, has lower cuff pressures, and has higher oropharyngeal leakage pressures when compared to the LMA Classic in patients undergoing surgery. However, when there is difficulty with ventilation, the LMA Classic remains the “gold standard” supraglottic airway device. Intubation through these devices can be achieved by using an intubation catheter and a fiberoptic bronchoscope. Both are available in pediatric and adult sizes.
The LMA Flexible has a wire-reinforced, flexible airway tube that allows it to be positioned away from the surgical field while minimizing loss of seal. This can be useful for procedures involving the head and neck. Insertion of the LMA Flexible is more difficult than the LMA Classic. Using a stylet or introducer may help with insertion of this device. It is available as a reusable or single-use device in adult and pediatric sizes.
Air-Q Masked Laryngeal Airways
The Air-Q is a device that can be utilized either as a primary airway or as an intermediary channel for intubation of the trachea. It has an elliptical, inflatable, cuffed mask and a slightly curved airway tube with a detachable connector. Several features serve to aid intubation: a short shaft, no aperture bars within the mask, a detachable connector so that the wide lumen of the shaft can be used for intubation, and a distal airway tube shaped to direct an endotracheal tube toward the larynx. When used as a conduit for intubation, each size of the Air-Q laryngeal mask has a corresponding maximum cuffed endotracheal tube size. After an endotracheal tube is placed, removal of the Air-Q device is aided by a removal stylet. The Air-Q is available in infant, pediatric, and adult sizes as a reusable or single-use airway device. The largest size can be used with up to an 8.5 mm standard endotracheal tube ( Fig. 16.11 ).
The I-Gel is a single-use supraglottic airway device composed of a soft, gel-like, noninflatable cuff. It has a widened, flattened stem with a rigid bite block that acts as a buccal stabilizer to reduce rotation and malpositioning, and a port for gastric tube insertion. It can be a primary airway, but also has a wide bore airway channel that can be used as a conduit for intubation with fiberoptic guidance. This supraglottic airway device comes in infant, pediatric, and adult sizes. Adult sizes can accommodate endotracheal tube sizes 6.0 to 8.0 mm.
Esophageal Tracheal Combitube and King Laryngeal Tube
The esophageal tracheal combitube (Combitube) and the King Laryngeal Tube (King LT) are primarily used for emergent airway control in prehospital settings when endotracheal intubation is not possible or feasible. The Combitube is an esophageal and tracheal double-lumen airway, whereas the King LT has a single lumen with a large proximal pharyngeal cuff and a distal esophageal cuff. The blind insertion techniques for these devices require minimal training and no movement of the head or neck. The Combitube is available in adult sizes, and the King LT is available in both pediatric and adult sizes.
A Combitube should be replaced after 8 hours of use owing to pressure the tube exerts on the pharyngeal mucosa. It can be replaced by deflating the oropharyngeal balloon and placing an endotracheal tube anterior or lateral to the Combitube.
Endotracheal intubation may be considered in every patient receiving general anesthesia ( Box 16.1 ). Orotracheal intubation by direct laryngoscopy in anesthetized patients is routinely chosen unless specific circumstances or the patient’s history and physical examination dictate a different approach. Equipment and drugs used for endotracheal intubation include a properly sized endotracheal tube, laryngoscope, functioning suction catheter, appropriate anesthetic drugs, and equipment for providing positive-pressure ventilation of the lungs with oxygen.
Provide a patent airway
Prevent inhalation (aspiration) of gastric contents
Need for frequent suctioning
Facilitate positive-pressure ventilation of the lungs
Operative position other than supine
Operative site near or involving the upper airway
Airway maintenance by mask difficult
Proper positioning is crucial to successful direct laryngoscopy when alignment of the oral, pharyngeal, and laryngeal axes is necessary for creating a line of vision from the lips to the glottic opening. Elevation of the patient’s head 8 to 10 cm with pads under the occiput (shoulders remaining on the table) and extension of the head at the atlanto-occipital joint serve to align these axes. The height of the operating table should be adjusted so that the patient’s face is near the level of the standing anesthesia provider’s xiphoid cartilage.
The laryngoscopic view obtained is classified according to the Cormack and Lehane score. Grade III or IV views are associated with difficult intubation ( Fig. 16.12 ).
Grade I: Most of the glottis is visible.
Grade II: Only the posterior portion of the glottis is visible.
Grade III: The epiglottis, but no part of the glottis, can be seen.
Grade IV: No airway structures are visualized.
Difficult Airway Management
Difficult laryngoscopy is defined as the inability to visualize any portion of the vocal cords after multiple attempts at direct laryngoscopy. Difficult endotracheal intubation is defined as endotracheal intubation requiring multiple attempts. These occur in about 0.8% to 7.0% of patients in the operating room setting. Failed intubation of the trachea occurs in about 1 in 2000 patients in an elective setting.
The information obtained through a comprehensive airway assessment should allow development of a plan to manage the patient’s airway. Airway devices have different advantages that make them beneficial in specific situations. Options include direct laryngoscopy, use of alternative airway devices such as video laryngoscopes and endotracheal tube guides, special techniques like awake or asleep fiberoptic endotracheal intubation, or rescue invasive techniques. In patients with anticipated or history of a difficult airway, the following management principles should be considered: (1) awake endotracheal intubation versus intubation after induction of general anesthesia, (2) initial intubation method via noninvasive versus invasive techniques, (3) video laryngoscopy as an initial approach to intubation, and (4) maintaining versus ablating spontaneous ventilation. A patient’s ability to cooperate with airway management should be considered when making an initial plan and a difficult airway cart should be immediately available for management of back-up plans. Intubation attempts should be minimized, and repeat laryngoscopy should only occur when a different tactic is used. The ASA difficult airway algorithm details approaches to alternative strategies of airway management once there is failure of a primary plan (see Fig. 16.1 ).
The laryngoscope is traditionally held in the anesthesia provider’s left hand near the junction between the handle and blade of the laryngoscope. If not opened by extension of the head, the patient’s mouth may be manually opened by counterpressure of the right thumb on the mandibular teeth and right index finger on the maxillary teeth (“scissoring”). Simultaneously with insertion of the laryngoscope blade, the patient’s lower lip can be rolled away with the anesthesia provider’s left index finger to prevent bruising by the laryngoscope blade. The blade is then inserted on the right side of the patient’s mouth so that the incisor teeth are avoided and the tongue is deflected to the left. Pressure on the teeth or gums must be avoided as the blade is advanced forward and centrally toward the epiglottis. The anesthesia provider’s wrist is held rigid as the laryngoscope is lifted along the axis of the handle to cause anterior displacement of the soft tissues and bring the laryngeal structures into view. The handle should not be rotated as it is lifted to prevent damaging the patient’s upper teeth or gums. Manipulation of the patient’s thyroid cartilage externally on the neck, commonly using backward upward rightward pressure (BURP), may facilitate exposure of the glottic opening.
The endotracheal tube is held in the anesthesia provider’s right hand like a pencil and introduced into the right side of the patient’s mouth with the natural curve directed anteriorly. The endotracheal tube should be advanced toward the glottis from the right side of the mouth as midline insertion usually obscures visualization of the glottic opening. The tube is advanced until the proximal end of the cuff is 1 to 2 cm past the vocal cords, which should place the distal end of the tube midway between the vocal cords and carina. At this point, the laryngoscope blade is removed from the patient’s mouth. The cuff of the endotracheal tube is inflated with air to create a seal against the tracheal mucosa. This seal facilitates positive-pressure ventilation of the lungs and decreases the likelihood of aspiration of pharyngeal or gastric contents. Use of the minimum volume of air in a low-pressure, high-volume cuff that prevents leaks during positive ventilation pressure (20 to 30 cm H 2 O) minimizes the likelihood of mucosal ischemia resulting from prolonged pressure on the tracheal wall. After confirmation of correct placement (end-tidal CO 2 , auscultation for bilateral breath sounds, ballottement of cuff in the suprasternal notch), the endotracheal tube is secured in position with tape. The success rate of endotracheal intubation using direct laryngoscopy in patients without a predicted difficult intubation is more frequent than 90%, and in patients with predicted difficult intubation is 84%.
Choice of Direct Laryngoscope Blade
The advantages of the curved blade, such as a Macintosh blade, include less trauma to teeth, more room for passage of the endotracheal tube, larger flange size that improves the ability to sweep the tongue, and less bruising of the epiglottis because the tip of the blade does not directly lift this structure. The advantages of the straight blade such as a Miller blade, are better exposure of the glottic opening and a smaller profile, which can be beneficial in patients with a smaller mouth opening.
The tip of the curved blade is advanced into the space between the base of the tongue and the pharyngeal surface of the epiglottis into the vallecula, which elevates the epiglottis and exposes the glottic opening ( Fig. 16.13A ). The tip of the straight blade is passed beneath the laryngeal surface of the epiglottis (see Fig. 16.13B ). Forward and upward movement of the blade exerted along the axis of the laryngoscope handle directly elevates the epiglottis to expose the glottic opening.
Laryngoscope blades are numbered according to their length. A Macintosh 3 and Miller 2 are the standard intubating blades for adult patients. The Macintosh 4 and Miller 3 blades can be used for larger adult patients ( Fig. 16.14 ).
Video laryngoscopes can help obtain a view of the larynx by providing indirect visualization of the glottic opening without alignment of the oral, pharyngeal, and tracheal axes and enable endotracheal intubation in patients who have conditions (limited mouth opening, inability to flex the neck) that can make traditional laryngoscopy difficult or impossible. Their ease of use is an advantage over fiberoptic bronchoscopy in these patients. They consist of a handle, light source, and a blade with a video camera at the distal end to enable the glottis to be visualized indirectly on a video monitor. Video laryngoscopes are classified as nonchanneled or channeled.
Nonchanneled blades are Macintosh-style curved blades, Miller-style straight blades, and angulated blades. Types of nonchanneled blades include GlideScope, C-MAC, and McGrath.
The Macintosh-style or Miller-style blades can be used for direct laryngoscopy or by viewing the monitor. These blades are inserted using the standard direct laryngoscopy techniques with or without a stylet in the endotracheal tube. The view obtained by looking at the monitor usually offers a slightly improved view compared to looking directly in the patient’s mouth because the camera is more distally located and provides a wider visual field. The advantage of these blades is user familiarity with the blade type and a display that can be used for instructional purposes.
The angulated blades allow for a more anteriorly oriented view that can be obtained with minimal flexion or extension of the patient’s head and neck. The tip of the laryngoscope blade may be placed in the vallecula or be used to lift the epiglottis directly. These blades usually require a preshaped stylet that matches the curvature of the blade and are usually inserted midline in the mouth, unlike the Macintosh-style blades. An endotracheal tube with the preshaped stylet is advanced using direct visualization in the pharynx until it can be seen on the monitor, after which the tube is advanced into the trachea close to the blade, based on the image on the monitoring screen. Tonsillar and pharyngeal injuries can occur when using video laryngoscopy, especially with rigid stylets when the stylet is advanced through the oropharynx looking at the video screen and not under direct visualization. A limitation of these devices is difficulty directing the endotracheal tube into the glottis despite good glottic visualization. This usually occurs when the laryngoscope is inserted too deeply. Withdrawing the blade slightly, although often giving a poorer laryngoscopic view, can improve the ability to direct the endotracheal tube through the glottic opening.
Channeled devices include the Airtraq and the King Vision Video Laryngoscope. These video laryngoscopes have a guide channel that directs an endotracheal tube toward the glottic opening via blades that are more angulated than traditional Macintosh blades. The endotracheal tube is preloaded into the guide channel and the video laryngoscope is inserted midline in the mouth until the epiglottis is visualized. The blade is advanced into the vallecula or the epiglottis may be directly elevated by the tip of the blade until the cords are visualized. The glottis needs to optimally align on the screen for successful intubation via the channel. Channeled blades tend to have thicker blades than nonchanneled blades requiring a greater interincisor distance.
These techniques can be hindered if upper airway secretions obscure the optics. Video laryngoscopes can also be used on awake patients with topical application of local anesthetic to the airway and are as easy to perform with comparable patient discomfort as fiberoptic intubation. Selected video laryngoscopes are detailed as follows.
The GlideScope has two main blade types: an angulated style blade and a Macintosh-style blade. The reusable blades are made of either titanium or medical-grade plastic (AVL, GVL, and Ranger). The titanium blade offers the advantage of being thinner and hence a lower profile (allowing for insertion with a smaller interincisor distance). The angulated blade is anatomically shaped with a fixed (60-degree) angle and should be used with the GlideRite rigid stylet as this stylet matches the shape of the blade. The blades have a fog-resistant video camera embedded in the undersurface that transmits the digital image to a high-resolution color monitor that can be mounted on a pole. A portable (Ranger) device is also available. There are a variety of different pediatric and adult sizes in reusable and single-use blades ( Fig. 16.15 ).