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W1996980879 abstract "Understanding the anatomy of the cervical spine and its anatomical relationships to the airway has daily importance to the anesthesiologist. Particularly important considerations include the contribution of chronic abnormalities of the cervical spine to the difficult airway, and the perioperative morbidity and mortality associated with cervical spine problems. Abnormalities of the cervical spine may necessitate changes in airway management. In reviewing these issues, we will not discuss cervical spine trauma [1-4] nor venous air embolism [5], as these subjects have been reviewed recently. We will generally limit our discussion to cervical spinal behavior in anterior flexion and posterior extension, the directions that are most relevant to the topic of airway management. The incidence of adverse events occurring in patients with chronic cervical spine disease undergoing anesthesia remains unknown, as is the total number of patients with chronic cervical spine disease undergoing anesthesia. Patients may be unaware of cervical spine disease. Chronic disease of the cervical spine may render tracheal intubation more difficult and therefore increase the risk of esophageal intubation. The ASA closed claims analyses by Caplan et al. [6] and Kroll et al. [7] document adverse respiratory and neurologic events in patients who underwent an anesthetic but in whom known or suspected chronic disease of the cervical spine was not discussed. Difficult tracheal intubation occurred in 87 cases (or 17%) of 522 closed respiratory claims and in 6% or 87 of all (1541) closed claims examined for the 10-year period, 1975-1985. The criteria for difficulty were not specified. Ninety-four of the same 522 cases (18%) were esophageal intubations. Kroll et al. [7] also had reported that 227, or 15%, of the same 1541 claims had nerve injuries and that 13 of those 227 nerve-injured patients (6%) claimed damage to the spinal cord, although the type and causal factors were not mentioned. Whether chronic cervical spine disease leads to a higher incidence of esophageal intubation, difficult tracheal intubation, or cervical spinal cord injuries is not established. There has been no study of the relationship between difficult intubation and cervical spinal cord damage, i.e., radiculopathy, myelopathy, or central spinal cord syndrome [8,9]. The central spinal cord syndrome is a clinical composite of neurologic signs [10], including weakness, urinary retention, and varying degrees of sensory loss below the level of the cord lesion, usually seen after an acute hyperextension injury in adults with underlying severe cervical spinal spondylosis and stenosis [11]. Spondylosis is a vertebral and disk degenerative disease with osteoarthritis of apophyseal joints, and osteophytic growth into the vertebral canal or foramina, the bony conduits through which the spinal nerves exit. The osteophytic bone growths impinge upon the airway and the spinal cord (Figure 1) and may damage the cord anteriorly against a thickened, bulging ligamentum flavum. In the most current ASA Closed Claims Project database of 3001 claims, the only closed claim of laryngoscopy-associated spinal cord injury involved a young, obese male who underwent general anesthesia and endotracheal intubation for repair of a detached retina (F. W. Cheney, personal communication from the ASA Closed Claims Project database, July 1994). The patient was noted to be quadriplegic upon awakening after anesthesia. Magnetic resonance imaging (MRI) of the cervical spine revealed a herniated cervical disk with marked cord compression and spondylosis. Deem et al. [12] described a patient with severe cervical spinal stenosis, spondylosis, and degenerative joint disease who underwent thoracolumbar decompression laminectomy in the prone position and developed quadraparesis postoperatively. The authors postulated that the mechanism of injury was the central spinal cord syndrome, due to ischemic injury to the spinal cord secondary to decreased spinal cord blood flow or direct cord compression. Cord compression can be secondary to hyperextension or hyperflexion in a patient with a compromised cervical spinal canal [13]. These authors recommended avoiding hypotension in anesthetized patients with cervical spondylosis, but, more importantly, carefully positioning the head and neck to maintain a neutral cervical spine position.Figure 1: Magnetic resonance imaging of the cervical spine in extension, midsagittal view. The patient has spinal stenosis with spondylotic osteophytic growth as the source of cord compression at C3-4, as well as anterior airway compression at C2-4.Adverse respiratory events in patients with chronic cervical spine disease can occur throughout the perioperative period. Wattenmaker et al. [14] performed a retrospective study of 128 rheumatoid arthritic patients who had undergone posterior cervical spine surgery. They observed a lower incidence of postextubation airway obstruction in patients tracheally intubated with the aid of a fiberoptic bronchoscope (one of 70) than in those intubated by direct larnygoscopy (eight of 58). They concluded that this was due to the decreased tissue trauma associated with fiberoptic intubation. All patients had remained intubated overnight. Postextubation airway obstruction occurred within minutes after extubation in most of the nine patients who developed postextubation airway obstruction. This obstruction was thought to be secondary to acute edema of the airway mucosa, but was not documented. An additional study using MRI might be helpful. Anatomy and Biomechanics The cervical spine is composed of seven vertebrae (Figure 2, Figure 3, and Figure 4) which support and permit movement of the head on the thorax and protect the spinal cord. The first cervical vertebra (C-1), also termed the atlas, directly supports the cranium at the occiput. The second cervical vertebra (C-2) is the axis. The fusion of the bodies from C-1 and C-2 is a peglike process superoanterior to C-2, now detached from C-1, called the odontoid process or the dens. The atlas is an osseus ring, with a vestigial spinous process, supporting the cranium. There are no intervertebral disks between the occiput and C-1, or between C-1 and C-2. The anterior tubercle of the transverse process of C-6 is known as Chassaignac's tubercle. The spinous process of C-7 (known as the vertebra prominens), is the most easily palpated.Figure 2: Three-dimensional (3D) reconstructive helical computed tomograph (CT) with a superior view of the cervical spine, displaying the basic bony anatomy.Figure 3: Three-dimensional reconstructive helical computed tomograph, superior view, illustrating the juxtaposition of the airway and the cervical spine. Sandwiched between these structures lies the esophagus. The airway image is a mucosal cast of the structures of the airway. At this level, one is looking down at the level of the larynx.Figure 4: Three-dimensional (3D) reconstructive helical computed tomograph (CT), posterosuperior view, at the level of C-1 and more caudad, illustrating the interpolation of the odontoid process into the structure of C-1.As the spinal cord passes through the cervical spinal canal, there is only limited space for the spinal cord and its adherent and stabilizing structures. On the average, this space's sagittal diameter in adults is approximately 20 mm. The spinal cord is largest in cross-sectional area from approximately C-3 to T-1, with the maximal diameter in adults being roughly 12 mm. With extension of the cervical spine, the cord and some of the ligaments may become buckled, whereas upon flexion, the same structures may become stretched. Any pathologic structures, such as osteophytic bone growths, that occupy some of the space available for the cord may place the cord or the neural roots in jeopardy by impingement or compression. The distance between the anterior border of the cervical vertebral bodies and the posterior laryngeal border is approximately 1 to 1.5 cm (Figure 5). This distance remains relatively stable throughout normal growth and development [15]. The larynx moves posterocephalad with flexion and anterocaudad with extension of the cervical spine. The natural lordotic curvature of the cervical spine tends to flatten with flexion, and become accentuated with hyperextension [4,16,17]. The cricoid cartilage is strongly pulled posteriorly toward the cervical spine by function of the cricopharyngeal muscle. Upon swallowing, this muscle serves to narrow the pharynx. Normally, in the neutral cervical position, the cricoid cartilage (Figure 5) in the adult is at level of the disk between C-6 and C-7. The epiglottic tip is usually at C-3.Figure 5: Three-dimensional (3D) reconstructive computed tomograph (CT) sagittal image of the cervical spine in extension with the airway in anatomical juxtaposition, from the level of the hard palate to within the debut of the trachea.The normal range of anteroposterior motion of the complete cervical spine, from full flexion to hyperextension, is from 90 to 165 total degrees of arc, thus describing an arc made from a fixed point, i.e., the chin as it moved from the point closest to resting upon the chest wall, to the furthest away with the head tilted backward [18]. The total degrees of arc describing the range of motion due to extension alone is reported to be approximately 50-100 degrees, and in flexion alone is 40-65 degrees [1,16,19,20] in normal adults. Each of the moveable components, or spinal segments, play a role in the fluid motion of the cervical spine. For discussion of cervical spine biomechanics, the cervical spine is composed of three distinct sections: upper, middle, and lower. The occipital-atlanto-axial complex, C0-2, is the most flexible single portion of the cervical spine in the sagittal plane (relative to the total number of vertebrae). The range of motion of the atlantooccipital joint alone (C0-1) is a maximum arc of approximately 43 degrees, depending on age [21], health, and source of data [22,23]. Normally, flexion, which is about one third of the total range of motion of the upper cervical spine, is restricted by skeletal contact between the anterior margin of the foramen magnum and the tip of the dens, as well as by limitation and stabilization by the tectorial membrane. Extension, the other two thirds of the combined range of motion, is normally limited by the anterior longitudinal ligament (which connects the anterior and lateral aspects of the vertebral bodies and disks) by the tectorial membrane (continuation of the posterior longitudinal membrane, which covers the posterior aspects of the vertebral bodies) and the ligamentum flavum (which connects the laminae). The anterior atlantooccipital membrane, a continuation of the cervical anterior longitudinal ligament, connects the occiput to the anterior ring of C-1. This membrane probably comes under tension with extension; however, it does not restrict extension. Combined flexion/extension of the atlantoaxial (C1-2) unit is maximally 20 degrees and is normally limited by the anterior atlantodental ligaments, ligamentum flavum, tectorial membrane, and other posterior ligaments. The flaval ligaments extend between the vertebral arches. The longitudinal ligaments cover the anterior and posterior surfaces of the vertebral bodies and disks. The interspinous ligaments join together the spinous processes. The middle portion of the cervical spine is comprised of the largest number of vertebrae, C-2 through C-5, with a total average range of motion of approximately 58 degrees, combining flexion and extension. The biomechanics of the middle and lower cervical spine are also established by bony contact and limited by the same ligaments as described above for the upper cervical spine [24]. The most caudad portion of the cervical spine, C5-7, is the transitional group contiguous with the thoracic spine. It has the most restricted range of motion, approximately 46 degrees, of the three cervical spinal sections. A series of ligaments, both passive and active, span and reinforce the osseous structure of the spine. They stabilize, limit, and guide the neck in flexion and extension. The active ligaments are constantly under tension, whereas the passive ones are under tension only at the extremes of the range of motion of the cervical spine. The flexion-stabilizing structures consist of the tectorial membrane and the posterior longitudinal ligament. The extension-stabilizing structures are represented by the ligamentum flavum, the tectorial membrane, the anterior longitudinal ligament, and the anterior atlantooccipital membrane. After injury, or with normal aging, these ligamentous structures can become calcified, resulting in limitation of motion of the cervical spine. The extension stabilizers are usually affected more than the flexion stabilizers. There are many different functional groups of cervical muscles, five of which move and stabilize the head and cervical spine. These five are the superficial cervical, posterior cervical, anterior vertebral, lateral vertebral, and suboccipital groups. There are 12 muscles of extension and five muscles of flexion. The more anterior neck muscle groups work to flex the neck, while the posterior groups extend it. Growth and Aging The upper airway structures descend relative to the cervical spine during the first three years of life, in part because the cervical spine grows more rapidly than the larynx. At puberty, there is additional descent of the glottis and the cricoid cartilage due to further growth of the thyroid cartilage. Therefore, the position of the larynx with respect to the cervical vertebrae changes with age. Westhorpe [25] studied the effect of movement of the cervical spine upon the upper airway structures in 50 children ranging in age from one day to 12 years compared with four normal adults. Lateral radiographs of the head and neck were obtained in each patient in the neutral position before induction of anesthesia and after induction in four positions: neutral, maximal extension, extension with the head on a low pillow (sniff position), and with a small pillow under the shoulders (for neonates only). By measuring the alignment of the angle between the oropharyngeal and the laryngeal-tracheal axes, Westhorpe concluded that the greater number of vertebrae cephalad to the larynx in the adult allow for greater axial alignment in the adult than in the child in the sniffing position. Anterior neck flexion aided axis alignment after the age of six years. Prior to this age, cricoid pressure was more helpful in axial alignment. Most of the normal range of cervical spine motion in flexion/extension is in the central region of the cervical spine. The C5-6 interspace allows the greatest range of motion in teenagers and adults; C4-5 is most mobile in younger children [26]. These represent the cervical spine segments most frequently affected by diseases of wear and tear, resulting in spondylosis. C-2 through C-4 are most often affected by inflammatory diseases (Figure 1) such as rheumatoid arthritis [27-30]. In the patient with rheumatoid arthritis, one can expect to encounter varying degrees of fusion of the cervical spine, atlantoaxial subluxation, superior migration of the dens, marked ligamentous destruction, and erosive synovitis, atlantoaxial impaction, and spondylodiscitis. Often the anesthetist is faced with possible preoperative skeletal traction with the patient in a halo. With aging, the loss of flexibility and extensibility of the cervical spine increases the distance from the posterior portion of the cricoid ring to the anterior portion of the vertebral body. Because of this and the decreased mobility of the laryngeal cartilages, an effective Sellick maneuver may be more difficult to perform. It may also compromise the ability of the Sellick maneuver to position the laryngeal aperture more posteriorly, and expose it to view during direct laryngoscopy. Degenerative disk disease without arthritis decreases cervical range of motion, according to the geometry and stiffness of the disk. The disk space narrows and the spinal column loses height. With encroachment upon the joint and spinal canal by hypertrophic bone, the patient with cervical spondylosis loses even more joint mobility and becomes susceptible to cord compression. With increasing age, the intervertebral foramina become narrowed, osteophytes are formed, and the ligamentum flavum bulges (especially in hyperextension). Extension and flexion are both diminished with a decrease in the disk height and an increase in the anteroposterior diameter of the disk. With normal aging, there is a decrease in elasticity of the atlantooccipital ligaments [32]. For every decade of life after the age of 30 years, there is approximately 10 degrees loss in the range of flexion and extension of the cervical spine. The incidence of spondylosis approaches 100% in the elderly. Physical Examination There is no reliable method of predicting the ease of maintaining an airway or performing laryngoscopy or intubation. A Mallampati class I or II airway may be associated with a difficult intubation, whereas a class III or IV airway may represent an easy intubation [33-37]. This may be because the Mallampati classification was based solely upon the oropharyngeal inlet of the complex airway system. Fortuitously, this classification may indeed somewhat take into account the ability of the axes of the airway to be passively placed into alignment. A recent study [38] considered the effect of the head and cervical spine position upon the predictability of the ease of intubation. For preoperative airway evaluation, the authors recommended using the visibility of the oropharyngeal structures (i.e., as in the Mallampati system) in the sitting position, combined with the measurement of the mandibular space, in full cervical spine extension, with the tongue out during phonation. For preoperative assessment, it is useful to evaluate the mobility of the cervical spine. To improve evaluation, we need a better understanding of the role of the cervical spine in airway problems associated with anesthesia. The range of neck motion has been incorporated into a risk algorithm for prediction of a difficult airway. The Wilson test [39] uses the total range of motion of the neck less than 90 degrees as an evaluation criteria to help to predict difficult intubation. In contrast, MacDonald et al. [40] found that neck range of motion did not help to predict difficult intubations. I propose the following approach to the preoperative evaluation of the cervical spine. Observe neck posture while the patient is walking and upon sitting (in a neutral relaxed position). Observe the fluidity of head and neck movements. A patient with cervical spine pathology may maintain his or her head in a relatively stiff posture due to muscle spasm or bony fusion. Instead of rotating the head toward the examiner, such a patient might rotate the whole upper body. After ascertaining that the patient has no history of neurovascular symptomatology with neck rotation or lateral flexion (as may occur with vertebrobasilar disease), active examination can begin. If there is a high probability of an unstable cervical spine, do not examine the passive range of motion of the neck. By palpation, inspect the neck for normal position and midline alignment of the hyoid bone, thyroid cartilage, and the spinous processes. Examine for loss of the normal cervical lordosis and for the presence of scoliosis. Scoliosis can be congenital. However, it is usually secondary to trauma or degenerative disease. A scoliotic curvature compounds the difficulty in airway management when other pathology, such as spondylosis, is present. If the patient has had previous lumbar spinal surgery, there is an increased likelihood that he or she may also have cervical pathology. When examining the patient for range of motion of the cervical spine, stabilize the thoracic spine by placing the palm of your hand upon the upper back. Patients with limited cervical extension will extend the thoracic spine posteriorly to compensate when asked to look toward the ceiling. In full hyperextension of the cervical spine, the base of the patient's occiput should touch the spinous process of the first thoracic vertebra. This contact is palpable. The patient's forehead should approximately parallel the ceiling. One can estimate, in degrees, the arc of the cervical spine during flexion and extension. By placing a tongue depressor between the patient's clenched teeth, the arc can be measured with greater accuracy. The tongue blade should describe an arc of greater than 120 degrees. During flexion, the patient should be able to touch the chin to the sternum, although this varies depending upon the length of the neck and the shape of the chest (e.g., barrel-shaped). As a rough estimate, there is approximately a 10 degrees limitation to flexion and extension for each finger the examiner can place between the patient's chin and sternum, or between the base of the occiput and the T-1 spinous process, respectively. After estimating the range of motion of the cervical spine, focus on the amount of extension at the atlantooccipital joint. Approximately 40 degrees of arc is normal, although it is not uncommon to have close to zero atlantooccipital interspace or gap [26,41]. This would reduce the extension of C0-1 to close to 0 degrees. To evaluate this, place the palm of one hand behind the neck and ask the patient to lift up the chin maximally while you ensure a lack of motion in the lower and middle cervical spine. Because some patients feel an impingement in the atlantooccipital joint when the mouth is open widely, evaluate the spinal range of motion with the mouth both open and closed. In such patients, opening the mouth less widely during laryngoscopy might permit greater hyperextension of the patient's neck. In a patient with a narrow occipital-C-1 gap, the hyperextensive force exerted on the cervical spine by laryngoscopy accentuates the natural lordosis. This lifts the glottic structures out of axial alignment, worsening the laryngoscopic view. For examination of maximum flexion of the occipital axial joints, ask the patient to flex the neck anteriorly with the chin tucked in but not down (similar to a military position of attention). A decreased range of motion of the cervical spine can result from a diffuse process with generalized ankylosis, spondylosis, or from any individual joint being affected by these diseases. Pain, adhesions, muscle spasms, or single joint involvement with arthritic changes can limit fluid movement of the cervical spine [21]. Observe the range of motion of the cervical spine. Note symptoms and the extent of motion that elicits these symptoms. How closely can the patient approximate the position in which you would be likely to intubate the trachea, i.e., the sniff, hyperextended, or the neutral positions? Ask about pillow height and sleeping position (lateral or supine) preferred. Ask whether sleeping on a thick pillow exacerbates symptoms of radicular pain, numbness, or weakness. The preoperative range of motion evaluation will also allow the anesthesiologist to set limits on allowances for intraoperative positioning [42], i.e., the prone position. Lateral cervical rotation is important to evaluate preoperatively [43,44], for it allows the anesthetist to set limits on rotation permitted during prone positioning after the patient is anesthetized and relaxed. If the surgeon is operating on the posterior cervical spine with cranial axial traction, he or she will often move and position the head, neck, and traction device while turning the patient prone, as the anesthetist protects the airway. In some patients, imaging of skeletal pathology and neuropathology may be helpful. MRI (Figure 6) seems to be an excellent method of imaging the airway/cervical spine interaction, although MRI is more commonly used to examine neural tissue. Plain films are useful in evaluating neuroskeletal clearances [45-48]. MRI examination of the spine in fact is so sensitive that it often uncovers disk bulges and protrusions in asymptomatic patients [49]. The computed axial tomography scan is helpful in obtaining a cross-sectional view of a specific transverse level in the neck, although, as shown earlier in Figure 2, Figure 3, and Figure 4, with helical computed tomographic reconstructive software, the computed tomograms can be reprocessed to both two- (both sagittal and coronal) and three-dimensional images, beautifully delineating the airway soft tissue and bony anatomy. With the new software readily available, both magnetic resonance and computed tomogram digitized data can be manipulated to give images in any plane of the anatomy scanned.Figure 6: Head and neck magnetic resonance image: midline sagittal view; normal anatomy.The preoperative interview of the patient with cervical pathology should include a discussion of the alternatives for airway management, especially if awake fiberoptic [50] intubation in planned. Perhaps all surgical patients should be asked preoperatively whether they have ever been in a motor vehicle accident, had neck injuries, and whether they have had any weakness, numbness, or paresthesias of their arms or hands. Sedation should be used judiciously. In one case report, a patient with cervical spinal stenoses experienced weakness of the extremities when sedated with droperidol and diazepam; the author cautioned against the use of these drugs for awake fiberoptic intubation because of the confounding effects upon the peri-intubation neurologic examination [51]. If the patient is receiving anticoagulant therapy, or has a history of epistaxis, oral intubation is preferred over nasotracheal intubation. Other techniques that reduce stress on the cervical spine during intubation include the Bullard laryngoscope, the Augustine guide, the fiberoptic light wand or stylet, and blind-nasal intubation [2,52-54]. In patients with destructive lesions involving the cervical spine, i.e., osteolytic neoplasms or Pott's disease, fiberoptic intubation should be considered. Cervical Spine and Airway Management Interactions There is no standard position universally used by anesthesiologists for mask ventilation or for laryngoscopy and endotracheal intubation. The goals to open and maintain patency of the airway are accomplished by increasing the luminal diameter, and straightening it as much as possible between the mouth or nose and glottis. There are only a few standard head and neck positions for endotracheal intubation. MRI can also be used to study the cervical spine and airway interactions, i.e., changes in airway patency with different head [55] and neck positions (Figure 7, Figure 8, Figure 9, and Figure 10). Please note the manner in which the axes of the airway seem to align when changing from the flexed to the neutral to the extended and finally to the sniff position. Also note the enlargement of the airway, with anteroinferior displacement of the tongue and the genioglossus muscles, and anterior folding of the epiglottis away from the posterior wall of the pharynx.Figure 7: Magnetic resonance image of a normal neck with the cervical spine held in mild flexion. Note the right angle between the oronasopharyngeal and the laryngeal axes. The epiglottic tip lies close to the posterior pharyngeal wall and the tongue is in close proximity to the palatine surface.Figure 8: Magnetic resonance image of a normal neck with the cervical spine in the neutral position. Note the normal lordosis. In this position, the patient's occlusal line (one drawn between the teeth with the mouth closed), would be perpendicular to the surface on which the patient is lying. Compared to the flexion view, the epiglottic tip is pulled slightly anterior.Figure 9: Magnetic resonance image of a normal neck with the cervical spine held in hyperextension. The tongue is pulled anteriorly away from the soft palate. The epiglottis is even more anterior.Figure 10: Magnetic resonance image of a neck with the cervical spine held in the sniffing position. The luminal diameter of the airway appears to be at its greatest throughout the nasal and oropharynges. The epiglottic tip is totally anterior.The neutral position (Figure 8) allows the cervical spine to rest in its natural alignment, with a slight lordotic curve. This position is achieved with the plane of the upper teeth perpendicular to the plane of the operating table. The position, which may be optimal for intubation of a patient at risk for neurological damage with airway manipulation, minimizes the luminal diameter of the airway at the base of the tongue [56,57]. In Figure 8, note that the tip of the epiglottis is pulled slightly more in the anterior direction than in flexion. In the neutral position, there is no significant difference in cervical spine movement on laryngoscopy with a straight or curved laryngoscope blade in healthy, young volunteers without known cervical spine disease [1]. The sniffing, sniff, or the amended (Jackson) position (Figure 10), is that position which involves anterior flexion of the lower cervical vertebrae and hyperextension of the head upon the cervical spine at the atlantooccipital joint. This is the position chosen by the professional sword swallower as well as the best position for laryngoscopy and endotracheal intubation of most patients with normal cervical spines. It best aligns the axes of the airway and minimizes the distance between the lips and the glottis. Note in Figure 10 that the airway is most patent from the nose and mouth to the epiglottic tip. The distance from the epiglottic tip to the posterior pharyngeal wall is maximal, as the epiglottis is folded anteriorly. In order for this position to be achieved, there must not be too much fusio" @default.
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W1996980879 title "Anesthetic Implications of Chronic Disease of the Cervical Spine" @default.
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