CERVICAL SPINE ANATOMY AND PHYSIOLOGY FOR THE ANESTHESIOLOGISTS

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CERVICAL SPINE ANATOMYAND PHYSIOLOGY FOR
THEANESTHESIOLOGISTS
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C-Spine Anatomy

• The subaxial spine (below the axis of C2)
• The upper (or atlantoaxial) C-spine, which
  includes the skull base, C1 and C2
• C1 (the Atlas)
• A ring, with large, lateral superior and inferior
  articular surfaces
• No vertebral body and no spinous process
• Attached relatively firmly to the skull, by the
  capsular ligaments of the atlanto-occipital
  joints, anterior and posterior atlanto-occipital
  membranes, and the posterior-longitudinal ligament

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• C2 (the Axis)
• A long, thumb-like upward extension of its
  vertebral body
• The odontoid process is held against C1 by a
  series of ligaments, the most important of which
  is the transverse ligament
• Anterior atlantodental interval (AADI)
• The space between the anterior aspect of the dens
  and the back of the anterior arch of C1
• Posterior atlantodental interval(PADI)
• From the back of the dens to the anterior aspect
  of the posterior arch of C1
• Changes in size of the AADI with flexion and
  extension are used as an index of atlantoaxial
  instability

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Normal Motion

• Three axes of motion
• Flexionextension (floor to ceiling),130140
• Lateral bending (shoulder-to-shoulder),8590
• Axial rotation (turning side-to side),160170
• The entire C-spine motion
• OcciputC1 joints/ligaments
• Tight and allow essentially no anteroposterior
  subluxation, minimal axial rotation, 510
  degrees of lateral bending, 1520 of extension,
  and only 5 of flexion

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• C1C2 unit
• Maximal rotation, flexion and extension 10
• C2C3 and below
• Flexion and extension are roughly equal
• C4C5C6
• 20 of total movement at each interspace,
  allowed maximum motion occurs
• Lateral bending is the result of roughly 510 of
  motion per segment below C2

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Movement with Direct Laryngoscopy

• The primary force applied by the laryngoscope is
  upward lift, combined with some rotational torque
• This lifting force can be as high as 5080N (40N
  is the force needed to lift 10 lb and we
  sometimes lift the head, which weighs 1214 lb,
  off of the pillow)
• Direct laryngoscopy with a Mac 3 blade results in
  vertical lift, progressive extension at occiput
  and C1, combined with flexion below C2C3
• More extreme sniffing positions

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C-Spine Pathology and Instability

• Atlantoaxial instability
• The odontoid process is no longer firmly held
  against the back of the anterior arch of C1
• To disruption/destruction of the transverse
  ligament (as seen in severe rheumatoid arthritis
  or Down syndrome)
• To damage to the odontoid process itself (e.g.,
  fracture across the base)
• A fracture of the anterior arch of C1

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Rheumatoid Arthritis

• Destruction of multiple joints in the neck and
  erosion/disruption of the transverse ligament
• 50 some involvement of the C-spine, C1C2 being
  the most common abnormality
• Having flexionextension x-rays prior to any
  planned airway manipulation
• Instability-radiology evidence of skullC1
  subluxation on C2, shown by an increase in the
  AADI with flexion to 45 mm

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Down Syndrome

• Laxity of the transverse ligament (and other
  ligaments) is associated with radiologic evidence
  of atlantoaxial instability in 1015 of
  patients younger than 20 years (the incidence
  decreases with increasing age)
• At least one screening radiograph be obtained
  before the age of 5 years suggested by the Down
  Syndrome Medical Interest Group and the American
  Academy of Pediatrics
• Be concern with any surgical procedure that
  requires direct laryngoscopy or extensive neck
  manipulation (e.g., tonsillectomies, myringotomy
  tubes)

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Problem of C1C2 Instability

• If the transverse ligament is damaged, lifting
  the skull with a laryngoscope will move C1
  anteriorly on C2, which results in an increase in
  the AADI and a reciprocal decrease in the PADI
• As the PADI decreases, the cord may be compressed
  in the space behind the odontoid
• Extensive rotation of the neck may also produce
  cord compression

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Airway Management of the Patient with Rheumatoid
Arthritisor Down Syndrome

• In elective surgical patients with known C1C2
  instability
• Managed by awake fiberoptic techniques or by any
  awake method
• If a general anesthetic is judged necessary prior
  to intubation (e.g., in a child)
• Intubation without lift or extension
• Down syndrome without x-ray abnormalities,
  without S/Sx, and absence of other airway
  abnormalities
• No any contraindications to direct laryngoscopy

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Traumatic Instability of the C-Spine

• C5 and C6 and related to the greater mobility of
  these spinal segments are most common traumatic
  injuries of the C-spine
• C2 were the most common fracture site noted by
  Rhee et al. and Goldberg et al.
• Injury to the C-spine can be limited to
  ligamentous structures and not associated with
  bony fracture

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• Clinically significant C-spine fractures about 2
  reported by Hoffman et al
• Midline neck pain
• Any focal neurologic deficit
• Altered level of consciousness
• Intoxication (alcohol or any drug)
• Severe pain anywhere other than the neck

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Airway Management in the Patient with Traumatic
C-spine Injuries

• Decisions about the method used to intubation
• The urgency of the situation
• ATLS guidelines clearly state Prevention of
  hypoxemia requires a protected, unobstructed
  airway and adequate ventilation that must take
  priority over all other conditions
• Direct laryngoscopy with manual in-line
  stabilization (MILS)

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• The skills of the practitioner and available
  airway tools
• Lightwand, Bullard scope, fiberoptic
  bronchoscope, cricothyroidotomy, and others
• Practitioners should use the method with which
  they are most familiar and experienced
• The cooperation of the patient
• Sometimes adequate topical anesthesia is
  impossible
• Assessment of the patients airway

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C-Spine Stabilization and Alternative Airway
Management Methods

• To minimize the risk of C-spine injury during
  direct laryngoscopy
• Soft collars no value in preventing C-spine
  motion
• Hard (Philadelphia) collars can limit lower neck
  flexion but not upper
• Complete halo-vest fixation prevent nearly all
  C-spine motion
• Axial traction minimize upper C-spine motion in
  normal patients, not prevent movement in severely
  unstable fractures
• Other airway management methods (e.g.,
  lightwands, intubating laryngeal mask airways,
  Bullard laryngoscopes, or WuScopes etc)

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Manual In-line Stabilization
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Other Intubation Methods

• Brimacombe et al. created a fracturedislocation
  injury at C3 in cadavers and compared motion with
  mask ventilation, direct laryngoscopy, esophageal
  Combitube, flexible fiberoptic endoscopy (nasal),
  and LMA insertion and intubation via an
  Intubating LMA (Fastrak)
• Minimal movement was seen with flexible
  fiberoptic nasal endoscopy
• The safety and efficacy of these alternative
  airway techniques have not been established under
  emergency conditions

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Summary

• No technique can be assumed safe in all
  situations
• The only directives currently available are part
  of ATLS guidelines
• If fiberoptic endoscopy is possible, it should be
  the primary management tool
• If fiberoptic endoscopy is not possible, then the
  technique with which the anesthesiologist is most
  familiar is indicated
• Manual in-line stabilization is advisable but may
  not prevent motion of a severely disrupted spine
  and is not of proven benefit
• All stabilization methods make direct
  laryngoscopy/ intubation more difficult