Anatomy for the Anesthetist

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Anatomy for the Anesthetist

• Marianne Cosgrove,
• CRNA, DNAP, APRN

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Components of the Respiratory System

• The nose
• The pharynx
• The larynx
• The trachea
• The bronchi
• The lungs

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Conducting Portion of the Respiratory System

• nasal cavities
• oral cavity
• pharynx
• larynx
• trachea
• bronchial tree

A.K.A. dead space
4
Lining of the Respiratory Tract

• Nonciliated stratified squamous epithelium
• anterior nose, oropharynx, laryngopharynx
• Ciliated pseudostratified squamous epithelium
• posterior nose, nasopharynx, laryngeal mucosa
  above cords
• Ciliated pseudostratified columnar epithelium
• larynx below cords, trachea, bronchiolar tree
• Nonciliated cuboidal epithelium
• terminals and respiratory bronchioles

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The Nose and Sinuses

• The external nose
• The internal nose
• bony septum
• nasal turbinates
• posterior nares
• The paranasal sinuses
• maxillary
• frontal
• sphenoid
• ethmoid

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Functions of the Nose

• Warms inspired air
• Humidifies air
• Cleans inhaled air
• Organ of olfaction
• Resonator for speech

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The Pharynx

• a musculomembranous tube extending from the
  undersurface of the skull to the level of C6 and
  lower border of the cricoid cartilage where it is
  continuous with the esophagus.

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The Pharynx

• Divisions
• nasopharynx
• oropharynx
• laryngopharynx
• Innervation
• sensory
• via glossopharyngeal (cranial nerve IX)
• motor
• via vagus (cranial nerve X)
• Primary motor function
• swallowing

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Divisions of the Pharynx

• nasopharynx
• Behind posterior nares and above soft palate
• oropharynx
• Extends from the soft palate to the base of the
  tongue

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Divisions of the Pharynx contd

• laryngopharynx
• Extends from the base of the tongue to the
  opening of the esophagus
• Contains the landmarks for endotracheal
  intubation epiglottis, aryepiglottic folds,
  arytenoid cartilages

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Landmarks for Intubation
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Esophagus

• upper 1/3 striated muscle
• voluntary
• airway protection against regurgitation via the
  cricopharyngeus muscle (A.K.A. upper esophageal
  sphincter (UES))
• motor innervation via the RLN
• lower 2/3rds
• involuntary tone/contraction under ANS control
• distal 3-5 cm ? lower esophageal sphincter (LES)
• A functional structure may be manually opened
  with 18 cm H2O pressure

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Classifications of the Airway
Mallampati
Cormack-Lehane
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The Larynx consists structurally of a
framework of articulating cartilages linked
together by ligaments which move in relation to
each other by the action of laryngeal muscles.
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The Larynx

• Location
• adult
• anterior neck at the level of C4-6
• child
• anterior neck at the level of C3-5

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The Larynx

• Blood supply
• Arterial
• subclavian artery to inferior thyroid artery to
  inferior laryngeal artery
• Venous
• inferior laryngeal vein to brachiocephalic vein
  to SVC

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The Laryngeal Cartilages

• Singular cartilages
• thyroid
• cricoid
• epiglottis
• Paired cartilages
• arytenoids
• corniculates
• cuneiforms

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Thyroid Cartilage

• Largest cartilage
• Two broad sheets of cartilage which unite in a V
  shape anteriorly to form the Adams Apple
• Attached to the hyoid bone by the thyrohyoid
  membrane
• Attached to the cricoid cartilage by the
  cricothyroid membrane
• Provides the anterior attachment for the vocal
  cords

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Cricoid Cartilage

• Consists of the only complete ring in the larynx
  which broadens into a plate like structure on the
  posterior aspect A.K.A. The Signet Ring
  Cartilage
• forms the inferior and posterior borders of the
  larynx
• Is the narrowest portion of the pediatric airway

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Epiglottis

• Leaf like, elastic
• Projects obliquely upward behind the tongue and
  in front of the entrance to the larynx
• Functions to cover the glottic opening to prevent
  entrance of solids and liquids into the airway
  during swallowing
• Attached to the posterior surface of the thyroid
  cartilage above the vocal cords
• First cartilage encountered during laryngoscopy

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Arytenoid Cartilages

• Pyramidal in shape sit on cricoid cartilage
• Each has a muscular process which is the
  insertion of the posterior and lateral
  cricoarytenoids
• Each has a vocal process which is the posterior
  attachment of the vocal cords

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Corniculate Cartilages

• Cone shaped structures situated in posterior part
  of the aryepiglottic folds
• Each is attached to the apex of an arytenoid
  cartilage

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Cuneiform Cartilages

• Elongated structures located slightly posterior
  to the corniculates at the base of the epiglottis

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C3
C4
C6
The Laryngeal Cartilages
Netter, Plate 71
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Other Laryngeal Structures

• Aryepiglottic folds
• Ventricular folds (false vocal cords)
• Vocal folds (true vocal cords)
• The glottis
• The rima glottis is the narrowest portion of the
  adult airway
• cricothyroid membrane
• palpated between the lower border of the thyroid
  cartilage and the cricoid ring
• allows for easy surgical access to the airway via
  cricothyrotomy in cant ventilate, cant
  intubate scenario

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Muscles of the Larynx muscle
action effect
Posterior cricoarytenoids (2) Rotate arytenoids outward ABduction (widens rima)
Lateral cricoarytenoids (2) Rotate arytenoids inward ADduction (approximates vocal cords)
Transverse arytenoid (1) Approximate arytenoids ADduction (approximates vocal cords)
Thyroarytenoids (2) Draw arytenoids forward Relaxes and shortens cords
Cricothyroids (2) Draw up arch of cricoid and tilt lamina back Tenses and elongates cords
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Posterior, Lateral Views of Laryngeal Muscles
Netter, Plate 72
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Lateral Dissection of Laryngeal Muscles
Netter, Plate 72
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Superior View of Laryngeal Muscles
Netter, Plate 73
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Action of Posterior and Lateral Cricoarytenoids
Netter, Plate 73
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Action of Cricothyroid Muscles
Netter, Plate 73
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Action of Transverse Arytenoid, Thyroarytenoid
Muscles
Netter, Plate 73
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Innervation of the Larynx

• Superior laryngeal nerve
• A branch of the vagus nerve contains internal
  and external branches
• Internal branch supplies sensory innervation
  above the vocal cords
• stimulation may precipitate
• laryngospasm
• External branch supplies motor innervation to the
  cricothyroid muscles

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Innervation of the Larynx

• Recurrent laryngeal nerve
• A branch of the vagus nerve
• Supplies motor innervation to all muscles of the
  larynx except the cricothyroid muscles
• Supplies sensory innervation to the larynx below
  the vocal cords
• May be damaged during thyroid/parathyroid surgery

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Damage to the Recurrent Laryngeal Nerve

• Unilateral transection hoarseness
• Bilateral damage from ischemia complete airway
  obstruction from laryngospastic cords
• Bilateral transection flaccid vocal cords
• May have some passage of air

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Laryngeal Nerves
Netter, Plate 74
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The Trachea

• Cartilaginous and membranous tube extending from
  the vocal cords to the carina to form the right
  and the left mainstem bronchi
• Lies anterior to the esophagus and is protected
  anteriorly with cartilaginous rings
• Posterior wall is membranous
• The carina lies at the level of T5

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Airway Measurements
female
male
Incisors to vocal cords 10-14 cm 12-16 cm
Incisors to carina 24-26 cm 26-28 cm
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The Bronchi

• Mainstem (A.K.A primary bronchus)
• Right
• Shorter, wider, and less acute angle off trachea
• In adults, forms a 25 degree angle
• In children less than 3 years old, forms a 50
  degree angle
• Divides into 3 lobar branches
• Inhaled foreign bodies are more likely to enter
  the R mainstem bronchus

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The Bronchi

• Mainstem (A.K.A primary bronchus)
• Left
• Longer, narrower, more horizontal than right
• In adults and children, forms a 40-60 degree
  angle off trachea
• Divides into two lobar branches

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The Tracheobronchial Tree, Respiratory
Bronchioles, and Alveoli

• Continued branching produces
• Segmental bronchi
• Small bronchi
• Bronchioles
• Terminal bronchioles
• Respiratory lobules

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The Terminal Bronchioles

• The tracheobronchial tree ends at the 16th level
  from the trachea at the level of the terminal
  bronchioles
• Diameter is lt1 mm, cilia disappears, cartilage is
  absent
• This marks the end of anatomic dead space

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Anatomic Dead Space

• Equal to approximately 1cc/lb in both adults and
  children
• Examples
• 70 Kg pt 155 lbs
• Approximate anatomic dead space 155 cc
• 4 kg infant 9 lbs
• Approximate anatomic dead space 9 cc

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The Respiratory Lobule

• Comprised of
• respiratory bronchiole
• alveolar duct
• alveolus (air sac)

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The Respiratory Bronchiole

• Where actual respiratory exchange begins
• Muscle layer of bronchial tree is thickest here
  (relatively speaking)
• Forms a thin band around the openings of the
  alveolar ducts
• No muscle is found beyond this point

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Classification of airways by order of
branchingCommon name
Generation of airway
Trachea 0
Main bronchi 1
Lobar bronchi 2-3
Segmental bronchi 4
Small bronchi 5-11
Bronchioles, terminal bronchioles 12-16
Respiratory bronchioles 17-19
Alveolar ducts 20-22
Alveolar sacs 23
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Trachea and Major Bronchi
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The Lungs

• Lie free in the pleural cavity attached only at
  the hilum
• The bronchi, major vessels, and lymphatics enter
  and leave here
• Each lung has a concave base
• Rests upon the diaphragm
• Each lung has an apex

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The Right Lung

• Three lobes
• Right
• Middle
• Lower
• Broader, shorter than the left lung due to
  elevation of the diaphragm from the liver
• The right apex extends further above the clavicle
  than the left

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The Left Lung

• Two lobes
• Upper
• Lower
• Smaller than the right due to the position of the
  heart

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The Thoracic Cavity

• Three divisions separated from each other by
  partitions of pleura
• Pleural space
• Contains the lungs
• Pericardial space
• Contains the heart, pericardium
• Mediastinal space
• Contains the major vessels, lymphatics

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The Bronchial Circulation

• Feeds the parenchyma of lung
• Venous return to the pulmonic vein
• Accounts for a normal 1-3 shunt (deoxygenated
  blood mixing with arterial blood)
• Not to be confused with pulmonary circulation
• Where respiration occurs

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Shunt vs. Dead Space

• Shunt
• perfusion without aeration
• Dead space
• aeration without perfusion
• A.K.A. an area of bi-directional air flow

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The Pleura

• A double layered serous membrane
• Parietal
• Lines the entire thoracic cavity, inner surface
  of ribs, superior surface of diaphragm
• Visceral
• Adheres to the surface of each lung
• The pleural space is a potential space between
  the pleura
• A small amount of serous fluid is present

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Muscles of respiration

• diaphragm
• responsible for 70 of tidal volume
• accessory muscles of respiration

inspiration expiration
sternocleidomastoid scalenes pectoralis major pectoralis minor serratus anterior serratus posterior superior upper iliocostalis external oblique internal oblique rectus abdominus lower iliocostalis lower longissimus serratus posterior inferior
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Cardiac Anatomy
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Coronary Arteries
Thebesian veins drain directly into cardiac
chambers, adding to physiologic SHUNT
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Other Zones of Anesthetic Interest
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Major Nerve Plexuses

• A nerve plexus is a network of intersecting
  nerves which combine sets of spinal nerves that
  serve the same area of the body into one large
  grouped nerve

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Cervical plexus (C1-C5)

• A plexus of the ventral rami of the first four
  cervical nerves
• Branches
• Lesser occipital nerve (C2)
• Greater auricular nerve(C2,3)
• Transverse cervical nerve (C2,3)
• Supraclavicular nerves (C3-4)

Supplies the skin behind the ear, at the angle of
the jaw, in the anterior and lateral triangles of
the neck to shoulder and below the clavicle
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Cervical Plexus, contd

• Branches, contd
• Muscular
• Ansa cervicalis
• Hypoglosssal
• Thyrohyoid, genohyoid

Innervate the rhomboids, serratus anterior, SCM,
trapezius, levator scapulae, and scalenus medius
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Cervical Plexus, contd

• Communicating
• From the SNS (superior cervical sympathetic
  ganglion)
• C1 communicates with hypoglossal
• supplies geniohyoid and thyrohyoid
• C2 and C3 form ansa hypoglossi
• supplies sternohyoid, sternothyroid, and omohyoid
  muscles

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Cervical Plexus, contd

• Mixed (sensory, motor, and sympathetic)
• Phrenic nerve (C5) ? diaphragm

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Cervical plexus
contributes to brachial plexus
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The Brachial Plexus

• Supplies the upper limb with sensory and motor
  innervation
• A branching network of nerves derived from the
  anterior (ventral) rami (roots) of spinal nerves
  C5, 6, 7, 8, and T1

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Brachial Plexus Divisions

• Roots (Randy)
• C5-T1
• Trunks (Travis)
• Upper, middle, lower
• Divisions (Drinks)
• Anterior, posterior
• Cords (Coffee)
• Lateral, medial, posterior
• Branches (Black)

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The Brachial Plexus
clavicle
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Distribution of terminal nerves
cords branches innervation to
lateral musculocutaneous median UE flexors (m) lateral aspect forearm from elbow to wrist (s) most difficult to block medial aspect forearm (s) see below
posterior axillary radial shoulder (m,s) UE extensors (m) thumb, 2nd finger, inner medial 3rd finger (s)
medial median ulnar dorsal-distal half 2nd, 3rd fingers medial ½ 4th finger (s) ventral-thumb, 2nd, 3rd, and ½ of 4th finger (s) 4th, 5th fingers, lateral hand (s)
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Brachial Plexus Block

• Four approaches
• 1) Interscalene
• - Trunks emerge between anterior and middle
• scalenes proximity of RLN, stellate
  ganglion, phrenic nerve, and vertebral artery
  predisposes to high rates of incidental blockade
  or intravascular injection
• 2) Supraclavicular (AKA subclavian)
• - Plexus is compacted here provides excellent
  blockade high incidence of pneumothorax (1-6)
• 3) Infraclavicular
• - Risk for pneumo, hemo, chylo (L sided) thorax
• 4) Axillary
• - Remember the musculocutaneous nerve!
• Visit www.nysora.com

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Celiac (solar) Plexus

• Formed (in part) by the greater and lesser
  splanchnic nerves of both sides, and also parts
  of the right vagus nerve
• includes a number of smaller plexuses which
  supply viscera
• hepatic
• splenic
• gastric
• pancreatic
• suprarenal
• renal
• testicular/ovarian
• superior mesenteric plexus
• inferior mesenteric plexus

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Lumbosacral plexus

• Lumbar plexus (T12-L4)
• Main branches
• iliohypogastric
• ilioinguinal nerve
• genitofemoral nerve
• Dorsal divisions
• lateral femoral cutaneous
• femoral nerve ? adductors of hip, extensors of
  knee, and skin over medial surfaces of thigh and
  leg
• saphenous is main branch
• Ventral divisions.
• obturator nerve ? adductors of hip and skin over
  medial surface of thigh
• accessory obturator nerve

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Lumbar plexus, contd
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Sacral plexus (L4-S4)

• gluteal nerves ? adductors and extensors of hip
  and skin over posterior surface of thigh
• sciatic nerve ? (L4-S3) 2 nerves contained within
  a sheath
• common peroneal
• tibial
• flexors of knee and ankle, flexors and extensors
  of toes, and skin over anterior and posterior
  surfaces of leg and foot
• posterior and medial cutaneous nerve ? skin over
  medial surface of leg
• pudendal nerve (S2-4)

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Sacral Plexus
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The Great Veins of the Neck

• Internal jugular
• Right IJ best for cannulation and passage of a PA
  catheter
• External jugular
• Beware of the large valve at the junction of the
  EJ and the subclavian
• Anterior jugular
• Subclavian

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The Great Veins of the Neck
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The Thoracic Duct
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Aortic Arch
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BrachiocephalicInnominate
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The Antecubital Fossa
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The Circle of Willis

• an anastomosis of the internal carotids and the
  vertebral arteries which is found at the base of
  the brain. All cerebral arteries are derived
  from this anastomosis.
• This circle is directly responsible for cerebral
  perfusion.
• During carotid X-clamping, collateral flow to the
  circle is via the contralateral carotid and the
  vertebro-basilar system.

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Cerebral Perfusion Pressure

• CPP MAP - ICP

or CVP, whichever is higher
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The Circle of Willis
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CSF circulation
CSF secreted by choroid plexus to Lateral
ventricles 1 2 to Foramen of Munro to 3rd
ventricle to Aqueduct of Sylvius to 4th
ventricle to Foramina of Luschka and
Magendie to Subarachnoid space to Reabsorption
by arachnoid villi
Total volume 150 ml
Adults form 400-500 ml/day (approximately 20
ml/hr)
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The Cranial Nerves

• with regard to their regions of innervation, are
  nerves of the head. They spread through the
  head-neck region, except for the parasympathetic
  portions of the vagus nerve which pass to the
  abdominal organs.

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Cranial Nerves I-VI Cranial nerves
Type Function
I. Olfactory S smell
II. Optic S sight
III. Oculomotor M eye movement, pupil constriction
IV. Trochlear M eye movement
V. Trigeminal (three branches) ophthalmic (S), maxillary (S), mandibular (M S) B chewing, great sensory of face
VI. Abducens M eye movement
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Cranial nerves VII-XIICranial nerves
Type Function
VII. Facial (five branches) temporal, zygomatic, buccal, mandibular, cervical B taste, great motor of the face
VIII. Acoustic (A.K.A. vestibulocochlear) S hearing, balance
IX. Glossopharyngeal B swallowing, afferent carotid body and sinus
X. Vagus (branches superior laryngeal and recurrent laryngeal nerves may be injured during intubation) B Great Wanderer afferent and efferent
XI. Accessory (A.K.A. spinal accessory) M larynx and pharynx
XII. Hypoglossal (may be injured during intubation) M tongue
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The Spine
Largest interspace is L5-S1 (A.K.A. Taylors
space)
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Spinal cord

• Extends from the foramen magnum to the level of
  L1 (adults), L3 (children)
• Terminates to conus medullaris and filum
  terminale
• lower spinal nerves form the cauda equina
• Tuffiers line the plane which crosses the
  iliac crests bilaterally
• Approximately the L4 level in most individuals
• Cord may extend below the L1 level in obese pts
• Conus is at approximately L3 in children

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Tuffiers Line
( T7)
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Spinal Cord termination
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Blood supply

• Derived from a single anterior and paired
  posterior spinal arteries
• Anterior spinal artery
• formed from the vertebral artery
• supplies anterior 2/3rds of the cord
• Posterior spinal arteries
• Arise from cerebellar artery

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Additional blood supply to the cord

• Intercostals (thorax)
• Lumbar arteries (abdomen)
• Artery of Adamkiewicz (great ventral radicular
  artery, arteria radicularis magna)
• arises from the aorta
• unilateralusually from the L side
• provides the major blood supply to the anterior,
  lower 2/3rds of the spinal cord

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Cross section of spinal cord
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Substantia gelatinosa

• Found in the dorsal horn of the spinal cord
• Plays a major role in processing and modulating
  nociceptive input from cutaneous nociceptors
• Major site of action for intrathecal opioids
• AKA Rexeds Lamina II

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Vertebrasuperior view
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Vertebra--lateral view
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Vertebra and disc
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Spinal Ligaments
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Spinal anesthesia
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Epidural Anesthesia
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Epidural Anesthesia
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Epidural Anesthesia
epidural space venous plexus ligamentum flavum
Epidural space widens as it descends the cord
widest at L2-3
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Schematic of Spinal vs. Epidural Anesthesia
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Miscellaneous
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Diaphragmatic Innervation

• Phrenic nerve (R L branches)
• Arises from C3, 4, 5
• This is the source of motor innervation
• (C3,4,5 keeps a man alive)
• Sensory innervation
• Lower 6 intercostal nerves

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Cardioaccelerator nerves

• Arise from T1-4
• Bradycardia usually noted in quadriplegia or high
  level of spinal anesthesia

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Landmarks for Sensory Levels
T4 Nipple
T6 Xiphoid
T7 Lower border of scapula
T8 Lower border of rib cage
T10 Umbilicus
L4 Iliac crest
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Dermatome Man
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Peripheral Nerve Stimulation

• Most common site of placement of PNS is along the
  groove of the ulnar nerve
• Elicits a response from the
• adductor pollicis brevis
• May use the facial nerve distribution for
  placement if arms are not accessible
• Elicits a response from the
• orbicularis oculi
• corrugator supercilii

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Arterial Supply of the Hand
118
Sites for arterial cannulation

• Radial artery
• Most commonly selected site
• Ulnar artery
• Major blood supply of the hand
• Difficult to cannulate deep, tortuous
• Brachial artery
• Large, easy to cannulate
• Risk of median nerve damage
• Axillary artery
• Femoral artery
• Good to use in low flow states
• Dorsalis pedis artery
• May have distortion of waveform falsely high SBP
  2º distance from aorta

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Positioning

• neuropathies following surgery are from
• stretching of nerves for sustained periods of
  time
• pressure on nerves for sustained periods of time
• leads to ischemia of the nerve ? neuropathy
• alopecia of occipital area particularly in
  low-flow states
• anesthetized pts are unable to compensate for
  awkward/painful positions
• muscle relaxation allows for positioning that
  would otherwise not be tolerated by the pt
• proper positioning considered a shared
  responsibility among OR team (however)

120
Positioning

• upper extremity
• ulnar nerve is the most frequently damaged in
  pts in the supine position
• neuropathy may manifest as sensory and/or motor
  deficit
• usually transient
• 70-90 of injured pts are male
• other predisposing factors to development of
  injury
• extremes of weight (particularly obese pts)
• extended bedrest (before and/or after surgery)
• long surgery
• preexisting neuropathy in the contralateral limb

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Brachial plexus injury

• most associated with median sternotomy
• particularly with dissection of IMA
• probably 2º uneven retraction of chest wall
• increased risk with
• arm abduction gt 90º from side
• compounded if head is turned contralaterally
• prone position with arms on rests beside head
• may occur with arms at sides if shoulders allowed
  to prolapse forward with no support

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Positioning

• lower extremity
• lithotomy position carries a high risk of
  perioperative nerve injury
• usually mild/self limiting
• severe ? footdrop
• common peroneal nerve
• most commonly injured nerve in the lower
  extremities
• relatively superficial
• wraps around the head of the fibula on the
  lateral aspect of the knee

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Lower extremity nerves, contd

• sciatic nerve
• adjacent to the hamstrings
• stretch from hyper flexion of the hip, especially
  when coupled with an extended leg/flexed foot
• femoral nerve
• more commonly injured with deep, lower abdominal
  retraction
• sustained compression of the iliac or femoral
  arteries leads to ischemia
• pronounced abduction of thigh (frog leg)

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Lower extremity nerves, contd

• obturator
• injured with pronounced abduction of the thigh
• neuropathies are usually sensory (numbness inner
  aspect of thigh)
• lithotomy position caveats
• padding of bony prominences is essential
• position changes of the LEs must be made
  simultaneously
• 1º risk factor for the development of neuropathy
  following lithotomy is obesity

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Supine position

• minimal circulatory and ventilatory changes noted
• FRC may be slightly ? due to cephalad
  displacement of diaphragm/abdominal contents
• stress on lower back
• may be attenuated with mild knee flexion
• pressure on heels
• legs crossed sural (upper leg) and peroneal
  (lower leg) pressure
• upper extremities should be neutral
• if supinated, abduction from body not to exceed
  90º
• pronation may cause undue pressure on the ulnar
  groove
• individualize to each pt

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Trendelenburg

• head down associated with many physiologic
  changes
• ? pulmonary compliance, FRC from diaphragmatic
  displacement
• ? myocardial O2 demand
• from ? preload, slight impedance of forward LVSV
• may ultimately ? CO
• ?ICP, IOP
• leads to facial, scleral edema possible retinal
  detachment, POVL
• ? R mainstem intubation vs. extubation
• ? risk of passive regurgitation possible
  aspiration
• arms should be secured if abducted
• shoulder braces should be placed on
  acromio-clavicular processes with padding

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Prone

• face down head and neck should remain in a
  neutral position
• turned head may obstruct vertebral artery flow
  and jugular drainage
• upper extremities are best placed at sides
• should not be abducted gt 90º if extended
  alongside the head
• physiologic changes include
• ? FRC with ? intraabdominal pressure
• FRC may actually be unchanged or facilitated
  in absence of increased IAP
• ? intraabdominal pressure
• may impede venous return via IVC thereby
  reducing preload/CO
• collaterals via epidural vessels may see ?
  intraoperative blood loss from congestion
• ? pulmonary compliance
• pooling of blood in lower extremities
• facial/ocular edema
• retinal artery occlusion may lead to blindness
• risk compounded by overhydration with
  crystalloid, prolonged periods of hypotension,
  direct pressure on the orbits, EBL gt 2.5 l,
  prolonged surgery
• pressure on breasts, genitalia
• ? risk for airway compromise during position
  changes or intraoperatively
• pt should be log rolled after induction with neck
  maintained in a neutral position

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Sitting

• venous air embolism (VAE) is the 1º complication
  associated with this position
• occurs when the operative site is above the level
  of the heart
• treatment
• have the surgeon flood the operative site with
  saline
• discontinue N2O
• aspirate air through a central venous catheter
• resuscitate with fluids, ionotropic support, ()
  pressure ventilation
• other effects of sitting include
• ?BP, preload, CO from pooling
• ?CPP (brachial reading underestimates pressure at
  the Circle of Willis!)
• ?intrathoracic blood volume V/Q mismatching

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Lateral decubitus

• side lying physiologic changes generally
  pulmonary overall V/Q mismatch from
• ? pulmonary compliance with ? perfusion to the
  upper lung ? ? dead space
• ? pulmonary compliance and FRC with ? perfusion
  to the dependent lung ? ? shunt
• compression of IVC
• pressure on axilla on dependent side
• brachial plexus injury common
• pulse oximetry on dependent hand recommended to
  assess perfusion
• Axillary roll a misnomer!
• pressure on medial aspects of knees
• potential injury to dependent eye/ear