Anesthesia for Orthopedic Surgery and Evoked Potentials Monitoring

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Anesthesia for Orthopedic Surgery and Evoked
Potentials Monitoring

• Jampierre Mato CRNA,MSN,ARNP
• Clinical Adjunct Professor
• Anesthesiology Nursing Program
• Florida International University

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The Specialty

• Orthopedics has grown immensely within the past 2
  to 3 decades, mainly due to the development of
  arthroscopic equipment and hardware to replace
  joints
• Total joint replacement (shoulder, elbow, wrist,
  hip, knee, and ankle)-may offer a vast
  improvement in quality of life
• Inter-vertebral disc replacements are now being
  offered
• Benefits of arthroscopy
• Much less invasive than open techniques
• Allows direct visualization and manipulation with
  specialized equipment
• Reduced discomfort and length of stay (many
  procedures done as outpatient)

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Tourniquets

• Pneumatic Tourniquets
• Provide virtually bloodless field
• Cuff should overlap only 3 to 6 inches
• Area underneath must be padded and wrinkle-free
• Overlap of cuff should be opposite of
  neurovascular bundle (e.g. on the humerus,
  overlap is on the lateral aspect-opposite the
  brachial plexus)
• Inflation pressure usually 100mmHg greater than
  systolic blood pressure

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Tourniquets

• Must exsanguinate extremity prior to inflation
  (elevate or use Esmarch bandage)
• Elevation is preferred in infected extremities
• Inflation pressures
• Should not exceed 300mmHg in upper extremities
• Should not exceed 500 mmHg in lower extremities

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Tourniquet Pain

• Compression of intra-neural blood vessels
• Causes secondary nerve ischemia
• Leads to stimulation of pain pathways
• Onset 45-60 minutes after inflation
• Similar to thrombotic vessel occlusion
• Activation of C fibers burning and aching
• Activation of A delta fibers pins and needles
• Difficult to treat, once it begins analgesics
  and anesthetics have little effect, may need to
  treat sympathetic activation (tachycardia and
  hypertension)-What is the only true treatment?

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Effects of Tourniquets
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Tourniquet Safety

• -Always place cuff where nerves are best
  protected in the musculature
• -Check proper function of machine
• -Never inflate for longer than 2 hours 10 to 15
  minute reperfusion interval required prior to
  re-inflation
• -Minimally effective pressure to occlude blood
  flow
• -Put display where you can see it
• Report 60 minutes, then 15 min increments after
  that to the surgeon and be sure to chart that you
  did so
• Always chart times on your record

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Hip Fractures
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Hip Surgery

• -ORIF Open Reduction with Internal fixation
• Done for fractures (usually frail/elderly)
• Requires use of special fracture table (legs
  split with traction applied)
• Frequent concomitant diseases (dementia,
  Parkinsons, CAD, diabetes, etc.)
• Frequently dehydrated
• Occult blood loss can be significant
• Intracapsular
• Subcapital, transcervical less blood loss
• Extracapsular
• Femoral neck, intertrochanteric, subtrochanteric
  expect higher blood loss
• -Bipolar hip replacement (not a total hip
  arthroplasty)
• -done when fracture is not amenable to permanent
  fixation
• - femoral head and partial femoral neck are
  resected and replaced with a prosthesis
• -acetabular component is not fixed to the
  acetabulum
• -procedure usually takes less than an hour

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Bipolar Hip Prosthesis

• Cup is not attached to acetabulum
• Utilized when patient will be non-ambulatory or
  will limit weight-bearing activities on hip for
  the rest of his life

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Fat Embolism

• High correlation with long bone, hip, and pelvic
  fractures
• Occurs, to some degree, in all hip fracture
  patients
• Patients typically have low oxygen saturation and
  low-grade fever
• Fat Embolism Syndrome
• Presents within 72 hours of injury
• 3 hallmark signs confusion, dyspnea, petechiae
• Fat globules released into the blood through
  tears in medullary vessels
• Theory that chylomicrons result from aggregation
  of circulating fatty acids
• Thrombocytopenia and prolonged clotting times may
  occur

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Fat Embolism Under GA

• Diagnosing fat embolism syndrome under general
  Anesthesia
• Decline in end tidal CO2
• Decline in arterial oxygen saturation
• Rise in pulmonary artery pressures
• Ischemic-appearing ST segment changes
• Right sided heart strain
• If severe, may lead to RVOT obstruction with
  resultant CV failure/arrest

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Anesthetic Choice in Hip Fracture

• General or Regional?
• Extensively evaluated
• Regional has lower mortality in the first 2
  months post surgery
• No significant difference in mortality after 2
  months
• General is associated with more thrombo-embolic
  events than regional
• Morbidity post-general is higher immediately post
  operatively

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Total Hip Arthroplasty

• -Usually done in lateral decubitis position
• Higher degree of visibility and range of motion
• -Most common indication is Osteoarthritis (OA)
  AKA Degenerative Joint Disease (DJD)
• -Surgical Concerns (large incision, muscle
  trauma)
• Acetabulum and femoral head/neck are very
  vascular
• Resection of femoral head and neck
• Reaming of femoral shaft to accept stem
• Reaming of acetabulum to accept cup
• Three life threatening complications
• Bone cement implantation syndrome (cement rarely
  utilized in primary arthroplasty)
• Peri-operative hemorrhage
• Thrombo-embolism

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Cement Implantation Syndrome

• Methylmethacrylate (MMA)
• Mixing Powder and liquid causes exothermic
  reaction
• Reaction causes expansion of cement and forces
  fat, blood, and air into the femoral venous
  channels
• Residual monomer (liquid) is a potent systemic
  vasodilator and pulmonary vasoconstrictor
• Release of tissue thromboplastin may trigger
  thrombo-embolism and cause hemodynamic
  instability

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Total Hip Replacement
Minimally invasive/muscle sparing techniques are
in widespread use
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Closed Hip Reduction

• May be necessary if prosthesis dislocates
• Often done with heavy MAC or IV general with
  short-acting muscle relaxant, unless
  contraindicated
• Extremes of flexion and internal rotation can
  dislocate a new prosthesis- abduction pillow is
  placed immediately post-operatively to avoid
  dislocation
• Repeated dislocation of a hip prosthesis may
  require revision of the prosthesis-this is
  usually a failure of either surgical technique or
  the implant itself

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Lateral Decubitus Position

• Used in thoracic, renal, and orthopedic
  procedures
• Presents unique challenges to the anesthetist
• Importance of body alignment (cervical/thoracic/lu
  mbar)
• Use of bean bag, axillary roll, pillows, sandbag
• Cardiovascular Considerations
• Respiratory Considerations
• FRC decreased
• Ventilation/Perfusion mismatch
• Atelectasis
• Use of PEEP (may worsen mismatch)

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Lateral Decubitus
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Total Knee Arthroplasty

• Usually done for osteoarthritis or late-stage
  rheumatoid arthritis
• Supine position
• Regional vs. general anesthesia
• Cement implantation syndrome (when is this a
  concern?)
• Tourniquet concerns (ensure it is working)
• Autologous blood donation
• Bleeding is usually an issue post-op (once
  tourniquet is down)

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Revision Joint Replacements

• Previous joint replacements may need to be
  revised
• Lifespan of current implants is postulated to be
  10 to 15 years (may be shorter or longer,
  depending on recipient use)
• Revision procedures tend to be lengthy and bloody
• Intra-operative cell salvage is usually
  recommended
• Infected joints need to be removed, with
  placement of antibiotic spacers until infection
  resolves-dont use cell savage in suspected
  infection cases

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Spinal Surgery

• -Done for a variety of diagnoses
• -herniated discs
• -spondylolisthesis/spondylosis
• -spinal canal stenosis
• -radiculopathy
• -myelopathy
• -osteophyte compression
• -scoliosis
• -kyphosis
• -post-traumatic stabilization

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Spondylolisthesis
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Common Diagnoses in Spine Surgery

• Intervertebral disc herniation
• Herniated disc may impinge on nerve roots and the
  cord itself
• Spinal stenosis
• Refers to narrowing of the spinal canal, for
  whatever reason (herniation, degenerative disc
  disease, spondylolisthesis, osteophyte formation,
  etc.)

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Minimally Invasive Spine Surgery

• Traditional spinal surgery (laminectomy, fusion,
  etc.)
• Large incisions
• Large amount of blood loss and prolonged wound
  healing
• Great post-operative discomfort
• Lengthy hospital stays
• Commonly required anterior approach for the
  lumbar spine (laparotomy incision)
• Mini-invasive spine surgery
• Small incisions
• Decreased blood less and faster wound healing
• Decreased post-operative discomfort
• Shorter hospital stay
• Allows more complex procedures to be performed at
  once
• Often allows access to lumbar spine that formerly
  required laparotomy

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Mini-Invasive Spine Procedures

• Lateral interbody fusion (LIF)
• Allows complete lumbar discectomy and cage
  placement/fusion through a small flank incision
• Trans-foraminal lumbar interbody fusion (TLIF)
  allows near-total discectomy with cage
  placement/fusion through a para-spinous incision
• Axia Lumbar Interbody fusion (AxLIF)
• Allows fusion of the L5-S1 interspace through a
  sub-sacral incision
• Micro-discectomy allows removal of a herniated
  portion of disc through an access port (may
  utilize microscope)
• Laminectomy allows for total or hemi-laminectomy
  through a port

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Microdiscectomy
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Positioning on Andrews Frame
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Positioning on Wilson Frame
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Scoliosis

• Lateral curvature of the spine
• 75-80 of cases are idiopathic
• Untreated, can lead to complex deformity
• SSEP and MEP monitoring
• Preoperative evaluation (cor pulmonale, pulmonary
  physiology changes)
• PFTs, ABGs, EKG
• Increased incidence of MH if caused by muscular
  dystrophy (in pediatric patients)

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Scoliosis
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Scoliosis Surgery

• Gold standard is multi-level fusion with
  instrumentation/rods
• Potential for large blood loss (weighing of
  laps/sponges and tight I O recording)- cell
  salvage usually utilized
• Wake up test is uncommon, due to modern
  monitoring of evoked potentials
• Severe respiratory disease may exist
  preoperatively, may be left intubated
  postoperatively
• Major concerns with positioning (may have severe
  deformities)
• Posterior, anterior, or thoraco-abdominal
  approaches may be necessary
• May require double lumen tube if utilizing
  anterior thoracic approach

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Monitoring of Evoked Potentials

• Types MEP, SSEP, EMG, VEP, BAEP
• Indications
• Evaluation of pathology
• Monitoring during any procedure which may
  compromise a nerve pathway

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Cuneatus and Gracilis Tracts

• Part of the dorsal-lemniscal sensory system
• Responsible for touch, pressure, and vibration
  sensation
• Located in the dorsal cord
• Integrity of dorsal tract is assessed by SSEP
  monitoring (somato-sensory evoked potentials)
• Sensations ascend on the ipsilateral side of the
  cord and cross into the contralateral side at the
  thalamus (considered a direct pathway to the
  cerebral cortex)
• Procedures that may require SSEP monitoring
  cerebral aneurysm clipping, spine surgery, CEA
  (questionable applicability), complex
  thoraco-abdominal aneurysm repairs (MEPs are
  more useful since ischemia usually occurs in the
  ventral horn)

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Reticular Activating System

• Considered a secondary way by which sensory
  information arrives at the cerebral cortex
• Deactivated during sleep
• General anesthetics produce their effects through
  action on the RAS

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Cortical Pathways

• SSEPs are recorded from the scalp
• A peripheral nerve (ulnar/median or tibial) is
  stimulated, bilaterally, to procedure a potential
  that is recorded in the scalp
• Stimulating electrodes are peripheral and
  detecting electrodes are central (the scalp)

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Evoked Potential Waveforms

• Amplitude height of the waveform
• Latency can be thought of as the frequency
• Decreased amplitude and/or increased latency
  indicate a compromise in nerve potential
  transmission
• Factors that affect waveforms temperature, PaO2,
  PaCO2, systemic blook pressure
• VEPs are most affected by our anesthetics,
  SSEPs are moderately affected, and BAEPs are
  marginally affected

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Anesthesia During Evoked Potentials Monitoring

• What can we do?
• Maintain normothermia
• Maintain blood pressure within 20 of baseline
  (critical in long-standing hypertension and/or
  small vessel disease)-consider invasive
  monitoring in select patients
• Use anesthetics with minimal effects on waveform
  character (TIVA)
• Maintain oxygenation (may be difficult during
  one-long ventilation)
• Maintain normocapnea

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The Ultimate Test of Nerve Pathway Integrity?

• Wake up and move everything!

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Foot and Ankle Surgery

• Ankle fracture
• Plate and screws
• Bunionectomy
• Hammer toe correction
• Plantar fasciotomy
• Achilles tendon repair

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Ankle Block

• Frequently used in podiatric cases
• Insert needle lateral to the posterior tibial
  artery at the superior aspect of the medial
  malleolus (posterior tibial nerve)
• Inject 5ml of local and 2ml as you withdraw the
  needle
• Insert needle at the lateral border of the
  achilles tendon with the line between the
  malleoli, advance toward the lateral condyle,
  inject 5ml of local (sural nerve)

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Posterior Tibial Nerve
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Sural Nerve
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Ankle Block Technique

• Draw a line between the superior edge of the
  medial malleolus across the anterior portion of
  the ankle
• Flex the foot and place the needle between the
  tendons medial to the big toe (deep peroneal
  nerve), inject 5ml of local
• With the remaining local, fan inject across the
  same plane across the ankle (saphenous nerve)

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Superficial Peroneal Nerve
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Needle Directions in Ankle Block
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Upper Extremity Procedures

• -Usually amenable to brachial plexus block
  (interscalene, supraclavicular, axillary)
• Shoulder arthroplasty or arthroscopy
• Requires beach chair/sitting position
• Venous air embolism precautions
• Airway concerns
• Cardiovascular considerations?
• Elbow arthroplasty or arthroscopy
• Prone position
• Turn head away from field
• Turn table 90 degrees

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Shoulder Arthroplasty
Painful!!
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Hand Surgery

• Hand surgery
• General vs. regional
• Bier block
• Axillary block
• Wrist block
• Tourniquet concerns
• Long cases
• Often awake, often uncomfortable (consider
  general)