Title: Anesthesia for Orthopedic Surgery and Evoked Potentials Monitoring
1Anesthesia for Orthopedic Surgery and Evoked
Potentials Monitoring
- Jampierre Mato CRNA,MSN,ARNP
- Clinical Adjunct Professor
- Anesthesiology Nursing Program
- Florida International University
2The 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)
3Tourniquets
- 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
4Tourniquets
- 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
5Tourniquet 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?
6Effects of Tourniquets
7Tourniquet 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
8Hip Fractures
9Hip 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
10Bipolar 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
11Fat 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
12Fat 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
13Anesthetic 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
14Total 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
15Cement 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
16Total Hip Replacement
Minimally invasive/muscle sparing techniques are
in widespread use
17Closed 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
18Lateral 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)
19Lateral Decubitus
20Total 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)
21Revision 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
22Spinal Surgery
- -Done for a variety of diagnoses
- -herniated discs
- -spondylolisthesis/spondylosis
- -spinal canal stenosis
- -radiculopathy
- -myelopathy
- -osteophyte compression
- -scoliosis
- -kyphosis
- -post-traumatic stabilization
23Spondylolisthesis
24Common 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.)
25Minimally 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
26Mini-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
27Microdiscectomy
28Positioning on Andrews Frame
29Positioning on Wilson Frame
30Scoliosis
- 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)
31Scoliosis
32Scoliosis 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
33Monitoring of Evoked Potentials
- Types MEP, SSEP, EMG, VEP, BAEP
- Indications
- Evaluation of pathology
- Monitoring during any procedure which may
compromise a nerve pathway
34Cuneatus 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)
35Reticular 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
36Cortical 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)
37Evoked 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
38Anesthesia 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
39The Ultimate Test of Nerve Pathway Integrity?
- Wake up and move everything!
40Foot and Ankle Surgery
- Ankle fracture
- Plate and screws
- Bunionectomy
- Hammer toe correction
- Plantar fasciotomy
- Achilles tendon repair
41Ankle 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)
42Posterior Tibial Nerve
43Sural Nerve
44Ankle 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)
45Superficial Peroneal Nerve
46Needle Directions in Ankle Block
47Upper 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
48Shoulder Arthroplasty
Painful!!
49Hand Surgery
- Hand surgery
- General vs. regional
- Bier block
- Axillary block
- Wrist block
- Tourniquet concerns
- Long cases
- Often awake, often uncomfortable (consider
general)