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Anesthetic considerations for spinal surgery
1. Anesthesia For Spinal Surgery
Dr.Alaka Purohit
Associate professor
DEPARTMENT OF ANAESTHESIOLOGY
S.M.S. MEDICAL COLLEGE
JAIPUR
2. Anesthesia For Spinal Surgery
•Spinal conditions requiring spinal surgery
•Surgical procedures
•Anesthetic considerations
•Unique challenges for spinal surgery
3. General Indications for
Spine Surgery
Neurologic dysfunction (compression)
Structural instability
Pathologic lesions
Deformity
Pain
8. Anesthetic considerations
Pre-Operative Assessment
Airway Assessment:
. TMD,
. Mouth opening
. Previous difficulty in intubation
. Restriction of neck movement due to disease,
traction or braces
. Stability of the cervical spine
. It is essential to discuss preoperatively
the stability of the spine with the surgeon.
11. Anaesthetic considerations (cont)
Neurological assessment:
The full neurological assessment should be documented.
1. In pts undergoing c-spine surgery, the anesthesiologist has a
responsibility to avoid further neurological deterioration during
maneuvers such as intubation , positioning and hypotensive
anaesthesia.
2. Muscular dystrophies may involve the bulbar muscles,
increasing the risk of postoperative aspiration.
3. The level of injury and the time elapsed since the insult are
predictors of the physiological derangements of the
cardiovascular and respiratory systems which occur
perioperatively.In < 3 weeks of the injury, spinal shock may
still be present. After this time, autonomic dysreflexia may
occur.
14. Anaesthesia technique
Premedication:
Consideration of immense pain in patients
with degenerative diseases – opiods
premedication sparingly used in patients
with difficult airways or ventilatory
impairment.
15. Anaesthesia technique(cont)
Induction:
Choice of induction technique:
i.v. or inhalation ?
Pt’s medical condition
Airway
C-spine stability
Choice of muscle relaxants:
Succinylcholine or NDNMBs ?
Pt’s medical condition
Airway
Risk of aspiration
Intra-operative monitoring
16. Anaesthesia technique (contd)
Intubation: (cervical spine surgery)
Awake or asleep
Awake intubation:
Risk of aspiration
Neuro assessment : an unstable c-spine
Presence of a neck stabilization device: halo traction
Direct or fiber-optic laryngoscopy
Direct laryngoscopy:
Intubation can be achieved without any neck movement
(manual in-line stabilization or a hard collar)
Fiber-optic laryngoscopy:
Fixed flexion deformities: involving upper T-spine/c-spine
Pts wearing stabilization devices such as halo vests
Anatomical reasons: micrognathia, limited mouth opening
17. Algorithm for decision making when intubating a pt for
proposed surgery involving the upper T or cervical spine
18. Anaesthesia technique(Contd)
Maintenance
Maintain a stable anesthetic depth
positioning of patient, check airways
Avoid sudden changes in anesthetic depth or BP
Maintain a constant depth of NMB
Common practice: 0.5 MAC Isoflurane / Halothane
continuous infusion of propofol
continuous remifentanyl or bolus opioids
Controlled hypotensive anaesthesia
Reversal
patient made supine
Thorough endotracheal and oral suction
Oxygenated with 100% oxygen
I.V.- Neostigmine
Glycopyrolate
Extubation: Fully awake with full motor power.
Emergence
Fully awake,telling name
Responding to commands
Able to manage his/her own airway
19. Unique challenges for spinal surgery
Positioning
Intra-operative monitoring
Spinal cord injury
Post-operative visual loss (POVL)
20. Positioning
Prone position : most spinal procedures
Supine position with head traction in
anterior approach to cervical spine
Sitting or lateral decubitus position :
occasionlly
23. Prone position
Induction and intubation in supine position
Turn prone as a single unit requiring at least four people
Neck should be in neutral position
Head may be turned to the side not exceeding the patients
normal range of motion or face down on a cushioned
holder.
Arms should be at the sides in a comfortable position with
the elbow flexed ( avoiding excessive abduction at the
shoulder
Chest should rest on parallel rolls (foams )or special
supports (frame) to facilitate ventilation
Check oral endotracheal tube, ckt, other attachments
Check breath sounds bilaterally
24. Anesthetic problems of the prone position
Airway:
ET tube kinking or dislodgement
Edema of upper airway in prolonged cases
Blood Vessels:
Arterial or venous occlusion of the upper extremity
Kinking of femoral vein with marked flexion of the hips,
abdominal pressure:
epidural venous pressure bleeding (frames elevates)
Pressure necrosis of the nose, ear, forehead, breasts (female),
and genitalias (males)
Monitor disconnects are hard to avoid;carefully manage.
25. Anesthetic problems of the prone position(contd)
Nerves:
Brachial plexus stretch or compression
Ulnar N compression: pressure to the olecranon
Peroneal N compression: pressure over the head of the fibula
Lateral femoral cutaneous N trauma: pressure over the iliac crest
Head and Neck:
Gross hyperflexion or hyperextension of the neck
External pressure over the eyes: retinal injury
Lack of lubrication or coverage of eyes: corneal abrasion
Headrest may cause pressure injury of supraorbital N.
Excessive rotation of the neck: brachial plexus problems
kinking of the vertebral artery
L-spine excessive lordosis may lead to neurologic injury
26. Spine Surgery- Monitoring
Routine
Arterial line
CVP/ PA catheter
Neurophysiologic:
. Wake up test
. SSEP
. MEP
. EMG
27. Wake-up test
Lightening anesthesia at an appropriate point during the
procedure and observing the patient’s ability to move to
command. It evaluates the gross functional integrity of the
motor pathway. It was first described in 1973.
Anesthesia requirements:
As easy and as rapid to institute as possible
Reliable but quickly antagonized
Wakening should be smooth
No pain during the test
No recall
28. Wake-up test
Anesthetic techniques:
Volatile-based anesthesia
Midazolam-based anesthesia
Propofol-based anesthesia
Remifentanyl-based anesthesia
Disadvantages:
Requires pt’s co-operation
Poses risks to pt: falling from the table and extubation
Requires practice
Prolong the duration of surgery
Provides information at the time of the wake-up only
Does not assess sensory pathways
29. SSEP (somato sensory evoked potentials)
1. The most common neurophysiological method for
monitoring the intra-operative spinal functional integrity
2. The stimulus applied to the peripheral N (tibial or ulnar)
3. The recording electrodes placed: cervical region, scalp, or
epidural space during surgery
4. Baseline data obtained after skin incision
5. Responses are recorded intermittently during surgery
6. A reduction in the amplitude by 50% and an increase in the
latency by 10% are considered significant.
7. SSEP tests only dorsal column function not motor
8. Rarely - post operative neurologic deficit reported despite preservation of
SSEP intraoperatively
31. Anesthetics and SSEPs
Satisfactory monitoring of early cortical SSEPs is
possible with 0.5–1.0 MAC isoflurane, desflurane or
sevoflurane.
Nitrous oxide potentiates the depressant effect of
volatile anesthetics
Intravenous anesthetics generally affect SSEPs less
than inhaled anesthetics
Etomidate and ketamine increases cortical SSEP
amplitude
Clinically unimportant changes in SSEP latency and
amplitude after the administration of opioids
32. Implication for SSEPs Monitoring
Eliminating N2O from the background anesthetic has been
shown to improve cortical amplitude sufficiently to make
monitoring more reliable
SSEP latency will take 5–8 min to stabilize after the step
changes in volatile anesthetic concentration
Adding etomidate, propofol or opioids is preferable to beginning
N2O or increasing volatile anesthetic concentrations when
anesthetic depth is inadequate
If a volatile anesthetic is nevertheless needed rapidly,
sevoflurane permits faster SSEP recovery after the acute need
for volatile anesthetic has been resolved
It is critical to avoid sudden changes in volatile anesthetic depth
or bolus administration of intravenous anesthetics during
surgical manipulations that could jeopardize the integrity of the
neural pathways being monitored
33. MEPs ( Muscle evoke potentials)
Motor cortex stimulated by
electrical or magnetic
means
Neurogenic responses:
peripheral N or spinal cord
Myogenic responses
34. Anaesthetics and MEPS( Muscle evoke potentials)
Inhalational anesthetics suppress myogenic MEPs in a dose-
dependent manner
Paired pulses or a train of pulses cannot overcome the
suppressive effects
N2O appears to be less suppressive than other inhaled agents.
Moderate doses of up to 50% N20 have been used successfully
to supplement other agents during myogenic MEP monitoring.
Fentanyl, etomidate, and ketamine have little or no effect on
myogenic MEP and are compatible with intra-operative
recording.
Benzodiazepines, barbiturates, and propofol also produce
marked depression of myogenic MEP. However, successful
recordings have been obtained during propofol anesthesia by
controlling serum propofol concentrations and increasing stimuli
rates.
35. Anesthetics and MEPs
Myogenic MEPs are affected by the level of neuromuscular
blockade
By adjusting a continuous infusion of muscle relaxant to
maintain one or two twitches in a train of four, reliable MEP
responses have been recorded
Motor stimulation can elicit movement, and this can
interfere with surgery in the absence of neuromuscular
blockade
Physiologic factors such as temperature, systemic blood
pressure, PaO2, and PaCO2 can alter SSEPs/MEPs and
must be controlled during intra-operative recordings
36. Spinal cord injury
1. Neurological damage during surgery and anesthesia is
not limited to the site of surgery.
2. Paraplegia and quadriplegia have been reported as
a result of poor pt positioning.
3. There are reports of pts with spinal disease who
have suffered neurological damage either at levels
remote from the site of surgery or during surgery
unconnected with their spinal disease.
4. Neurological damage is more likely at or near the site
of surgery on the spine.
37. Spinal cord injury
Risk factors:
• Length and type of surgical procedure
• Spinal cord perfusion pressure
• Underlying spinal pathology
• Pressure on neural tissue during surgery
38. Spine surgery: Conditions of
Increased Risk
Spinal distraction
Sub laminar wiring
Induced hypotension
Inadvertent cord compression
Certain instrumentation (Luque rods)
Ligation of segmental arteries
39. Risk Factors for Postoperative
Airway Compromise
Duration of surgery
Amount of blood transfusion
Obesity, airway pressure
Operations of greater than 4 cervical
levels or involving C2
Epstein NE. J Neurosurg
94:185 2001
40. Methods of Reducing Blood Loss
and Limiting Homologous
Transfusions
Proper positioning to reduce intraabdominal
pressure
Surgical hemostasis
Deliberate hemodilution (?)
Preoperative donation of autologous blood
41. Controlled Hypotensive
Anaesthesia
• Definition: It is the elective lowering of arterial B.P.
• Advantage : Minimization of surgical blood loss
Better wound visualization
• Methods : Proper positioning
Positive pressure ventilation
Administration of hypotensive drugs
sodium nitropruside B - Blockers
Nitroglycerine Propofol
Trimethaphan Inhalational
Adenosine (Halothane/ isofluran)
42. Controlled Hypotensive Anaesthesia (contd)
Safe level of hypotension :
- In healthy young individuals mean arterial
pressure as low as 50 to 60 mm of Hg is tolerated
with out complication.
- Chronically hypertensive patients have altered
autoregulation of CBF and reduction of MAP more
than 25% of base line not tolerated.
- Patient with H/o transient ischemic attacks may not
tolerate any decline in cerebral perfusion.
43. Controlled Hypotensive Anaesthesia (contd)
Relative contra indication :Pt having
predisposing illnesses that lesson the margin of
safety for adequate organ perfusion
Severe anaemia
Hypovolemia,
Atherosclerotic vascular disease
Renal and Hepatic insufficiency
Cerebrovascular disease
Uncontrolled glaucoma
44. Controlled Hypotensive Anaesthesia (contd)
Complications: ( more likely in pt with anaemia)
Cerebral thrombosis
Hemiplegia
Acute tubular necrosis
Massive hepatic necrosis
Myocardial infarction
Cardiac arrest
Blindness from retinal artery thrombosis
or ischemic optic neuropathy
45. Controlled Hypotensive Anaesthesia (contd)
Monitoring:
• Intra arterial blood pressure monitoring
• E.C.G. with S.T. segment analysis
• Central venous monitoring
• Measurement of urinary output
• Monitoring of neurologic function (rarely)
47. Post-operative visual loss (POVL)
•POVL is a rare but devastating complication
•1/1100 after prone spinal surgery
•Causes:
Ischemic optic neuropathy (ION) (81%)
Central retinal artery occlusion (13%)
Unknown diagnosis (6%).
48. Conclusions
Understand and appreciate the anatomy and
physiology of the spinal cord
Communicate with your surgeons
Explore new techniques but remember to
perfuse and monitor the patient