Mod10: Anesthesia for Spinal Surgery Flashcards by Olivier Mba

Indications for Spinal Surgery

Spinal cord injury / trauma

Spinal column deformities

Scoliosis

^{secondary to Tumor, Vascular Malformation, Abscess, Hematoma}

Nerve root/cord compression

Degenerative vertebral column

HNP (Herniated Nucleus Pulposus (“Herniated disk”)

^{usuallay seen at L4-L5 or C5-C6}

Spondylosis/Stenosis

^{Affect s Lower cervical > lumbar}

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_{Spinal Surgery - Acute Spinal Cord Injury - Consider in all trauma}

Head trauma

^{consider what type of injury?}

Cervical spine injury (most common)

_{Prompt examination to assess function above level of injury critical}

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_{Spinal Surgery - Acute Spinal Cord Injury - Consider in all trauma}

Which spinal cord injury should considered with all trauma, until rulled out?

Thoracic spine injury

_{Prompt examination to assess function above level of injury critical}

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_{Spinal Surgery - Acute Spinal Cord Injury - Consider in all trauma}

Abdominal/long bone trauma

^{consider what type of injury?}

Lumbar spine injury

_{Prompt examination to assess function above level of injury critical}

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_{Spinal Surgery - Trauma with suspected spinal cord injury}

Advanced Trauma Life Support (ATLS) protocol

^components:

In-line stabilization

Strip

Full exam

CT Scan STAT if needed

_{Prompt examination to assess function above level of injury critical}

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_{Spinal Surgery - Acute Spinal Cord Injury}

Oberved damage depends on:

Level of injury or trauma

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_{Spinal Surgery - Acute Spinal Cord Injury}

Diaphragmatic paralysis

^{how does is relate to the level of injury? most common cause of death:}

C3-C5 injuries

C5 = partial (C5 stays alive)

C4 = complete (C4 breathes no more)

Requires immediate ventilatory support

Respiratory failure most common cause death

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_{Spinal Surgery - Acute Spinal Cord Injury}

C6-C7 injuries

^{manifestations:}

↓ respiratory function (↓ VC 60%)

Inability to cough/clear secretions => infections/pneumonia

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_{Spinal Surgery - Acute Spinal Cord Injury}

Quadriplegia a/w transection above:

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_{Spinal Surgery - Acute Spinal Cord Injury}

Paraplegia a/w transection above:

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_{Spinal Surgery - Acute Spinal Cord Injury}

All trauma patients are considered to have unstable cervical spine injuries until proven otherwise

^{How is cervical spine injury r/o?}

Imaging studies (MRI, CT scan)

^{May not be practical in unstable patient}

Plain radiographs (AP & lateral)

^{Sensitivity is <100%}

_{Imaging the spine does not take precedence over life-saving diagnostic and therapeutic procedures}

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_{Spinal Surgery - Acute Spinal Cord Injury}

The cervical spine may be cleared clinically if the following preconditions are met:

Fully alert and orientated
No head injury
No drugs or alcohol
No neck pain
No abnormal neurology
No significant other ‘distracting’ injury (another injury which may ‘distract’ the patient from complaining about a possible spinal injury).

Provided these preconditions are met, the neck may then be examined.

If there is no bruising or deformity, no tenderness and a pain free range of active movements, the cervical spine can be cleared.

Radiographic studies of the cervical spine are not indicated.

If any of the followings present (bruising or deformity, tenderness and a painful or compromised range of active movements), a good radigraphic study (e.g. MRI, CT) would be needed to Clear the cervical spine.

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_{Acute Spinal Cord Injury - Cervical spine Not yet cleared}

Airway Management options:

AFOI

Blind nasal

Intubating LMA

Glidescope

DL with manual in-line stabilization

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_{Acute Spinal Cord Injury - Cervical spine Not yet cleared - Airway Mgt}

Considerations for AFOI:

Cooperative patient

Hemodynamically stable

Airway trauma doesn’t prevent visualization

General induced after voluntary movement of extremities confirmed

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_{Acute Spinal Cord Injury - Cervical spine Not yet cleared - Airway Mgt}

Consider Blind nasal - but contraindicated with:

Some facial fractures

(LeFort fractures)

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_{Acute Spinal Cord Injury - Cervical spine Not yet cleared - Airway Mgt}

DL with manual in-line stabilization

^{considerations:}

Truly emergent

Minimizes flexion/extension

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_{Spinal surgery - Acute Spinal Cord Injury}

Spinal Cord Shock

^{what is it?}

ACUTE spinal cord transection

Loss of spinal reflexes & flaccid paralysis below level of injury

Duration → 1-3 weeks

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_{Spinal surgery - Acute Spinal Cord Injury}

Manifestations of Spinal Cord Shock:

Hypotension

^{Loss of sympathetic tone below injury}

Bradycardia

^{If damage above T1-T4 where cardioaccelerator fibers are located - The body is unable to mount a sympathetic response and increase HR}

Loss of compensatory changes (e.g. tachycardia) with blood loss, position changes, or PPV

^{HR remains 40-60 bpm, even with hypotension because the body is unable to compensate for the lack of fluid}

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_{Spinal surgery - Acute Spinal Cord Injury}

Management of Spinal Cord Shock:

Prevent further damage

^{during movement, positioning, & airway management}

High dose corticosteroids

^{Methylprednisolone first 24 hr to reduce swelling around the cord}

^{Improves neurologic function, especially below the areas of damage}

_{Spinal surgery - Acute Spinal Cord Injury}

Induction of anesthesia in Spinal Cord Shock:

IV fluid bolus

^{They might be hypotensive purely from trauma, coupled with hypotension and bradycardia from the spinal shock - Prevents CV collapse on induction}

Ketamine

^{This where we could use the benefice of ketamine}

Vasopressors may be required

^{To maintain adequate perfusion to the cord}

Succinylcholine

^{Safely used within first 24 hrs of injury}

^{Can see succinylcholine induced hyperkalemia later (after the 1st 24 hrs)}

Adequate spinal cord perfusion pressures

^{Adequate volume - Normal level BP - Avoid hyperventilation**}

^{(Hyperventilation => Hypocarbia => vasodilation => ↓ spinal cord blood flow)}

_{Spinal surgery - Induction of anesthesia in Spinal Cord Shock}

Succinylcholine-Induced Hyperkalemia:

Proliferation of acetylcholine receptors outside neuromuscular synaptic cleft

Occurs 24 hrs after SCI

^{Max: 4 wks - 5 mos - Decreases: after 6 mos (unless the pt remains bedbound)}

V-fib/cardiac arrest

^{Giving Sux after the 1st 24 hrs could results in a huge release of K+ with all the the associated negative effects of Hyperkalemia}

NDMR do not prevent

Safe to administer Sux for the first 24 hrs after acute injury

^{If unsured, do no give Sux!!! Use a different NMB agent}

Avoid succinylcholine in SCI patients 24 hrs after injury and up to 5 months

_{Spinal surgery - Acute Spinal Cord Injury}

Autonomic Hyperreflexia

Return of spinal reflexes

Follows period of spinal shock

Anytime from 4 wks to many years after injury

Occurs in 85% with lesion T5 or T6 & above

_{Spinal surgery - Acute Spinal Cord Injury - Autonomic Hyperreflexia}

Pathophysiology:

Inhibition of normal descending inhibitory impulses in cord

Sympathetic discharge below lesion reacts to noxious stimulus unopposed

_{Spinal surgery - Acute Spinal Cord Injury - Autonomic Hyperreflexia}

Precipitating factors:

Distention of the bladder & rectum (most typical)

Any noxious/painful stimulus

_{Spinal surgery - Acute Spinal Cord Injury - Autonomic Hyperreflexia} ## Footnote **Clinical manifestations:**

Severe HTN with bradycardia ^{Cutaneous vasoconstriction below the cord} Vasodilation above the cord (nasal stuffiness) ^{Baroreceptor reflex} Headache Subarachnoid hemorrhage Seizures Cardiac dysrhythmias Acute left ventricular failure (Pulmonary Edema)

_{Spinal surgery} ## Footnote **Feared complication of spine surgery:**

**Paralysis** Intraoperative compromise of spinal cord function must be detected as early as possible & reversed immediately

_{Spinal surgery - Spinal Cord Monitoring} Two methods used to detect intraoperative compromise of spinal cord function:

**“Wake-up test”** ^{Intraoperative awakening of patient after completion of instrumentation} **Neurophysiologic monitoring** ^{Somatosensory Evoked Potentials (SSEP’s)} ^{Motor Evoked Potentials (MEP’s)} _{Poor prognosis if pt wakes up w/ paralysis and hasn’t been monitored for spine integrity --- if find intraop, can adjust / remove instrumentation and try to get at least “some” function back. Need to detect ASAP}

_{Spinal surgery - Spinal Cord Monitoring} Intraoperative awakening of patient after completion of instrumentation:

**“Wake-Up Test”** Surgical anesthesia and muscle relaxation are reversed ^{Balanced technique typically used} ^{Opioids important → analgesia while awake} Pt asked to move both hands first followed by both feet ^{Unsatisfactory movement feet → release distraction rod one notch → repeat test} Surgical anesthesia is reestablished

_{Spinal surgery - Spinal Cord Monitoring} **“Wake-Up Test”** ^{pt's position - feasbility & drugs used to facilitate test:}

Prone w/ ETT in place, wake up test is very difficult Usually use Remi and Prop infusions with 0.3-0.4 MAC inh agents for SSEP, MEP.

_{Spinal surgery - Spinal Cord Monitoring} **Propofol** vs **Precedex** gtt for **wake up test**?

We use **precedex** a lot for MRI for stereotactic guided placement of deep brain stimulator electrodes for parkinson’s pt’s. Precedex (dexmedetomidine) – 1mcg/kg loading dose over 10 mins, then 0.2 – 1 mcg/kg/HR (usually start at 0.6mcg/kg/hr and TTE)

_{Spinal surgery - Spinal Cord Monitoring} **Post-op** concern of **“Wake-Up Test”**:

**Recall!!!** Occurs in 0-20% of patients **Fully inform pt preoperatively of possibility**

_{Spinal surgery - Spinal Cord Monitoring} **Complications** a/w “**Wake-Up Test**”:

Pain Air embolism Dislocation of instrumentation Accidental extubation

_{Spinal surgery - Spinal Cord Monitoring} Which test noninvasively assesses neural function by measuring electrophysiological responses to sensory of motor pathway stimulation:

_Neurophysiological Monitoring_ via **Evoked potentials**

_{Spinal surgery - Spinal Cord Monitoring} Evoked potentials **waveform analysis** ^{what to look for and analyze:}

**Latency** ^{Time between stimulation and potential detection} **^{↑ latency → damage pending}** **Amplitude** ^{Height of peak} **^{↓ amplitude → damage pending}** Inc latency or dec amplitude means LESS responsiveness to stimulation Ascending sensory and descending motor pathways

_{Spinal surgery - Spinal Cord Monitoring - Neurophysiological Monitoring} Two types of Evoked potentials:

SSEP’s MEP’s

_{Spinal Cord Monitoring - Neurophysiological Monitoring - Evoked potentials} ## Footnote **SSEP’s:**

Reflect dorsal (**Posterior**) columns of spinal cord Supplied by posterior spinal artery Proprioception and vibration (**Sensory**) NOT MOTOR _{AMPS: Anterior = Motor; Posterior = Sensory}

_{Spinal Cord Monitoring - Neurophysiological Monitoring - Evoked potentials} ## Footnote **MEP’s:**

Reflect **anterior** columns of spinal cord Supplied by anterior spinal artery **Motor** pathways Technically _more difficult to use_

_{Neurophysiological Monitoring - Evoked potentials - Effects of anesthetic agents} ## Footnote **Volatile anesthetics:**

↑ latency & ↓amplitude (MEP \> SSEP) by themselves ^{May get false reading when you get up to 1.0 MAC} ^{Keep pt on 0.5 MAC with some other agents} Recordable during low dose & obliterated with high doses Combined with N20 further compromises quality of the signal =\> Avoid N20!!! _Inhalational agents_ have **greater depressant effects** than _intravenous agents_

_{Neurophysiological Monitoring - Evoked potentials - Effects of anesthetic agents} **Opioids & Benzodiazepines**

Negligible effect on Latency and amplitude of these signals

_{Neurophysiological Monitoring - Evoked potentials - Effects of anesthetic agents} ## Footnote **Propofol:**

Excellent signal quality ^{Great drug to use!!!}

_{Neurophysiological Monitoring - Evoked potentials - Effects of anesthetic agents} **Ketamine** & **Etomidate**

Enhance the quality of signals ^{But not used as often as far as TIVA goes}

_{Neurophysiological Monitoring - Evoked potentials - Effects of anesthetic agents} **Anesthetic technique’s commonly used** during Neurophysiological Monitoring??

Ultra short acting opioid infusion (**Remi**) + **Propofol** + low dose inhaled anesthetic (**\< 0.5 MAC**) with **BIS** monitoring _{Why BIS monitoring?} _{Supplement Neuro monitoring since we are using less than 0.7 MAC.} _{The goal is normally ETMAC = 0.7 to prevent recall} **TIVA** w_ithout muscle relaxants_ for **MEP**

_{Neurophysiological Monitoring - Evoked potentials} Performed by:

Technician in the room Continually monitors SSEPs and occasionally MEPs Change of **50% or \>** is **significant** Changes around **20%** can be r/t *_anesthesia_* or *_surgeon_*

_{Neurophysiological Monitoring - Evoked potentials} Factors that could cause changes 50% of \> in SSEP:

Hypercarbia Hypoxia - Hypotension Hypothermia Changes d/t to these factors happen slowly overtime

_{Neurophysiological Monitoring - Evoked potentials} **ACUTE alterations** in **SSEP amplitude/latency** ^{could indicate:}

**Spinal cord compromise** ^from: Direct trauma - Ischemia - Compression - Hematoma

_{Neurophysiological Monitoring - Evoked potentials} **ACUTE alterations** in **SSEP amplitude/latency** ^Management:

Stop surgery Return BP to normal or 20% above Decrease or D/C volatile agents Draw ABG to r/o metabolic abnormality (?) Release distraction on cord “Wake-up test” to exclude neurologic deficits