Chapter 18 - spine sx

Question 1

What factors are you looking for in deciding if patient will be difficult intubation and difficult ventilatoin? What is your goal with intubation in a patient with cervical stenosis?

Answer 1

Goal: minimize neck movement with mask ventilation and laryngoscopy + intubation

Factors for difficult ventilation:

• MP3 or 4, OSA, snoring, edentulous, neck circum > 40 cm, short + stocky neck, large beard, large tongue, prior history

Factors for difficult intubation:

• MP3 or 4, OSA, neck circum >4 cm, poor cervical ROM, unable to assume sniff position, large tongue, TM < 6cm, poor upper lip bite, poor submandib compliance (head/neck radiation), interincisor distance < 3 cm, prior history

Question 2

does severe cervical stenosis necessitate awake FOB? what is your goal with intubation?

Answer 2

Goal: minimize neck movement with mask ventilation and laryngoscopy + intubation

Awake vs Asleep:

• indicators of difficult vent
• indicators of difficult intub
• cooperative vs uncooperative
• full stomach
• large amount of secretions or blood or debri (trauma patient; will obscure FOB view)

Asleep

• consider if patient not full stomach + does not have predictors of difficult ventilation
• use glidescope to minimize neck movement (or glidescope assisted FOB)
• manual in-line stabilization (if not in C-Collar)

Question 3

how is chronic pain managed during spine surgery (how would you manage patient in pre-op period and intra-op period)?

Answer 3

Preop

• if patient on chronic pain meds, tell patient to take their usual pain meds
• Patients who fail to take their chronic pain meds:
  
  • calculate daily oral morphine equivalent, and provide some opiod morning of surgery
• multi-modal analgesia: gabapentin, celebrex (if allowed by sx), long acting opioid

Intra-op

• methadone or ketamine -> shown to reduce pain 48hrs post-op
  
  • methadone - 0.2 mg/kg IV
  • ketamine - 0.5mg/kg IV + infusion 10 mcg/kg/min intraop (stop at closure)
• use

Question 4

Describe SSEPs and MEPs

Answer 4

SSEPs

• integrity of dorsal columns of spinal cord
• stimulation delivered on a peripheral nerve, sensed at cerbral cortex

MEPs

• integrity of anterior spinal cord (motor tracts)
• stimuli delivered at cerebral cortex, sensed at peripheral motor nerve
• cannot use NMBD
• very sensitive to anesthesia

Question 5

what could loss of neuromonitoring signal represent (loss of signal at surgical site, loss of signal at non-surgical site, global loss of signal)?

Answer 5

neuromonitor signal loss: dec amplitude, inc latency

Surgical site signal loss:

• ischemia from trauma
• compression
• transection

non-surgical site signal loss:

• check position of affected limb (nerve compression, arterial compression) 2/2 positioning of patient

global loss of signal:

• anesthetic overdose
  
  • high volatile anes conc, bolus of IV agent, muscle relaxant
• hypotension
• severe anemia (decrease O2 tissue perfusion)

Question 6

what does propofol, volatile anes, etomidate, and ketamine do to waveform amplitude and latecy of neuromonitoring?

Answer 6

Propofol + volatiles anes

• increase latency, dec amplitutde

Etomidate + ketamine

• no change in latency, inc amplitutde

Question 7

What will your anesthesia plan be for patients undergoing neurophysiologic monitoring (SSEPs, MEPs, or both)?

Answer 7

goal - constant depth of anesthesia

• serve as baseline neuromonitoring signal

MEPs more sensitive to anesthesia

Maintenance

• amnesia, unconsciousness, autonomic control -
  
  • low dose volatile anes (MAC < 0.7 - 0.5)
  • or low-mod dose propofol infusion
• analgesia + reduce anesthetic conc
  
  • opioid infusion (remi) -> does not affect monitoring
• muscle relaxation
  
  • SSEP -> provide
  • MEPs - > do not give
    
    • during intubation, use sux or antagnoize Roc before baseline signal obtained
• IV boluses during sx
  
  • avoid; let OR team know if you have to give

Question 8

what are considerations for prone positioning in a patient undergoing spine surgery?

Answer 8

1) Neutral position of cervical spine
* maintain neck in neutral position with foam headrest or cervical traction devices
2) eye and ear pressure

• avoid turning face to one side
  
  • assoc with blindness and stroke
• frequent checks of eye and ear position q30-60 min

3) Arm positioning (minimize brachial plexus injury)

• c-spine surgery -> arms secured at sides
• lumbar surgery -> superman; arms positioned at 90degres in all planes, arm boards, avoid excessive abduction

4) abdomen and breast protection

• bolsters from tip of shoulders to iliac crest
• decrease pressure of breast and abdomen (hang freely)
  
  • allows for venous return and diaphragmatic excrusion during ventilation

Question 9

patient is undergoing spine surgery, and the surgeon asks you for induced hypotension to minimize blood loss. would you do this? are there other ways to minimze blood loss?

Answer 9

• brain and spinal cord autoregulate b/w 50 - 150 mmHg
• pathology may disrupt autoregulation -> blood flow becomes pressure dependent

Induced Hypotension

• cardiac ischemic injury
• ischemic optic neuropathy (esp in prone position)
• end organ hypo-perfusion
• cause reigonal ischemia to surgical site (esp since autoregulation may be disrupted)

minimize blood loss

• consier antifibrinolytics

Question 10

What is context sensitive half-time? How would you use your knowledge of propofol pharmacology to ensure a rapid but safe emergence?

Answer 10

context sens half time

• time it takes to decrease plasma concentration of a drug by 50% after a steady-state infusion has been turned off
• Propofol - turn off approx 40 minutes before surgical finish (if this was a long procedure)
  
  • keep in mind, propofol does not cause muscle relaxation -> self extubate in prone position
  • Can use EEG to give some insignt into tapering anesthesia.