1. Spinal Cord Monitoring
Dr. M. Fennelly
Consultant Anaesthetist
The Royal National Orthopaedic Hospital

2. Why do I want
to know about
this?!!

3. How? Stagnara ‘Wake up test’ Ankle clonus test Neurophysiological
-Evoked potentials

4. Intra-operative physiological monitoring
Spinal cord (Scoliosis)
Sciatic/ Femoral nerve (THR)
Brachial plexus
Pedicle screws
Vascular surgery
Parotid surgery

5. Concept of monitoring

6. Mechanisms of Injury ……
…….Indirect mechanical

7. Mechanisms of Injury ……L4 L5
Direct
mechanical

8. aorta
Segmental a.
Anterior
spinal a.
Radicular a.

9. Reduced cord perfusion
Mechanisms of injury
Ischaemic cord injury
Compression +
Distraction
Oedema
Hypotension =
Reduced cord perfusion

10. ( To posterior tibial nerve, peroneal nerve
Somatosensory Evoked Potentials
Epidural spinal somatosensory evoked potential
Cortical somatosensory evoked potentials
C2 somatosensory potentials
( To posterior tibial nerve, peroneal nerve
stimulation)

17. Preoperative electrode placement
Out of surgical field
Anterior approach surgery
Spinally injured
Spondylolisthesis
Brachial plexus exploration

22. Relaxation unimportant
Anaesthetic considerations for SSEP
Relatively forgiving
Relaxation unimportant

23. Effects of local anaesthetics
and opiates
on S.S.E.P.
Loughnan, Fennelly et al. Anaesthesia and analgesia 1995

25. S.S.E.P. or M.E.P. ?

26. M.E.P.
Motor
end-plate

27. WHY ? Dissociation of SEP and MEP Earlier prediction of damage
Specific pathway monitoring

32. M.E.P. Problems
Anaesthetic
Stimulus patterns

35. Anaesthesia Nitrous oxide Isoflurane Muscle relaxation
Propofol infusion
Fentanyl
Alfentanil
Remifentanil

41. Factors affecting E.P.s Hypoxia Hypotension Carbon dioxide Temperature
Nerve integrity
Anaesthetic agents
Side

43. Interpretation What is a significant change? Latency Amplitude  50%
Other parameters
N.B. Must monitor minimum 20 minutes after final correction

44. Action Exclude technical failure Exclude anaesthetic change
Release correction / distraction
(Decompress)

45. How long have you got ?
Aortic cross clamp 30 minutes

46. Why is the S.M.E.P. more sensitive to
anaesthetic agents
Than the S.S.E.P. ?
 Synapses in pathway 

47. History at RNOH...
Sensory nerve conduction in the human spinal cord: epidural recordings made during scoliosis surgery.
Jones SJ. Edgar MA. Ransford AO.
Journal of Neurology, Neurosurgery & Psychiatry. 45(5):446-51, 1982 May.
Spinal cord monitoring in scoliosis surgery. Experience with 1168 cases.
Forbes HJ.Allen PW. Waller CS.Jones SJ.Edgar MA.Webb PJ.Ransford AO.
Journal of Bone & Joint Surgery - British Volume. 73(3):487-91, 1991 May.
Temporal summation--the key to motor evoked potential spinal cord monitoring in humans.
Taylor BA. Fennelly ME. Taylor A. Farrell J.
Journal of Neurology, Neurosurgery & Psychiatry. 56(1):104-6, 1993