Spinal Cord Monitoring

Dr. M. FennellyConsultant AnaesthetistThe Royal National Orthopaedic Hospital

Why do I wantto know about

this?!!

How?

Stagnara ‘Wake up test’Ankle clonus testNeurophysiological

-Evoked potentials

Intra-operative physiological monitoring

Spinal cord (Scoliosis)Sciatic/ Femoral nerve (THR)Brachial plexusPedicle screwsVascular surgeryParotid surgery

Concept of monitoring

…….Indirect mechanical

Mechanisms of Injury ……

L4L4

L5L5

Mechanisms of Injury ……

Direct mechanical

aorta Segmental a.

Radicular a.Anteriorspinal a.

Mechanisms of injury

Ischaemic cord injuryCompression

+Distraction

+Oedema

+Hypotension

=Reduced cord perfusion

Epidural spinal somatosensory evoked potential Cortical somatosensory evoked potentialsC2 somatosensory potentials

( To posterior tibial nerve, peroneal nerve stimulation)

Somatosensory Evoked Potentials

Preoperative electrode placement

Out of surgical fieldAnterior approach surgerySpinally injuredSpondylolisthesisBrachial plexus exploration

Anaesthetic considerations for SSEP

Relatively forgivingRelaxation unimportant

Effects of local anaesthetics and opiateson S.S.E.P.

Loughnan, Fennelly et al. Anaesthesia and analgesia 1995

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

Motorend-plate

M.E.P.

WHY ?

Dissociation of SEP and MEPEarlier prediction of damageSpecific pathway monitoring

M.E.P. Problems

•Anaesthetic•Stimulus patterns

Anaesthesia

Nitrous oxideIsoflurane

Muscle relaxation

Propofol infusionFentanylAlfentanilRemifentanil

Factors affecting E.P.s

HypoxiaHypotensionCarbon dioxideTemperatureNerve integrityAnaesthetic agentsSide

Interpretation

What is a significant change?LatencyAmplitude 50%Other parameters

N.B. Must monitor minimum 20 minutes after final correction

Action

Exclude technical failureExclude anaesthetic changeRelease correction / distraction(Decompress)

How long have you got ?

Aortic cross clamp 30 minutes

Why is the S.M.E.P. more sensitive toanaesthetic agents

Than the S.S.E.P. ?

Synapses in pathway

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