Who Needs Intra-operative
monitoring?
 |
Surgical procedures carried out within or
near the spinal column or those involving transient interruption of
blood flow to the spinal cord (e.g repair of thoraco-abdominal aortic
aneurysms) are associated with a risk of neurological impairment
ranging from loss of sensation to complete paraplegia.
These deficits can arise as a result of
direct trauma, stretching of nerves or occlusion of blood flow. Much
effort has therefore been made to develop techniques which allow the
health of the spinal cord to be assessed continuously during these
risky surgical procedures. |
Sensory Evoked Potential
(SEP) Monitoring
Surgical teams currently monitor the status of
ascending spinal sensory pathways by applying stimuli to the patient’s ankle
or wrist and observing the resultant changes in somatosensory evoked
potentials (SEP’s) recorded from the brain. This form of intra-operative
monitoring uses changes in the SEP waveform to alert medical teams of
possible complications and there is no doubt that this technique has
protected many patients from surgically induced neurological deficits.
However, the technique of SEP monitoring has
attracted some criticism, much of which has been published in peer reviewed
journals:
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Unchanged SEP waveforms have on occasions
misled surgeons into continuing with surgery, resulting in unforeseen
post-operative neurological complications such as severe paraplegia.
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Altered SEP’s have prompted surgeons to
back-off from procedures, only to find that the patient has suffered no
loss in sensory status upon recovery.
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As SEP’s are generally small in magnitude,
they can be difficult to monitor reliably in some patients, particularly
those presenting with a pre-existing neuropathology.
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Although SEP monitoring is used as an
indicator of the health of the spinal cord as a whole, some would argue
that for anatomical reasons, the descending motor fibres may be at greater
risk during surgery. This would suggest that it would be of tremendous
benefit to monitor descending motor fibres exclusively or in combination
with SEP monitoring.
Transcranial Electrical Motor
Evoked Potentials (tceMEPs) & Digitimer Ltd
In collaboration with leading clinical
neurophysiologists, Digitimer developed the
D185 MultiPulse
Cortical Stimulator in order to provide a more reliable method of
minimizing the risk of surgically induced paraplegia while maximizing the
level of surgical correction that could be safely conducted. This unique
device is used transcranially to electrically stimulate the brain's motor
cortex, resulting in a descending motor evoked potential (MEP) which is
conducted down the spinal cord to upper and lower limb extremities. The
pathways stimulated in this manner are the same as those used by the brain
to trigger and control voluntary movement. As with SEP monitoring, any
alterations in the MEP waveforms can provide the surgical staff with crucial
warning of possible complications.
MEP Monitoring - The Way
Forward?
A 1000 patient, 2 centre clinical trial of the
Digitimer D185 in the USA, has demonstrated that MEP monitoring during
spinal surgery was (1) more accurate for predicting motor outcome than the
SEP was for predicting sensory outcome; and (2) that useful motor responses
were achievable with a higher probability than useful sensory responses.
Furthermore, in cases where SEP monitoring alone may have misled the surgeon
into aborting or curtailing a procedure, additional use of MEP monitoring
can more reliably indicate whether it is safe for the surgeon to continue
the procedure to completion.
Evidence from the 5 year study outlined above
has prompted the FDA to clear the Digitimer D185 for marketing. It is hoped
that with this move, the technique of intra-operative MEP monitoring will be
more commonly used by cardiovascular and neurosurgeons worldwide. Digitimer
Ltd now offer the D185 stimulator to hospitals and neurophysiological
monitoring organizations throughout the world. |
+ 55 11 3662-0762
+ 55 11 3825-7311
