This presentation was a retrospective case series that illustrated a difference between transcranial motor evoked potentials (tceMEPs)(MEPs) collected with the patient supine prior to positioning, and prone after positioning.

1. Intraoperative TceMEP:
Supine vs. Prone
Prepositioning vs. Postpositioning:
A Retrospective Case Review
By
David Barnkow, Au.D, D.ABNM
April 28, 2020

2. The Study:
- All cases were performed by the same surgeon and neurophysiologist
team.
- The anesthesia was proved by a small pool of anesthesiologists familiar
with the surgeons preferences.
- Anesthetic regimen was combination of approximately 0.5 MAC of
inhalation agents and target-controlled infusion (TCI) with propofol and
remifentanil, etc.
- Small dose rocuronium (typically 10-20 mg) was administered at
intubation.

3. The Study:
- Included data was the
left hand tceMEP
response with
substitution of right hand
response if left hand data
was absent.
- TceMEP traces were
converted to ASCII files
and transferred to
Microsoft Excel
spreadsheets.
Supine Prone
Post-intubation, Supine, Pre-positioning

4. The Study:
- The supine data was collected after intubation and central venous lines were complete
while the patient was on the hospital gurney that brought them into the operating room.
- The prone data was collected after the patient was positioned prone on the operating
table with the head supported in a Mayfield frame.
- Stimulation was elicited using corkscrew electrodes to assume consistent stimulation sites
across collection conditions.
- Stimulation electrodes were placed at C3 and C4.
- Stimulation across patients varied with 4, 5, and 6 pulse trains, and stimulus durations of
50 us and 75us. Stimulation parameters expect for intensity, rarely changed within any
individual patient.

5. The Study:
The 640 individual data
points that comprised each
waveform were averaged
across all 56 subjects to
create and average supine
and prone waveforms.

6. The graph
ordinate values
are relative and
do not
correlate to
actual
response
amplitudes.
Supine Average Response

7. Prone Average Response

8. Supine vs Prone

9. Observation:
- For my practice, prone tceMEPs
appear slightly longer in absolute
latency, slightly more complex
morphology, and greater in
amplitude compared to supine
responses.
Discussion:
- Patient Temperature: Supine
data was collected while the
patient was asleep but under
blankets.
-Prone data was collected after
the patient had been exposed
for approximately 20 minutes to
room air with no covers or
heating.

10. Discussion:
- Anesthetic State:
- Neuromuscular Blockade: The
patient typically had at least 30
minutes more to metabolized any
muscle relaxants for prone data
collection.
- Anesthetic Agents: The
anesthesiologist has had time to
stabilize the patient’s drug doses
prior to prone data collection.

11. Final Thoughts:
- Did the data change? Yes, a
little.
- Did the change represent a
sentinel event (Require surgeon
advisement)? No.
- Do I need a better statistician?
Definitely!
- Will I share this data? Sure, if
you really think it will help.