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Gomes et al. Vessel Plus 2023;7:24 https://dx.doi.org/10.20517/2574-1209.2023.60 Page 9 of 16

The role of neuromonitoring in the context Of TAA and TAAA repair
Intraoperative neuromonitoring (IONM) has become a valuable aid in the context of complex anatomy
aortic aneurysm repair. As recent publications have demonstrated, it can support intraoperative decision-
making, either during open or endovascular repair [36,95] . Motor-evoked potentials (MEP) monitor the
integrity of the descending corticospinal pathway, whereas somatosensory-evoked potentials (SSEP) assess
[96]
the functionality of the dorsal column somatosensory tract for proprioception and vibration .

Kolesár et al. experimentally demonstrated a region-specific sensitivity of the spinal cord to ischemia ,
[97]
reporting that motoneurons in the ventral horns are more sensitive to ischemia than neurons in other
segments of the spinal cord, which can explain why MEP is more sensitive for SCI monitoring than SSEP.
[98]
MEP are significantly reduced or not detectable within two minutes of acute ischemia , providing
intraoperative real-time information to the surgeons and anesthesiologists. Bianchi et al., in a study
including 100 patients submitted to TAAA repair, observed that the percentage of cases with postoperative
SCI was significantly higher in those patients who presented irreversible MEP deterioration during the
procedure compared to the ones with reversible deterioration . The authors concluded that actions
[99]
intended to reverse MEP deterioration seem to be worthwhile in the endeavor of reducing the SCI risk. It is
essential to highlight that MEP and SSEP have some limitations, such as: (1) volatile anesthetics interfering
with the amplitude of the SSEP; therefore, their use should be kept to a minimum so this IONM modality
can be accurately used; (2) the limb ischemia produced by the introducers and sheaths used during the
endovascular interventions can significantly interfere with the evoked potentials interpretation; and (3)
MEP and SSEP are not able to differentiate between moderate and severe SCI [64,100] . The use of MEP or SSEP
is recommended with a level B of evidence by a multi-society guideline on the management of patients with
[26]
thoracic aortic disease .
Near-infrared spectroscopy (NIRS) is another IONM option in the context of aortic surgery. NIRS is a
method for indirectly evaluating spinal cord oxygenation and perfusion, as it indicates the blood oxygen
saturation in the tissue underneath the NIRS sensor . Considering the collateral network concept,
[101]
[102]
numerous connections exist between the intraspinal and paraspinal networks . Therefore, multiple
electrodes placed at the thoracic and lumbar levels on the surface of paraspinal muscles could provide an
indirect assessment of the oxygenation and perfusion of the spinal cord . It has the advantage of being a
[101]
noninvasive modality that can be applied not only during the surgical procedure but also during the
postoperative management in the intensive care unit. Despite the encouraging publications on the use of
NIRS in the context of aortic surgery, Vanpeteghem et al. stated in a review study that there is no sufficient
evidence available for a precise cutoff that should be considered for SCI . No consensus has been
[103]
established recommending the clinical applicability of NIRS in aortic surgery to date.

RESCUE STRATEGIES WHEN SCI IS DIAGNOSED IN THE PERIOPERATIVE PERIOD OF
TAA AND TAAA REPAIR [Table 4]
SCI with intraoperative onset
During the TAA or TAAA repair, constant attention to the neuromonitoring data is crucial to prompt
maneuvers intended to improve spinal cord perfusion. Decreased MEP or SSEP should immediately trigger
actions to increase MAP > 90 mmHg, such as the careful infusion of volume and the use of vasopressors, as
well as the increase in CSF drainage to keep CSFP < 10 mmHg in the high-risk patients who received a
lumbar drain preoperatively. If persistent changes in IONM are observed, maneuvers such as
reimplantation of intercostal arteries during open repair or temporary aneurysm sac perfusion (TASP) and
modification of the sequence of implantation of components during endovascular approach could aid in
increasing the blood flow to the spinal cord.