Cardiovascular Surgical Procedures
The monitoring approach for aortic repair is determined by the location of the pathology along the aorta, but the general framework includes SSEPs, tcMEPs, and EEG to collectively monitor cerebral and spinal cord perfusion throughout the procedure.
During thoracic and thoracoabdominal aortic repair, the risk of spinal cord ischemia rises sharply after approximately 30 minutes of cross-clamping. SSEP and tcMEP changes — typically occurring within two minutes of perfusion loss — provide the earliest objective indication that spinal cord ischemia is developing, allowing the team to implement perfusion augmentation strategies, adjust clamp position, or increase mean arterial pressure before infarction occurs. Where cerebrospinal fluid (CSF) drainage is employed, IONM waveforms provide objective confirmation of spinal cord response.
For infrarenal and femoral artery clamping, monitoring focus shifts to the lower extremities. Lower limb SSEPs and tcMEPs detect peripheral ischemia with high sensitivity — waveform loss is typically immediate upon cessation of perfusion and reverses promptly upon restoration.
In aortic arch repair with hypothermic circulatory arrest (HCA), EEG provides the most reliable means of confirming cerebral protection. As brain temperature decreases, EEG activity slows progressively — typically beginning around 28°C — and eventually produces a burst-suppression or isoelectric pattern at temperatures between 18–22°C. EEG-confirmed cerebral electrical silence provides objective evidence that the brain is adequately protected prior to initiating circulatory arrest.
The integrity of the recurrent laryngeal nerve is monitored, Utilizing a 4 channel recording electrode on the endotracheal tube . These electrodes can guard against possible pressure or damage to the nerves caused by retraction or by any mechanical/surgical manipulation. Additionally a flush tipped 90mm direct nerve stimulation probe is provided . These have proven to be an invaluable tool for nerve preservation during excision of mass and can be useful in pre/post excision signal acquisition, to document the integrity of the nerve.
Neuromonitoring for Cardiovascular Procedures
Cardiovascular procedures carry neurological risk through mechanisms of ischemia, embolism, hemodynamic compromise, and direct neural manipulation. IONM provides continuous, real-time surveillance of the brain, spinal cord, and peripheral nerves — enabling the surgical team to detect compromise at the earliest possible moment and intervene before injury becomes permanent.
Carotid Endarterectomy (CEA):
Bilateral EEG is the primary monitoring modality for carotid endarterectomy. A pre-incision baseline is established, against which all subsequent EEG patterns are compared. The critical monitoring periods are:
Carotid clamp placement: EEG slowing or attenuation ipsilateral to the clamp indicates cerebral ischemia to the affected hemisphere. These changes typically emerge within the first two minutes of cross-clamping and provide the earliest available signal of inadequate collateral perfusion.
Shunt placement and removal: Thrombosis or air embolism associated with shunt insertion can produce focal or diffuse EEG changes consistent with acute ischemia or infarction. EEG monitoring during shunt placement, repositioning, and removal provides real-time detection of any embolic event.
Bilateral upper extremity SSEPs serve as a secondary monitoring modality, corroborating EEG findings by independently confirming the functional status of the primary sensory cortex on each hemisphere.
