Vascular surgery

Method

Carotid artery stenosis

If carotid artery stenosis has progressed to the point where conservative treatments are no longer sufficient, surgical therapy must be performed, usually using endarterectomy, for which there are different procedures.

In general, the carotid artery is clamped, exposed and opened on one side. The blockage causing the carotid artery stenosis is often removed with part of the inner vessel wall. Under certain circumstances, the carotid artery can be closed with a plastic or vein patch.

Neuromonitoring during surgical treatment of carotid artery stenosis

In general, the measurement of somatosensory evoked potentials (SEP) is recommended for neuromonitoring in vascular surgery and in particular for the surgical treatment of carotid artery stenosis.^[1] Usually, the median nerve is electrically stimulated with needle electrodes placed in one arm and the SEPs are recorded with electrodes placed on the head surface.

This measurement can be used to monitor neuronal activity to detect reduced perfusion in one of the two hemispheres of the brain at an early stage. If the SEP signals change in terms of their latency and amplitude, this may indicate reduced perfusion due to carotid artery occlusion. The surgeons can then adjust the treatment of carotid artery stenosis accordingly in a timely manner.^[1]

Stimulation method during surgical treatment of carotid artery stenosis

The following recommended settings are general, may vary depending on the manufacturer and neuromonitoring device, and should be clarified accordingly in advance.

 >> For stimulation of the median nerve, a frequency of f=4.7 Hz is recommended.

 >> ‘Positive’ single pulses with a pulse width of 200 µs should be applied to the median nerve.

 >> The motor threshold should be determined by slowly increasing the current. A motor response in the hand area confirms successful stimulation.

 >> The current should be about 10% above the motor stimulus threshold.

 >> An average motor threshold in the median nerve is about 12 mA.

In addition to vascular surgery, intraoperative neuromonitoring is used for the implantation of a cochlear implant.

References

1. Leitlinie Neuromonitoring in der Kardioanästhesie – Carotis-TEA.pdf. (2014)