Neurosurgery

Fig. 29.10. Principles of MEP monitoring. MEPs are elicited with transcranial electrical stimulation (left) using two distinct stimulus techniques. The single-stimulus technique allows recording of D-waves (top), and the multipulse technique allows recording of muscle responses.

DECREASE OF D-WAVE AMPLITUDE D-wave at baseline

DECREASE OF D-WAVE AMPLITUDE D-wave at baseline

amplitude reduction

amplitude reduction

D-wave after resection

D-wave after resection

Fig. 29.11. The amplitude of D-waves is a measure of the number of fast-conducting fibers in the corticospinal tract. This amplitude is the primarily monitored parameter for intraoperative assessment of the functional integrity of the motor system in the spinal cord. A decrease of up to 50% from the baseline amplitude is associated with intact motor control in all instances.

Fig. 29.11. The amplitude of D-waves is a measure of the number of fast-conducting fibers in the corticospinal tract. This amplitude is the primarily monitored parameter for intraoperative assessment of the functional integrity of the motor system in the spinal cord. A decrease of up to 50% from the baseline amplitude is associated with intact motor control in all instances.

tibialis). These muscle MEPs are interpreted in an all-or-none fashion. Their presence indicates intact functional integrity of the voluntary motor system in the spinal cord. Their absence indicates jeopardized functional integrity of the motor pathways, highly associated with an at least temporary disruption of voluntary motor control. The stimulation and recording of D-waves and muscle MEPs can be repeated every second. Therefore, the feedback information is provided in real time. Figure 29.4 summarizes the technique of stimulation and recording.

D-waves and muscle MEPs must be interpreted together. Loss of muscle MEPs during a spinal cord tumor resection indicates at least a temporary disruption of motor function of the spinal cord. The more incremental change of the D-wave amplitude then allows further interpretation of the motor outcome. A loss of muscle MEPs is highly associated with a temporary motor deficit in the lower extremities, even if the D-wave amplitude is unchanged. In the majority of cases, this is even side specific. As long as the D-wave amplitude remains above a cut-off value of about 50% of its baseline value, this motor deficit is temporary, with the patient recovering to pre-operative strength within hours to days, or sometimes weeks. A further

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The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.

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