From the Guidelines
Somatosensory Evoked Potential (SSEP) monitoring works by recording cerebral cortical electrical potentials with scalp electrodes during electrical stimulation of the posterior tibial or peroneal nerves of the lower extremities, which are conducted via the lateral and posterior columns of the spinal cord. This monitoring technique is used to assess the integrity of sensory pathways in real-time during surgical procedures that may put these pathways at risk, such as aortic reconstruction 1. The process involves delivering small electrical pulses to peripheral nerves and measuring the time it takes for the signal to travel from the stimulation site to the recording site (latency) and the size of the response (amplitude).
Key Aspects of SSEP Monitoring
- SSEP monitoring is less sensitive to anesthetic drugs and paralytic agents compared to Motor Evoked Potential (MEP) monitoring, making it a more straightforward technique to use in certain surgical settings 1.
- However, SSEP monitoring has limitations, as it only assesses the integrity of the lateral and posterior columns of the spinal cord, and may not detect injuries to the anterior motor column 1.
- The technique requires specialized equipment, including a stimulator, recording electrodes, and a computer system for real-time analysis, and is typically performed under total intravenous anesthesia (TIVA) to minimize the effects of anesthesia on SSEP signals.
Clinical Applications and Limitations
- SSEP monitoring can influence surgical strategy, as seen in a study where it led to corrective interventions in 27% of patients undergoing descending aortic reconstruction 1.
- Despite its utility, SSEP monitoring alone has not been shown to improve outcomes in patients undergoing thoracic aortic aneurysm (TAA) repair, and may be associated with delayed ischemia detection and high rates of false-negative and false-positive results compared to transcranial MEPs 1.
- The choice between SSEP and MEP monitoring should be based on the specific clinical context and the type of surgical procedure being performed, considering the strengths and limitations of each technique 1.
From the Research
Overview of Somatosensory Evoked Potential Monitoring
Somatosensory evoked potential (SSEP) monitoring is a technique used to assess the integrity of the brain, spinal cord, and nerve roots during surgical procedures. It involves recording the electrical potentials from the scalp after electrical stimulation of the peripheral nerves of the upper or lower limbs 2, 3, 4, 5, 6.
How SSEP Monitoring Works
The process of SSEP monitoring includes:
- Electrical stimulation of the peripheral nerves, typically in the upper or lower limbs
- Recording of the electrical potentials from the scalp using electrodes
- Analysis of the amplitude and latency of the recorded potentials to detect any changes or abnormalities 2, 3, 5
- Comparison of the recorded potentials with baseline values to identify any significant changes 2, 3
Applications of SSEP Monitoring
SSEP monitoring has various clinical applications, including:
- Detection of position-related ulnar nerve injury during lumbosacral spine surgery 2
- Monitoring of sensory and motor functions during decompression and instrumentation of the lumbosacral spine 3
- Identification of pre- and intraoperative risk factors associated with neurological deterioration in cervical surgery 4
- Detection of peripheral ischemia and potential injury resulting from positioning of the surgical patient 6
- Assessment of the functional integrity of the sensory pathways in central and peripheral nervous system disorders 5
Benefits of SSEP Monitoring
The use of SSEP monitoring can provide several benefits, including:
- Early detection of neural and vascular compromise during surgical procedures
- Localization of the area of compromise, whether central or peripheral
- Prevention or minimization of neurological deterioration and potential injuries
- Improvement of patient outcomes through prompt intervention and correction of any detected issues 2, 3, 4, 5, 6