Electroretinogram by Donnell J Creel

Figure Reference: Med.Utah.edu (linked, pl click)

In general, intraopertive neurophysiological monitoring teams do not conduct ERG or EOG in the Operating room set up, it is rather cumbersome and difficult to get a reliable readings combined with the difficulty of placing the recording electrode and risks that are associated with the procedure.  However, Donnell in its Chapter on"The electroretinogram" presents the latest developments that record the status of retinal function using skin electrodes and he also sheds light on the recent advancement in ERG the multifocal retiongram. Whether you are going to conduct this test or not, if you are interested in all the evoked potentials and the basics, this is an excellent reading material. Enjoy.

 The Electroretinogram: Clinical Applications by Donnell J. Creel

Electrophysiological testing of patients with retinal disease began in clinical departments in the late nineteen forties. Under the influence of the Swedish pioneers, Holmgren (1865) and Granit (1933), the electroretinogram was being dissected into component parts and early intraretinal electrode studies were beginning to tell which cells or cell layers gave rise to the various components. A detailed discussion of the electroretinogram, or ERG as it is commonly abbreviated, is found in the accompanying chapter by Ido Perlman. A little after the introduction of the ERG as a test of the state of the patient’s retina, another diagnostic test called the electrooculogram (EOG) was introduced to the clinic (Arden et al., 1962). The EOG had advantages over the ERG in that electrodes did not touch the surface of the eye. The changes in the standing potential across the eyeball were recorded by skin electrodes during simple eye movements and after exposure to periods of light and dark. Over the years ERG recording techniques have become progressively more sophisticated in the clinical setting. With the advent of perimetry, optical coherence tomography (OCT) and pattern ERG techniques, more precise mapping of dysfunctional areas of the retina is now possible. The most recent advance in ERG technology is the multifocal electroretinogram (mfERG). The mfERG provides a detailed assessment of the health of the central retina.

Pedicle Screws & Triggered EMGs!

Spine (Phila Pa 1976). 2010 Jan 15;35(2):E43-8.

Usefulness of electromyography compared to computed tomography scans in pedicle screw placement.

Duffy MF, Phillips JH, Knapp DR, Herrera-Soto JA.
STUDY DESIGN: This is a retrospective analysis of 30 pediatric deformity surgeries. OBJECTIVE: The purpose of this study was to evaluate the accuracy of neuromonitoring in comparison to postoperative computed tomography scans for pedicle screw position. SUMMARY OF BACKGROUND DATA: Triggered electromyography potentials in aiding the placement of lumbar pedicle screws are considered useful; however, this method is less accepted in thoracic screw placement. METHODS: Thirty pediatric deformity surgeries were reviewed. All screws were placed using fluoroscopic assistance. Electromyography data were obtained on all screws. Every patient underwent postoperative computed tomography scanning. Computed tomography scans were assessed by all authors, and each screw was classified. Sensitivity, specificity, negative predictive value, and likelihood ratios were determined for the cut-off value of an electromyography > or =6 mA. RESULTS: A total of 329 screws were reviewed. No complications occurred. An overall accuracy of 93% was obtained. No retained screw had greater than 2 mm medial pedicle wall breach. Nine screws were removed intraoperatively due to medial breach. The mean electromyography potential for all classes of screws was not statistically different (P > 0.1). The negative predictive value of the test was 0.92 in the thoracic spine and 0.93 in the lumbar spine. The negative likelihood ratios were 0.96 and 0.35 for the thoracic and lumbar spines respectively, and the positive likelihood ratio was 1.4 for the thoracic spine and 12.5 for the lumbar spine. CONCLUSION: Thoracic and lumbar pedicle screws are safe surgical options in the treatment of pediatric scoliosis. Comparison of electromyography potentials and postoperative computed tomography scans showed no statistically significant difference for all classes of screws. The likelihood ratio for electromyography testing was more clinically significant in the lumbar spine. A triggered electromyography value greater than or equal to 6 mA has a high likelihood of that screw being in the "safe zone." However, there is no true electromyography cut-off value that guarantees accurate placement and avoidance of neurologic injury.

Anesthesia and Neuromonitoring by Reza Gorji, MD

Reza Gorji from University of NY writes at the Neuroanesthesia.net about various neuromonitoring methods and the effect of anesthesia, what types of anesthetic agent is advisable for certain types of EPs and EEGs during surgical procedures.

Anesthesia and Neuromonitoring: Electroencephalography and Evoked Potentials Reza Gorji, MD, Department of Anesthesiology, University Hospital, State University of NY, Syracuse, NY

• Anesthesia and Neuromonitoring (EEG & EP) Patients undergoing neurologic/orthopedic procedures involving the peripheral and central nervous system may be at increased risk from hypoxia/ischemia to vital neurologic structures. Intraoperative neuromonitoring may improve patient outcome by:
  

a. Allowing early detection of ischemia/hypoxia before irreversible damageoccurs

b. Indicating the need for operative intervention (shunts placed in carotid surgery) to minimize nerve damage The role of anesthesiology in neuromonitoring is one of understanding the appropriate anesthetic techniques, applying knowledge of medicine, surgery, physiology and pharmacology to get the best possible outcome.

This monograph will discuss the

various clinically important neuromonitors and offer solutions as they apply to clinical anesthesia.

It is divided in 3 broad sections: Electroencephalography, sensory evoked potentials and motor evoked potentials.

Neuromuscular Scoliosis?- Intraoperative Neuromonitoring!!

Michael G Fehlings* and Michael O Kelleher

Correspondence 

*Suite 4WW-446, 399 Bathurst Street, Toronto, ON M5T 2S8, Canada

Email michael.fehlings@uhn.on.ca

This article has no abstract so we have provided the first paragraph of the full text.

• The avoidance of iatrogenic neurological injury is of paramount importance during spinal surgery, and multimodality intraoperative monitoring using a combination of MEPs, SSEPs and electromyographic (EMG) signals is increasingly used in this setting.^{1, 2} During corrective procedures for neuromuscular scoliosis, however, the successful application of intraoperative monitoring is a challenge, particularly in the most severely deformed and neurologically compromised patients.³ Difficulties in obtaining reliable baseline recordings of conventional (cortical and subcortical) SSEPs and transcranial

  MEPs in patients with neuromuscular scoliosis has prompted the use of an epidural electrode to record spinal SSEPs and evoke neurogenic MEPs.

Benign Or Metastatic Tumor Removal &The importance of IntraOperative Neuromonitoring

Resection of a benign brachial plexus nerve sheath tumor using intraoperative electrophysiological monitoring.

Kwok K, Davis B, Kliot M.
Department of Neurosurgery,
University of California at Davis, Sacramento, California 95825, USA. keithkwok2004@yahoo.com

OBJECTIVE: Benign peripheral nerve sheath tumors arising from the brachial plexus are rare. Neurosurgeons often lack the clinical and surgical experience to optimize the management of these uncommon tumors. We filmed a video depicting the surgical resection of a benign peripheral nerve sheath tumor involving the brachial plexus. METHODS: An illustrative case was used to demonstrate the proper management of a brachial plexus nerve sheath tumor including the important role of intraoperative electrophysiological neuromonitoring during tumor resection. RESULTS: Using an illustrative case, we describe a systematic approach in the evaluation and surgical management of patients with a brachial plexus nerve sheath tumor. The importance of taking a thorough clinical history, performing a thorough physical examination, applying high-resolution magnetic resonance imaging techniques to visualize the pathology, and using intraoperative electrophysiological neuromonitoring during surgical exposure and resection of the tumor are stressed. Combined with appropriate postoperative treatment, these techniques minimize the risks and increase the likelihood of achieving a good clinical outcome. CONCLUSION: Brachial plexus nerve sheath tumors are challenging mass lesions that should be evaluated and surgically resected by an experienced team of physicians to optimize clinical outcome.

Neuromonitoring during surgery for metastatic tumors to the spine: intraoperative interpretation and management strategies.
Quiñones-Hinojosa A, Lyon R, Ames CP, Parsa AT.

Department of Neurological Surgery,
Brain Tumor Research Center, University of California-San Francisco,
505 Parnassus Avenue, M-779, San Francisco, CA 94143-0112, USA.
quinones@neurosurg.ucsf.edu

Resection of metastatic tumors of the spine poses great technical challenges, with the potential of creating severe neurologic deficits. Several modalities of electrophysiologic monitoring, including SSEPs and MEPs, have evolved to aid in resection of these tumors. This review has presented additional techniques-such as mapping of the dorsal columns with antidromic-elicited SSEPs to plan the myelotomy and direct intra-medullary stimulation-that help to identify the extent of the tumor margin at its interface with functional tracts. Neuromonitoring can potentially minimize the sensory and motor damage that can occur during resection of metastatic tumors of the spine. Further experience with these techniques should allow improved results follow-ing surgical procedures in functionally eloquent are as of the spinal cord during the surgical management of metastatic tumors