Safety and Efficacy of Using SightSaver Visual Evoked Potential (VEP) for VEP Monitoring in Prone Spine Surgery

Not Applicable

Completed

Conditions: Ischemic Optic Neuropathy

Interventions: Device: VEP under TIVA
Device: VEP under balanced anesth.
Drug: Propofol
Drug: Desflurane

Registration Number: NCT02643615

Lead Sponsor: Ohio State University

Brief Summary: Post-operative visual loss (POVL) following non-ocular surgical procedures is an infrequent but severe complication. Little is understood about this complication, but most cases seem to result from loss of blood flow to the optic nerve. This is a pilot, single center, prospective, randomized, two-arm study involving 20 subjects at The Ohio State University Wexner Medical Center who are scheduled to undergo spine surgery that requires prone position and at least two hours of general anesthesia or total intravenous anesthesia (TIVA) and intraoperative neurophysiological monitoring. Patients will be randomized to either general anesthesia or TIVA, and wear the SightSaver device to monitor visual evoked potentials (VEPs) during surgery in order to detect possible changes in optic nerve function that may lead to POVL. We hypothesize that this new, flexible, disposable device will yield better results and more patient satisfaction than devices currently used for visual monitoring during prone spine surgeries.

Detailed Description: The exact mechanism underlying POVL is poorly understood, but nearly all cases seem to involve ischemic optic neuropathy (ION). Posterior ION is more commonly the result of spinal procedures. The spine surgery associated risk factors include: prone position, Trendelenburg positioning, blood loss, prolonged procedure, use of vasoconstriction agents to correct blood pressure, direct ocular compression, and hypotension \[1,2\]. Given the fact that the suspected mechanism is a gradual infarction of the optic nerve, POVL could theoretically be prevented based on early detection of reversible optic nerve dysfunction. Visual evoked potentials (VEP) are a highly sensitive method for detecting optic nerve dysfunction, including ischemia.

During intraoperative neurophysiological monitoring (IONM), an emitted light passes through the lens, reaching the retina and causing hyperpolarization. The signal generated by the retina in response to a flash of light is known as the electroretinogram (ERG). This response may be recorded using conventional neurophysiological equipment and reflects overall retinal function. The VEP peaks are generated during the passage of electrical signal from the retina via the optic pathways to the primary visual cortex, and can also be registered during IONM. Measurements of VEP peaks under anesthesia can vary depending on type of anesthetic regimen, some producing more interference with the electrical impulses than others.

The problems encountered during VEP monitoring are numerous: a reusable device must be cleaned in between patients, tightly fitting goggles pose a risk of damaging the eyes, goggles may fall off or move intraoperatively and be difficult to reposition once the procedure is underway. Also, the light emitting diodes tend to be too weak to produce an adequate stimulus. This pilot study presents a new different approach from current methods. The SightSaverTM visual stimulator design consists of the following key advantages over the current technologies: hygienically superior to re-usable goggles, provides physical protection to the ocular region, use of higher intensity diodes and adhesive foam padding shaped to contours of periocular region.

This pilot, single center, prospective, randomized, two-arm study will involve 20 subjects at The Ohio State University Wexner Medical Center who are scheduled to undergo spine surgery that requires prone position and at least two hours of general anesthesia or TIVA and intraoperative neurophysiological monitoring. Eligible subjects that provide voluntary and written informed consent will be included in the study with a 1:1 randomization ratio of two arms, n=10 patients per each of two anesthesia regimen groups: general anesthesia and TIVA. All patients will wear the SightSaverTM visual stimulator. IONM of VEP with include insertion of half-inch needle electrodes placed just under the skin on either side of the eye, at the top of the forehead and three along the back of the head. Flashes of light, delivered at continuous intervals, will be emitted from diodes mounted in the SightSaverTM visual stimulator. After the baseline VEP is established for the patient, monitoring of VEP will occur at every 30 minutes during surgery. If during the monitoring process, a significant VEP waveform change has occurred, an alert will trigger the surgical staff to check four different parameters: technical issues with goggles, anesthetic changes, significant blood loss or a blood pressure change. Analysis of data collected will be used to evaluate the efficacy of SightSaverTM visual stimulator for intraoperative VEP-based detection of significant visual changes during prone spine surgeries.

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 20

Inclusion Criteria

Male or Female older than 18 years of age
American Society of Anesthesiologists (ASA) status of I to IV and scheduled to undergo elective spinal prone position procedures under general anesthesia or TIVA only with intraoperative neurophysiological monitoring with an expected duration of surgery to be at least 2 hours
If female, have been surgically sterilized or are postmenopausal; if of child-bearing potential, must have a negative serum pregnancy test the day of surgery
Ability and willingness to sign informed consent
Literate in the English language

Exclusion Criteria

Prisoner status
Women who are pregnant or lactating/breast feeding
Patients with a history of contact allergies to foam and/or plastic devices
Any condition, which, in the opinion of the investigator, would make the subject ineligible for participation in the study, such as a history of unstable cardiovascular, pulmonary, renal, hepatic, neurologic (seizures), hematologic or endocrine abnormality (hyperthyroidism, unstable Diabetes type I/II)

Study & Design

Study Type: INTERVENTIONAL

Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
VEP under TIVA	VEP under TIVA	Patients undergoing prone spine surgery will receive an anesthesia regimen using propofol (TIVA) for maintenance
VEP under balanced anesthesia	VEP under balanced anesth.	Patients undergoing prone spine surgery will receive an anesthesia regimen using Desflurane as part of balanced general anesthesia
VEP under TIVA	Propofol	Patients undergoing prone spine surgery will receive an anesthesia regimen using propofol (TIVA) for maintenance
VEP under balanced anesthesia	Desflurane	Patients undergoing prone spine surgery will receive an anesthesia regimen using Desflurane as part of balanced general anesthesia

Primary Outcome Measures

Name	Time	Method
Efficacy in Detecting Subtle Intraoperative VEP Changes Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA.	VEP waveforms recorded every 30 minutes during the entire procedure for up to 6 hours.	Number of Participants with Subtle Intraoperative VEP Changes Observed Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA

Secondary Outcome Measures

Name	Time	Method
The Difference in VEP Changes in Amplitude Among Both Groups	every 30 minutes during the entire procedure for up to 6 hours	The difference in VEP changes in amplitude with a single and double stimuli using the SightSaver visual stimulator under balanced general anesthesia versus TIVA.
Safety of Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA	From start of surgery up to 24 hours after surgery	Number of participants experiencing adverse events related to the study procedures during prone surgery and 24 hours after surgery under balanced general anesthesia versus TIVA