Ischemic Optic Neuropathy
Conditions
Keywords
Visual Evoked Potentials
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.
Interventions
DEVICEVEP under TIVA
Propofol will be administered for anesthesia maintenance in patients randomized to the TIVA arm of the study. In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
DEVICEVEP under balanced anesth.
Balanced general anesthesia with desflurane will be administered for anesthesia maintenance in patients randomized to the balanced general anesthesia arm of the study, In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
DRUGPropofol
Propofol will be administered for anesthesia maintenance in patients randomized to the TIVA arm of the study. In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
DRUGDesflurane
Balanced general anesthesia with desflurane will be administered for anesthesia maintenance in patients randomized to the balanced general anesthesia arm of the study, In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
Sponsors
Ohio State University
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
PREVENTION
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to No maximum
Healthy volunteers
No
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)
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| 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
| Measure | Time frame | Description |
|---|---|---|
| The Difference in VEP Changes in Amplitude Among Both Groups | Every 30 minutes during surgery for up to 6 hours | VEP waveforms were evaluated using either present baseline - reproducible positive-negative-positive complex of substantial amplitude (≥2 µV) that appeared 100-200 ms after pulse stimulus onset; marginal Baseline - low amplitude (\<2 µV) reproducible P100 waveform; or absent baseline - no repeatable response present. Any activity of \<0.5 µV was not considered a response. Best derivation for each particular patient was used for monitoring electroretinogram (ERG) recording and confirming the stimulation. |
| 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 |
Countries
United States
Participant flow
Participants by arm
| Arm | Count |
|---|---|
| VEP Under TIVA Patients undergoing prone spine surgery will receive an anesthesia regimen using propofol (TIVA) for maintenance
VEP under TIVA: Propofol will be administered for anesthesia maintenance in patients randomized to the TIVA arm of the study. In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
Propofol: Propofol will be administered for anesthesia maintenance in patients randomized to the TIVA arm of the study. In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery. | 9 |
| VEP Under Balanced Anesthesia Patients undergoing prone spine surgery will receive an anesthesia regimen using Desflurane as part of balanced general anesthesia
VEP under balanced anesth.: Balanced general anesthesia with desflurane will be administered for anesthesia maintenance in patients randomized to the balanced general anesthesia arm of the study, In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be inserted subcutaneously around the visual area and the SightSaverTM visual stimulator will be placed to monitor VEP during surgery.
Desflurane: Balanced general anesthesia with desflurane will be administered for anesthesia maintenance in patients randomized to the balanced general anesthesia arm of the study, In order to record the VEPs, standard half-inch sub-dermal needle electrodes will be ins | 11 |
| Total | 20 |
Baseline characteristics
| Characteristic | VEP Under Balanced Anesthesia | VEP Under TIVA | Total |
|---|---|---|---|
| Age, Categorical <=18 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical >=65 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical Between 18 and 65 years | 11 Participants | 9 Participants | 20 Participants |
| Age, Continuous | 56.2 years STANDARD_DEVIATION 16.1 | 52.3 years STANDARD_DEVIATION 14.8 | 54.5 years STANDARD_DEVIATION 15.3 |
| Region of Enrollment United States | 11 participants | 9 participants | 20 participants |
| Sex: Female, Male Female | 4 Participants | 6 Participants | 10 Participants |
| Sex: Female, Male Male | 7 Participants | 3 Participants | 10 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 9 | 0 / 11 |
| other Total, other adverse events | 0 / 9 | 0 / 11 |
| serious Total, serious adverse events | 0 / 9 | 0 / 11 |
Outcome results
Primary
Efficacy in Detecting Subtle Intraoperative VEP Changes Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA.
Number of Participants with Subtle Intraoperative VEP Changes Observed Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA
Time frame: VEP waveforms recorded every 30 minutes during the entire procedure for up to 6 hours.
| Arm | Measure | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|
| VEP Under TIVA | Efficacy in Detecting Subtle Intraoperative VEP Changes Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA. | 1 Participants |
| VEP Under Balanced Anesthesia | Efficacy in Detecting Subtle Intraoperative VEP Changes Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA. | 1 Participants |
Secondary
Safety of Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA
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
Time frame: From start of surgery up to 24 hours after surgery
| Arm | Measure | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|
| VEP Under TIVA | Safety of Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA | 0 Participants |
| VEP Under Balanced Anesthesia | Safety of Using SightSaver Visual Stimulator During Spine Prone Surgeries Under Balanced General Anesthesia Versus TIVA | 1 Participants |
Secondary
The Difference in VEP Changes in Amplitude Among Both Groups
VEP waveforms were evaluated using either present baseline - reproducible positive-negative-positive complex of substantial amplitude (≥2 µV) that appeared 100-200 ms after pulse stimulus onset; marginal Baseline - low amplitude (\<2 µV) reproducible P100 waveform; or absent baseline - no repeatable response present. Any activity of \<0.5 µV was not considered a response. Best derivation for each particular patient was used for monitoring electroretinogram (ERG) recording and confirming the stimulation.
Time frame: Every 30 minutes during surgery for up to 6 hours
| Arm | Measure | Value (MEDIAN) |
|---|---|---|
| VEP Under TIVA | The Difference in VEP Changes in Amplitude Among Both Groups | 0.66 micorvolts (µV) |
| VEP Under Balanced Anesthesia | The Difference in VEP Changes in Amplitude Among Both Groups | 0.48 micorvolts (µV) |
Secondary
The Difference in VEP Changes in Amplitude Among Both Groups
The difference in VEP changes in amplitude with a single and double stimuli using the SightSaver visual stimulator under balanced general anesthesia versus TIVA.
Time frame: every 30 minutes during the entire procedure for up to 6 hours
| Arm | Measure | Value (MEAN) |
|---|---|---|
| VEP Under TIVA | The Difference in VEP Changes in Amplitude Among Both Groups | 14.21 milliseconds (ms) |
| VEP Under Balanced Anesthesia | The Difference in VEP Changes in Amplitude Among Both Groups | 17.94 milliseconds (ms) |