FAQ

How can the Eclipse be used for Intensive Care Monitoring?
EEG and evoked potential studies are established monitoring tools in the neurological intensive care unit (NICU) to aid diagnosis and guide prognosis. Continuous EEG monitoring has been shown to have a decisive or contributing impact on medical decision making in more than 75% of patients. EEG monitoring can also reveal previously unsuspected non-convulsive seizures. SEPs and BAEPs can provide useful prognostic information in coma. SEPs have been shown to predict likelihood of nonawakening with a high level of certainty. Processed EEG, mid-latency auditory evoked potentials and train-of-four EMG monitoring can aid in controlling the levels of sedation by titrating to known electrophysiological measures.

Eclipse features for the ICU include:

1. Continuous or serial EEG, EMG and evoked potential monitoring.
2. Easy to interpret displays.
3. Absolute or relative - to - baseline trending of all processed EEG, burst suppression index and evoked potential measures.
4. Event indication and automatic data saves when measurements exceed predefined limits.
5. Import and trend vital signs from external physiological monitors.
6. Fast review of all patient data.
7. Remote review via LAN or Internet.

How can I be sure the stimulation intensity for SEP monitoring is adequate?
In order to elicit a SEP evoked response, the stimulus intensity must be greater that the threshold to generate a motor response. In the case of median nerve SEPs, the stimulus intensity should be large enough to cause a thumb twitch. When monitoring, the intensity should be set to two or three times the threshold value to insure a supramaximal response. Ideally the stimulus threshold intensity, and optimal stimulation electrode placement, can be determined prior to anesthesia. When this is not practical, monitor for a peripheral response (Erbs point for example) to insure the presence of an action potential.

What is the Stim Error status indicator?
A “Check Stim Imp” message appears on the status bar when the stimulation electrode impedance is either too high (high impedance electrodes or open leads) using constant current stimulation, or too low (low impedance or shorted electrodes) when using constant voltage stimulation. The error message informs you that the leads are either open or shorted or that the stimulator cannot output the requested current or voltage because of high or low electrode impedance.

What is stimulator voltage or current compliance?
When a constant current stimulator is used, the stimulator will attempt to deliver the requested current through the stimulation electrode impedance to the limit of the stimulator’s voltage capacity. The maximum voltage that a constant current stimulator can support is termed the compliance voltage. The maximum current that a constant voltage stimulator can supply is the compliance current. When the stimulator output exceeds its compliance it will no longer function as constant current (voltage) device.

In the case of a constant current stimulator, the stimulator will supply constant current to the patient until the product of the current and stimulation electrode impedance is equal to or greater than the compliance voltage. For example the compliance voltage of the Eclipse high level electrical stimulator is 400V. If the stimulation intensity is set to 40mA, then the maximum stimulation electrode impedance is 400V/40mA = 10K Ohms. The stimulator will not function in the constant current mode for Impedances greater than 10K Ohms. Taking this example one step further, assume the electrode impedance is now 20K Ohms. The maximum current will be 400V/20K = 20mA. In this case Set Current = 40mA, Patient Current = 20mA and the “Check Stim Imp” message will be displayed indicating the fault.

This, by the way, is the reason that low stimulation impedance is required when attempting to supply high stimulation current.

What is the difference between fast and slow charge transcranial electrical motor evoked potential (TCeMEP) stimulation?
Charge (Coulombs) is the product of pulse duration (seconds) and current (Amps), and is the salient parameter for eliciting a peripheral, direct or TCeMEP nerve response to electrical stimulation. Fast charge techniques, as implemented in the Digitimer D185, for example, provide constant voltage stimulation using a pulse width of 0.05ms and can deliver a maximum charge per pulse of 0.075mC. The Eclipse stimulator uses constant voltage and provdes both slow and fast charge stimulation with maximum pulse widths of 0.350ms and 0.075ms respectively. The “slow charge” technique produces a comparable maximum charge per pulse of .070mC.

The two techniques, as described in Hausmann et al Clinical Neurophysiology 113 (2002) 1532-1535, can both be used reliably for intraoperative monitoring and are comparable with respect to feasibility, intra-individual variability and mean parameters of MEP responses. However, it was found that fast charge stimulation provides a higher stimulation efficiency and requires about 35% less total charge than the slow charge technique.

What are safety concerns and patient exclusion factors for the use of intraoperative TCeMEP stimulation?
The most common side effects of TCeMEP stimulation are movement related injuries due to stimulation. Stimulation of the temporalis muscle, may cause tongue or lip lacerations and in one case mandibular fracture. The use of soft bite plates can be used to help prevent injuries of this type.

Excessive patient twitch, may cause traumatic injury when a surgical intsrument is close to a neurologic structure. Preventive strategies may include adjustment of stimulus intensity parameters and timing of the stimulus pulse by video feedback of the operative field.

A metal plate in the skull, history of craniotomy or skull fracture are common exculsionary criteria. Other common exclusion factors include the presence of cochlear implants, cardiac pacemeakers, dorsal column stimulators or other implanted electronic devices. A history of seizures is also used by some centers to exclude patients for TCeMEP stimulation.

For additional details on the subject of current practice and safety relating to TceMEP stimulation intaroperatively see the articles by Legatt and MacDonald.

What is the FSI (Full Scale Input)?
The Full Scale Input setting is directly related to amplifier gain. Lower/higher FSI corresponds to higher/lower amplifier gain. Input signals at the electrodes are amplified, with gain determined by the FSI setting, to usable levels and then applied to the input of an Analog to Digital (A/D) converter. FSI should be chosen to utilize the maximum range of the A/D converter without causing the signal to overload the A/D resulting in top and bottom clipping. Note that setting a very high FSI (low gain) would not maximize the range of the A/D and would also result in low resolution, “boxy” waveforms with excess noise. Choose an intermediate value to optimize signal response. In most cases the default FSI suggested in the Standard Tests are adequate.

Is positive up or down?
The electrode display polarity is such that a positive voltage applied to the electrode assigned to the positive input of a channel will cause the trace to deflect upward while a positive voltage applied to the electrode assigned to the negative input of a channel will cause the trace to deflect downward. For example: If Fpz is the positive input and Cz’ the negative input, (Fpz – Cz) the trace will deflect upward as Cz’ becomes negative with respect to Fpz.

What is the best way to set the Artifact Level?
First off, artifacting is not always bad. Artifact rejection sets acceptance limits for collecting EEG and EP data. When the incoming (live) data exceeds the artifact limits, it will be rejected as invalid and not collected for that epoch. Artifacting allows you to automatically reject signals contaminated with interference exceeding your preset limits. The artifact level should be carefully set so that the incoming signal will neither be distorted by extraneous interference (artifact level set too high) nor rejected completely (artifact setting too low). Artifact levels for EP recording, for example, should always be set to accept approximately eighty (80) percent of incoming sweeps. Use the Live input feature to examine the incoming data for non-physiological data. Always attempt to remove or minimize extraneous artifacts from the power line before proceeding.

What are commonly used montages for EEG and EP monitoring?
The pattern of connections between the electrodes and the recording channels is known as a montage. EEG and EP montages vary according to the monitored procedure, the number of recording channels available and accessibility of recording and stimulation sites (EP). The montage should be chosen to maximize the sensitivity of the recorded response over the neural pathways at risk, provide a control response and, in the case of SEP monitoring, test for adequate stimulation and generation of the peripheral nerve action potential.

In certain situations, the most sensitive recording locations cannot be accessed, either because of interference with the surgical field or due to the inconvenience or time constraints of applying electrodes. In those instances other locations, in close proximity to the optimal one, should be chosen.

EEG montages for monitoring should be designed symmetrically about the midline in order to obtain left-right amplitude and phase information. Two montages suitable for EEG monitoring are: 1) A1-Cz, A2-Cz, F7-Cz, F8-Cz and 2) F7-P3, F8-P4, P3-C3, P4-C4. (Refer to the International 10-20 System of electrode placement for details of electrode nomenclature and scalp locations)

Montages will vary according to the type of procedure and available recording channels. This is particularly true for evoked potentials since each stimulus modality will, in general, evoke a maximal response over different peripheral nerves and cortical areas. However, a median nerve SEP protocol provides a good example of a typical montage used during cervical spine surgery.

Test for adequate stimulation by recording the action potential of the peripheral nerve at the brachial plexus (Erb's point). If possible, record the signal at a site below the surgical field to test for continuity of the neural pathway. Stimulate the median nerve at the wrist using left and right unilateral electrical stimulation. Record the subcortical response at the cervical spine the cortical potentials at the contralateral and ispilateral (control site) somatosensory cortex. The montage for this example would be: ErbLeft- Fpz, ErbRight-Fpz, Cv2-Fpz, C3'-Fpz, C4'-Fpz.

What types of electrodes can be used in the OR and ICU?
Electrodes can be either surface or needle, disposable or reusable. And, combinations of these types can be used in most applications with some precautions.

Reusable or disposable surface electrodes require skin preparation but can provide low electrode impedance and good mechanical stability when applied with tape or collodion. Surface elecodes are a good choice for long terms monitoring in the ICU. Needle electrodes are simple to apply and provide good electrode impedance, but may require tape or some other means to prevent dislodging during the procedure, and require special handling. Corkscrew electrodes afford ease of use, low electrode impedance and provide good mechanical stability.

One little appreciated fact concerns recording with electrodes made of different materials (silver-silver chloride and gold, gold and stainless steel, stainless steel and aluminum, etc). Such electrodes will produce DC potentials and noise, generated by the electrochemical reaction of the dissimilar metals and electrolytes of the skin and body fluids. DC potentials, under some conditions can be as high as 1 or 2 volts which may saturate the preamplifier and cause the amplifier output and resultant traces to be flat.

Noise can be also be generated by stainless steel electrodes which use an aluminum crimp to secure the wire lead to the needle. Electrodes of this type can produce high amplitude (10 -200 µV), high frequency (2KHz) noise, mimicking EMG activity.

Our recommendations are to use needle electrodes with leads and use electrodes of the same material, preferably Ag-AgCl.

Check our Accessories Section for a selection of commonly used electrodes accessories.

What risks are involved when using needle electrodes?
Needle electrodes are a fast and convenient way to apply electrodes. However, care must be taken when applying and removing needle electrodes in order to avoid injury to the patient, and to prevent possible infection.

Never attempt to use a disposable needle electrode more than once, or try to re-sterilize a disposable electrode. They are designed for one-time use only and cannot be safely re- sterilized. After use, carefully replace the protector cap and dispose according to your facility’s guidelines.

Reusable electrodes should be sterilized in accordance with the manufacturer’s directions and your facility’s sterilization guidelines.

What is the Options File?
The options file is a component of the Eclipse program and describes the particular features and installation date of your system. The XP Controller and computer shipped from the factory are linked by the options file. When the system is powered on, the options file checks the Eclipse Controller module for a matching serial number. If there is no match, the Eclipse main screen will show the options list grayed out and the system cannot be used for monitoring. If you are using a different computer than the one originally supplied with your system with a new XP Controller and the system does not work, you may download a later version of the Options File here.

How can I view multiple sites remotely?
The Eclipse has extensive remote monitoring features and capabilities to connect via LAN, Internet or Modem. To remotely review data from several sites, a new instance of the Eclipse program must be opened for each site. To do so, exit to the desktop and double click the Eclipse icon to open a second, third, etc instance. The connection between the monitoring locations and remote site must be via Internet or LAN. In addition, each monitoring location must have its own IP address and patient data must be saved to a shared folder. Refer to the Eclipse User’s Manual for details.

How do I connect an anesthesia monitor to view vital signs?
You may connect a supported vital signs monitor (VSM) to the serial port of the Eclipse computer. Refer to the Vital Signs System Setup Notebook page for a list of supported devices. The vital signs link uses an RS232 serial communications protocol and requires a null modem cable and, in some cases, a connector adapter. Connect the factory for additional information.

Connect the null modem cable and adapter to the VSM serial output connector and the other end to the Eclipse computer. Select the supported VSM from the System Setup Notebook. All VSM measures all available to display in the Current Value Window or to trend. Select the desired measures from the Trend Setup Page.

How can I reduce the stimulus artifact from the trace display or EMG audio?
Stimulus artifact is caused by pickup of the electrical stimulus pulse by the recording electrodes. Stimulus artiface can be generated in a number ways.

Common Mode
The stimulator can produce a voltage on the body with respect to earth ground called the common mode voltage (CMV) The CMV stimulus artifact is dependent upon many factors including: stimulator and recording electrode impedances and matching, stimulus intensity and impedance of the patient with respect to earth ground. CMV stimulus artifact will appear at all recording sites with varying amplitude and polarity, depending upon the recording electrodes impedance balance. Balanced electrodes (both recording and stimulating) will produce the lowest artifact. CMV stimullus artifact will also be reduced when the patient ground electrode impedance is low. Always use a large surface area electrode and prep the skin.

Volume Conduction
Stimulus artifact is generated by volume conduction within the body when the stimulator and electrodes leads are near each other, for example median nerve stimulation at the wrist recording from the APB.

Capacitive Coupling
Stimulus artifact will also be produced by capacitive coupling when the recording electrodes leads are in close proximity to the stimulator electrodes. Reduce the artifact by moving the stimulator leads and module away from the recording electrodes leads.

Electrode and Tissue Effects
The artifact morphology is affected by tissue and electrode type. While both the capacitance and resistance of the electrode skin interface affect the artifact tail duration, the capacitance plays a more dominant role.

Thick skin or bone under the stimulating or recording electrodes will increase the stimulus tail duration.

Surface electrodes tend to produce stimulus artifact with tails that may extend into the recording area of interest. Using a simulating electrode with small active surface area and low capacitance, the duration of the artifact can be reduced to less than 1 ms. Needle electrodes, having a small surface area will produce less of an artiafct tail than a surface electrode.

Eclipse Artifact Reduction Features
Eclipse has two unique features to eliminate trace and audible click stimulus artifact. Trace artifacts can be suppressed by selecting the “Suppress Electrical Stimulus Artifact” checkbox located on the runtime notebook Stim. Seq. Page. The artifact is suppressed for 2 ms indicated by a short red line.

Stimulus click artifact can be suppressed by selecting the “Mute Stimulus Artifact” checkbox located on the runtime notebook Speaker Page.