The next generation TOF-monitor

Technical

Neuromuscular Transmission (NMT) monitors can be used to indicate the level of neu-romuscular block by stimulating a peripheral nerve and evaluating the muscle response. TetraGraph undertakes this function by electrical stimulation of the peripheral nerve and directly measuring the evoked response of the muscles, thus providing quantitative, automatic measurement of muscle response to a stimulus. The measurement of evoked electromyographic (EMG) response can be performed even in clinical situations in which neuromuscular monitoring cannot be performed using accelerometers or sensors based on movement of strain gauges. The TetraGraph’s main mode of operation is by delivery of a set of four stimuli, a Train of Four (TOF), and calculating the Train of Four (TOF) ratio. Other modes include Post-Tetanic Count (PTC) and Single Twitch (ST).

TetraGraph NMT monitor

The baseline TOF ratio (before administration of a neuromuscular blocker) is 1.0 (100%). During a partial non-depolarizing block, the ratio decreases (fades) as the degree of block increases. As the degree of block increases, the fade increases, and the ratio decreases from 100%, eventually becoming 0%. Once the TOF ratio is 0%, the fourth twitch in the train (T4) disappears, and only 3 responses remain - or a TOF count of 3. Fade continues as the depth of block increases, until T3 becomes 0, and the TOF count is 2. Once T2 disap-pears, T1 remains (TOF count is 1). Once T1 disappears, the TOF count becomes 0. Once T0 is reached the PTC option is initiated.

Train Of Four

The Monitor will indicate that the electrodes are in contact with the skin by changing the colour of the icons for both Stimulating and Evoked Response sensors. RED indicates that the sensors are not connected or that the impedance is too high. GREEN Indicates that the electrode is correctly connected.

To begin, the unit can be started using either Auto or Man-ual setting mode. During an Auto setup, the unit will auto detect the maximal current before the main test screen appears. In Auto mode, parameters for Stimulus in mA and Pulse Width in Microseconds (µs) are preselected on the main test screen, but can be adjusted if required by select-ing Manual mode. If the device is unable to determine the maximal current then Manual mode must be used.

Display

Manual mode requires these parameters to be set by the user, as illustrated on the figure to the left.

To commence monitoring press the TOF (Train of Four), or ST (Single Twitch). Alternatively, monitoring can be started by pressing the Paused box. This will start monitoring in the TOF mode.

During monitoring, data can be displayed in three differ-ent ways (except during ST mode). Bar graph, Trend or Waveform. These can be accessed via the boxes below the progress bar as indicated.

To pause monitoring at any time, press Pause, immediate-ly followed by Confirm which will appear adjacent to the Pause box. Pause will highlight red. Stimulation will cease while paused.

If TOF count reaches zero then PTC option will be activated. If selected a further TOF will be triggered and if TOF count is still zero then PTC will be initiated.

In Single Twitch mode, the unit will provide a fixed current to stimulate the nerve. As the block increases, the twitch response will decrease shown by the waveform as indicated.

Train of Four, mode TOF Single Twitch mode ST

The bar indicated progress to the next stimulation.

Use the boxes to select, bar graph, trend or waveform.

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Performance and Technical Specification

Ulls väg 29B, SE-756 51 Uppsala, Sweden

info@senzime.com +46 (0)18-51 56 40

INFO

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Stimulation Patterns Single Twitch (ST) at 1 Hz; Train-of-Four ratio (TOF) (in %) Train of Four Count (TOFC); Post-tetanic Count (PTC)

Operating Duration 8 hours (battery)

TOF Interval User selected - every 20 sec, 1 min, 5 min, 15 min, 60 mins

Automatic Stimulus Setup Yes, auto detection of maximal current; supramaximal current 20% above maximal current.

Patient cable 2.5m Quick insert/release

Stimulation

Current 0-60 mA @ 5,000 Ohm

Pulse Width 200 μs or 300 μs

Pulse Type Monophasic square wave

Voltage 300V, Max delivered charge of 18μC

Sensor capture 1000 samples/sec @ 0.05 µV/bit

Graphics

Display Colour LCD, Touch Screen

MEP Display of waveforms

TOF Bar of four pulse amplitudes, trend of successive TOF values

TOFC TOF Count, integer and trend

ST Amplitude of response, mV and % of baseline ST

PTC Number of post-tetanic ST responses

Day-Date Programmable format

Patient ID 12 characters, numeric plus hyphen

Audible stimulus indication On/Off

Battery charge Recharge from mains via USB cable

Standards Designed to meet IEC 60601-1; IEC 60601-1-2; IEC 60601-2-40

Data Interface USB file transfer to PC