3M Sarns TCM II - Product Description; Theory of Operation

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Product Description
Functional Description (Continued)
Temperature Display Module
The Temperature Display Module may be used to
monitor the temperature of the patient or extracorpo-
real circuit. Temperature probes are connected to a
Temperature Probe Module, which is installed in the
rear of the system. One Temperature Probe Module
will translate information from three probes for display
on the three digital displays. Up to nine temperature
readings are available with the use of three Tempera—
ture Probe Modules and nine temperature probes.
Probe Display switches are used to select which
probe’s information will be displayed. LEDs, next to
alphabetically marked labels, indicate which probe has
been selected. These labels have an erasable writing
surface for marking the probe location in the patient or
extracorporeal circuit. High and low temperature
alarm limits may be set for one probe per module.
Gradient rewarming frees the operator from constant
monitoring and setting of temperatures. When Probe
G is measuring the venous blood temperature, gradient
rcwarming may be used to limit the warming rate of
water to 6° or 10" above the temperature of the venous
blood. Selecting a gradient while in Rewarm mode
limits the maximum water temperature to 42°C;
selecting a gradient while in Maintain mode allows the
operator to select a maximum water temperature lower
than 42°C.
The Temperature Display Module’s remote control
function duplicates the main unit cooling, warming,
and maintain controls and the cardioplegia pump On/
Off switch. The module may be mounted on a vertical
pole up to 7.5 ft. (2,3 m) from the main unit; the
remote controls allow convenient operation of the main
unit while monitoring temperatures.
For safety, the Test switch may be used to check the
temperature conversion circuitry and displays. A
remote monitor circuit automatically checks for
internal problems; it will cause all the panel lights to
go off if a problem is detected.
Theory of Operation
For an arterial heat exchanger or blanket supply, water
is drawn by the pump 1) from a cold water reservoir
for maximum cooling, 2) in a closed path past electric
heaters for maximum warming, or 3) in a path with
either cold reservoir water added or heat added to
attain and maintain a set temperature. Microprocessors
translate and compare thermistor probe measurements
to the selected temperature; then they operate the
correct valves and electric heaters to adjust the water
temperature. The microprocessors also translate the
probe measurements for digital display.
When a gradient relative to the venous blood tempera—
ture is used for rewarming, microprocessors measure
the difference between venous blood temperature and
water temperature and control the valves and heaters to
maintain the correct differential.
The'Sarnsl'M TCM II is designed to provide protection
against excessively high temperatures. The maximum
temperature available for operator selection is limited
to 42°C. The software compares the primary and
redundant temperature probes in the heaters to verify
temperature accuracy; the software will give an alarm
and shut off the heaters if the temperature reaches
425 “C. [n the event of sofiwate failure, a completely
separate monitoring system with an emergency circuit
will shut off the heaters at 43.0°C.
The ice maker is a compressor type refrigeration
system which uses Tetrafluoroethane (121—1343) for the
refrigerant gas, The water freezes onto a cold plate
located in the large tank. A sensor, near the cold plate,
turns off the compressor when approximately 50 lbs. of
ice has collected. The microprocessor disables the
compressor when in Defrost mode.
For Cardioplegia Water Supply, water is l) drawn by a
pump from a water reservoir, supplied to an external
port, and returned; or 2) drawn from the large water
reservoir, supplied to a small water reservoir, and
returned to the large reservoir. The pump operates at
three speeds to change the water flow rate. The mode
and speed selections are activated by the cardioplegia
switch.
For patient temperature monitoring, a thermistor, at the
tip of each telethermometer probe, senses external
temperature. When there is a shift in the external
temperature, the electrical resistance of the thermistor
changes accordingly. This resistance change is mea—
sured by the Temperature Probe Modules, and trans—
mitted for display.
The remote controls function in the same manner as
their counterparts on the main unit. Choosing a mode
on the remote panel causes the appropriate information
to be sent to the main unit. The main unit acknowl—
edges receiving the information by returning the
information to the remote unit and fighting the correct
remote LED. The display of the LEDs on the remote
unit indicates the change has been received on the
main panel.
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