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MR850 Technical Manual * Revision J * Issued November 2005 * Ref. 185041340 (185041713 internal)
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connected. Breathing circuit recognition is performed via three electrical connections on the
heater wire adaptor. Re-configuring the electrical connection pins on a heated circuit and the
way it connects to this adaptor identifies the type of heated circuit. In this way three separate
heater wire circuits can be identified by the MR850.
4.2 Humidifier Controls
4.2.1 Power Button
The humidifier will power on if this button is held down briefly, but must be held
for one second to turn the humidifier off.
Note: For software version 5.45, 5.70 the power button need only be pressed
briefly to turn off the MR850.
CAUTION:
Although the display is not illuminated, the unit may still be
energized. Be sure to disconnect power from the MR850 before servicing.
After power-on the humidifier starts an internal diagnostic routine which checks
for possible problems in the humidifier setup. If everything is working correctly,
normal control is initiated.
4.2.2 Mode Button
When held down for one second, the mode button toggles the humidifier
between Non-Invasive and Invasive mode. The Mode indicator LED shows the
user which mode is selected.
Invasive mode is for use with patients whose upper airways have been
bypassed by either a tracheostomy or endotracheal tube. In this mode of
operation the humidifier attempts to deliver optimal humidity to the patient (37
°C, 100 % RH). This mode is the default mode on power up of the humidifier.
The humidifier normally controls the chamber outlet temperature to 37 °C, and
the airway temperature to 40 °C, maintaining a +3 °C temperature gradient
along the inspiratory limb
1
.
If however this temperature gradient is not maintained, the chamber set point is
reduced in 0.5 °C steps (minimum setting of 35.5 °C), in order to reduce
condensate buildup in the breathing circuit
2
. If the chamber set point is less
than 37 °C and sufficient temperature gradient has been maintained along the
inspiratory limb, then the chamber set point is increased back up to 37 °C in 0.5
°C steps.
Non-Invasive mode is suitable only for patients whose natural humidification
system (i.e. upper airways) has not been bypassed, but are receiving gas via a
facemask or similar.
The humidifier normally controls the chamber outlet temperature to 31 °C, and
the airway temperature to 34 °C, maintaining a +3 °C temperature gradient
along the inspiratory limb
1
.
1
If automatic or manual humidity compensation has been activated then the displayed temperature may be higher
than 37 °C (Invasive mode) or 31 °C (Non-Invasive mode).
2
The humidity compensation algorithm takes precedence over the condensation control algorithm.