The University of Kansas
Respiratory Care Education

Servo 300

The Siemens Servo 300 has two units, the control unit and the patient unit, connected by a cable. The control unit pictured on the right contains the ventilator settings and electronic circuits used to control the pneumatic or patient unit.
The patient unit houses the pneumatic components. The gas delivery system consists of high-performance solenoid valves that have a response time of 6 milliseconds.

The control unit is divided into 8 different sections.
Section 1 is the Patient Range which is set first. There are three options: adult, pediatric, and neonatal ranges for continuous flow during expiration, maximum peak flow, maximum measured tidal volume, and apnea alarm time.

The second section is for airway pressure settings: upper pressure limit, pressure control level above PEEP, pressure support above PEEP, PEEP, and trigger sensitivity.
The airway pressure bargraph shown enlarged at left provides visual indicators for all pressure settings.

The sensitivity control or trigger is the bottom knob in the airway pressure section. Pressure triggering is available if the setting is zero or less. Any area in the green or red section provides flow triggering. Zero equals a flow trigger of 32 ml/sec. The flow trigger for the red area ranges from 12 ml/sec at the start of the red area to zero flow.

Section 3 contains the modes which are Stand by , Pressure Control, Volume Control, Pressure Regulated Volume Control, Volume Support, SIMV-VC + PS, SIMV-PC + PS, and Pressure Support/CPAP. Each mode has a touch pad and indicator. The Set Parameter Guide (SPG) may be initiated by pressing the touch pad next to the mode. All the controls that need to be set for that mode will illuminate. Pressing the mode touch pad again will cause the first illuminated light that needs to be set to start flashing, starting with the Patient Range. After the Patient Range is set, the process is repeated for each illuminated indicator until all the controls are set. SPG will cancel if no touch pad has been pressed for one minute.
Volume Support is really pressure support in which the level of pressure is automatically adjusted to achieve a preset target volume. The level of volume (pressure) support can change by as much as 3 cm H20 with each breath until the delivered tidal volume is equal to the target volume. If the patient's compliance improves and the target volume is exceeded, the pressure support level drops by as much as 3 cm H20 at a time to maintain the desired volume. Volume (pressure) support ends when the flow falls to 5% of the peak inspiratory flow or after 80% of the set breath cycle time. 

Apnea while in Volume Support will cause an alarm and a switch to PRVC mode. The PRVC mode indicator flashes and the Volume Support mode indicator remains illuminated. The mode will revert back to Volume Support when the alarm is manually Reset. The indicator for PRVC will no longer flash. 

Apnea in the Pressure Support/CPAP mode will not cause a switch to any other mode. The patient will not receive any breaths and the unit just alarms. The reason the CMV frequency needs to be set in Pressure Support is to determine what 80% of the set breath cycle time would be for termination of a pressure supported breath. In the case of a leak, for example, the flow may not fall to 5% of the peak flow and inspiration would continue indefinitely or until the patient could forcefully exhale hard enough to cause a 3 cm H20 increase in pressure. Patient work of breathing would increase without a backup time cycle mechanism to end inspiration.


Pressure Regulated Volume Control is really pressure controlled breaths with an automatically adjusted pressure control level similar to Volume Support. A target tidal volume is set and the pressure level changes as needed to provide the target volume. In both Volume Support and PRVC, the pressure level may not go any higher than 5 cm H20 below the Upper Pressure Limit.

The Respiratory Pattern section contains the control for CMV frequency which needs to be set in all modes. The inspiratory time % determines the inspiratory time and peak flow, just like with the 900C. If the inspiratory time set is less than 80 ms, the indicator light will flash. The actual inspiratory time and inspiratory flow (L/s) is displayed along with the measured breaths/min and set breaths/min. Pause Time % adjust the time for an inspiratory hold. Inspiratory Rise Time % sets the time it takes to reach the preset pressure or preset flow, depending on the mode. If the SIMV frequency is set higher than the CMV frequency, the indicator light will flash.

In the volume section, one control knob sets the minute volume. As the minute volume is adjusted, the tidal volume is also observed to change, based on the CMV breaths/min. The top two green displays are set values and the bottom red displays are measured. Measured volumes are inspiratory tidal volume, exhaled tidal volume, and exhaled minute volume. The Upper Alarm Limit and Lower Alarm Limit controls are also shown. All volume values are displayed on the volume bargraph. The yellow indicator flashes during Set Parameter Guidelines to show that the alarms should be set. The Neonatal 1/10 indicates that the alarm limits have been divided by 10.
The top set of diodes shows the Upper Alarm Limit and the bottom set shows the Lower Alarm Limit. The middle area shows both the measured or actual minute volume as well as the preset minute volume.

The top section has the Oxygen Concentration control and a display which shows 40% oxygen. Below the FIO2 knob is a control to deliver 100% oxygen. If the control is turned up to the "O2 Breaths" position, 100% oxygen is given for 20 breaths. The knob is turned down to the "Start Breaths" position to initiate a manual breath at 100% oxygen. The High and Low O2 alarms are automatically set at 6% above and below the FIO2 setting. The indicator light above the display is part of the SPG system. The light below illuminates when 100% oxygen breaths are given.
The lower section is for alarms. A message display window gives information about the history of the alarm and also is where any of the 32 built-in alarms are displayed.

Next to each alarm there is a touch pad, red indicator, and yellow caution light. Pressing the touch pad will display information about the alarm condition in the message display window. The Technical Alarm indicates the need for repair service.

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RC Ed WebMaster

Last update: 07/31/96