Dräger Narkomed 2B Operator's Instruction Manual page 19

Oxygen Flush
Oxygen Ratio
Controller (ORC)
A manually operated, self-closing oxygen flush valve is located on the
front of the machine. A bezel is mounted around the pushbutton in order
to prevent accidental engagement. The valve, when actuated, delivers an
unmetered oxygen flow of approximately 55 l/min directly to the
Narkomed 2B's fresh gas common outlet. The SYSTEM POWER switch
does not have to be in the ON position to use the oxygen flush.
The ORC is a pneumatic oxygen/nitrous oxide interlock system. It
maintains a fresh gas oxygen concentration of 25 ±4% and permits
independent control of the oxygen and nitrous oxide flows.
The ORC proportionally limits the nitrous oxide flow whenever the
selected oxygen and nitrous oxide flow control valve settings would
otherwise result in a hypoxic fresh gas mixture. For example, if you open
the nitrous oxide flow control valve excessively without making a
corresponding increase in the oxygen flow control valve setting, the flow
of nitrous oxide will not increase even though its flow control valve
setting has been greatly increased. Similarly, if you decrease the oxygen
flow without also decreasing the nitrous oxide flow, the nitrous oxide
flow will automatically drop in proportion to the oxygen flow.
WARNING: In circle systems the gas mixture in the patient circuit is
not necessarily the same as that in the fresh gas flow. This
is particularly true at low fresh gas flow rates when the
patient rebreathes a significant portion of previously
exhaled gases. It is important that the gas mixture in the
patient circuit be monitored, and that the fresh gas flow be
adjusted to meet the requirements of the patient as well as
to compensate for any patient uptake, system leakage, or
gas withdrawn through sample lines and not returned.
WARNING: The ORC interlocks only the flows of oxygen and nitrous
oxide. Hypoxic fresh gas concentrations are possible if
carbon dioxide is used as an additional gas.
Section 2
General Description
2-7