INTERMEDIATE PRESSURE SYSTEM
PRESENTED BY: Dr CHITTRA
MODERATED BY: Dr JYOTI PATHANIA
The intermediate pressure system receives
gases from the pressure regulator or the
pipeline inlet to the anesthesia machine
COMPONENTS
pneumatic part of the master switch
pipeline inlet connections
pipeline pressure indicators
piping
gas power outlet
oxygen pressure failure devices
oxygen flush
pressure regulators
flow control valves
pneumatic part of master switch
 downstream of inlets
for cylinder and pipeline
supplies
 master switch may be
totally electronic that
when activated controls
the various pneumatic
components of the
anesthesia machine
pipeline inlet connection
 pipeline inlet connection is the entry point for
gases from the pipelines
 Mandatory N2O and O2, usually have air and
suction too
 Inlets are non-interchangeable due to specific
threading as per the Diameter Index Safety
System (DISS)
 unidirectional valve to prevent reversed gas flow
 filter with a pore size of 100 µm
pipeline pressure indicator
 present on panel on front of machine and may be color
coded
 On some newer electronic machines, LEDs indicate
pipeline pressure
 The workstation standard requires that indicator be on
the pipeline side of the check valve in the pipeline inlet
 If the indicator is on the pipeline side of the check
valve, it will monitor pipeline pressure only
 If the indicator were on the machine side of the check
valve, it would not give a true indication of the pipeline
supply pressure unless the cylinder valves were closed
 pressure should be between 50 and 55 psig
PIPING
must be able to withstand four times the
intended service pressure without rupturing
 anesthesia workstation standard specifies
that leaks between the pipeline inlet or
cylinder pressure reducing system and the
flow control valve not exceed 25 mL/minute
If yoke and pressure reducing system are
included, the leakage may not exceed 150
mL/minute
GAS POWER OUTLET
may serve as the source of driving gas for the
anesthesia ventilator or to supply gas for a jet
ventilator
Oxygen failure safety device
whenever the oxygen supply pressure is
reduced below the manufacturer-specified
minimum, the delivered oxygen concentration
shall not decrease below 19% at the common
gas outlet
oxygen failure cut off valves(fail-safe)
 A Fail-Safe valve is present in the gas line supplying
each of the flowmeters except O2
 This valve is controlled by the O2 supply pressure
and shuts off or proportionately decreases the
supply pressure of all other gasses as the O2 supply
pressure decreases
 2 kinds of fail-safe valves
Pressure sensor shut-off valve (Ohmeda)
Oxygen failure protection device (Drager)
pressure sensor shut off valve
 The valve is threshold in nature, and it is either open or closed
 Oxygen supply pressure opens the valve, and the valve return
spring closes the valve
 nitrous oxide pressure-sensor shut-off valve has a threshold
pressure of 20 psig
 oxygen supply pressure greater than 20 psig is exerted on the
mobile diaphragm
 This pressure moves the piston and pin upward, and the valve
opens.
 oxygen supply pressure is less than 20 psig, and the force of
the valve return spring completely closes the valve
 Nitrous oxide flow stops at the closed fail-safe valve, and it
does not advance to the nitrous oxide flow control valve
oxygen failure protection device
 OFPD interfaces the oxygen pressure with that of
other gases
 based on proportioning principle
 pressures of all gases controlled by OFPD decrease
proportionally with the oxygen pressure
 consists of seat-nozzle assembly connected to springloaded piston
 There is a continuum of intermediate configurations
between the extremes of oxygen supply pressure
 These intermediate valve configurations are
responsible for the proportional nature of the OFPD
 The oxygen supply pressure
is 50 psig on left panel,
pushes the piston upward,
forcing the nozzle away from
the valve seat
 Nitrous oxide advance
toward the flow control valve
at 50 psig
 The oxygen pressure in the
right panel is zero psig
 The spring is expanded and
forces the nozzle against the
seat, preventing flow through
the device
 Finally, the center panel
shows an intermediate
oxygen pressure of 25 psig
 The force of the spring
partially closes the valve
 The nitrous oxide pressure
delivered to the flow control
valve is 25 psig
The oxygen ratio monitor controller (ORM
[newer] or ORMC, both by Dräger) shuts off
nitrous oxide when oxygen pressure is less
than 10 psi
The newest Dräger machine, the Fabius GS,
uses a Sensitive Oxygen Ratio Controller (SORC)
It's fail-safe component shuts off nitrous oxide
if the oxygen flow is less than 200 mL/min, or
if the oxygen fresh gas valve is closed.
oxygen supply failure alarm
 whenever the oxygen supply pressure falls below a
manufacturer-specified threshold ,usually 30 psig , at
least a medium priority alarm shall be activated within
5 seconds
 They aid in preventing hypoxia caused by problems
occurring upstream in the machine circuit
 These devices do not offer total protection against a
hypoxic mixture being delivered, because they do not
prevent anesthetic gas from flowing if there is no flow
of oxygen
 Equipment problems or operator errors that occur
downstream are not prevented by these devices
 do not guard against accidents from crossovers in the
pipeline system or a cylinder containing the wrong gas
second stage pressure regulator
 Some machines have pressure regulators in the
intermediate pressure system just upstream of
flow indicators
 These receive gas from either the pipeline or the
pressure regulator and reduce it further to
around 26 psi for nitrous oxide and 14 psi for
oxygen.
 purpose of this pressure regulator is to eliminate
fluctuations in pressure supplied to the flow
indicators caused by fluctuations in pipeline
pressure.
 not present in every workstation
Most Ohmeda machines have a second-stage
oxygen pressure regulator set at a specific
value ranging from 12 to 19 psig
Oxygen flowmeter output is constant when
the oxygen supply pressure exceeds the set
value
pressure-sensor shut-off valves are set at a
higher threshold value (20–30 psig)
ensures that oxygen is the last gas flow to
decrease if oxygen pressure fails
oxygen flush
oxygen flush receives oxygen from pipeline
inlet or cylinder pressure regulator and directs
a high unmetered flow directly to the
common gas outlet
The anesthesia workstation requires that
oxygen flush be a single-purpose, self-closing
device operable with one hand and designed
to minimize unintentional activation
flow of 35 to 75 L/minute must be delivered
 its activation may or may not result in other gas flows
being shut off
 may result in either a positive or negative pressure in
machine circuit.
 pressure is transmitted back to other structures in
machine, and may change the vaporizer output and the
flow indicator readings
 The anesthesia workstation standard requires that the
connection of the flush valve delivery line to the
common gas outlet be designed so that activation does
not increase or decrease the pressure at the vaporizer
outlet by more than 10 kPa or increase the vapor
output by more than 20%
HAZARDS
accidental activation and internal leakage
flush valve may stick in ON position
Barotrauma and awareness
activation during inspiration delivered by the
anesthesia ventilator results in delivery of high
tidal volumes and hence barotrauma may
occur.
flow adjustment control
regulates flow of oxygen, air, and other gases
to the flow indicators
mechanical and electronic
anesthesia workstation standard requires that
there be only one flow control for each gas
must be adjacent to or identifiable with its
flowmeter
mechanical flow control valve
controls rate of gas flow through its associated
flowmeter
COMPONENTS
BODY
STEM AND SEAT
CONTROL KNOB
 control knob is joined to the stem
oxygen flow control knob is fluted and large
All other flow control knobs must be round
Accidental changes in position can also be
minimized by a shield, bar, or other protective
barrier and by placing them high above the
working surface to lessen the likelihood of
contact with objects on that surface
 knob should be turned clockwise only until the
gas flow ceases
 Further tightening may damage to the pin or seat
 Sometimes, flow control valve remains open
when the machine is cleaned or moved
 If gas supply to open flow control valve is
restored and associated flow indicator is not
observed, indicator may rise to top of the tube
where its presence may not be noticed
 the sudden indicator rise may damage it and
impair the flowmeter accuracy
Flow control valves should be closed when not
in use
If there is no yoke plug or cylinder in the yoke
or the one-way valve in the pipeline inlet does
not work well, gas from an unused gas system
could flow retrograde through a flowmeter
with an open flow control valve and leak to
atmosphere
The stem or seat can block the flow
electronic flow control device
 Electronically activated flow control devices can be
used to alter gas flows
 knob is turned clockwise to increase the flow
 flow adjustment may utilize a solenoid valve
 usually a mixing area collects the gas mixture
 one control alters oxygen concentration and another
control the total flow
 If less than 100% oxygen is desired, the difference is
made up from the second gas
 Flow and pressure transducers as well as temperature
sensors are used to maintain accuracy
THANKS