INTERMEDIATE PRESSURE SYSTEM

PRESENTED BY: Dr CHITTRAMODERATED BY: Dr JYOTI PATHANIA

The intermediate pressure system receives gases from the pressure regulator or the pipeline inlet to the anesthesia machine

COMPONENTSpneumatic part of the master switchpipeline inlet connections pipeline pressure indicatorspipinggas power outletoxygen pressure failure devicesoxygen flushpressure regulators flow control valves

pneumatic part of master switchdownstream 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

PIPINGmust 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 devicewhenever 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 O2This 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 spring-loaded

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 (S-ORC)

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 regulatorSome 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 flushoxygen 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%

HAZARDSaccidental activation and internal leakageflush 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 controlregulates flow of oxygen, air, and other gases

to the flow indicatorsmechanical and electronicanesthesia workstation standard requires that

there be only one flow control for each gasmust be adjacent to or identifiable with its

flowmeter

mechanical flow control valvecontrols rate of gas flow through its associatedflowmeter COMPONENTSBODYSTEM AND SEAT

CONTROL KNOB

control knob is joined to the stemoxygen flow control knob is fluted and largeAll other flow control knobs must be roundAccidental 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 seatSometimes, 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