Speaker : Dr Omar Kamal
To safeguard human life from unknown human errors.
Safety devices are to prevent delivery of hypoxic mixture
Regulation to prevent excessive pressure which is traumatic to patient
1979: American National Standards Institute (ANSI)
1988: American Society for Testing and Materials (ASTM) F1161-883
1994: ASTM F1161-944 (reapproved in 1994 and discontinued in 2000)
2000: ASTM F1850-005
2000 ASTM F1850-00 standard, newly
continuous breathing system pressure,
exhaled tidal volume, ventilatory CO2 concentration,
anesthetic vapor concentration, inspired oxygen concentration,
oxygen supply pressure, arterial oxygen saturation of hemoglobin,
arterial blood pressure, and continuous electrocardiogram
Master Switch
Power Failure Indicator
Reserve Power
Electrical Outlets
Circuit Breakers
Data Communication Ports
High pressure division
Intermediate pressure division
Low pressure division
Gas cylinder
Color coding
Cylinder labels
Symbol of gas
Pin index safety system
Safety relief device
Filling within service pressure
Oxygen black body,white shoulders
Nitrous oxide blue
Air white and black
Carbon dioxide gray
Helium brown
Entonox black with blue/white shoulders
The safety relief device is composed of atleastone of
- Frangible disc [bursts under extreme pressure]
- Fusible plug [wood’s metal which has a low melting Point ]
- Safety relief valve [ opens at extreme pressure ]
Check valves at the cylinder inlet and pipeline inlet
Cylinder pressure indicator [ bourdon’ s pressure gauge]
Pressure regulator
Pressure relief valves
Washer [ bodok seal ] – rubber made of neoprene
Gauge is usually color coded.
Name and symbol of gas are written over dial.
If bourdon tube ruptures gas is vented from back side
Gauges are angled and placed in such a way that it can be easily read by anesthetist.
Instructions like “use no oil’’ “open the valve slowly’’ are written on the gauge
Pressure regulators have safety relief valves
Safety valve blow off at a set pressure of 525 k pa(70psi)
Pipeline
• wall outlet : labelled and colour coded
• primary valve or automatic shut off valve
• secondary valve or isolation valve
• schraeders probes, quick connectors or diameter index safety system to prevent interchangeability
• pipeline hoses – colour coded
The 2000 ASTM F1850-00 standard states that
“The anesthesia gas supply device shall be designed so that whenever oxygen supply pressure is reduced to below the manufacturer specified minimum, the delivered oxygen concentration shall not decrease below 19% at the common gas outlet.”
fail-safe valve
is located downstream from the nitrous oxide supply source.
This valve shuts off or proportionally decreases the supply of nitrous oxide (and other gases) if the oxygen supply pressure declines
Datex-Ohmeda machines
Threshold principle
This valve operates in a threshold manner and is either open or closed.
Oxygen supply pressure opens the valve, and the valve return spring closes the valve
OFPD is based on a proportioning principle
The pressure of all gases controlled by the OFPD will decrease proportionally with the oxygen pressure.
consists of a seat nozzle assembly connected to a spring-loaded piston
The oxygen flow control knob is distinctively fluted, projects beyond the control knobs of the other gases, and is larger in diameter
All knobs are color-coded for the appropriate gas,
the chemical formula or name of the gas is permanently marked on each.
If a single gas has two flow tubes, the tubes are arranged in series and controlled by a single flow control valve.
- Bobbin rotates on flow which prevents it from sticking.
- Antistatic spray in flowmeter- master and slave safety mechanism for gas delivery
between N2O and O2- Downstream placement of oxygen flowmeter- Radio florescent plastic sheet behind flow meter- Float stop- Auxiliary oxygen flowmeter
An oxygen leak from the flow tube can produce a hypoxic mixture, regardless of the
arrangement of the flow tubes
Proportionating devices –
• link 25 in datexohmeda[mechanical,pneumatic
and electronic linkage]
• S-ORC( sensitive oxygen ratio controller)
ORMC( oxygen ratio monitor controller) in draeger,
• Mandatory minimum oxygen flow :
150 to 250 ml/min
It allows independent adjustment of either valve, automatically intercedes to maintain a minimum 25% oxygen concentration with a maximum N2O– oxygen flow ratio of 3 : 1
increases oxygen flow to prevent delivery of a hypoxic mixture.
14-tooth sprocket (nitrous oxide flow control valve) , 28-tooth sprocket (oxygen flow control valve)
2 : 1 gear ratio
Pneumatic oxygen–nitrous oxide interlock systems designed to maintain a fresh gas oxygen concentration of at least 25%
ORMC and S-ORC limit nitrous oxide flow to prevent delivery of a hypoxic mixture
Movement of the shaft regulates the nitrous oxide slave control valve, which feeds the nitrous oxide flow control valve.
If the oxygen pressure > N2O , the nitrous oxide slave control valve opens wider to allow more nitrous oxide to flow.
As the N2O flow is increased manually, this pressure forces the shaft toward the oxygen chamber limiting the flow of N2O
whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig (205 kPa)
at least a medium priority alarm shall be enunciated within 5 seconds
Limitations
Depend on pressure and not flow
Do not prevent anesthetic gas from flowing if there is no flow of oxygen
Crossovers in the pipeline system or a cylinder containing the wrong gas
Leaks downstream
Ritchie whistle
Present in older machines – ohmeda
When the oxygen pressure drops below 260 kpa( 38 psi ), oxygen failure whistle valve opens
Whistle sounds continuously, until oxygen pressure has fallen to approx 40.5 kpa ( 6 psi )
At 30 psi ( 200 kpa ) , it cuts off the supply of anesthetic gases to the patient
Criteria required for oxygen failure warning devices :
Alarm should be auditory(60 dB), for atleast 7 s duration measured at 1 m..
alarm gets activated when oxygen supply pressure falls to approx 200 kpa
Alarm linked to gas shut off device
Vaporizers - Interlocking Selectatecmechanism, low filling port..
Unidirectional [check ] valve
Back pressure relief valve [opens when the pressure exceeds 200 cm H2O]
Common gas outlet
Receives oxygen from the pipeline inlet or cylinder pressure regulator and directs a high unmetered flow directly to the common gas outlet
labeled “O2+.”
activated regardless of whether the master switch is turned ON or OFF.
flow between 35 and 75 L/minute delivered
The button is commonly recessed or placed in a collar to prevent accidental activation
activation does not increase or decrease the pressure at the vaporizer outlet > 10 kPa or increase the vaporoutput > 20%
Limitations
Accidental activation and internal leakage
The flush valve may stick in the ON position
Oxygen flush activation during inspiration -barotrauma
Its purpose is to prevent backflow into the vaporizer during positive-pressure ventilation, thereby minimizing the effects of intermittent fluctuations in downstream pressure on the concentration of inhaled anesthetic
APL valve open when pressure exceeds 60 cm H2O
Pressure in reservoir bag shouldn’t exceed 60 cm H2O.
Oxygen analyser
Canister – Dessicated absorbents without KOH or ba(OH)2 and with lesser amounts of NaOHproduce less heat and no fires
VENTILATORS – Pressure sensors to detect excessive airway pressure due to ventilator malfunction
Alternative oxygen control
Scavenging system
Wheels in anesthetic workstation is made of antistatic low friction rubber.
More accurate and corrected tidal volume through compliance and fresh gas compensation
Fresh gas decoupling prevent hyperinflation of the lung
Electronic PEEP
Electronic selection of ventilation parameters
Reduced external connections
It is the only machine safety device that evaluates the integrity of the low-pressure circuit
Oxygen concentration–sensing element must be exposed to room air for calibration to 21%.
Absolute criteria:
1. Lack of essential safety features such as:A. O2/N2O proportioning systemB. O2 failure safety device (‘‘fail--safe’’ system)C. O2 supply failure alarmD. vaporizer interlock deviceE. noninterchangeable, gas-specific pin indexed and
diameter-indexed safety systems for gas supplies.
1. Presence of unacceptable features such as: A. measured flow vaporizers (e.g., Copper Kettle)B. more than one flow control knob for a single gas
delivered to the common gas outletC. vaporizer with a dial such that the concentration
increases when the dial is turned clockwiseD. connections in the scavenging system that are the
same (15 or 22mm diameter) as in the breathing system.
2. Adequate maintenance no longer possible
1. Lack of certain safety features such asA. a manual/automatic bag/ventilator selector switchB. a fluted O2 flow-control knob that is larger than the
other gas flow-control knobsC. an O2 flush control that is protected from unintentional
activation D. an antidisconnection device at the common gas outletE. an airway pressure alarm.
2. Problems with maintenance.3. Potential for human error.4. Inability to meet practice needs such as
A. accepting vaporizers for newer agentsB. ability to deliver low fresh gas flows (FGFs)C. a ventilator that is not capable of safely ventilating the
lungs of the target patient population
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