Safety features in anesthesia machine

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1. Safety features in anesthesia machine Speaker : Dr Omar Kamal

2. Why safety features? 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

3. Standards for Anesthesia Machines and Workstations 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

4. 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

5. Electrical components Master Switch Power Failure Indicator Reserve Power Electrical Outlets Circuit Breakers Data Communication Ports

6. Pneumatic components High pressure division Intermediate pressure division Low pressure division

7. High pressure system Gas cylinder Color coding Cylinder labels Symbol of gas Pin index safety system Safety relief device Filling within service pressure

8. Colour coding Oxygen black body,white shoulders Nitrous oxide blue Air white and black Carbon dioxide gray Helium brown Entonox black with blue/white shoulders

9. Pin index safety system

10. Safety relief device The safety relief device is composed of atleast one 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 ]

11. 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

12. Safety features in cylinder pressure indicator 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

13. Safety features on pressure regulator Pressure regulators have safety relief valves S afety valve blow off at a set pressure of 525 k pa(70psi)

14. 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

15. Oxygen Supply Pressure Failure Safety Devices 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 .”

16. 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

17. Pressure sensor shut off valve

18. 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

19. Oxygen failure protection devices

20. 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

21. F lowmeters 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.

22. - 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

23. An oxygen leak from the flow tube can produce a hypoxic mixture, regardless of the arrangement of the flow tubes

24. Hypoxia prevention safety devices Proportionating devices – link 25 in datex ohmeda [ 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

25. Datex-Ohmeda Link-25 Proportion-Limiting Control System 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

26. North American Dräger Oxygen Ratio Monitor Controller

27. P neumatic 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

28. 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

29. Oxygen Supply Failure Alarm 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 D epend 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

30. Ritchie whistle Present in older machines – ohmeda W hen the oxygen pressure drops below 260 kpa ( 38 psi ), oxygen failure whistle valve opens W histle 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

31. Criteria required for oxygen failure warning devices : A larm 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

32. Vaporizers - Interlocking Selectatec mechanism, low filling port.. Unidirectional [check ] valve Back pressure relief valve [opens when the pressure exceeds 200 cm H2O] Common gas outlet

33. Oxygen flush valve Receives oxygen from the pipeline inlet or cylinder pressure regulator and directs a high unmetered flow directly to the common gas outlet labeled “O 2 +.” 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 vapor output > 20%

34. Oxygen flush valve

35. Limitations Accidental activation and internal leakage The flush valve may stick in the ON position Oxygen flush activation during inspiration - barotrauma

36. Check valve 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

37. Breathing system 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 NaOH produce less heat and no fires

38. 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 .

39. Safety features of newer machines 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

40. Oxygen analyser It is the only machine safety device that evaluates the integrity of the low-pressure circuit O xygen concentration–sensing element must be exposed to room air for calibration to 21%.

41. Anesthesia Machine Obsolescence Absolute criteria : Lack of essential safety features such as: O 2 /N 2 O proportioning system O 2 failure safety device (‘‘fail--safe’’ system) O 2 supply failure alarm vaporizer interlock device noninterchangeable , gas-specific pin indexed and diameter-indexed safety systems for gas supplies.

42. Presence of unacceptable features such as: measured flow vaporizers (e.g., Copper Kettle) more than one flow control knob for a single gas delivered to the common gas outlet vaporizer with a dial such that the concentration increases when the dial is turned clockwise connections in the scavenging system that are the same (15 or 22mm diameter) as in the breathing system. Adequate maintenance no longer possible

43. Relative criteria Lack of certain safety features such as a manual/automatic bag/ventilator selector switch a fluted O 2 flow-control knob that is larger than the other gas flow-control knobs an O 2 flush control that is protected from unintentional activation an antidisconnection device at the common gas outlet an airway pressure alarm. Problems with maintenance . Potential for human error . Inability to meet practice needs such as accepting vaporizers for newer agents ability to deliver low fresh gas flows (FGFs) a ventilator that is not capable of safely ventilating the lungs of the target patient population

44. Checking Anaesthetic Equipment 2012

45. THANK YOU