Anesthesia MACHINE and safety measures in anesthesia machine

Anesthesia machine and safety measures in anesthesia machine

1. The Anesthesia Machine WAFUKHO

2. vaporizer bellow Corrugated tube Soda lime Flow meter ventilator APL valve Scavenging system

3. NE FUNCTIONS OF MACHINE Controls the patient’s ventilation and oxygen delivery Administer inhalation anesthetics N/B. Proper functioning of the machine is crucial for patient safety incorporates built-in safety features and devices, monitors, and multiple microprocessors that can integrate and monitor all components.

4. Safety Misuse of gas delivery system is more likely than failure of device to cause adverse outcomes Preventable mishaps can be traced to- lack of familiarity with the equipment or failure to check machine Most common problems Breathing circuit Vaporizers Ventilators Oxygen supply

5. Describe the safety features in an anaesthesia machine (20MKS) Gas supplies: From the central pipeline to the machine as well as cylinders.   Pin index system Cylinder colour coding Pressure relief valves Pressure regulators Schrader probe Flexible colour coded hose pipes Diameter index safety system(DISS) Non interchangeable screw thread (NIST) Pippeline pressure indicators Oxygen pressure failure system Oxygen flush

6. Describe the safety features in an anaesthesia machine (20MKS) Flow meters.   Providing stops at the full ON or OFF position, so that excessive pressure may not damage either the valve seat or get disengaged at the full ON position so that gas escapes out of the meters. Control knob: Oxygen flow control knob is the largest and fluted for easy identification. A protective barrier around the control minimises accidental changes in settings. Tubes, which measure flow, have different lengths and diameters. Some machines have a pin-index system at each end. Tubes are made leak-proof with neoprene washers (O-rings) at both ends of the flow meter assembly. The tubes have an antistatic coating on both surfaces, preventing the bobbin from sticking. The bobbin is visible throughout the length of the tube.  

7. Describe the safety features in an anaesthesia machine (20MKS) Vaporizers.   Most vaporizers have a push (release) button to be activated before the dial can be turned on. All modern vaporizers come equipped with an interlock mechanism, which prevent from more than one vaporizer being put to use at the same time, thus causing an accidental overdose. Newer modern vaporizers have a separate transport setting, which prevents spillage of the liquid agent into the bypass channel, which may cause potential overdosing when the vaporizers are used All newer vaporizers have keyed/funnel filling systems with unique sizing of the fillers/funnels. Specific changes are also made on the bottle end of the filling adaptors.  

8. Describe the safety features in an anaesthesia machine (20MKS) Scavenging.   All connections in the scavenging system are of 30 mm diameter, which is distinctly different from the airway accessories making misconnections improbable.   Transfer tubings in the system are different by colour and configuration to that of breathing gase .   Tubings are resistant to kinking and are occlusion proof. Scavenging systems also incorporate negative and positive pressure relief valves to make sure no dangerous pressures are transmitted into the breathing system in the event of malfunction of the system.

9. Describe the safety features in an anaesthesia machine (20MKS) Monitoring oxygen analyser in the breathing circuit. ASTM standards do require that low oxygen alarm level cannot be set below 21%. [5] Gas volume monitoring is performed with spirometers, This monitoring gives us a measure of the tidal volume and minute volume, as well as disconnection. Airway pressure monitoring, The purpose of airway pressure monitors is to prevent either high (to prevent barotraumas) or low pressures (leaks or disconnection).   Disconnection monitors are an integral component of newer anaesthesia machines. [51] They can be based on the gas flows (volume measurements), pressure in the circuit, or gas detection like capnography

10. Describe the anti-hypoxia mechanism found on the anaesthesia machine (5marks)   Hypoxia prevention devices . Mandatory minimum oxygen flow Most modern machines have a minimum pre-set oxygen flow, which will automatically start once the machine is powered on.   Minimum oxygen ratio Anaesthesia workstation standards require that a device be provided that protects against a user selection of a gas mixture with an O 2 concentration below 21%. Mechanical linkage Mechanically linking the oxygen and nitrous oxide flow control valves can ensure that at a certain set percentage of concentration (of oxygen) both flows either increase or decrease in proportion to the

11. Describe the anti-hypoxia mechanism found on the anaesthesia machine (5marks)   Electronic linkage An electronic proportioning valve controls the oxygen concentration to a pre-set minimum, depending on the feedback it receives from a computer that constantly calculates the maximum safe limit of other gases that can be delivered. Alarms machines also activate an alarm when a user tries to set a flow with a lower than desired O 2 concentration.

12. Outline Anesthesia Machine High pressure system Intermediate pressure system Low pressure system Safety systems throughout

13. The Anesthesia Machine High Intermediate Low Pressure Circuit

14. High Pressure System Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine (2000 psig for O2 , 750 psig for N2O ) Consists of: Hanger Yolk (reserve gas cylinder holder) Check valve (prevent reverse flow of gas) Cylinder Pressure Indicator (Gauge) Pressure Reducing Device (Regulator) Usually not used, unless pipeline gas supply is off

15. Characteristics of medical gas cylinders.

16. E- Size Compressed Gas Cylinders Cylinder Characteristics Oxygen Nitrous Oxide Carbon Dioxide Air Color White ( green-USA) Blue Gray Black/White (yellow) State Gas Liquid and gas Liquid and gas Gas Contents (L) 625 1590 1590 625 Empty Weight (kg) 5.90 5.90 5.90 5.90 Full Weight (kg) 6.76 8.80 8.90 Pressure Full (psig) 2000 750 838 1800

17. Oxygen vs. Nitrous cylinder Oxygen is stored in a gas form. Depletes linearly with volume and psi Full tank 2000 psi 625 Liters 1/2 tank 1000 psi 312.5 Liters Nitrous Oxide is stored in both liquid and gas form. 75% of the contents will be depleted before the psi drops. Full tank 750 psi 1590 Liters 1/2 tank 750 psi 795 Liters Frost line

18. Hanger Yolk 1. Hanger Yolk: orients and supports the cylinder, providing a gas-tight seal and ensuring a unidirectional gas flow into the machine 2. Index pins: Pin Index Safety System (PISS) is gas specific p revents accidental rearrangement of cylinders (e.g.. switching O2 and N2O)

19. Pin - Indexed Yoke Assemblies Cylinder Valve Connections

20. Pressure Reducing Device Pressure Regulator Reduces the high and variable pressures found in a cylinder to a lower and more constant pressure found in the anesthesia machine (45 psig) Reducing devices are preset so that the machine uses only gas from the pipeline (wall gas), when the pipeline inlet pressure is 50 psig. This prevents gas use from the cylinder even if the cylinder is left open (i.e. saves the cylinder for backup if the wall gas pipeline fails) Pipeline pressure is just a little bit higher than the tank side after the pressure regulator.

21. 45 50

22. CT Pressure Reducing Device Cylinders should be kept closed. Otherwise, if the wall gas fails, the machine will automatically switch to the cylinder supply without the anesthetist being aware that the wall supply has failed (until the cylinder is empty too).

23. Intermediate Pressure System Receives gasses from the regulator or the hospital pipeline at 50 psig Consists of: Pipeline inlet connections Pipeline pressure gauges Piping Oxygen pressure failure devices “Fail Safe” Valve Oxygen supply failure alarm Oxygen flush Additional pressure regulators Flow control valves

24. Pipeline Inlet Connections 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) Each inlet must contain a check valve to prevent reverse flow (similar to the cylinder yolk)

25. Pipeline Connectors

26. Nuts Nipples Body Adaptors Nut and Nipple Combinations

27. Oxygen Pressure Failure Devices Machine standard requires that an anesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%.

28. Fail-Safe valve A Fail-Safe valve is present in the gas line supplying each of the flowmeters (AIR AND N20). 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 Historically there are 2 kinds of fail-safe valves Pressure sensor shut-off valve ( Ohmeda ) Oxygen failure protection device ( Drager )

29. A, The valve is open because the oxygen supply pressure is greater than the threshold value of 20 psig. B, The valve is closed because of inadequate oxygen pressure. Nitrous doesn’t flow to the flow meter. Ohmeda’s pressure sensor's shut - off valve

30. Drager’s Oxygen Failure Protection Device (OFPD) Based on a proportioning principle rather than a shut-off principle The pressure of all gases controlled by the OFPD will decrease proportionately with the oxygen pressure

31. Oxygen Supply Failure Alarm All anesthesia machines have a standard requirement that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig) a medium priority alarm shall blow within 5 seconds.

32. Oxygen Supply Failure Alarm

33. Limitations of Fail-Safe Devices/Alarms Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on pressure and not flow. These devices do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the wrong gas

34. Oxygen Flush Valve

35. Oxygen Flush Valve Direct communication between the oxygen high - pressure circuit and the low - pressure circuit Delivers 100% oxygen at a rate of 35 to 75 L / min to the breathing circuit High pressure of 50 psig

36. Oxygen Flush Valve Several hazards Barotrauma Awareness dilutes the inhaled anesthetic

37. Second-Stage Reducing Device Located just upstream of the flow control valves Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to 26 psig for N2O and 14 psig for O2 Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure

38. 2 ND STAGE O2 PRESSURE REGULATOR

39. Low Pressure System Extends from the flow control valves to the common gas outlet Consists of: Flow meters Vaporizer mounting device Check valve Common gas outlet

40. LOW PRESSURE CIRCUIT Low Pressure Circuit

41. Flowmeter assembly When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float

42. Flow Meter Assemblies

43. Flow Meter Assemblies Flow Control Valve Flow Meter Subassembly FLOW TUBES fine flow tube - 200 mL/min to 1 L/min coarse flow tube – 1 L/min to between 10 and 12 L/min OXYGEN SHOULD BE LAST IN LINE!

44. The flow meter sequence is a potential cause of hypoxia A and B, In the event of a flow meter leak, a potentially dangerous arrangement exists when nitrous oxide is located in the downstream position . C and D, The safest configuration exists when oxygen is located in the downstream position

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

46. Proportioning Systems Mechanical integration of the N2O and O2 flow-control valves Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1

47. Limitations of Proportioning Systems Machines equipped with proportioning systems can still deliver a hypoxic mixture under the following conditions: Wrong supply gas Defective pneumatics (ventilator) Leak downstream (e.g.. Broken oxygen flow tube) Inert gas administration: Proportioning systems generally link only N2O and O2

48. N 2 O and O 2 flow control valves are identical. A 14-tooth sprocket is attached to the N 2 O flow control valve, and a 28-tooth sprocket is attached to the O 2 flow control valve. A chain links the sprockets. The combination of the mechanical and pneumatic aspects of the system yields the final oxygen concentration. The Datex -Ohmeda Link-25 proportioning system can be thought of as a system that increases oxygen flow when necessary to prevent delivery of a fresh gas mixture with an oxygen concentration of less than 25%

49. North American Dräger Oxygen Ratio Monitor Controller (ORMC) The ORMC is composed of an O2 chamber, a N2O chamber, and a N2Oslave control valve, all of which are interconnected by a mobile horizontal shaft. The pneumatic input into the device is from the O2 and the N2O flow meters. These flow meters have resistors located downstream from the flow control valves that create backpressures directed to the O2 and N2O chambers. The value of the O2 flow tube's resistor is three to four times that of the N2O flow tube's resistor, and the relative value of these resistors determines the value of the controlled fresh gas concentration of O2. The backpressure in the O2 and the N2O chambers pushes against rubber diaphragms attached to the mobile horizontal shaft. Movement of the shaft regulates the N2O slave control valve, which feeds the N2Oflow control valve.

50. Group text Highlight 4 differences between oxygen and nitrous cylinders Color code these gases; oxygen, nitrous, air and carbon dioxide Describe PISS Elucidate DISS

51. GROUP TEST What hazards are associated with the oxygen flush valve? The oxygen flush valve delivers 100% oxygen at a rate of 35 to 75 L / min to the breathing circuit . TRUE OR FALSE Discuss Oxygen Pressure Failure Devices/ Fail-Safe valve

52. WISE WORDS if there is even a slight chance of getting something that will make you happy, risk it. Life is too short and happiness is too rare

53. WORDS OF WISDOM

54. references Butterworth, K, et al. The Anesthesia Machine. Morgan & Mikhail's Clinical Anesthesiology, 5e , 2013.