Prof.A K Sethi’s EORCAPS 2008 Prof. A K Sethi’s EORCAPS 2008 ANAESTHESIA MACHINE Purpose of Anaesthesia Machine • To Select & mix measured flow of gases to vapour and administer gases safely • To allow placement of drugs and devices which are for immediate use • To serve as a frame for placement of various accessories such as ventilator and monitor Dr. RAJIV GAMBHIR Prof. A K Sethi’s EORCAPS 2008 Prof. A K Sethi’s EORCAPS 2008 High Pressure System Pressure Division of Machine Intermediate Pressure System High Pressure Cylinder - O2: 2000 PSI, N20: 750 PSI Pressure reducing device Intermediate Pressure Cylinder 35 – 50 PSI Pipe line 45-60 PSI • • • • • Low Pressure 14 – 20 PSI Prof. A K Sethi’s EORCAPS 2008 Brief Note on Cylinder • • • • • • • • • • • Pipeline Connections Pipe / Cylinder Pressure Gauge Gas power outlet Master Switch Oxygen Pressure alarms Oxygen flush Flow Control Valves Low Pressure System flow meter • • Hanger yoke assembly • Cylinder Pressure Gauge • Pressure reducing device Flow meters Vapourizer circuit central valves Back pressure safety devices Low pressure pipe line Common gas outlet Prof. A K Sethi’s EORCAPS 2008 Capacity of Cylinder Compressed gas cylinder: material / mixture container at an absolute pressure exceeding 40 pounds / Sq inch at 70oC Size: Letter A to G - with size increasing Construction: Steel with chrome molybdenum, which makes it 20% lighter Service pressure: The pressure at which gas is pressurized – the cylinder should be able to withstand 1.66 times the service pressure Woods metal: Each valve stem has a safety device which allows the cylinder to become exhausted during excess heat / pressure - bismuth, lead, tin, cadmium 1 gas vents to atmosphere from the back Mode of working: Analogy – two children of different weight on a teeter totter balancing each other Prof. Index Pins 5. A K Sethi’s EORCAPS 2008 High pressure system… Pressure Gauge Components: Pressure Regulator 38 mm 1. Nipple 4. Ensure unidirectional flow of gases to machine parts of yoke SCREW Hanger yoke assembly consists of: 1. Provide a gas tight seal and 3. Body which is threaded into the frame of machine 2. A K Sethi’s EORCAPS 2008 High pressure system… Pressure Regulator… A pneumatic balance is one in which the torque form a high pressure side is balanced against the torque form a low pressure side The torque on the high pressure side is force times lever arm Force is the product of pressure and area The lever arm is d1 Thus a high pressure acting over a small area and a short lever arm may be balanced by a lower pressure operating on a large area with a large lever arm d2 2 .Prof. Orient and support the cylinder. 2. Tube sealed at inner end and connected to needle pointer – 4. During sudden increase in pressure. A K Sethi’s EORCAPS 2008 High pressure system Prof. Retaining screw which tighten the cylinder in the yoke 3. adjustable spring pressure RESTING POSITION 1. Diameter 38 mm 2. Pneumatic balance 2. Demand valve a. Colour coded / calibrated 2. A K Sethi’s EORCAPS 2008 High pressure system… Prof. Other end open to gas supply Safety features: N2O: 3 & 5 NIPPLE WASHER Purpose: To deliver gases at constant pressure to patient and maintain constant flow Types: 1. A K Sethi’s EORCAPS 2008 High pressure system… Pressure Regulator… Prof. fixed pressure b. Washer O2: 2 & 5 INDEX PINS CO2: 1 & 6 Prof. A K Sethi’s EORCAPS 2008 High pressure system… Hanger Yoke Assembly Hanger yoke assembly is to: Pin Index Safety System BODY 1. A robust flexible coiled tube in cross section 3. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Oxygen Flush Valve Prof. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Prof. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Oxygen Flush Valve… Objective: To supply 100% oxygen at high flow rates (35 – 75 lt / min) & at intermediate pressure Standards: • • • • • Single purpose for oxygen only Self closing Permanently marked Placed in a recess / collar Should not produce back pressure effects Hazards: • Baro trauma • Altered anaesthetic gas concentration 3 . the set oxygen concentration shall not decrease at the common gas outlet" In addition.. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Central Pipelines & Connections Oxygen Pressure Failure Protection The fail safe device O2 AIR N20 VACUUM GAS SPECIFIC WALL OUTLETS NON INTERCHANGEABLE SCREW THREAD (NIST) ensures that: "Whenever oxygen pressure reduces and until flow ceases. the flow of all other gases are shut off Oxygen failure protection device (OFPD): Flow is reduced proportionally Second-stage O2 pressure regulator: Ensures constant oxygen flowmeter input until supply pressure is less than 12-16 psi Oxygen ratio monitor controller (ORM): It shuts off nitrous oxide when oxygen pressure is less than 10 psi × × × Prof. audible and visible Fail-safe systems don't prevent hypoxic mixtures. Pressure sensor shut off valve: At 20 psi oxygen. Which is a function of Hypoxic Guards Prof.. the loss of oxygen pressure results in alarms. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Oxygen Pressure Failure Protection… Oxygen Pressure Failure Protection.Prof. A K Sethi’s EORCAPS 2008 Intermediate pressure system Prof. A K Sethi’s EORCAPS 2008 Intermediate / Low pressure system… Prof. Pneumatic linkage 4 . A K Sethi’s EORCAPS 2008 Low pressure system… Prof.Prof. A K Sethi’s EORCAPS 2008 Low pressure system Flow Control Valve… Flow meters Principle of working: • Float is buoyed by flowing gas that passes between the float and walls of the tube • Narrowing of cross sectional area at the float creates resistance to flow and causes pressure drop • Float will settle where the force represented by pressure difference multiplied by cross section area equals to gravity Purpose is to measure flow Early flow meters: • Tube under water • Inside water meter • Outside water meter Rate of flow depends upon: • Pressure drop – wt. Mechanical linkage 2.5 cm Opened anti-clock wise • Electronic flowmeters allow automated anesthesia record-keeping • 5-10 times more accurate Prof. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Flow Control (Needle) Valve Flow Control Valve… Electronic flowmeters: • Flow rate is indicated with a bar graph on a monitor screen Standards: • • • • • Placed below flow meter Colour coded Touch coded Separated by 2. A K Sethi’s EORCAPS 2008 Low pressure system… Flow meters… Hypoxic Guard Modern Flow meter: Variable angle & constant pressure Extended range flow meters: • • • • • Dual taper Dual floats In series In parallel Flow meter with 25 : 75 design DUAL TAPER DUAL FLOATS IN SERIES • Mandatory minimum oxygen flow • Minimum oxygen ratio device • Slave Mechanism • Link 25 1. A K Sethi’s EORCAPS 2008 Intermediate pressure system… Prof. Of float / cross section area • Size of opening • Physical properties of gas – normally calculated at 760 mmHg at 20oC • F1 = Fo X do / d1 Prof. A K Sethi’s EORCAPS 2008 Safety Features of Anaesthesia Machine… High pressure system: Safety Features of Anaesthesia Machine… Vapourizers • Pressure regulating valves • Pressure relief valves • Construction of advanced Tec series • Bimetallic strip for temp. A K Sethi’s EORCAPS 2008 New Concerns Regarding Modern Machines Newer Safety Features • Reduced external connections: internal modular or manifold • Electronic control and measurement of vaporization (Anaesthesia delivery units) • Automated checkout and monitoring • Streamlined communication with information management systems (IMS) • • • • • Consumption of oxygen from an open cylinder ? Monitor of ventilation in a hidden-piston ventilator ? Emergent and rapid initiation of the machine ? Wrong agent into a vaporizer ? Mixture of modern and conventional machines ? 5 . A K Sethi’s EORCAPS 2008 Prof. compensation • Colour coded Key filling system Intermediate pressure system: • Gauges of manometer • Low oxygen pressure cut off systems Miscellaneous Low pressure systems: • Antistatic wheels Flow meters • Placement of knobs at distance • Down stream placement of knob • Back light display • Link devices • Back pressure check valves • Audible alarms etc This list is by no means exhaustive and newer anaesthesia machines have added lots of new features to enhance the safety Prof. A K Sethi’s EORCAPS 2008 Prof.Prof. A K Sethi’s EORCAPS 2008 Prof. A K Sethi’s EORCAPS 2008 Low pressure system… Safety Features of Anaesthesia Machine Other Components… • Back bar (Selectatec) • Back pressure safety devices Bulk storage / pipe line supply: • Indicators system / Service area alarms • Shut off valves • Gas specific wall outlets Cylinders: • • • • An Empty Selectatec Bar Selectatec Series Mounted Manifold Bypass Circuit DISS for large cylinders PISS for small cylinders Relief valves – woods metal Colour coding of cylinder A Non Return Pressure Relief Valve Prof. Prof. Reducing Oxygen Flow To 10% Of Indicated Halothane Vaporizer Filled With Methoxyflurane Prof.8 25 0% FAULT DETECTION 20 15 10 FAULT DETECTION Buffington et al. A K Sethi’s EORCAPS 2008 Critical Incidents 1980… HENCE WE MUST ALWAYS REMAIN EDUCATED PREPARED AND VIGILANT TO AVOID CRITICAL INCIDENTS 90 80 70 60 50 40 30 20 10 0 81 TOTAL MISADVENTURES 53 HUMAN ERROR 27 FAILURE TO CHECK ANAESTHESIA MISADVENTURES Craig & Wilson (1981) Prof. A K Sethi’s EORCAPS 2008 • • • 1089 1000 TOTAL MISADVENTURES 800 600 400 223 200 1. 2.9 25. FDA 1986 Checklist 50 60% NOT DETECTED 45 40% DETECTED 40 20% 44 35 30 PERSONAL CHECKLIST FDA 1986 CHECKLIST 29.. 1980… 200 180 160 140 120 100 80 60 40 20 0 190 1980… • • • • 100% TOTAL PARTICIPANTS SUCCESSFUL PARTICIPANTS UNSUCESSFUL PARTICIPANTS 6 13 PARTICIPANTS 80% Prof. How Well Are Equipment Faults Recognized? 190 Attendees To Identify Five Deliberate Faults Within 10 Minutes Discs Removed From Unidirectional Valves Pin Index System Altered To Allow O2/n2o Switch Oxygen-failure Shut-off Valve Disabled So That Nitrous Oxide Continued To Flow When Oxygen Source Pressure Fell To Zero Cyclopropane And Oxygen Flowmeter Tubes Interchanged. A K Sethi’s EORCAPS 2008 New Solutions to Old Problems Might Raise New Problems Prof. FAILURE TO CHECK 0 ANAESTHESIA MISADVENTURES 4.. A K Sethi’s EORCAPS 2008 How Well Are Equipment Faults Recognized?. 3. Cooper et al (1984) 5. (1984) March & Crowley (1991) 6 . A K Sethi’s EORCAPS 2008 56 How Well Are Equipment Faults Recognized? 188 Anaesthesiologists To Identify Four Deliberate Faults In Two Machines Number Of Faults Were Not Known To Them PERSONAL CHECKLISTS Vs. A K Sethi’s EORCAPS 2008 1980… Critical Incidents 1980… 1200 Prof. 4. 11. A K Sethi’s EORCAPS 2008 Modified Anesthesia Machine Pre-use Checklist FDA 1993… 1. 9. 6. The Checklist Must Be Modified suitably Prof.Prof. 3. 10. A K Sethi’s EORCAPS 2008 Prof. Set Alarm Limits Of All Monitors Check Final Status Of Machine 7 . A K Sethi’s EORCAPS 2008 Prof. 5. A K Sethi’s EORCAPS 2008 Anaesthesia Machine Pre-use checklists Modified Anesthesia Machine Pre-use Checklist FDA 1993 The Anesthesia Gas Machine Must Be Equipped with: • • • • • • An Ascending Bellows Ventilator FDA GUIDELINES 1986 REVISED FDA GUIDELINES 1993 AAGBI GUIDELINES EUROPEAN GUIDELINES NO GUIDELINES IN INDIA & • Monitors (5) • Capnograph • Pulse Oximeter • Oxygen Analyzer • Spirometer • Breathing System Pressure Monitor If Not So Equipped. 14. A K Sethi’s EORCAPS 2008 Pre-use Training 1990… 81% 62% PRE-TRAINING POST-TRAINING RESIDENTS Survey Of Pre-use Check 2000… A Test Group Of 16 Residents Were Exposed To Instructional Review (Including Videotaped Sessions) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Prof. 13. (1996) Prof. 2. Calibrate. Verify Backup Ventilation Equipment Check Oxygen Cylinder Supply (One Cylinder Must Be At Least Half Full~ 1000 Psi ) Check Central Pipeline Supplies Check Initial Status Of Low Pressure System Perform Leak Check Of Low Pressure System Turn Master Switch On Test Flowmeters Modified Anesthesia Machine Pre-use Checklist FDA 1993… 8. A K Sethi’s EORCAPS 2008 “This Performance Improvement Underlines The Need For Training Required For Anaesthesioloists On A Continuous Basis To Enhance Patient Safety” 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 100% 80% 29% 50 60% POOR EXCELLENT 12% DONE NOT DONE 40% 20% 50 0% TRAINING RESPONDERS WORLD WIDE WEB. 7. Calibrate Oxygen Monitor Check Initial Status Of Breathing System Test Ventilation Systems And Unidirectional Valves Perform Leak Check Of Breathing System Adjust And Check Scavenging System Check. Lampotang et al (2005) Olympio et al. 12.