FALL23_ANESTHESIAmachineDYNAMICS_NRAN80323.pptx

ANESTHESIA MACHINE DYNAMICS Gregory Collins, DNP, CRNA PHYSICAL SCIENCE IN NURSE ANESTHESIA NRAN 80323 ANESTHESIA MACHINE DYNAMICS READING: NAGELHOUT / CH 16 / 229-271 OUTLINE: SUPPLY CYLINDER/ PIPELINE PROCESSING O2 PRESSURE FLOWMETERS VAPORIZERS DELIVERY BREATHING CIRCUIT CO2 ABSORBENT DISPOSA...

ANESTHESIA MACHINE DYNAMICS Gregory Collins, DNP, CRNA PHYSICAL SCIENCE IN NURSE ANESTHESIA NRAN 80323 ANESTHESIA MACHINE DYNAMICS READING: NAGELHOUT / CH 16 / 229-271 OUTLINE: SUPPLY CYLINDER/ PIPELINE PROCESSING O2 PRESSURE FLOWMETERS VAPORIZERS DELIVERY BREATHING CIRCUIT CO2 ABSORBENT DISPOSAL GE Aestiva GE Avance Dräger Apollo COMMON MANUFACTURERS: • Dräger (Germany) • GE Healthcare (USA) • Mindray (China) • Penlon (UK) • Phillips (Netherlands) • Space Labs (USA) • Maquet (Norway) ANESTHESIA MACHINE REQUIRED components of an anesthesia workstation/machine: • • • • • • • • • • • • • OXYGEN flush valve Vaporizers Common gas outlet Pipeline gas supply Machine checklist Digital data interface Battery backup (30 min) Alarms Required monitors Electrical supply cord OXYGEN cylinder attached Cylinder hanger yoke Flowmeters: → Unique shape for O2 knob → Valve stops → O2 flow indicator always far right or most bottom → O2 enters manifold downstream ANESTHESIA MACHINE WHAT IS THE PURPOSE OF THE ANESTHESIA MACHINE? SUPPLY • How do the gasses arrive to the anesthesia machine? PROCESSING • How does the anesthesia machine prepare gases before delivery to patient? DELIVERY • How is the gas/patient interaction controlled and monitored? DISPOSAL • How are waste gases disposed of? ANESTHESIA MACHINE SUPPL Y PROCESSING DELIVE RY DISPOS AL SUPPLY How do the gasses arrive to the anesthesia machine? SUPPL Y SUPPLY How do the gasses arrive to the anesthesia machine? PIPELINE: (INTERMEDIATE pressure) • Wall outlets • Connecting valves and hoses • Filters & check valves • Pressure gauges CYLINDERS: (HIGH pressure) • Hanger yokes/yoke block • Filters & check valves • Pressure gauges • Pressure regulators SUPPLY PIPELINE SUPPLY: • Gas storage in remote location in hospital • Piped into operating room outlets • Hoses connect outlets to anesthesia machines SUPPLY PIPELINE SUPPLY: SUPPLY PIPELINE SUPPLY: NUT NIPPLE/STEM THREADS NONINTERCHANGABL E CONNECTIONS DIAMETER INDEX SAFETY SYSTEM SUPPLY PIPELINE SUPPLY: DIAMETER INDEX SAFETY SYSTEM SUPPLY PIPELINE SUPPLY: CHECK VALVE: • Prevents: → Gas leakage from machine upon disconnect → Higher pressure gas from machine backflowing into pipeline FILTER: • Prevents particulate contamination from pipeline to machine SUPPLY PIPELINE SUPPLY: PRESSURE GAUGES Regulated from source, arrives at wall outlet, and supplied to machine at 50 psi SUPPLY CYLINDER SUPPLY: • • • • Size E cylinders Intended for emergency/backup use Mounted to rear of anesthesia machine Hanger yokes: → Orient cylinders → Provide gas-tight seal → Ensure unidirectional flow into machine (check valve) SUPPLY CYLINDER SUPPLY: CYLINDER IDENTIFICATION: • Color coded to aid in identification and prevent unintended interchange • Cylinder label is only “DIFINITIVE” means of identification CYLINDER SUPPLY: SUPPLY PIN INDEX SAFETY SYSTEM CYLINDER SUPPLY: SUPPLY PIN INDEX SAFETY SYSTEM CYLINDER SUPPLY: SUPPLY FILTER: • Prevents particulate contamination from cylinder to machine CHECK VALVE: • Prevents: → Gas leakage from machine upon cylinder disconnect/removal → Higher pressure gas from machine backflowing into cylinder → Cross-filling of cylinders SUPPLY CYLINDER SUPPLY: SERVICE PRESSURE: CAPACITY: PIN CONFIGURATIO N: CYLINDER SUPPLY: SUPPLY CALCULATING CYLINDER CONTENTS CALCULATING TIME UNTIL EMPTY ONLY ACCURATE FOR OXYGEN AND AIR, NOT FOR SUPPLY CYLINDER SUPPLY:NITROUS OXIDE Exists as liquid inside cylinder (critical temp 36.5o C) Typically filled 90-95% with liquid N2O Weight is only accurate measurement of N2O Vapor above liquid interface is stable, delivered to anesthesia machine • Saturated vapor pressure is 745-750 psi at room temperature • Once N2O liquid is depleted, about ¼ of N2O vapor capacity remains (~400L) • Pressure gauge is not reliable in determining remaining N2O! • • • • CYLINDER SUPPLY: PRIMAR Y PRESSU RE < 2,200 psi REGULA CYLINDER TOR SUPPLY 45 MACHIN psi E SUPPLY CYLINDER SUPPLY: PRESSURE GAUGES Regulated from cylinder and supplied to machine at 45 psi SUPPLY PROCESSING How does the anesthesia machine prepare gases before delivery to patient? PROCESSING PROCESSING MACHINE PRESSURE SYSTEMS HIGH LOW INTERMEDIA TE PROCESSING COMPONENTS OF MACHINE PRESSURE SYSTEMS HIGH-PRESSURE: • Hanger yoke • Yoke block w/ check valves • Cylinder pressure gauges • Cylinder pressure regulators INTERMEDIATEPRESSURE: LOWPRESSURE: • Pipeline inlets, valves, gauges • Ventilator power inlet • Oxygen pressure-failure devices • Flowmeter valve • Oxygen second-stage regulator • Oxygen flush valve • Flowmeter tubes • Vaporizers • Check valve • Common gas outlet PROCESSING OXYGEN FIVE TASKS OF OXYGEN (PRESSURE)! (PRESSURE): 1) 2) 3) 4) 5) Supplies fresh gas to flowmeter Powers oxygen flush mechanism Activates fail-safe mechanisms Activates low-pressure alarms Compresses bellows of mechanical PROCESSING 4 3 1 5 2 PROCESSING 3 1 4 2 5 PROCESSING REGULATION OF OXYGEN PRESSURE: OXYGEN CYLINDER OXYGEN PIPELINE (HIGH PRESSURE) (INTERMEDIATE PRESSURE) 1) Cylinder regulator 1) Second-stage regulator 2) Second-stage regulator 2) Flow-control 3) Flow-control valve/flowmeter valve/flowmeter PROCESSING OXYGEN CYLINDE R FLOWCONTROL VALVE/ FLOWMETER CYLINDER REGULATOR SECONDSTAGE REGULATOR PROCESSING FLOWCONTROL VALVE/ FLOWMETER SECONDSTAGE OXYGENREGULATOR PIPELIN PROCESSING SECOND-STAGE OXYGEN REGULATOR: • Receives O2 at INTERMEDIATE PRESSURE (45 or 50 psi) • Regulates pressure to lower, manufacturer-specific value (12-19 psi) • Maintains consistent pressure to flowmeter to ensure consistent output PROCESSING PROCESSING OXYGEN FLUSH VALVE: • Used to quickly fill breathing circuit with oxygen • Delivers 35-75 L/min • Potential for barotrauma if activated during inspiratory cycle of mechanical ventilation • Direct to common gas outlet – bypasses flowmeters, vaporizers • Potential for dilution of anesthesia in breathing PROCESSING N2O N2 O PROCESSING OXYGEN FAIL-SAFE MECHANISM: • Prevents or limits delivery of N2O when oxygen pressure falls PROCESSING PROCESSING OXYGEN LOW-PRESSURE ALARM: • Alerts provider when pipeline oxygen pressure falls below preset value • Immediate goals to address loss of pipeline oxygen pressure: → Maintenance of oxygenation → Maintenance of ventilation PROCESSING PROCESSING VENTILATOR DRIVE GAS: • Ventilator chamber pressurized with 100% oxygen, compressing bellows to deliver prescribed Vt • More modern machines convert to air in case of oxygen pressure failure • Piston-driven ventilators (Dräger) use only electricity PROCESSING FLOWMETER ASSEMBLY: • Precisely controls and measures fresh gas flow • Glass, tapered tube – Thorpe Tube • Mobile indicator float inside tube indicates amount of flow • More modern machines use electronic flowmeters with digital displays FLO W PROCESSING PROCESSING FLOWMETER SAFETY FEATURES: • Oxygen control knob distinguished in visual and tactile form • Oxygen flow indicator always far right or most bottom PROCESSING FLOWMETER SAFETY FEATURES: • Physical order/arrangement of flowtubes • Oxygen always most “downstream” before common manifold PROCESSING FLOWMETER SAFETY FEATURES: HYPOXIC GUARD / PROPORTIONING SYSTEM • Link flows of O2 and N2O so that final FiO2 delivered is at least 23-25% • Ratio usually kept near 3:1 (N2O:O2) • Can be mechanical (Link-25) or electronic (sensitive oxygen ratio controller) • Hypoxic mixture still possible: → Pipeline crossover or cylinder discrepancy → Defective pneumatics or mechanics → Leak downstream of flow control valves → Presence of inert “third” gas PROCESSING HYPOXIC GUARD / PROPORTIONING SYSTEM: Link-25 PROCESSING HYPOXIC GUARD / PROPORTIONING SYSTEM: Sensitive Oxygen Ratio Controller (S- PROCESSING FLOWMETER SAFETY FEATURES: MINIMUM OXYGEN FLOW • When master switch is powered on, oxygen flows at 50-300 ml/min (depending on manufacturer) before any other gas/agent • Minimum oxygen flow always present when machine is powered on, even with oxygen flow control valve closed PROCESSING PROBLEMS WITH FLOWMETERS: • Leaks • Inaccuracy • Ambiguous scale CARE OF FLOWMETERS: • Always watch float when adjusting • Always turn off after case and confirm off before powering on machine • Protect flowmeters and common manifold when transporting machine • Low-pressure leak test to confirm patency PROCESSING VAPORIZERS: • Allow capture and measured delivery of vapor above liquid volatile anesthetic BARAS H PROCESSING VARIABLE-BYPASS VAPORIZER: • “Variable-bypass” refers to the method for regulating anesthetic agent concentration output • Concentration control dial setting determines ratio of incoming gas that flows through the bypass chamber to that entering the vaporizing chamber • Gas in vaporizing chamber flows over a wick system saturated with the liquid anesthetic, becomes saturated with vapor (“flow-over” method) • Most modern variable-bypass vaporizers are TEMPERATURE COMPENSATED → Temperature-compensating device maintains constant vapor concentration output for a given concentration dial setting, over PROCESSING VARIABLE-BYPASS VAPORIZER PROCESSING VARIABLE-BYPASS VAPORIZER BIMETAL LIC STRIP PROCESSING VARIABLE-BYPASS VAPORIZER PROCESSING TEC 6 AND D-VAPOR VAPORIZERS: • Unique for administration of DESFLURANE • Heated (to 39o C) and pressurized (2 ATM) to compensate for high vapor pressure/high MAC • Fresh gas flow never comes into direct contact with liquid agent • Appropriate amount of vapor added to fresh gas in DUALCIRCUIT system → One circuit dependent on concentration control dial → One circuit dependent on amount of fresh gas flow • Require power source • Equipped with low-output indicator and alarm PROCESSING TEC 6 AND D-VAPOR VAPORIZERS PROCESSING TEC 6 AND D-VAPOR VAPORIZERS PROCESSING ALADIN CASSETTE VAPORIZER: • Different appearance, similar function to variable-bypass vaporizer • Internal control unit (CPU), control dial located in machine digital interface • CPU receives data from control dial and pressure/flow sensors in chambers • CPU regulates flow between chambers to obtain desired vapor concentration output PROCESSING ALADIN CASSETTE VAPORIZER PROCESSING VAPORIZER HAZARDS/SAFETY FEATURES: • Misfilling (wrong agent/wrong vaporizer) → Agent specific, keyed filling devices • Tipping → Secured to manifold, transport setting • Improper (over-)filling → Fill port located at maximum safe-fill level PROCESSING VAPORIZER HAZARDS/SAFETY FEATURES: • Simultaneous agent administration → Interlock systems • Leaks → Durable construction, manifold design • MRI suite → Non-magnetic, MRI compatible design PROCESSING VAPORIZER HAZARDS/SAFETY FEATURES: INTERMITTENT BACK PRESSURE: • • • • • Known as “pumping effect” Positive-pressure ventilation or O2 flush valve use can push gas flow back into vaporizer (fresh gas flow against closed expiratory valve) Increased by rapid respiratory rates, high peak inspired pressures, and rapid decreases in pressure during exhalation Minimized by CHECK-VALVE located between vaporizer and common gas outlet Minimized by construction of smaller vaporizing chambers in PROCESSING DELIVERY How is the gas/patient interaction controlled and monitored? DELIVE RY DELIVERY COMMON GAS OUTLET (CGO): • Delivers contents of fresh gas + vaporizer manifolds to breathing circuit • Accessory CGO located external on machine, used to check lowpressure system for leaks • More modern machines lack Accessory CGO ACCESSORY CGO DELIVERY BREATHING CIRCUIT: • Provides conduit for: → Fresh gas, volatile anesthetic TO patient → CO2, exhaled gas, exhaled volatile anesthetic AWAY from patient DELIVERY BREATHING OPEN CIRCUIT: → A non-contained system where the patient exchanges gas with the atmosphere SEMI-OPEN → No rebreathing of exhaled gas → Fresh gas flow (FGF) is greater than minute ventilation SEMI-CLOSED → Allows rebreathing of exhaled gas → FGF is less than minute ventilation CLOSED → Complete rebreathing of exhaled gas → Very low FGF → No scavenging of exhaled gas DELIVERY BREATHING RESERVO CIRCUIT: TYPE IR OPEN SEMIOPEN SEMICLOSED CLOSED NO YES YES YES REBREATHI NG EXAMPLES NO Open drop Nasal cannula NO Circle system (FGF > minute ventilation) PARTIAL Circle system (FGF < minute ventilation) COMPLETE Circle system Very low FGF DELIVERY COMPONENTS: BREATHING CIRCUIT: Traditional “circle system” (COMMON GAS OUTLET) • Fresh gas inlet • Inspiratory unidirectional valve • Inspiratory limb of circuit • Y-connector • Right-angle connector • Expiratory limb of circuit • Expiratory unidirectional valve • Adjustable Pressure Limiting (APL) valve • Reservoir bag • Reservoir bag/ventilator selector switch • Ventilator • Ventilation pressure gauge DELIVERY BREATHING CIRCUIT: INSPIRATION DELIVERY BREATHING CIRCUIT: EXPIRATION DELIVERY UNIDIRECTIONAL VALVES: • Create a pattern of gas flow that forces exhaled gas through CO2 absorbent • Subject to damage, occlusion, sticking – particularly expiratory valve • Common reason for increase in FiCO2 DELIVERY INSPIRATIO N EXPIRATIO N DELIVERY POSITIVE-PRESSURE DELIVERY EXPIRATION DELIVERY ADJUSTABLE PRESSURE LIMITING (APL) VALVE: Operator-adjustable relief valve Vents excess gas (pressure) to scavenger system Provides control of pressure in circuit Only active in SPONTANEOUS or MANUAL ventilation modes • Acts as “PEEP” valve during SPONTANEOUS ventilation • Acts as “POP-OFF” valve during MANUAL ventilation • • • • DELIVERY APL VALVE FUNCTION DELIVERY BREATHING CIRCUIT PRESSURE GUAGE: • Measures pressure in circuit – airway pressure • Manual gauge redundant/duplicate to digital display OXYGEN ANALYZER: • Monitors oxygen concentration in circuit • Only device/mechanism on machine to detect hypoxic mix DELIVERY MECHANICAL VENTILATION: GAS-DRIVEN BELLOWS • “Bag in the Bottle” • Uses force of compressed gas to compress bellows • Gas within the bellows inspired/expired by patient ASCENDING BELLOWS (“standing”) • Bellows ascend during expiration • Circuit disconnect results in fallen bellows, visual sign of disconnect DESCENDING BELLOWS (“hanging”) • Bellows descend during expiration • Circuit disconnect results in descended bellows, difficult to distinguish disconnect DELIVERY DELIVERY MECHANICAL VENTILATION: GAS-DRIVEN BELLOWS • Inspiratory phase: → Driving gas enters chamber, increases chamber pressure → Increased chamber pressure closes relief valve (via pilot line) & compresses bellows • Expiratory phase: → Decreased chamber pressure opens relief valve (via pilot line) → Driving gas exits chamber to scavenging system → Bellows fill with exhaled gas from patient → Once bellows are full, excess exhaled gas (pressure) diverted to scavenging system • Gas flow from anesthesia machine is continuous and independent of ventilator activity DELIVERY DELIVERY MECHANICAL VENTILATION: MECHANICALLY-DRIVEN PISTON VENTILATOR • Piston operates like plunger of syringe in zero-compliance cylinder • Consume much less gas than traditional gas-driven bellows • Very accurate tidal volume delivery → FRESH GAS DECOUPLING • Reservoir bag in circuit, acts as “storage” for rebreathing • No visual alert to circuit disconnect DELIVERY MECHANICAL VENTILATION: MECHANICALLY-DRIVEN PISTON VENTILATOR FRESH GAS DECOUPLING DELIVERY MECHANICAL VENTILATION: MECHANICALLY-DRIVEN PISTON VENTILATOR FRESH GAS DECOUPLING DELIVERY MECHANICAL VENTILATION: TRADITIONAL (BELLOWS): FRESH GAS DECOUPLING (PISTON): • Continuous FGF is entering circuit from flowmeters or O2 flush valve • Ventilator delivers prescribed Vt • Ventilator relief valve is closed, no gas escapes • Total volume delivered to patient included prescribed Vt + FGF • FGF from flowmeters or O2 flush is diverted by decoupling valve into reservoir bag • During expiratory phase, decoupling valve opens allowing accumulated fresh gas to refill piston chamber • Ventilator relief valve is open during expiration, excess FGF and/or exhaled gas escapes to scavenging DELIVERY MECHANICAL VENTILATION: VENTILATOR MODES • Volume-Controlled Ventilation (VCV) • Pressure-Controlled Ventilation (PCV) • Synchronized Intermittent Mandatory Ventilation (SIMV) • Pressure-Support Ventilation (PSV) • Pressure-Controlled Ventilation with Volume Guarantee (PCV-VG) • Continuous Positive Airway Pressure (CPAP) • Bilevel Positive Airway Pressure (BiPAP) DELIVERY CARBON DIOXIDE ABSORBENT SYSTEMS: • Allows rebreathing of exhaled gases, conserving volatile anesthesia, fresh gases, and airway moisture • FGF vs minute ventilation determines the amount of rebreathing in circle system (SEMI-OPEN vs SEMI-CLOSED) • Older systems use dual-canister system, dependent on integrity of housing to seal circuit, more modern machine use proprietary DELIVERY CARBON DIOXIDE ABSORBENT SYSTEMS: • Granules (size 4-8 mesh) composed of alkaline compounds react with CO2 to chemically eliminate • Ca(OH)2 is primary ingredient in most systems, including classic SODA LIME • Fundamental reaction: CO2 + Ca(OH)2 → CaCO3 + H2O + heat • H2O is byproduct, but also necessary catalyst for reaction • Color indicator: ethyl violet → Changes to violet color when pH decreases below 10.3 → Indicates exhaustion of absorbent capacity → Not completely reliable; fluorescent light and desiccation DELIVERY CARBON DIOXIDE ABSORBENT SYSTEMS: DELIVERY CARBON DIOXIDE ABSORBENT SYSTEMS: CARBON MONOXIDE PRODUCTION • Strong base absorbents, particularly when desiccated, can degrade VAs to produce CO • Factors increasing potential for CO production: → Desflurane > isoflurane, sevoflurane not typically implicated → High degree of desiccation → Absorbents containing KOH and/or NaOH → Low FGF rates → High temperature → High VA concentration DELIVERY CARBON DIOXIDE ABSORBENT SYSTEMS: COMPOUND A PRODUCTION • Sevoflurane has potential to undergo base degradation reaction with absorbent • Compound A: fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl • Demonstrated to be nephrotoxic in rats at routine breathing circuit concentrations • No current evidence of postoperative renal dysfunction related to sevoflurane • Package insert for sevoflurane recommends no more than 2 MAC hours at < 2 lpm FGF • Factors increasing potential for Compound A production: → Low-flow or closed-circuit anesthetic techniques DISPOSAL How are waste gases disposed of? DISPOS AL DISPOSAL SCAVENGING SYSTEM: • Scavenging is the collection and removal of waste anesthetic gas from the operating room COMPONENTS: 1)Gas collecting assembly 2)Transfer tubing 3)Scavenging interface 4)Gas disposal tubing 5)Gas disposal assembly DISPOSAL SCAVENGING SYSTEM: • Interface where breathing circuit meets suction is critical component OPEN INTERFACE • Found on more modern systems • Open to atmosphere, eliminates need for pressure relief valves • Failure to apply appropriate suction can lead to leak of waste gas into OR • No potential for positive/negative pressure injury CLOSED INTERFACE • Found on older systems • Equipped with positive and negative pressure relief valves • DISPOSAL OPEN INTERFACE CLOSED INTERFACE SUMMARY Outline the purpose of the anesthesia machine. List and define the components of pipeline and cylinder gas supply. Describe the safety systems used to prevent unintended gas interchange in pipeline and cylinder gas supply. List the service pressure, capacity, and pin configuration of O2, N2O, and medical air. Calculate cylinder contents and time remaining for O2 and medical air. Discuss the unique characteristics of N2O cylinder dynamics. Label high, intermediate, and low-pressure systems on anesthesia machine diagram. Provide expected gas pressure reading at any given position on anesthesia machine diagram. List and elaborate upon the five tasks of oxygen pressure. Trace the path of oxygen from cylinder and pipeline through stages of pressure regulation. Describe the form, function, and safety features of flow control valves and flowmeters. Outline the general functions of an anesthetic vaporizer. Compare and contrast variable bypass, Tec6/D-Vapor, and cassette type vaporizers. List the potential vaporizer safety hazards and the corresponding safety features. SUMMARY Define the four general classifications of breathing circuits. List and elaborate upon the components of the anesthesia breathing circuit. Describe the form and function of the APL valve. Compare and contrast the two potential varieties of gas-driven bellows type ventilators. Follow the paths of gas flow through a ventilatory cycle in gas-driven bellows type ventilators. Differentiate piston from gas-driven bellows type ventilators. Define fresh gas decoupling. Describe the function and components of a carbon dioxide absorbent system. Discuss the general chemistry involved in the carbon dioxide absorbent system, including color indicator. List and elaborate upon the potentially dangerous interactions between absorbent and VAs. Describe the components of the scavenging system. Compare and contrast open and closed interface scavenging systems.