Anaesthesia Machine

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Slide 1 :

DR. VITHAL DHULKHED Professor and HOD of Anesthesiology, Krishna Institute of Medical Sciences, Karad, Maharashtra ,India email:drvithalk@hotmail.com- ANAESTHESIA MACHINE – THE BASIC PRINCIPLES

Slide 2 :

INTRODUCTION : Evolution from simple pneumatic device to computer workstation, Features are centralized display and functional integration. Be familiar with machine to enable Preop checks To understand, knowledge of pneumatics electronics and computer science required

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Machine standards: Standards -guidelines to manufacturers for minimum performance, design characteristics and safety requirements 2000: American society for testing and materials (ASTM) F1850 – 00

Slide 4 :

Pressure Units to remember 1 atm. pressure (sea level) =1bar =760mmHg ˜ 1Kg/cm2 = 14.5 lb/inch2 (psi) ˜ 100 kilopascals (kPa) = 10 meter water height = 1000 cm H2O =1000mbar =1000 hectopascal (hPa)

Slide 5 :

1846 THE ETHER INHALER

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PAST TO PRESENT Ether Apparatus, Mennell’s , Magill’s Ether Apparatus 1927 Boyle Apparatus KION SIEMEN’S DATEX OHMEDA ADU

Slide 7 :

An over view

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Slide 9 :

The Electric System: Master switch: activates the pneumatic and electric functions. Off or stand by position :the battery recharge, electric outlets active. Power failure indicator Back up battery. Electric outlets. power monitors

Slide 10 :

Pneumatic system: Divided into 3 systems High pressure, intermediate pressure and low pressure system. High pressure system: cylinders and pressure regulators.

Slide 11 :

Pipeline source: Oxygen, nitrous oxide and air. A check valve located down stream Diameter Index Safety System (DISS) Cylinder source : Gasket for airtight seal, The gas enters through nipple. back- flow check valve down stream. Pin Index Safety System (PISS). Bourdon Pressure gauge:indicates cylinder pr. a fixed orifice variable flow, pressure type For each gas pipeline pressure indicators cylinder pressure indicators

Slide 12 :

Capacity of cylinders (from CGA Pamphlet P-2)

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Pressure regulator: Force =Pressure × Area Pc × A1 = Pr × A2 Pc/ Pr = A2 / A1 oxygen, 2200 psig to 50 psig,(45 cyl). Nitrous Oxide 750 psig to 50 psig ,(45 cyl).

Slide 14 :

Intermediate pressure system. Safety device for Oxygen Supply Pressure Failure : Ensure oxygen 19% min. at the common gas outlet. Pneumatic and Electronic alarm devices: oxygen pr. below 30 psig alarm within 5 seconds.

Slide 15 :

Fail Safe valve: Pressure Sensor Shut off Valve: oxygen pr > 20 psig opens valve for N2O Oxygen Failure Protection Device: proportioning principle. Second stage pressure regulation: oxygen 12 and 19 psig. used for N2O also.

Slide 16 :

Ohm’s Law: Voltage = Current × Res. In hydraulic system: Pr= Flow x Res i.e. F × R Pr/ wt of bobbin constt F ? 1 / R (? Area) Hagen – Poiseuille eqn for laminar flow .: Flow rate = ? r 4 P /8 ?l Flow through orifice ? area v (pr. diff / Dens) Low pressure system Flow meter assembly

Slide 17 :

Prefer digital system Solenoid valves control flow on or off channels Computer ontrolled. Various other types. Electronic flow meter

Slide 18 :

Proportionating Systems Link–25 system chain link nitrous oxide and oxygen 14 tooth & 28 tooth sprockets Supply at 26 psig & 14psig Ensure oxygen supply at the common gas outlet. between 23% and 25%.

Slide 19 :

Oxygen ratio monitors controller (ORMC) Sensitive oxygen Ratio Controller (S – ORC] Similar. Resistors (3: 1 ratio for O2: N2O) Ensure 25% oxygen by limiting N2O flow. ORMC shuts off N2O if oxygen pr. < 10 psig S – ORC oxygen flow < 200 l/min.

Slide 20 :

Anti-Hypoxic Device Duel lever system acts on needle valves Rgulate oxygen and nitrous oxide flows > 1: 3 ratios

Slide 21 :

VAPORISER Physics The pressure created by vapor phase over liquid at equilibrium at particular temp is the saturated vapor pressure. e.g. Halothane saturated vapor pr. 243 torr at 20 C. The vaporizing chamber concentration of halothane i.e 243/760 X 100 %= 32%

Slide 22 :

Vaporizer Vaporizer interlock Ensures only one vaporizer on Trace vapor output minimal when off Vaporizers are locked into gas circuit, ensuring they are seated correctly.

Slide 23 :

(FGF) splits into carrier gas (<20%, saturates with vapor) and bypass gas (> 80%). rejoin at outlet. splitting ratio controlled by control dial, temp compensn. valve. Operating principles of variable bypass vaporizers

Slide 24 :

Constant at 250 mL to15 L/min, due to wick , baffle: Output linear at 20-35 deg C, due to temp compensating devices,Wicks Constructed of metals with high specific heat thermal conductivity Effect of flow rate

Slide 25 :

Effect of intermittent back pressure pumping effect positive pressure, oxygen flush valve increase vaporizer output. check valves between the vaporizer outlet and the common gas outlet, smaller vaporizing chambers, or tortuous inlet chambers.

Slide 26 :

Vaporisers Effect of Low Atmospheric Pressure – Flow to vaporising chamber increased Vapor output increased if measured as partial Pr. volume % to be set . = Vol % indicated on Vaporiser× 760 / amb. pr

Slide 27 :

How much liquid agent does a vaporizer use per hour? Ehrenwerth and Eisenkraft (1993) give the formula: 3 x Fresh gas flow (FGF) (L/min) x volume % = mL liquid used per hour

Slide 28 :

Effect of pressure on flowmeter Actual flow = Indicated flow / ?(d0/d1) d0 = density at atm. Pr d1 = density at amb. Pr If pr = 2 ATM d1 = 2, ? (d0/d1) = .71 :. Actual flow = .71 of indicated flow

Slide 29 :

Vapor travels via shut off valve , pr. reg. valve (pr at 1.1 atm 74mmHg at 10L/min) Pr in the 2 circuit at same level by inter facing electronically pneumatically by transducer, control electronic system & pr. reg. valve. sump at 390c Desflurane vaporizer

Slide 30 :

Various agents used in sp. cassettes Color, magnetic coded Variable bypass type Check Valve at inlet CPU controlls flow control valve Sensors monitor flows Information from, RGM, agent type, temp, Pr, flow rate of FGF its composition determine Conc. Alladin Vaporiser

Slide 31 :

Circle system Circle components: fresh gas inflow source, inspiratory & expiratory unidirectional valves, ins& exp corrugated tubing,Y connector, APL valve, reservoir bag, CO2 absorbent canister Resistance of circle systems <3 cm H2O. Dead space is increased (by all respiratory apparatus). 0.46 if intubated and 0.65 if mask. Mechanical dead space upto the Y-connector.

Slide 32 :

Circle system advantages and disadvantages Circle advantages: constant inspired concentrations conserve respiratory heat and humidity useful for all ages (may use down to 10 kg, about one year of age, or less with a pediatric disposable circuit) useful for closed system or low-flow low resistance (less than tracheal tube, but more than a NRB circuit) Circle disadvantages: increased dead space malfunctions of unidirectional valves

Slide 33 :

TRADITIONAL CIRCLE BREATHING SYSTEM APL VALVE BAG SELECTOR SWITCH CO2 CANISTOR FGF VENT Y PIECE Ideal arrangement Unidirectional valve near the patient and APL just downstream from exp. Valve.

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Slide 35 :

KING’S CIRCLE SYSTEM BAIN’S CIRCUIT

Slide 36 :

Anaesthesia Ventilator Substitute for breathing bag Power source, preumatic or electric Ascending bellows,Descending bellows or piston type,computer controlled stepper motor Advance ICU features incorporated

Slide 37 :

Ascending bellows- Insp. Phase – Driving gas enters housing chamber pr. also in pilot line Relief valve closes Bellows ompressed Exp. Phase Driving gas exits Pressure in housing also over the relief valve Fresh gas and expired gases fill the bellows when 2 – 3cm H2O pressure in bellows the relief valve opens

Slide 38 :

Use fresh gas decoupling system (FDS) Insp. Phase FDS Closes FGF diverted to bag Exp., vent. exhaust valves closed Gas delivered to patient Exp. Phase – Bellows or piston refill under slight –ve Pr. from reservoir bag ( FDS opens) Excess gases open exhaust valve Descending bellows or Piston

Slide 39 :

Tidal Volume compensation Dynamic, Automatically adjusts for changes in: fresh gas flow lung compliance compression losses Accurate Volume Delivery Allows the clinician to focus on the patient rather than on the ventilator controls 0 to 30 LPM of Fresh Gas can be compensated for

Slide 40 :

FRESH GAS COMPENSATION Traditionally in anaesthesia ventilators fresh gas is delivered continuously to the system. With no method of compensation the fresh gas increases the delivered tidal volume during inspiration. The higher the fresh gas flow, the greater the tidal volume. Fresh gas compensation provides accurate delivery of tidal volume

Slide 41 :

Fresh Gas Compensation cont’d Fresh gas contribution = fgf in ml x inspiratory time 60 Example: fgf = 5L/min tidal vol = 600ml freq = 10 I:E =1:2 Inspiratory time = 60 x 1 = 2secs 10 3 fresh gas contribution = 5000 x 2 = 166ml 60 Therefore tidal volume needs to be reduced by this amount New TV to achieve correct ventn = 600 – 166 = 434ml

Slide 42 :

DYNAMIC COMPLIANCE COMPENSASTION Compression of the gas within the breathing system reduces the tidal volume delivered to the patient. To ensure that the correct tidal volume is delivered the system , compliance must be calculated - this is done at start up & the value retained in memory. When a patient is connected the combined compliance is obtained - system + patient. The tidal volume is then increased to compensate for the compressed volume within the system

Slide 43 :

Dyn. Compliance Compensation -cont’d At start up a known volume is delivered to the system & the pressure recorded. Compliance is then calculated: Compliancesystem = __volume in ml__ pressure in cmH20 Required tidal volume for accurate ventilation = set tidal volume x _1 + Csys Ctotal - Csys Csys = system compliance Ctotal = compliance of system + patient

Slide 44 :

Dyn. Compliance Compensation-cont’d Example: At start up - known volume = 200ml; pressure = 25cmH20 Csys = 200 = 8ml/cmH20 25 With patient connected - volume = 500ml; pressure = 20cmH20 Ctotal = 500 = 25ml/cmH20 20 New TV = 500 x 1 + 8__ = 500 x 1+ 0.47 25 - 8 = 735ml

Slide 45 :

Low-flow adaptation Concern about env contamination waste of expensive volatile agents for minimal (<0.5 lpm) or low flow (<1.0 lpm) small volume of the breathing circuit smaller time constant Gas analyzer extraction returned to circuit, Monitoring FiO2 accurate at endotr. tube

Slide 46 :

Low-flow adaptation…… Flow meters, Spirometers, well calibrated , accurate O2/N2O proportionating capability scavenger system should not extract gas changes in FGF shouldn ‘t alter set TV, adequate warning for reductions in peak airway pr

Slide 47 :

The future of the "Anesthesia Machine" Fast, inexpensive, small, powerful computers, wireless technology, and the internet are revolutionizing anesthesia Accurate record keeping, and improved patient care through the use of expert systems Anesthesiologists must take a leading role in the development and implementation of new technology

Slide 48 :

THANK YOU

Slide 49 :

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Anaesthesia Machine
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