Lakhasly

Ventilators are commonly used in the operating room and in the ICU to deliver mechanical ventilation to the lungs.Breath controlcomplexitygives rise to the needto identifyanddescribe "modes"ofventilation. Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 12 Multi-compartment model of the respiratory system connected to a ventilator using electronic analogs 2nd Semester 2023-2024 13 Assist Lec.: Athra'a Sabeeh 14 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Modern ventilatormachines have two separate but inter connectedsystems;apneumaticflowsystemandanelectronic controlsystem. Thepneumaticflowsystemenablestheflowofgasthroughthe ventilator.Thegases(oxygenandmedicalgradeair)enterthe air / oxygenmixer which they combine at the required percentage.Thegasesthenenteralargereservoirtanktobe compressed.Anelectronicallycontrolledflowvalveproportion thegasflowfromthereservoirtanktothepatient'sbreathing circuit. Insomeventilators,anaircompressorisusedinplace of acompressedair tank.Ventilatorsrequireelectricpower, oxygen, and compressed air usually supplied via external powersourceaswellasviahospital'scentralgassupply(with supplypressureofapproximately3-6bar). Inareaswithout centralgassupplyorduringtransportationofpatientswithin thehospital, it isnecessary toensurethe functioningof the devicebyothermeans.Potential solutions includetheuseof separate compressors, compressed gas cylinder packs, and accumulators. Ventilator Functional Block Diagram Gas mixer allowsthe user to vary theoxygen concentration of inspiratory gas between 21%and100%byvolume: a. Mechanical gas mixers(old technology). b. Electronically-controlled gas mixer integrated in ventilator(standard now). Gas mixers usually responsible for ensuring that breathing gas to be supplied is prepared and delivered in required quantity and rate. It is often the threshold ranges whichposethegreatest challenges to thesemeteringsystems. For volume of 20 mlwith an oxygen concentration of 30% by volume, 17.7 mlof gasmust be deliveredviacompressedair valveand2.3mlviaoxygenvalve. The pressure or flow generator is responsible for delivering mixed gas prepared by the gas mixer according to selected ventilation parameters. Flow generator is a controlled valve whose output provides defined gas flow with output pressure is not specified. Pressure generator behaves similar to compressor, whose output provides defined pressure with unspecified gas flow. It's often used to drive ventilators notdependentoncompressedairthat useambient air forventilation. 2nd Semester 2023-2024 Assist Lec.: Athra'a Sabeeh 15 Breathing System Breathing system forms interface between patient and the ventilator. Clinical ventilators are usually connected to patient via inspiratory and expiratory hose (dual-hose circuit). Expiratory valve is closed during the inspiratory phase where gas flow delivered through inspiratory portpasses through breathing gas humidifier before entering patient's lungs to make it adapted to climatic conditions in patient's lungs. After inspiratory phase, patient exhales when expiratory valve is opened, expiratory gas passes through ventilator again, but not reused for following inspiration. Based on this characteristic, the breathing systems of ventilators are also referred to as non rebreathing circuits. Gas Humidifier Humidifiers are used to warm and humidify inspiratory gas. Dry and relatively cool supply gas would dry out the patient's airways with risk of causing irreversible damage to the ciliated epithelium. Active gas humidifiers are located in the inspiratory limb and use electrical energy to heat a water bath. When the cold, dry gas passes over the water surface it absorbs water molecules and is thuswarmed and humidified. Example: Pass-over humidifiers and Bubble- through humidifiers. Passive breathing gas humidifiers, termed heat and moisture exchangers (HMEs), are placed close to patient and designed to buffer significant fraction of moisture and heat expired by patient. Retained moistureis then usedto conditioninspiredgas passingthrough HMEduringnextinspiration. 2nd Semester 2023-2024 Assist Lec.: Athra'a Sabeeh 16 17 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Expiratory (Exhalation) Valve Expiratory valve switches between inspiration and expiration phases of Ventilation If valve is not opened completely during expiration, positive end-expiratory pressure (PEEP) is created in lungs. PEEP is therapeutically important as it increases gas exchange surface oflungs. Adequate PEEP can also prevent collapse of individual alveolar areas. If expiratory valve is controlled during inspiratory phase, it can compensate for undesired pressure rises in breathing system Caused, for example, bypatient coughing. 2nd Semester 2023-2024 Assist Lec.: Athra'a Sabeeh 18 19 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 OperatingandDisplayUnit Operatinganddisplayunitistheinterfacebetweenventilatoranduser.Oftentouchscreensdesignedtodisplay pressureandflowcurvesaswellasmultiplemenusforsettingdifferentventilationmodes,adjustingalarmlimits ormeasuredvalueoverviews,etc.Parametersettingsenteredinoperatingunitcontroldevicecomponentsand thereforedetermineventilationpatternappliedtothepatient. AlarmSystemandPatientMonitor Ensuresthatventilationparametersset inoperatinganddisplayunitareactuallyapplied.Thissystemissues audibleandvisualalarmstoalertstaff tocritical changes inthepatient'sconditionor technicalmalfunctions monitorsthefollowing:

1. Inspiratoryoxygenconcentration(controlledbythegasmixer)
2. VentilationPressureandVolume(tomonitorthepressure/flowgenerator)
3. Inspiratorybreathinggastemperature(whenusingactivegashumidifier) Patientmonitoringisusedtomonitorthepatient'svitalfunctions
4. Electrocardiogram(ECG)
5. Bloodpressure(noninvasiveand/orinvasive)
6. Oxygensaturation
7. Carbondioxideconcentrationinthebreathinggas 20 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Modernventilatormachinesconsistoftwoseparatebutinter-connectedsystems:thepneumaticflowsystemand anelectroniccontrolsystem. Thepneumaticflowsystemenablestheflowofgasthroughtheventilator.Oxygenandmedicalgradeairenterthe ventilatorat3.5bar(50psi)pressurethroughbuilt-in0.1micronfilters.Thenormaloperatingrangeis2to6bar or28to86psi.Thesegassesenter theair/oxygenmixerwheretheycombineat therequiredpercentageand reducedinpressureto350cmH2O.Thegassesthenenteralargereservoirtankwhichholdsabout8litersof mixedgasses,whencompressedto350cmH2O.Anelectronicallycontrolledflowvalveproportionsthegasflow fromthereservoirtanktothepatientbreathingcircuit.Insomeventilators,anaircompressorisusedinplaceofa compressedairtank.Theprimaryobjectiveofthedeviceistoensureproperlevelofoxygenintheinspiratoryair anddeliveratidalvolumeaccordingtotheclinicalrequirements. Asthegassesleavetheventilator, theypassbyanoxygenanalyzer,asafetyambientairinletvalveandaback-up mechanicaloverpressurevalve.Theambientvalveprovidesthepatienttheabilitytobreatheroomairwhenthe ventilatorfailsorthepressureinthepatientcircuitdropsbelow-10cmofH2O.Inthepatientbreathingcircuitis abi-directionalflowsensortomeasurethegasflows.Theexhaledgassesexitthroughanelectronicallycontrolled exhalationvalve locatedat theventilator.With the introductionofmicroprocessors forcontrol ofmetering devices,electromechanicalvalveshavegainedpopularity.Themicroprocessorcontrolseachvalvetodeliverthe desiredinspiratoryairandoxygenflowsformandatoryandspontaneousventilation.Ahighpressurevalveisused toprovidesafetyincasethepressureinthepatientcircuitexceeds110cmH2O. Types of Ventilators ModernVentilators(Microprocessorcontrolled) The electronic control system may use one or more microprocessors and software to perform monitoring and control functions in a ventilator. These parameters include setting of the respiration rate, flow waveform, tidal volume, and oxygen concentration of the delivered breath, peak flow and PEEP. The PEEP selected in the mandatory mode is only used for controlof exhalation flow. The microprocessor utilizes the above parameters to compute the desired inspiratory flow trajectory. The system consists of monitors for pressure flow and oxygen fraction. The sensors are connected to electronic processing circuits which makes them available for digital readouts. The signals are also compared with pre-set alarm levels so that if they fall outside a pre-determined normal range, alarms are sounded. The pressure sensors are normally of semiconductor strain gauge typeplaced in a bridge configuration. For measurement of fraction of oxygen in the inspired air, afuel cell type oxygen sensor is used.This sensorgenerates acurrentproportionaltopO2. 2nd Semester 2023-2024 Assist Lec.: Athra'a Sabeeh 21 22 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Anewtechniqueforventilatingpatientsat frequenciesmuchhigher thantherespirationratehasrecentlybeen introduced.ThismethodhasbeenshowntoimproveCO2washoutandprovideadequateoxygenationwithoutthe requirementforhighinspiratorypressures.Thekeyprincipleinthistechniqueistoprovidetidalvolumesequalto orsmallerthanthedeadspace,atveryhighrates. Inconventionalpositivepressureventilation,CO2eliminationis directlycontrolledbytheamountofappliedminuteventilation.However,itisknownthatmeanairwaypressureis theparameterthatbestcorrelateswithimprovementinoxygenation.Gastransportduringconventionalventilation isattributed totwobasicmechanisms: (i)convectionor flowof gas throughtheconductingairways, and(ii) moleculardiffusionof gasses intothealveoli andpulmonarycapillaries. Thetidalvolume(VT)applied tothe patientattheY-piececanbedividedintothevolumeusedtoventilatethedeadspace(VD)andthealveolarvolume (VTalv).Onlythealveolarvolumetakespartinthegasexchangeprocess.Therefore, HighFrequencyVentilators V Talv=VT-VD Theportionofthetidalvolumeusedtoventilatethedeadspacedoesnottakepartincapillarygasexchangeandis thereforewasted. Toovercome theproblemofwastedventilation inconventionalventilation, the inspiratory pressureisincreasedinordertoincreasethetotal tidalvolume.Unfortunately,however, thisalsoincreasesthe mechanicalstressonthelungandhasbeenassociatedwithvarioustraumas.Highfrequencyventilationhasbeen showntoprovideadequatealveolarventilationandoxygenationwithout therequirement forhighinspiratory pressures.Theventilatorgenerateshighfrequencyratefrom5to20Hz(300to1200pulse/minute).Although severalmethodsareavailabletogeneratethehighfrequencypressurewaves, theBabylog8000makesuseofan oscillatingdiaphragmmechanism. 23 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Thismechanismis computer-controlled and canpreciselydetermine the shape of thepressure swings. An alternativemethodofachievingHFventilationisbasedonthejetprincipleinwhichasmalldiametertubeispassed downatrachealcannulaandiseitherterminatedatitsdistalendorextendedintothetracheaitself.Shortpulsesof higherpressureoxygenareintroducedintotheairwaythroughthecannulaatfrequencieswellabovethenormal respirationrate.Thistechniquehasthedisadvantageofforcingvolumeintothepatientandthenleavingthepatient toexhalepassively,whichmayleadtosometrappedvolumeinsidethelungincreasingthemeanlungpressure. Thisproblemisovercomebyensuringthatthepressureduringtheexhalationphaseisnegativewithrespecttothe setPEEP. 24 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Themaintaskofahumidifieristoreplacehumidityintheupperairpassageswhichhasbeenlostbyintubation. Thehumidityshouldbeascloseto100%aspossible,orspeakingintermsofwater,theabsolutecontentperliter breathinggasshouldbemorethan30mg,regardlessofenvironmentalconditions.Therefore,inordertoprevent damagetothepatient'slungs,theairoroxygenappliedduringrespiratorytherapymustbehumidified.Thus,all ventilatorsincludearrangementstohumidifytheair,eitherbyheatvaporization(stream)orbybubblinganair streamthroughajarofwater.Whenwaterorsometypeofmedicationsuspendedintheinspiredairasan aerosol istobeadministeredtothepatient, adevicecalledanebulizer isused. Inthisdevice, thewateror medicationispickedupbyahighvelocityjetofair/oxygenandmadetoimpactagainstoneormorebafflesto breakthesubstanceintocontrolled-sizeddropletswhicharethenappliedtothepatientviaarespirator.More effectiveandefficientnebulizersarebasedontheuseofhighintensityultrasoundenergywhichvibratesthe substance(waterormedication) toproduceahighvolumeofminuteparticles.Ultrasonicnebulizersdonot dependuponbreathinggasforoperationandthustherapeuticagentscanbeconvenientlyadministeredduring ventilationprocedure.Aspiratorsareoftenincludedaspartofaventilator toremovemucusandotherfluids fromtheairways.Alternatively,aseparatesuctiondevicemaybeutilizedtoachievethesamepurpose. Humidifiers,NebulizersandAspirators
8. Breathing pattern I.VolumeControl (VC) Aventilator canbeclassifiedas either a pressure, volume, or flow controller. When classifyingmodesof ventilation, we do not need to be so specific. Because control of volume implies control of flow andviceversa,wecanrefer to twobasicmodesofventilation: volume control and pressure control. II. Pressure Control (PC) Pressure controlmeans that the airway pressure waveform is preset (for example by setting peak inspiratorypressureandend expiratory pressure). Tidal volume and inspiratory flow are then dependent on these settings and the elastance and resistance of therespiratorysystem. Dual Control (DC) There are clinical advantages and disadvantages to volume and pressure control. Simply put, volume control results in amore stableminute ventilation (and hence more stable gas exchange) than pressure control if lung mechanics are unstable. On the other hand, pressure control allows better synchronizationwith thepatient because inspiratoryvolumeand floware not limited to arbitrary preset values. While it ispossibletocontrol only one variable at a time, a ventilator can automatically switch between pressure control andvolume control in an attempt to guarantee minute ventilation while maximizingpatientsynchrony. 25 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Modes of Ventilation A. Primary breath control variable 26 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Therearetwotypesofdualcontrol.Dualcontrolbetweenbreathsmeansthattheventilatorcontrolspressure duringeachbreathbut adjusts thepressure limit toachievea tidal volume target over several breaths. Alternatively, theventilatorcanswitchbetweenvolumeandpressurecontrolduringasinglebreath(dual controlwithinbreaths,figurebelow). Modes of Ventilation
9. Breathing pattern B. Breath sequence The second component of the breathing pattern specification is the breath sequence. A breath is defined as a positive change in airway flow (inspiration) paired with a negative change in airway flow (expiration), both relative to baseline flow and associated with ventilation of the lungs. But the definition allows the superimposition of, say, a spontaneous breath on a mandatory breath or vice versa. On the other hand, mandatory breaths are superimposedonspontaneousbreaths during high-frequencyoscillatoryventilation. The classification of modes requires the definition of two basic types of breaths: spontaneous and mandatory. A spontaneous breath is a breath for which the patient controls the start time and the tidal volume. That is, the patient both triggers (starts) and cycles (ends) the breath. A spontaneous breath may either beassistedor unassisted. A mandatory breath is a breath for which the machine sets the start time and/or the tidal volume. That is, the machine triggers and/or cyclesthe breath. 2nd Semester 2023-2024 27 Assist Lec.: Athra'a Sabeeh there are three possible sequencesof breaths, designatedas follows: I. ContinuousMandatory Ventilation (CMV): all breaths are mandatory II. ContinuousSpontaneous Ventilation (CSV): all breaths are spontaneous III. Intermittent Mandatory Ventilation (IMV): breaths can be either mandatory or spontaneous.Breaths can occurseparately or breaths can be superimposedon each other. When the mandatory breath is patient-triggered, it is commonly referred to as synchronized IMV (SIMV). However, because the trigger variable can be specified in the description of phase variables, we will use IMV instead ofSIMVto designate generalbreath sequences. When we add the breath sequence to the control variable in classifying a mode, we get a greater ability to discriminate modes. We can distinguish between, say, pressure controlled IMV and pressure controlled CSV. If we confine ourselves to classifying modes based solely on the breathing pattern, we see that there are only eight possibilities: VC-CMV, VC-IMV, PC-CMV, PC-IMV, PC-CSV, DC-CMV, DC-IMV, and DC-CSV. Note that VC-CSV is impossible by definition. 2nd Semester 2023-2024 Assist Lec.: Athra'a Sabeeh 28 29 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Wehavediscussed"controlvariables"andthedifferencesbetweenpressure,volume,anddualcontrolbut,we havenotreallyexplainedwhatismeantby"control"inthefirstplace.Therearetwogeneralwaystocontrola variable;openloopcontrolandclosedloopcontrol.The vast majority of ventilators used in the world provide "conventional" ventilation. This employs breathing patterns that approximate those produced bya normal spontaneouslybreathing person. 2nd Semester 2023-2024 6 Assist Lec.: Athra'a Sabeeh 7 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 Automating Ventilator Lung Volume and Capacity Volumes:There arefourvolumes: (1) tidal volume(Vt) is the volumeofgasinhaled or exhaled duringeach respiratorycycle. (2) inspiratoryreservevolume(IRV)is the maximalvolumeofgas inspiredfromend-inspiration. (3) expiratoryreservevolume(ERV)is the maximalvolumeofgasexhaled fromend-expiration. (4) residualvolume(RV)is the volumeofgas remainingin the lungsfollowingamaximalexhalation. Capacities:There are four capacities, each of which contains two or more primary volumes: (1) total lung capacity (TLC) is the amount of gas contained in the lung at maximal inspiration. (2) vital capacity (VC) is the maximal volume of gas that can be expelled from the lungs by a forceful effort following maximal inspiration, without regard for the time involved. (3) inspiratory capacity (IC) is the maximal volume of gas that can be inspired from the resting expiratory level. (4) functional residual capacity (FRC) is the volume of gas in the lungs at resting end-expiration. Tidal volumes are large enough to clear the anatomical dead space during inspiration and the breathing rates are in the range of normal rates. Gas transport in the airways is dominated by convective flow and mixing in the alveoli occurs by molecular diffusion. There is also a class of "high frequency ventilator" that delivers tidal volumes less than dead space volume at frequencies up to 15 Hz. High frequency ventilators, in theory, minimize the risk of damage to diseased lung tissue that could be caused by volumetric over distention with normal tidal volumes.Control Type Description ExampleControl Scheme ExampleMode Example Ventilator Setpoint Outputmatchesfixedinput Tidalvolumeorpeak pressureheldconstantby adjustingcontrolvariable Pressurecontrol Assist control Pressuresupport SiemensServo Hamilton Galileo PB840 Servo Outputmatchesdynamic input Pressuremade proportionalto volume and/orflow Proportional Assist Automatic Tube Compensation NotavailableinUS DragerEvita4 Setpoint Dual Control Automaticswitchbetween pressureandvolumecontrolto maintain operator defined setpoint Volume control overrides pressurecontrolwith breathifsettidalvolume notmet PressureLimited Ventilation Volume Assured PressureSupport DrigarEvita4 Bird8400ST Adaptive DualControl Automaticadjustmentof pressuresetpointtomaintain anoperatorselectedvolume setpoint Pressure limit adjusted to maintain set tidal volume, using lungmechanics Pressure Regulated Volumecontrol AutoFlow SiemensServo300 DragerEvita4 Optimal Dual Control Automatic adjustment of both pressure and volume setpointto minimizeothervariables Pressurelimitandtidal volume adjustedtominimize workofbreathing,usinglung mechanics AdaptiveSupport Ventilation HamiltonGalileo 32 Assist Lec.: Athra'a Sabeeh 2nd Semester 2023-2024 A.Thephasevariable isasignal that ismeasuredandusedbytheventilator toinitiatesomepart, or phase, of thebreathcycle.Thevariablecausingabreathtobeginis thetriggervariable.Avariablewhose magnitudeisconstrainedtosomemaximumvalueduringinspirationiscalledalimitvariable.Thevariable causingabreathtoendisthecyclevariable.Duringexpiration,theventilatorusuallymaintainssomelevelof pressureatoraboveatmosphericpressure,whichisreferredtoasthebaselinevariable.Thus, to understand ventilators wemustfirstunderstandtheirfourmechanical characteristics:

1. Inputpower
2. Powerconversionandtransmission
3. Controlsystem
4. Output(pressure,volume,andflowwaveforms) The physical model (Pneumatic model) of breathing mechanics most commonly used is a rigid flow conducting tube connectedto anelastic compartment.?Thesimplestmechanical devicewecouldadvise to assistaperson'sbreathingwouldbeahand-driven, syringe-typepumpthat isfittedtotheperson'smouth andnoseusingamask.Avariationof thisistheself inflating, elastic resuscitation bag.?Open loopcontrol isessentiallynocontrol.2.?2.3.

Ventilators are commonly used in the operating room
and in the ICU to deliver mechanical ventilation to the
lungs. In the operating room, ventilation is given to
anaesthetized and often pharmacologically paralyzed
patients with predominantly normal lungs. These
ventilators are relatively simple and are designed to deliver
varying concentrations of oxygen, air, nitrous oxide and
volatile agents to patients through an anesthetic circuit. In
the ICU ventilators are more sophisticated and provide
respiratory supportto patients with respiratoryfailure.
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Breathing (Spiration or Ventilation)
is the process of moving air into and from the lungs to facilitate gas exchange
with the internal environment, mostly to flush out carbon dioxide and bring in
oxygen.
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Respiratory
failure is a state in which the pulmonary oxygen uptake is
soseverely disturbed that the supply of oxygen to and/or removal of carbon
dioxide from the tissues is inadequate. Respiratory failure can be caused
by relative hypoventilation, characterized by an increase in arterial carbon
dioxide tension, increased work of breathing or failure of diffusion at the
alveolar– capillary membrane, characterized by decreased arterial oxygen
tension.
Respiratory failure that require artificial respiratory ventilation is caused by
the following respiratory diseases:

1. Hypoxia, lowoxygencontent in the blood due to improper ventilation.
   This is caused by pulmonary emphysema (stretch alveoli-loss of lung
   elasticity), chronic bronchitis, pulmonary tumors, aspiration pneumonia,
   interstitial fibrosis, or pulmonary infraction (tissue death from lack of
   bloodsupply).


2. Hypercapnia, poor alveolar ventilation causing an accumulation of
   carbon dioxide in the blood. It results from central venous system
   disorder, diseases of nerves and muscle weakness, metabolic
   diseases, and pulmonary emphysema, chronic bronchitis, or lung
   obstruction.
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   Mechanicalventilators
   A mechanical ventilator is an automatic machine
   designedtoprovideallorpartof theworkthebodymust
   producetomovegasintoandoutofthelungs.
   ❑Thesimplestmechanical devicewecouldadvise to
   assistaperson’sbreathingwouldbeahand-driven,
   syringe-typepumpthat isfittedtotheperson’smouth
   andnoseusingamask.Avariationof thisistheself
   inflating, elastic resuscitation bag. Both of these
   requireone-wayvalvearrangements tocauseair to
   flowfromthedeviceintothelungswhenthedeviceis
   compressed, and out from the lungs to the
   atmosphere as the device is expanded. These
   arrangementsarenotautomatic,requiringanoperator
   tosupply theenergy topushthegas into the lungs
   throughthemouthandnose.Therefore,suchdevices
   arenotconsideredmechanicalventilators.
   ❑ Automating Ventilator was designed so that continual operator
   intervention is not needed for safe, desired operation and it
   requires:

1. Astableattachment (interface)of the deviceto the patient,


2. Asourceofenergyto drive the device,


3. Acontrolsystemto regulate the timing and size of breaths


4. Ameans of monitoring the performance of the device and the condition
   of the patient.
   The vast majority of ventilators used in the world provide “conventional”
   ventilation. This employs breathing patterns that approximate those
   produced bya normal spontaneouslybreathing person.
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   Automating Ventilator
   Lung Volume and Capacity
   Volumes:There arefourvolumes:
   (1) tidal volume(Vt) is the volumeofgasinhaled or exhaled duringeach respiratorycycle.
   (2) inspiratoryreservevolume(IRV)is the maximalvolumeofgas inspiredfromend-inspiration.
   (3) expiratoryreservevolume(ERV)is the maximalvolumeofgasexhaled fromend-expiration.
   (4) residualvolume(RV)is the volumeofgas remainingin the lungsfollowingamaximalexhalation.
   Capacities:There are four capacities, each of which contains two or more primary volumes:
   (1) total lung capacity (TLC) is the amount of gas contained in the lung at maximal inspiration.
   (2) vital capacity (VC) is the maximal volume of gas that can be expelled from the lungs by a forceful effort
   following maximal inspiration, without regard for the time involved.
   (3) inspiratory capacity (IC) is the maximal volume of gas that can be inspired from the resting expiratory level.
   (4) functional residual capacity (FRC) is the volume of gas in the lungs at resting end-expiration.
   Tidal volumes are large enough to clear the anatomical dead space during inspiration and the breathing rates are in
   the range of normal rates. Gas transport in the airways is dominated by convective flow and mixing in the alveoli
   occurs by molecular diffusion. There is also a class of “high frequency ventilator” that delivers tidal volumes less
   than dead space volume at frequencies up to 15 Hz. High frequency ventilators, in theory, minimize the risk of
   damage to diseased lung tissue that could be caused by volumetric over distention with normal tidal volumes. While
   this class of ventilator has been studied a great deal over the last two decades, its use is still controversial.
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   Lung volume capacity
   Ventilator-Patient Model
   Ventilators are powered with energy in the form of either electricity or compressed gas. That energy is transmitted
   (by the ventilator's drive mechanism) in a predetermined manner (by the control circuit) to assist or replace the
   patient's muscular effort in performing the work of breathing (the desired output). Thus, to understand ventilators
   wemustfirstunderstandtheirfourmechanical characteristics:


5. Inputpower


6. Powerconversionandtransmission


7. Controlsystem


8. Output(pressure,volume,andflowwaveforms)
   The physical model (Pneumatic model) of breathing mechanics most commonly used is a rigid flow conducting tube
   connectedto anelastic compartment.
   When airway pressure rises above baseline (as indicated by the ventilator’s airway pressure display), inspiration is
   assisted. The pressure driving inspiration is called trans-respiratory system pressure (figure below). It is defined as
   the pressure at the airway opening(mouth, endotracheal tubeor tracheostomy tube)minusthepressure atthe body
   surface. Trans- respiratory system pressure has two components, trans airway pressure (defined as airway opening
   pressureminuslungpressure)andtransthoracic pressure(definedaslungpressureminusbodysurfacepressure).
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   The basic electrical model is a resistor in series with a capacitor, which may be expanded to include two lungs, the
   chest wall, and ventilator circuit properties. This model is a simplification of the actual biological respiratory
   system from the viewpoint of pressure (voltage), volume (charge), and flow (current), but it has been very
   practical. The mathematical model that relates pressure, volume, and flow during ventilation is known as the
   equation ofmotion forthe respiratorysystem:
   Pvent+ Pmus=E.V+R.V
   .
   where
   •
   •
   •
   •
   •
   •
   Pvent is the pressuregeneratedby the ventilator,
   Pmus is the pressuregeneratedby the ventilatormuscles,
   Eis respiratory systemelastance,
   Vis lungvolume,
   Ris respiratorysystemresistance, and
   Vdot is flow (the derivativeofvolumewithrespect to time).
   A pressure controller maintains a consistent airway pressure waveform despite changes in elastance and
   resistance, with volume and flow being dependent on the pressurewaveform and the mechanical properties of
   the respiratory system. In contrast, volume and flow controllers maintain consistent volume and flow
   waveforms despite changing mechanical properties, with airway pressure being the dependent variable. A
   ventilator can control only one variable at a time but may actually switch among them during a breath. Breath
   controlcomplexitygives rise to the needto identifyanddescribe “modes”ofventilation.
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   Multi-compartment model of the respiratory system connected to a
   ventilator using electronic analogs
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   Modern ventilatormachines have two separate but inter
   connectedsystems;apneumaticflowsystemandanelectronic
   controlsystem.
   Thepneumaticflowsystemenablestheflowofgasthroughthe
   ventilator.Thegases(oxygenandmedicalgradeair)enterthe
   air / oxygenmixer which they combine at the required
   percentage.Thegasesthenenteralargereservoirtanktobe
   compressed.Anelectronicallycontrolledflowvalveproportion
   thegasflowfromthereservoirtanktothepatient'sbreathing
   circuit. Insomeventilators,anaircompressorisusedinplace
   of acompressedair tank.Ventilatorsrequireelectricpower,
   oxygen, and compressed air usually supplied via external
   powersourceaswellasviahospital’scentralgassupply(with
   supplypressureofapproximately3–6bar). Inareaswithout
   centralgassupplyorduringtransportationofpatientswithin
   thehospital, it isnecessary toensurethe functioningof the
   devicebyothermeans.Potential solutions includetheuseof
   separate compressors, compressed gas cylinder packs, and
   accumulators.
   Ventilator Functional Block Diagram
   Gas mixer allowsthe user to vary theoxygen concentration of inspiratory
   gas between 21%and100%byvolume:
   a.
   Mechanical gas mixers(old technology).
   b.
   Electronically-controlled gas mixer integrated in ventilator(standard now).
   Gas mixers usually responsible for ensuring that breathing gas to be supplied is
   prepared and delivered in required quantity and rate. It is often the threshold
   ranges whichposethegreatest challenges to thesemeteringsystems. For volume
   of 20 mlwith an oxygen concentration of 30% by volume, 17.7 mlof gasmust be
   deliveredviacompressedair valveand2.3mlviaoxygenvalve.
   The pressure or flow generator is responsible for delivering mixed gas prepared
   by the gas mixer according to selected ventilation parameters. Flow generator is
   a controlled valve whose output provides defined gas flow with output pressure
   is not specified. Pressure generator behaves similar to compressor, whose output
   provides defined pressure with unspecified gas flow. It’s often used to drive
   ventilators notdependentoncompressedairthat useambient air forventilation.
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   Breathing System
   Breathing system forms interface between patient and the ventilator. Clinical ventilators are usually connected to
   patient via inspiratory and expiratory hose (dual-hose circuit). Expiratory valve is closed during the inspiratory
   phase where gas flow delivered through inspiratory portpasses through breathing gas humidifier before entering
   patient’s lungs to make it adapted to climatic conditions in patient’s lungs. After inspiratory phase, patient exhales
   when expiratory valve is opened, expiratory gas passes through ventilator again, but not reused for following
   inspiration. Based on this characteristic, the breathing systems of ventilators are also referred to as non
   rebreathing circuits.
   Gas Humidifier
   Humidifiers are used to warm and humidify inspiratory gas. Dry and relatively cool supply gas would dry out the
   patient’s airways with risk of causing irreversible damage to the ciliated epithelium. Active gas humidifiers are
   located in the inspiratory limb and use electrical energy to heat a water bath. When the cold, dry gas passes over
   the water surface it absorbs water molecules and is thuswarmed and humidified. Example: Pass-over humidifiers
   and Bubble- through humidifiers. Passive breathing gas humidifiers, termed heat and moisture exchangers
   (HMEs), are placed close to patient and designed to buffer significant fraction of moisture and heat expired by
   patient. Retained moistureis then usedto conditioninspiredgas passingthrough HMEduringnextinspiration.
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   17 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Expiratory (Exhalation) Valve
   Expiratory valve switches between inspiration and expiration phases of Ventilation If valve is not
   opened completely during expiration, positive end-expiratory pressure (PEEP) is created in lungs.
   PEEP is therapeutically important as it increases gas exchange surface oflungs. Adequate PEEP can
   also prevent collapse of individual alveolar areas. If expiratory valve is controlled during
   inspiratory phase, it can compensate for undesired pressure rises in breathing system Caused, for
   example, bypatient coughing.
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   19 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   OperatingandDisplayUnit
   Operatinganddisplayunitistheinterfacebetweenventilatoranduser.Oftentouchscreensdesignedtodisplay
   pressureandflowcurvesaswellasmultiplemenusforsettingdifferentventilationmodes,adjustingalarmlimits
   ormeasuredvalueoverviews,etc.Parametersettingsenteredinoperatingunitcontroldevicecomponentsand
   thereforedetermineventilationpatternappliedtothepatient.
   AlarmSystemandPatientMonitor
   Ensuresthatventilationparametersset inoperatinganddisplayunitareactuallyapplied.Thissystemissues
   audibleandvisualalarmstoalertstaff tocritical changes inthepatient’sconditionor technicalmalfunctions
   monitorsthefollowing:

1. Inspiratoryoxygenconcentration(controlledbythegasmixer)


2. VentilationPressureandVolume(tomonitorthepressure/flowgenerator)


3. Inspiratorybreathinggastemperature(whenusingactivegashumidifier)
   Patientmonitoringisusedtomonitorthepatient’svitalfunctions


4. Electrocardiogram(ECG)


5. Bloodpressure(noninvasiveand/orinvasive)


6. Oxygensaturation


7. Carbondioxideconcentrationinthebreathinggas
   20 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Modernventilatormachinesconsistoftwoseparatebutinter-connectedsystems:thepneumaticflowsystemand
   anelectroniccontrolsystem.
   Thepneumaticflowsystemenablestheflowofgasthroughtheventilator.Oxygenandmedicalgradeairenterthe
   ventilatorat3.5bar(50psi)pressurethroughbuilt-in0.1micronfilters.Thenormaloperatingrangeis2to6bar
   or28to86psi.Thesegassesenter theair/oxygenmixerwheretheycombineat therequiredpercentageand
   reducedinpressureto350cmH2O.Thegassesthenenteralargereservoirtankwhichholdsabout8litersof
   mixedgasses,whencompressedto350cmH2O.Anelectronicallycontrolledflowvalveproportionsthegasflow
   fromthereservoirtanktothepatientbreathingcircuit.Insomeventilators,anaircompressorisusedinplaceofa
   compressedairtank.Theprimaryobjectiveofthedeviceistoensureproperlevelofoxygenintheinspiratoryair
   anddeliveratidalvolumeaccordingtotheclinicalrequirements.
   Asthegassesleavetheventilator, theypassbyanoxygenanalyzer,asafetyambientairinletvalveandaback-up
   mechanicaloverpressurevalve.Theambientvalveprovidesthepatienttheabilitytobreatheroomairwhenthe
   ventilatorfailsorthepressureinthepatientcircuitdropsbelow–10cmofH2O.Inthepatientbreathingcircuitis
   abi-directionalflowsensortomeasurethegasflows.Theexhaledgassesexitthroughanelectronicallycontrolled
   exhalationvalve locatedat theventilator.With the introductionofmicroprocessors forcontrol ofmetering
   devices,electromechanicalvalveshavegainedpopularity.Themicroprocessorcontrolseachvalvetodeliverthe
   desiredinspiratoryairandoxygenflowsformandatoryandspontaneousventilation.Ahighpressurevalveisused
   toprovidesafetyincasethepressureinthepatientcircuitexceeds110cmH2O.
   Types of Ventilators
   ModernVentilators(Microprocessorcontrolled)
   The electronic control system may use one or more microprocessors and software to perform monitoring and
   control functions in a ventilator. These parameters include setting of the respiration rate, flow waveform, tidal
   volume, and oxygen concentration of the delivered breath, peak flow and PEEP. The PEEP selected in the
   mandatory mode is only used for controlof exhalation flow. The microprocessor utilizes the above parameters to
   compute the desired inspiratory flow trajectory. The system consists of monitors for pressure flow and oxygen
   fraction. The sensors are connected to electronic processing circuits which makes them available for digital
   readouts. The signals are also compared with pre-set alarm levels so that if they fall outside a pre-determined
   normal range, alarms are sounded. The pressure sensors are normally of semiconductor strain gauge typeplaced
   in a bridge configuration. For measurement of fraction of oxygen in the inspired air, afuel cell type oxygen sensor
   is used.This sensorgenerates acurrentproportionaltopO2.
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   22 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Anewtechniqueforventilatingpatientsat frequenciesmuchhigher thantherespirationratehasrecentlybeen
   introduced.ThismethodhasbeenshowntoimproveCO2washoutandprovideadequateoxygenationwithoutthe
   requirementforhighinspiratorypressures.Thekeyprincipleinthistechniqueistoprovidetidalvolumesequalto
   orsmallerthanthedeadspace,atveryhighrates. Inconventionalpositivepressureventilation,CO2eliminationis
   directlycontrolledbytheamountofappliedminuteventilation.However,itisknownthatmeanairwaypressureis
   theparameterthatbestcorrelateswithimprovementinoxygenation.Gastransportduringconventionalventilation
   isattributed totwobasicmechanisms: (i)convectionor flowof gas throughtheconductingairways, and(ii)
   moleculardiffusionof gasses intothealveoli andpulmonarycapillaries. Thetidalvolume(VT)applied tothe
   patientattheY-piececanbedividedintothevolumeusedtoventilatethedeadspace(VD)andthealveolarvolume
   (VTalv).Onlythealveolarvolumetakespartinthegasexchangeprocess.Therefore,
   HighFrequencyVentilators
   V Talv=VT–VD
   Theportionofthetidalvolumeusedtoventilatethedeadspacedoesnottakepartincapillarygasexchangeandis
   thereforewasted. Toovercome theproblemofwastedventilation inconventionalventilation, the inspiratory
   pressureisincreasedinordertoincreasethetotal tidalvolume.Unfortunately,however, thisalsoincreasesthe
   mechanicalstressonthelungandhasbeenassociatedwithvarioustraumas.Highfrequencyventilationhasbeen
   showntoprovideadequatealveolarventilationandoxygenationwithout therequirement forhighinspiratory
   pressures.Theventilatorgenerateshighfrequencyratefrom5to20Hz(300to1200pulse/minute).Although
   severalmethodsareavailabletogeneratethehighfrequencypressurewaves, theBabylog8000makesuseofan
   oscillatingdiaphragmmechanism.
   23 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Thismechanismis computer-controlled and canpreciselydetermine the shape of thepressure swings. An
   alternativemethodofachievingHFventilationisbasedonthejetprincipleinwhichasmalldiametertubeispassed
   downatrachealcannulaandiseitherterminatedatitsdistalendorextendedintothetracheaitself.Shortpulsesof
   higherpressureoxygenareintroducedintotheairwaythroughthecannulaatfrequencieswellabovethenormal
   respirationrate.Thistechniquehasthedisadvantageofforcingvolumeintothepatientandthenleavingthepatient
   toexhalepassively,whichmayleadtosometrappedvolumeinsidethelungincreasingthemeanlungpressure.
   Thisproblemisovercomebyensuringthatthepressureduringtheexhalationphaseisnegativewithrespecttothe
   setPEEP.
   24 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Themaintaskofahumidifieristoreplacehumidityintheupperairpassageswhichhasbeenlostbyintubation.
   Thehumidityshouldbeascloseto100%aspossible,orspeakingintermsofwater,theabsolutecontentperliter
   breathinggasshouldbemorethan30mg,regardlessofenvironmentalconditions.Therefore,inordertoprevent
   damagetothepatient’slungs,theairoroxygenappliedduringrespiratorytherapymustbehumidified.Thus,all
   ventilatorsincludearrangementstohumidifytheair,eitherbyheatvaporization(stream)orbybubblinganair
   streamthroughajarofwater.Whenwaterorsometypeofmedicationsuspendedintheinspiredairasan
   aerosol istobeadministeredtothepatient, adevicecalledanebulizer isused. Inthisdevice, thewateror
   medicationispickedupbyahighvelocityjetofair/oxygenandmadetoimpactagainstoneormorebafflesto
   breakthesubstanceintocontrolled-sizeddropletswhicharethenappliedtothepatientviaarespirator.More
   effectiveandefficientnebulizersarebasedontheuseofhighintensityultrasoundenergywhichvibratesthe
   substance(waterormedication) toproduceahighvolumeofminuteparticles.Ultrasonicnebulizersdonot
   dependuponbreathinggasforoperationandthustherapeuticagentscanbeconvenientlyadministeredduring
   ventilationprocedure.Aspiratorsareoftenincludedaspartofaventilator toremovemucusandotherfluids
   fromtheairways.Alternatively,aseparatesuctiondevicemaybeutilizedtoachievethesamepurpose.
   Humidifiers,NebulizersandAspirators


8. Breathing pattern
   I.VolumeControl (VC)
   Aventilator canbeclassifiedas
   either a pressure, volume, or
   flow controller. When
   classifyingmodesof ventilation,
   we do not need to be so
   specific. Because control of
   volume implies control of flow
   andviceversa,wecanrefer to
   twobasicmodesofventilation:
   volume control and pressure
   control.
   II. Pressure Control (PC)
   Pressure controlmeans that
   the airway pressure
   waveform is preset (for
   example by setting peak
   inspiratorypressureandend
   expiratory pressure). Tidal
   volume and inspiratory flow
   are then dependent on
   these settings and the
   elastance and resistance of
   therespiratorysystem.
   Dual Control (DC)
   There are clinical advantages and
   disadvantages to volume and pressure
   control. Simply put, volume control results
   in amore stableminute ventilation (and
   hence more stable gas exchange) than
   pressure control if lung mechanics are
   unstable. On the other hand, pressure
   control allows better synchronizationwith
   thepatient because inspiratoryvolumeand
   floware not limited to arbitrary preset
   values. While it ispossibletocontrol only
   one variable at a time, a ventilator can
   automatically switch between pressure
   control andvolume control in an attempt
   to guarantee minute ventilation while
   maximizingpatientsynchrony.
   25 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Modes of Ventilation
   A. Primary breath control variable
   26 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Therearetwotypesofdualcontrol.Dualcontrolbetweenbreathsmeansthattheventilatorcontrolspressure
   duringeachbreathbut adjusts thepressure limit toachievea tidal volume target over several breaths.
   Alternatively, theventilatorcanswitchbetweenvolumeandpressurecontrolduringasinglebreath(dual
   controlwithinbreaths,figurebelow).
   Modes of Ventilation


9. Breathing pattern
   B. Breath sequence
   The second component of the breathing pattern specification is the breath sequence. A breath is defined as a
   positive change in airway flow (inspiration) paired with a negative change in airway flow (expiration), both
   relative to baseline flow and associated with ventilation of the lungs. But the definition allows the
   superimposition of, say, a spontaneous breath on a mandatory breath or vice versa. On the other hand,
   mandatory breaths are superimposedonspontaneousbreaths during high-frequencyoscillatoryventilation.
   The classification of modes requires the definition of two basic types of breaths: spontaneous and
   mandatory. A spontaneous breath is a breath for which the patient controls the start time and the tidal
   volume. That is, the patient both triggers (starts) and cycles (ends) the breath. A spontaneous breath may
   either beassistedor unassisted.
   A mandatory breath is a breath for which the machine sets the start time and/or the tidal volume. That is, the
   machine triggers and/or cyclesthe breath.
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   Assist Lec.: Athra’a Sabeeh
   there are three possible sequencesof breaths, designatedas follows:
   I.
   ContinuousMandatory Ventilation (CMV): all breaths are mandatory
   II. ContinuousSpontaneous Ventilation (CSV): all breaths are spontaneous
   III. Intermittent Mandatory Ventilation (IMV): breaths can be either mandatory or
   spontaneous.Breaths can occurseparately or breaths can be superimposedon each other.
   When the mandatory breath is patient-triggered, it is commonly referred to as synchronized IMV (SIMV).
   However, because the trigger variable can be specified in the description of phase variables, we will use IMV
   instead ofSIMVto designate generalbreath sequences.
   When we add the breath sequence to the control variable in classifying a mode, we get a greater ability to
   discriminate modes. We can distinguish between, say, pressure controlled IMV and pressure controlled CSV. If
   we confine ourselves to classifying modes based solely on the breathing pattern, we see that there are only
   eight possibilities: VC-CMV, VC-IMV, PC-CMV, PC-IMV, PC-CSV, DC-CMV, DC-IMV, and DC-CSV. Note that VC-CSV
   is impossible by definition.
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   29 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
   Wehavediscussed“controlvariables”andthedifferencesbetweenpressure,volume,anddualcontrolbut,we
   havenotreallyexplainedwhatismeantby“control”inthefirstplace.Therearetwogeneralwaystocontrola
   variable;openloopcontrolandclosedloopcontrol.
   ❑Open loopcontrol isessentiallynocontrol. Forexample, earlyhighfrequencyventilatorssimply
   generatedpulsesofgasflowwithoutmeasurementorcontrolofpressure,volume,orflow.Flowintothe
   patientwasafunctionof therelativeimpedancesof therespiratorysystemandtheexhalationmanifold.
   Thus,bothpressureandvolumewereaffectedbyanydisturbancesinthesystem, suchaschanginglung
   mechanics,thepatient’sventilatoryefforts,andleaks.
   ❑Closed loopcontrol is an improvement in that thedeliveredpressure, volume, and flowcanbe
   measuredandusedas feedback information tocontrol thedrivingmechanism. Theactual output is
   measured(asafeedbacksignal)andcomparedtothedesiredvalue(intendedbythesetinput).Ifthereisa
   difference,anerrorsignalissenttothecontrollertoadjusttheoutputtowardsthedesiredoutput.Thus,
   inspiratoryvolumes, flows,andpressurescanbemadetomatchorfollowspecifiedinputvaluesdespite
   disturbancessuchaschangesinpatientloadandminorleaksinthesystem.Notethatclosedloopcontrol
   doesnotrequireanelectronicsystem.Asimplepressureregulatorisanexampleofmechanical feedback
   control.


10. Control type
    30 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
    Theventilatortypicallymonitorsbothexhaledvolumeandrespiratorysystemcomplianceonabreath-by-breath
    basis.Then, ifthetidalvolumefallsbelowthedesiredvalue,theventilatoradjuststhesetpressurelimittobring
    thetidalvolumeclosertothetarget(requiredpressurechange=exhaledvolume/calculatedcompliance).We
    say“target” tidalvolumebecausetheventilatoraims toachieveit,but forvariousreasons,maymiss(which
    shouldtriggeranalarm).ExamplesofadaptivedualcontrolcanbeseeninmodeslikePressureRegulatedVolume
    Control(Servo300ventilator)andAutoFlow(DrägerEvita4ventilator).
    To date, themost advanced control strategymay be called optimumdual control. Here, the ventilator
    automatically adjustsboth thepressureandvolume setpoints tooptimizeotherperformancevariables as
    respiratorymechanics change. The termoptimum implies that somemeasure of systemperformance is
    maximizedorminimized.Theonlyexampleof thisatpresent istheAdaptiveSupportmodeontheHamilton
    Galileo(perhapsnotthebestchoiceofnamesinlightof thisclassificationscheme). Inthismode,eachbreathis
    pressurecontrolledandthepressurelimitisautomaticallyadjustedbetweenbreathstomeetanoptimumtidal
    volume.
    Theoptimumtidalvolumeisbasedontheestimatedminutealveolarventilationandtheoptimalfrequency.The
    minuteventilationisestimatedfromthepatient’sbodyweight.Theoptimalfrequencyisbasedonthemeasured
    expiratorytimeconstantusinganequationthatminimizes theworkofbreathing. Thecontrol softwarealso
    implements“lungprotectivestrategies”bynotallowingtidalvolumeorfrequencytogettoolargeortoosmall.
    Forexample, themaximumfrequencyisbasedonaminimuminspiratorytimeequal toonetimeconstantand
    minimumexpiratorytimeoftwotimeconstants.
    Control
    Type Description ExampleControl
    Scheme ExampleMode Example
    Ventilator
    Setpoint Outputmatchesfixedinput
    Tidalvolumeorpeak
    pressureheldconstantby
    adjustingcontrolvariable
    Pressurecontrol
    Assist control
    Pressuresupport
    SiemensServo
    Hamilton Galileo
    PB840
    Servo Outputmatchesdynamic
    input
    Pressuremade
    proportionalto volume
    and/orflow
    Proportional
    Assist
    Automatic Tube
    Compensation
    NotavailableinUS
    DragerEvita4
    Setpoint Dual
    Control
    Automaticswitchbetween
    pressureandvolumecontrolto
    maintain operator defined
    setpoint
    Volume control overrides
    pressurecontrolwith
    breathifsettidalvolume
    notmet
    PressureLimited
    Ventilation
    Volume Assured
    PressureSupport
    DrigarEvita4
    Bird8400ST
    Adaptive
    DualControl
    Automaticadjustmentof
    pressuresetpointtomaintain
    anoperatorselectedvolume
    setpoint
    Pressure limit adjusted to
    maintain set tidal volume,
    using lungmechanics
    Pressure
    Regulated
    Volumecontrol
    AutoFlow
    SiemensServo300
    DragerEvita4
    Optimal Dual
    Control
    Automatic adjustment of both
    pressure and volume setpointto
    minimizeothervariables
    Pressurelimitandtidal
    volume adjustedtominimize
    workofbreathing,usinglung
    mechanics
    AdaptiveSupport
    Ventilation HamiltonGalileo
    32 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
    A.Thephasevariable isasignal that ismeasuredandusedbytheventilator toinitiatesomepart, or
    phase, of thebreathcycle.Thevariablecausingabreathtobeginis thetriggervariable.Avariablewhose
    magnitudeisconstrainedtosomemaximumvalueduringinspirationiscalledalimitvariable.Thevariable
    causingabreathtoendisthecyclevariable.Duringexpiration,theventilatorusuallymaintainssomelevelof
    pressureatoraboveatmosphericpressure,whichisreferredtoasthebaselinevariable.
    • Modesofventilationcanbedescribedatvariouslevelsofdetail,dependingonhowandwithwhomwe
    needtocommunicate.Atthehighestlevelofdetail,wecanfullycharacterizeamodebyaddingthespecific
    controlstrategyitemploys.Thisbeginswithnamingthephasevariables(pressure,volume,flow,andtime),
    followedbydetailingtheoperational logic, and, if necessary, givingtheparametervaluesused inthe
    conditionalstatements.
    Amodeisapatternofmandatoryandspontaneousbreaths.Becausethesebreathsmayvarydrasticallyinthe
    way they arecontrolled,wemust specify thephasevariables for both typesof breaths. For example, a
    ventilatormayprovidevolumecontrolledmandatorybreathsthataretimetriggered, flowlimited,andvolume
    cycled, interspersedwithpressure controlled spontaneousbreaths that arepressure triggered, pressure
    limited,andflowcycled.Eachtypeofbreathhasacompletelydifferentsetofphasevariables.


11. Control Strategy
    33 Assist Lec.: Athra’a Sabeeh 2nd Semester 2023-2024
    B.OperationalLogic
    Ventilatorscanalsousepressure,volume,flow,ortime(andtheirderivativessuchasminuteventilation)as
    conditional variables. Aconditional variable isusedbyaventilator’soperational logic systemtomake
    decisions. Theoperational logicof a ventilator is a simpledescriptionof howthe computer uses the
    conditionalvariables.Operationallogicoftentakestheformof“if-then”statements.Thatis, ifthevalueofa
    conditionalvariablereachessomepresetlevel,thensomeactionoccurstochangetheventilatorypattern.
    Forexample, ifapresettimeintervalhaselapsed(thesighinterval), thentheventilatorswitchestothesigh
    pattern.Anotherexampleistheswitchbetweenpatient-triggeredbreathsandmachine-triggeredbreaths
    thatoccurduringintermittentmandatoryventilation.Anevenmoresophisticatedexampleistheoperational
    logicfordualcontrolwithinbreaths.
    Classification of Ventilators
    1.Basedonthe Methodof Initiatingthe InspiratoryPhase
    •Controller: A ventilator which operates independent of the patient’s inspiratory effort. The inspiration is
    initiated by a mechanism which is controlled with respect to time, pressure or another similar factor.
    Controlled ventilation is required forpatients whoare unableto breathe ontheir own.
    •Assistor: A ventilator which augments the inspiration of the patient by operating in response to the patient’s
    inspiratory effort. A pressure sensor detects the slight negative pressure that occurs each time the patient
    attempts to inhale and triggers the process of inflatingthe lungs. Thus the ventilator helps the patientto inspire
    when needed. Asensitivity adjustmentprovided on theequipmenthelps to select the amountof effortrequired
    on the patient’s part to trigger the inspiration process. The assist mode is required for those patients who are
    able to breathe but are unable to inhale a sufficient amount of air or for whom breathing requires a great deal
    of effort.
    •Assistor/Controller:A ventilatorwhich combines boththe controller andassistor
    functions. In these devices, if the patient fails to breathe within a pre-determined time, a timer automatically
    triggers the inspiration process to inflate the lungs. Therefore, the breathing is controlled by the patient as long
    as it is possible, but in case the patient should fail to do so, the machine is able to take over the function. Such
    devicesare mostfrequentlyusedin critical care units.
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12. BasedonPowerTransmission
    •Direct Power Transmission: A ventilator which delivers the gas directly from the source of compressed gas to
    the patient.
    •Indirect Power Transmission: A ventilator which has separate patient and power systems. Thepressure in the
    powersystemdeterminesthe flowrate.


13. Basedon PressurePattern
    •Positive-Atmosphere: A ventilator which produces apositive pressure in the patient’s lungs during inspiration,
    withan end expiratory pressure thatis equal to theatmosphericpressure. In this mode, themean airwaypressure
    is always higher than the atmospheric pressure and the patient normally breathes spontaneously with this mode
    of operation.
    •Positive-Negative: A ventilator which produces apositive pressure in the patient’s lungs during inspiration and
    below atmospheric pressure in the airway during part of expiratory phase. A positive-negative pressure pattern
    results in a lowmean airwaypressure.
    •Positive-Positive: A ventilator whichproduces a positive pressure in the patient’s lungs during inspiration, with
    an end expiratory pressure that is greater than the atmospheric pressure. In order to obtain an end expiratory
    pressure that is greater than the atmospheric pressure, it is necessary to start the inspiratory phase before the
    airwaypressurereachesthe atmosphericpressure.
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14. BasedontheTypeofSafetyLimit
    •Volume Limited: A ventilator in which pre-determined volume cannot be exceeded during inspiration. Volume
    limit normallyrefersto tidal volume.
    •Pressure Limited: A ventilator designed in such a way that predetermined pressure cannot be exceeded during
    inspiration.
    •Time Limited: A ventilator in which predetermined phase time cannot be exceeded. It limits the expiratory
    phase time if the patient does not initiate the inspiratory phase and is common to ventilators used for assisted
    ventilation.


15. BasedonCyclingControl
    •Cyclingfrom InspirationtoExpiration


16. VolumeCycled:Aventilator whichstarts the expiratory phaseafter a presettidal volumehasbeen delivered
    into the patient circuit. This device normally has a pressure over-ride valve so that if, while the machine is in
    the process of administering the set volume, the pressure exceeds a predetermined maximal value, the
    ventilator willcycle whether or notthe appropriatevolumehasbeen administered.


17. PressureCycled:Aventilator whichbegins the expiratoryphaseafter apresetpressurehasbeen attained.


18. TimeCycled: Aventilator which initiates the expiratory phase after a preset time period for the inspiratory
    phasehas passed.
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    CyclingfromExpirationtoInspiration


19. Pressure Cycled: A ventilator which begins the inspiratory phase after a pre-set end expiratory pressure
    has been attained.


20. Time Cycled: A ventilator which initiates the inspiratory phase after a preset time period for the
    expiratoryphase has passed.


21. Patient Inspiratory Effort Cycled: A ventilator which starts the inspiratory phase in response to the
    inspiratory effort.


22. BasedontheSourceofPower
    •Pneumatic:A ventilator poweredbycompressedgas.
    •Electric:A ventilatorpoweredby an electrical device suchas an electric motor,or similar gadget
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    Maintenance and troubleshooting


23. Regular Inspection
    Often, the most straightforward preventative maintenance for ventilators is some of the most effective. For
    instance, regularly performing quick checks of the systems will go a long way. This involves a brief visual
    inspection for anything amiss in the wiring, console, or screens. It also involves running a performancecheck to
    makesureallthemodesof theventilator and the variousalarmsareworkingcorrectly. This may seem obvious,
    but amid the daily rush of tending to patients in a pandemic and flu season, it's easy to overlook simple
    equipmentinspections.


24. Examine BatteryLife
    You will usually only need to change your ventilator batteries once a year. However, it's important to
    periodically check the ventilator's battery life, especially for ventilators that experience a high volume of
    patients. This can be done by unplugging the AC line and checking to see if the ventilator still functions.
    Facilities should only do this periodically, and, as much as possible, you should make sure the ventilators are
    notrunninginthe battery modeunlessit's necessary.
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    Maintenance and troubleshooting


25. Change Filters
    A ventilator's filter protects the patient from inhaling unsafe materials and protects the machine and those
    tending to the patient from encountering anything harmful that may be on the patient's breath. Making sure
    these filters are clean is essential. Medical facilities need to check the specific guidelines of how often they need
    to change differentventilatorfilters and whether the frequencyvariesdependingonpatientvolume.


26. Regular Disinfecting
    Disinfecting equipment is standard in hospital settings, but to keep ventilators running properly, disinfecting
    should not end with the console and tubing. If your ventilators use collector vials, you must remove and clean
    them often, sometimes even daily, when they experience high use. And, of course, facilities should always
    disinfect all respiratory equipment before using it on a new patient. It is important to regularly perform
    maintenance on all of the ventilators in your facility. The well- being of patients and providing exceptional care
    is the priority of every healthcare professional. By ensuring that your equipment is properly maintained, you
    are able to focuson whatis important.
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    40
    Block diagram of a ventilator