VENTILATOR BASICS AND GRAPHICS DR.AMENA FATIMA

COMMON TERMS

Pressures PIP- peak inspiratory pressure:amount of pressure generated to deliver prescribed tidal volume. Varies depending upon resistance or compliance.

CAPACITIES VITAL CAPACITY (VC):Volume ofgas exhaled after deepest possible inspiration FUNCTIONAL RESIDUAL CAPACITY :volume of air remaining in lungs at the end of a normal expiration.This is the volume where gas exchange is constantly taking place. TOTAL LUNG CAPACITY:max vol of air in the lungs after a max inspiration.

RESISTANCE Opposition to flow of air through the airways.{tissue 20% +airway (Raw) 80%} Raw=peak pressure(beginning)-plateau pressure(alveoli)/flow. Raw directly proportion to length and flow,inversely to radius(r4)

COMPLIANCE It is the relative ease with which the lung can be stretched with a given force. C= delta V/delta P STATIC COMPLIANCE-while there is no gases flows in or out of the lungs.(70-100 ml of H2O) CST=exhaled tidal volume/plateau pressue –PEEP DYNAMIC COMPLIANCE-while gases are moving in the lungs.(50-80ml H2O) CDYN=exhaled tidal volume/PIP-PEEP

TIME CONSTANT Time required, in seconds, to inflate a lung region to % of its filling capacity if the filling pressure was to remain constant. T=R xC

TIDAL VOLUME The amt of gas moved into or out of the lung in a single normal inspiration or expiration. 5-8ml/kg (350ml) vol reaching alveoli +2ml/kg (150ml) vol in conducting airway,,the anatomical dead space. TV=minute ventilation/RR

WORK OF BREATHING It consist of mechanical work-by respiratory muscles to overcome elastic force (compliance) and non-elastic force(resistance) to expand chest wall and lungs AND by breathing apparatus-circuit+ETT. Metabolic work-oxygen consumption of respiratory muscles.O2 cost of breathing(5%) Calculated by area under pressure-volume curve. Increased WOB if inc.RR,use of accessory muscles of respiration,abnormal thoraco abdominal movements,>5% of total O2 consumption.

Phases of respiration Expiratory-inspiratory changeover Inspiration Inspiratory –expiratory changeover expiration

Phase variables Trigger variable-that initiates inspiration Limit variable –places a maximum value on parameter chosen to be controlled during inspiration viz.,pressure,volume,flow or time. Cycle variable-variable causing a breath to end Baseline variable-describes what is happening to the breath during expiration.

Sensitivity Also known as triggering effort. It is a ventilator setting contolled by clinician and is the inspiratory effort that the patient must apply to initiate inspiration. If setting is too low-pt must generate more work to trigger gas flow. If setting is too high-auto cycling of ventilator occurs.

Trigger variable Time trigger-when ventilator initiates a breath at a preset time interval,determined by resp frequency.(controlled or mandatory breath) Pressure trigger-here a decreased in pressure within inspiratory circuit is sensed and insp begins.normal sensitivity setting here is -0.5to -2 cm of H2O.take into consideration if peep is present. with pressure triggering the patient works to create the neg pressure in circuit and continues this work for a period (in millisec)known as lag time.

Trigger variable Flow triggering-a base flow of 5-10 l/min is set to ventilator and the clinician has to set how much the expiratory flow has to be decreased by the pt to initiate inspiration.it is usually 1-3l/min.

Limit variable Preset target value for pressure,volume or flow that cannot be exceeded. It has a max setting but doesnot cycled the ventilator.

Cycled variable Volume cycled-the ventilator cycles to end inspiration and begin expiration when a predetermined volume is delivered in pts circuit. Time cycled-inspiration ends and expiration begin after a pre determined time interval is reached.it can be done by simply timing mechanism or by setting the rate and adjusting the I:E ratio or percentage of inspiratory time. Pressure cycled-insp ends and exp begins when a predetermined max pressure is reached. Flow cycled-insp ends and exp begins when the flow rate decays to a predetermined percentage of its peak value-this crical flow rate in which cycling occurs is the terminal flow rate.

Baseline variable It is the variable controlled during expiration time…,usually pressure is the variable controlled here.it is zero if the setting is at atmospheric pressure or the set PEEP when applied.

Inspiratory pause When the lungs are held in an inflated state at a set pressure or volume for a specified time(<2 sec) at the end of inspiration. Also called as inspiratory plateau or inflation hold.the readind of p-plateau taken at this point.

Inspiratory Pause } Inspiration Flow (L/min) Time (sec) Expiration

Types of breath Machine cycled Patient cycled Mandatory breath-that is triggered,limited and cycled by ventilator.( tot WOB) Assissted breath-triggered by pt ,then limited and cycled by ventilator. Supported breath-triggered by patient,limited by ventilator and cycled by patient. Spontaneous breath-triggered,limited and cycled by patient.(tot WOB)

Spontaneous Breath Inspiration Time (sec) Flow (L/min) Expiration

Mechanical Breath Inspiration Time (sec) Flow (L/min) Expiration

Spontaneous Breath Expiration Paw (cm H20) Time (sec) Inspiration

Peak Inspiratory Pressure Mechanical Breath Peak Inspiratory Pressure PIP Paw (cm H2O) Inspiration Expiration TI TE } PEEP Time (sec)

Typical Flow Patterns SQUARE DECELERATING ACCELERATING SINE

Mechanical Ventilation Graphics SCALARS LOOPS

scalars When pressure,volume or flow are plotted against time. Variables on y-axis,time on x-axis Flow/time Pressure /time Volume/time

Loops When ventilator variables plotted against ecah other. Volume/pressure loop Flow/volume loop

Flow/time scalar Flow in l/min on y-axis,time in sec on x-axis. Flow above zero line is insp and below is expiratory. Flow can be constant or decelerating. Flow not affected by pt lung mechanics. Uses:1.insp and exp flow rates.2.type of breath(vol/press control).3.type of inspiratory flow pattern(in vol ventilation).4.adequacy of insp time.5.presence of auto-PEEP.6.expiratory resistance and response to bronchodilators.7.presence and degree of continuous air leaks.

Mechanical Breath Inspiration Time (sec) Flow (L/min) Expiration

Inspiratory Flow Pattern Beginning of expiration exhalation valve opens Peak inspiratory flow rate PIFR Inspiration Insp. time TI Expiratory Time TE Flow (L/min) Total cycle time TCT Time (sec) Beginning of inspiration exhalation valve closes Expiration

Expiratory Flow Pattern Beginning of expiration exhalation valve opens Inspiration Expiratory time TE Time (sec) Flow (L/min) Duration of expiratory flow Expiration Peak Expiratory Flow Rate PEFR

Inadequate Inspiratory Flow Patient’s effort Active Inspiration Normal Abnormal Time (sec) Flow (L/min)

Air Trapping Normal Patient Time (sec) Flow (L/min) } Expiration Inspiration Normal Patient Time (sec) Flow (L/min) } Air Trapping Auto-PEEP Expiration

Response to Bronchodilator Before After Time (sec) Flow (L/min) Long TE PEFR Shorter TE Higher PEFR

volume/time scalar Vol of gas in ml on y-axis and time in sec on x-axis.insp vol by up slpoe and exp vol on down slope as the set tidal volume is reached. Uses: air leak or air trapping.

Inspiratory Tidal Volume Volume vs Time Inspiratory Tidal Volume Volume (ml) Inspiration Expiration TI Time (sec)

Air Leak/Air Trapping Volume (ml) Volume lost Time (sec)

Pressure/time scalar Pressure in cm of H2O on y-axis and time in sec on x-axis.the waveform rises at 0 at base line or from the applied PEEP. The press curve resembles a shark fin,,negative deflection shows pt’s insp efforts.the depth denotes WOB( as in auto-peep,pneumothorax) Uses:1.breath type delivered.,2.pt versus machine trigger.,3.work required to trigger the breath.,4.breathing timing.,5. adequacy of insp flow.,6. airway pressure.

Peak Inspiratory Pressure Mechanical Breath Peak Inspiratory Pressure PIP Paw (cm H2O) Inspiration Expiration TI TE } PEEP Time (sec)

CONTROLLED BREATH (Time Triggered) Mechanical Paw (cm H2O) Time (sec) Time Triggered Breath

Assisted Breath (Patient Triggered) Mechanical Paw (cm H2O) Time (sec) Patient Triggered Breath

Assisted vs Controlled Pressure (cmH20) Time (sec)

Spontaneous vs. Mechanical Inspiration Paw (cm H2O) Spontaneous Expiration Expiration Inspiration Time (sec)

Components of Inflation Pressure PIP } Transairway Pressure (PTA) Paw (cm H2O) Exhalation Valve Opens Pplateau (Palveolar) Inspiratory Pause Expiration Begin Inspiration Time (sec) Begin Expiration

Inadequate Inspiratory Flow Inadequate Flow Adequate Flow (cm H2O) Paw Time (sec)

Volume-pressure loops Vol (ml) on y-axis,press(cm of H2O) on x-axis. Lower curve of loop insp press and upper expiratory.the angle of curve depicts lung and chest wall compliance. The v-p loops are elliptical in shape,pressure control loops are more rectangular,pltted in anti clockwise manner. Patient efforts as trigger tail to the left of vertical axis.(larger tail=larger WOB) The spontaneous breath v-p loop is plotted in a clock wise manner.

Pressure-Volume Loop (Type of Breath) Vol (ml) I E I I Paw (cm H2O) Controlled Assisted Spontaneous I: Inspiration E: Expiration

Components of Pressure-Volume Loop VT Expiration Volume (mL) Inspiration PIP Paw (cm H2O)

PEEP and P-V Loop VT PIP Volume (mL) PEEP Paw (cm H2O)

Work of Breathing B A: Resistive Work B: Elastic Work A Volume (ml) Pressure (cm H2O)

Inadequate Sensitivity Volume (mL) Paw (cm H2O) Increased WOB

Air Leak/Air Trapping Volume (ml) Air Leak Pressure (cm H2O)

Flow starvation/flow dyssynchrony Active patient effort after initiation of ventilator indicates pt not receiving enough flow-flow starvation shown as concave appearance on insp limb.

Inadequate Inspiratory Flow Volume (ml) Active Inspiration Inappropriate Flow Normal Abnormal Paw (cm H2O)

Increased Raw Higher PTA Volume (ml) Higher PTA Paw (cm H2O)

Lung Compliance Changes and the P-V Loop Volume Targeted Ventilation Preset VT COMPLIANCE Increased Normal Decreased Volume (mL) Paw (cm H2O) PIP levels

Lung Compliance Changes and the P-V Loop Increased Normal Decreased VT levels Pressure Targeted Ventilation Volume (mL) Paw (cm H2O) Preset PIP

With little or no change in VT Overdistension With little or no change in VT Normal Abnormal Volume (ml) Pressure (cm H2O) Paw rises

Flow-volume loops Flow (L/min) on y axis and vol(ml) on x axis. Mostly insp flow above horizontaland expi flow below.shape of exp loop determines the pts lung characteristics. Uses:to assess the effect of bronchodilator therapy.,2.changes in airway resistance.,to detect auto-peep and vol leaks.

Flow-Volume Loop Inspiration PIFR FRC VT PEFR Expiration Flow (L/min) Volume (ml) FRC VT Flow (L/min) PEFR Expiration

Air Leak Inspiration Expiration Volume (ml) Air Leak in mL Normal Flow (L/min) Volume (ml) Air Leak in mL Normal Abnormal Expiration

Air Trapping Inspiration Expiration Flow (L/min) Volume (ml) Normal Does not return to baseline Volume (ml) Normal Abnormal Expiration

Increased Airway Resistance Inspiration Flow (L/min) Volume (ml) Normal Abnormal “Scooped out” pattern Decreased PEFR Expiration

Airway Secretions/ Condensate in the Circuit Inspiration Flow (L/min) Volume (ml) Normal Abnormal Expiration

Modes of Ventilation Mechanical Spontaneous Volume Targeted Pressure

Spontaneous Breath Flow L/m Pressure cm H2O Volume mL Time (sec)

CPAP Flow L/m Pressure cm H2O CPAP level Volume mL Time (sec)

PSV Patient Triggered, Flow Cycled, Pressure limited Mode Time (sec) Flow Cycling Flow L/m Set PS level Pressure cm H2O Volume mL Time (sec)

CPAP + PSV Flow Cycling Flow L/m Pressure cm H2O Volume mL Time (sec) Set PS level Pressure cm H2O CPAP level Volume mL Time (sec)

Controlled Mode (Volume- Targeted Ventilation) Time triggered, Flow limited, Volume cycled Ventilation Preset Peak Flow Flow L/m Dependent on CL & Raw Pressure cm H2O Preset VT Volume Cycling Volume mL Time (sec)

Assisted Mode (Volume-Targeted Ventilation) Patient triggered, Flow limited, Volume cycled Ventilation Flow L/m Pressure cm H2O Preset VT Volume Cycling Volume mL Time (sec)

SIMV (Volume-Targeted Ventilation) Pressure Flow Volume (L/min) (cm H2O) (ml) Spontaneous Breaths

Controlled Mode (Pressure-Targeted Ventilation) Time Triggered, Pressure Limited, Time Cycled Ventilation Time-Cycled Pressure Flow Volume (L/min) (cm H2O) (ml) Set PC level Time (sec)

Assisted Mode (Pressure-Targeted Ventilation) Patient Triggered, Pressure Limited, Time Cycled Ventilation Time-Cycled Pressure Flow Volume (L/min) (cm H2O) (ml) Set PC level Time (sec)

SIMV Mode (Pressure-Targeted Ventilation) Flow Volume (L/min) (cm H2O) (ml) Set PC level Time (sec) Spontaneous Breath

SIMV + PS (Pressure-Targeted Ventilation) Time-Cycled Flow-Cycled Pressure Flow Volume (L/min) (cm H2O) (ml) Set PC level Set PS level Time (sec) PS Breath

SIMV+PS (Volume-Targeted Ventilation) Flow-cycled Flow Pressure Volume (L/min) (cm H2O) (ml) Set PS level PS Breath

SIMV + PS + CPAP (Pressure-Targeted Ventilation) Flow Volume (L/min) (cm H2O) (ml) Set PC level Set PS level CPAP level Time (sec)

SIMV+PS + CPAP (Volume-Targeted Ventilation) Flow Pressure Volume (L/min) (cm H2O) (ml) Set PS level CPAP level Time (sec)

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