Monitor the patients disease pathology and response to therapy Estimate respiratory mechanics

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1 Understanding Graphics during Mechanical Ventilation Why Understand Ventilator Graphics? Waveforms are the graphic representation of the data collected by the ventilator and reflect the interaction between patient & ventilator. Monitor appropriateness of ventilator function Fine-tune ventilator settings and modes to: Improve patient comfort Decrease WOB Optimize ventilation Monitor the patients disease pathology and response to therapy Estimate respiratory mechanics What Parameters do Graphics Display? Flow Time What about VOLUME? is CALCULATED from the measurement of flow over time. 1

2 How Are These Parameters Measured? is measured directly, usually at the patient wye, with a tube connected to a pressure transducer integral with the ventilator. is an integration of the Flow Signal and Inspiratory Time. Fleisch Pneumotachograph- A system of capillary tubes and pressure transducer Vortex Pneumotachograph- Ultrasonic detection of created turbulence Orifice Pneumotachograph- drop across a fixed or variable resistance Turbine Pneumotachograph- Photocell detects rotation of turbine Heated Anemometer - Measures flow over a heated wire Fast response, accurate results with virtually no resistance How are These Parameters Displayed? Scalars Proximal Airway /Time Insp & Exp Flow Rate/Time Insp & Exp /Time Loops / Flow/ SCALARS 2

3 Three Basic Scalars Airway / Time Flow / Time / Time Step One Identify the Three Parts of a Scalar A. TRIGGER What causes the breath to begin? Machine Controlled Time Patient Spontaneous Flow or B C B. LIMIT What regulates gas flow during the breath?, Flow or C. CYCLE What causes the breath to end? Flow,, or Time A Types of Scalars: The Scalar VOLUME Vt Square Flow Decelerating Flow TIME REMEMBER: is a function of FLOW over TIME 3

4 Uses for the Scalar Identification of Air-Trapping (AutoPEEP) Identification of Active Exhalation Determination of Vt & Estimation of Ve Identification of Airway Leaks Determination of Patient/Ventilator Asynchrony Types of Scalars: The Scalar cmh2o -Control Ventilation: PIP VARIABLE -Control Ventilation: PIP CONSTANT PIP PIP PEEP The area under the Curve is the Mean PAW Uses for the Scalar Identification of Airway Obstruction Identification of Active Exhalation Determination of Bronchodilator Response Respiratory Mechanics (C and Raw) Identification of Breath Type Determination of Ppeak & Pplat Identification of Mode of Ventilation Triggering Effort Patient/Ventilator Asynchrony Flow Starvation 4

5 Types of Scalars: The Flow Scalar -Control Ventilation -Control Ventilation Square Wave Decelerating Wave LPM TIME PEFR Vt can be ESTIMATEDby measuring the area found within the inspiratory flow tracing Uses for the Flow Scalar Identification of Air-Trapping (AutoPEEP) Patient/Ventilator Dys-Synchrony Identification of Airway Obstruction Active Exhalation Bronchodilator Response Respiratory Mechanics (C & Raw) Inspiratory Flow & Flow Starvation Adequacy of Ti in PV ventilation Leaks Patient/Ventilator Asynchrony Vt ml PEEP cmh2o PIP LOOPS 5

6 Two Basic Loops Flow / / Types of Loops: The Flow/ Loop Inspiration above the x-axis Exhalation below the x-axis PIFR is plotted horizontally Vt Flow is plotted vertically PEFR Q: Why did the expiratory flow start so early? The Flow/ Loop -Controlled -Controlled Flow Flow Inspiration PEFR Exhalation FV Loops - CLOCKWISE Motion 6

7 Types of Loops: The / (PV) Loop Inspirationon the right Exhalation on the left Vt is plotted horizontally (PH) is plotted vertically (VV) Angle of Football is Dynamic Compliance PIP The Various Shapes of the PV Loop Controlled Assisted Spontaneous Positive Breath PV Loops - COUNTERCLOCKWISE Motion Spontaneous Breath PV Loops CLOCKWISE Motion Graphic Representation of Conventional Ventilatory Modes 7

8 Ventilation 101: Two Basic Types of Ventilation -Controlled Ventilation Clinician chooses a mandatory volume that will be delivered and the pressure resulting from that will be variable depending on compliance and resistance -Controlled Ventilation Clinician chooses a mandatory pressure that will be delivered and the tidal volume varies depending on compliance and resistance -Controlled Ventilation Trigger Limit Cycle Machine Patient Operator Pre-set Flow,square or decelerating Time Flow -Controlled Ventilation Guaranteed Vt Variable PIP Fixed, Square-Wave Flow Flow is Back-End Loaded Slower alveolar filling Flow Linear Increase in Airway with peak at end of inspiration 8

9 Benefit of VC Ventilation Vt is not affected by changes in the patient s lung mechanics. EXAMPLE: Patient with Decreasing Lung Compliance Ventilation: No Change in Vt Increased PIP Ventilation: Decreased Vt No Change in PIP ml ml cmh20 cmh20 Problems With VC Ventilation Relatively high peak pressure may result in barotrauma Flow rate is pre-set and may not meet patient s demand Flow dysynchrony may increase WOB and may compromise: comfort gas exchange cardiac function -Controlled Ventilation Trigger Machine Patient Operator Limit Pre-set pressure Flow Cycled Time Flow 9

10 Benefits of PC Ventilation Variable flow able to meet patient demand Reduced inspiratory muscle workload Lower PIP s Adjustable Ti Flow Flow is Front-End Loaded Rapid filling of the alveoli Improved gas distribution Ventilation 102: AC with Spontaneous Breaths Ventilation 102: CPAP/PSV (what I can t call BiPAP) 10

11 Ventilation 102: SIMV with PSV Breaths Graphic Abnormalities PV Loops: Problem #1 Changes in Compliance Normal Compliance - Black Loop Increased Compliance - Gray Loop The Football is more vertical Decreased Compliance - Brown Loop The Football is more horizontal 11

12 The Safe Window of Lung Ventilation Overdistension/Volutrauma Edema fluid accumulation Surfactant degradation High oxygen exposure Mechanical disruption Derecruitment/Atelectrauma Repeated alveolar closure & re-expansion Stimulation of inflammatory response Inhibition of surfactant Localized hypoxemia Compensatory overexpansion of healthy alveoli Zone of Derecruitment and Atelectasis Zone of Overdistention Safe Window PV Loops: Problem #2 What Does This Show? 1. Inspiration or Exhalation? 2. Beginning, Middle or End? 3. More than or More than? Overdistension PEEP PV Loops: Problem #2 Overdistension (Volutrauma) Overdistension occurs when the volume limit of some components of the lung have been exceeded. Causes an abrupt decrease in lung compliance near the termination of inspiration Results in a Beaking of the P/V Loop Indicated by a C20/Cof <1.0 12

13 PV Loops: Problem #3 What Does This Show? 1. Inspiration or Exhalation? 2. Beginning, Middle or End? 3. More than or More than? Underdistension PV Loops: Problem #3 Underdistension (Atelectrauma) Recruitment Interval: Lungs don t begin to expand and gain volume until about 12cm pressure is forced in 10 PV Loops: Correcting Atelectrauma with PEEP Optimization PEEP Increased to 12cmH2O, Lungs begin to expand and gain volume very soon after the initiation of ventilation 10 13

14 PV Loops: Problem # 4 -Air Leak Expiratory Limb of any VOLUME Graphic has a straight line back to zero. PV LOOP (Counterclockwise) Flow FV LOOP (Clockwise) VOLUME SCALAR PV Loops: Problem # 5 Hysteresis & WOB Area of the curve to the RIGHT of the slope line depicts the ventilator WOB necessary to overcome Raw Area = WOB Area of the curve to the LEFT of the slope line depicts the ventilator WOB necessary to overcome Crs Area = WOB & Flow Scalars Showing Inadequate Inspiratory Flow Patient s inspiratory effort requires more flow than the ventilator provides creating cusping during the initial phase of inspiration cmh2o LPM Flow provided by ventilator does not respond to patients increased flow demand Time 14

15 PV Loops Problem # 6 -Cusping VT A CUSPING PEEP PIP Insufficient PSV How to Correct Flow Starvation Increase ventilator flowrate Shorten Inspiratory time Change to a demand flow mode such as SIMV and/or PSV 15

16 Prolonged Expiratory Flow due to Expiratory Resistance Visualization of a prolonged expiratory flow indicates that there is an obstruction to exhalation. This obstruction may be caused by obstruction of a large airway, bronchospasm, water/medications in expiratory filter or failure of ventilator expiratory valve Flow Time Normal Expiratory Flow Prolonged Expiratory Flow Air Trapping/AutoPEEP Secondary to Insufficient Expiratory Time Expiratory flow is unable to return to baseline prior to the initiation of the next mechanical breath Incomplete exhalation causes gas trapping, dynamic hyper-expansion and the development of intrinsic PEEP Sufficient Expiratory Time Expiratory Flow Returns to Baseline Before Next Breath Starts Insufficient Expiratory Time Expiratory Flow Does Not Return to Baseline Before Next Breath Starts Airway Obstruction/Secretions 16

17 Airway Obstruction/Secretions BEFORE SXN AFTER SXN BE Patient/Ventilator Dysynchrony: Prolonged Inspiratory Time Presence of an end-inspiratoryplateau indicates patient has finished inhaling before the ventilator is ready to cycle into exhalation May increase WOB and dys-synchrony of the ventilator May increase intra-thoracic pressure compromising cardiovascular status May result in insufficient expiratory time and gas trapping End-Inspiratory Flow Plateau Correcting Prolonged Inspiratory Time with Flow Cycling Peak Inspiratory Flow V 5% 20% 40% T 17

18 Patient/Ventilator Dysynchrony: Inappropriate Flow Trigger Graphic Representation of the Avea Intrabreath Demand Flow Intrabreath Decision Point Decelerating Flow is Changed to a Constant Flow DURING Inhalation to Increase to Assure Vt Inflection Points & P-Flex 18

19 Respiratory Mechanics in ARF Reduced range of volume excursion = Decreased Lung Compliance Flattening at low and high volumes = Lower and upper inflection points NORMAL ARDS *Bigatello: Br J Anaest 1996 Inflection Points on the PV Curve Upper Inflection Point UPflex Represents the pressure that, if exceeded will result in regional overdistension Regional overdistension mayoccur at lower pressures Lower Inflection Point - LPflex Represents the minimal pressure required for adequate alveolar recruitment The start of alveolar recruitment Collapse CP Represents the expiratory pressure at which alveoli begin to collapse. CP UPflex LPflex Performing a P-Flex The Slow-Flow Static PV Curve Can be easily performed in the ICU Slow (< 10 lpm) inspiratory flow with large Vt and ZEEP The inspiratory curve of the dynamic PV loop closely approximates the static curve UPIflex Servillo: AJRCCM 1997 Lu: AJRCCM 1999 LPIflex 19

20 Using the PFlex to Ensure Safe Ventilation Maintain PPLAT less than the Upper PFlex(or <35cmH2O) to avoid regional overdistension Utilize smaller Vt s(4-6 cc/kg) to minimize overdistension Set PEEP above the Lower PFlex to prevent alveolar collapse and cyclical atelectasis Questions? 20