Mechanical ventilation Basics and waveforms
- 1. MECHANICAL VENTILATION Basics & Waveforms Interpretation By Dr. HARDEEP JUNIOR RESIDENT 2ND YEAR MD, INTERNAL MEDICINE
- 2. TERMS AND DEFINITIONS RELATED TO MECHANICAL VENTILATION
- 3. Definition of Pressures and Gradients in the Lungs Airway opening pressure (Pawo), is most often called mouth pressure (PM) or airway pressure (Paw). Other terms that are often used to describe the airway opening pressure include upper- airway pressure, mask pressure, or proximal airway pressure. Unless pressure is applied at the airway opening, Pawo is zero or atmospheric pressure. Intrapleural pressure (Ppl) is the pressure in the potential space between the parietal and visceral pleurae. Ppl is normally about −5 cm H2O at the end of expiration during spontaneous breathing. It is about −10 cm H2O at the end of inspiration. Because Ppl is difficult to measure in a patient, a related measurement is used, the esophageal pressure (Pes), which is obtained by placing a specially designed balloon in the esophagus; changes in the balloon pressure are used to estimate pressure and pressure changes in the pleural space.
- 5. Transthoracic pressure (PW) is the pressure difference between the alveolar space or lung and the body’s surface (Pbs): PW = Palv − Pbs. It represents the pressure required to expand or contract the lungs and the chest wall at the same time. It is sometimes abbreviated to PTT, meaning transthoracic). Transpulmonary pressure (PL or PTP), or transalveolar pressure, is the pressure difference between the alveolar space and the pleural space (Ppl): PL = Palv − Ppl. alveolar inflation and is therefore sometimes called the alveolar distending pressure. All modes of ventilation increase PL during inspiration, either by decreasing Ppl (negative pressure ventilators) or increasing Palv by increasing pressure at the upper airway (positive pressure ventilators). The term transmural pressure is often used to describe pleural pressure minus body surface pressure
- 6. Transrespiratory pressure (PTR) is the pressure difference between the airway opening and the body surface: PTR = Pawo − Pbs. Transrespiratory pressure is used to describe the pressure required to inflate the lungs and airways during positive pressure ventilation. In this situation, the body surface pressure (Pbs) is atmospheric and usually is given the value zero; thus Pawo becomes the pressure reading on a ventilator gauge (Paw). Transairway pressure (PTA) is the pressure difference between the airway opening and the alveolus: PTA = Paw − Palv. It is therefore the pressure gradient required to produce airflow in the conductive airways. It represents the pressure that must be generated to overcome resistance to gas flow in the airways (i.e., airway resistance).
- 8. LUNG CHARACTERISTICS The compliance (C) of any structure can be described as the relative ease with which the structure distends. It can be defined as the opposite, or inverse, of elastance (e), where elastance is the tendency of a structure to return to its original form after being stretched or acted on by an outside force. Thus, C = 1/e or e = 1/C. Resistance is a measurement of the frictional forces that must be overcome during breathing. These frictional forces are the result of the anatomical structure of the airways and the tissue viscous resis- tance offered by the lungs and adjacent tissues and organs. Normal compliance in spontaneously breathing patients: 0.05 to 0.17 L/cm H O or 50 to 170 mL/cm H O Normal compliance in intubated patients: Males: 40 to 50 mL/cm H2O, up to 100 mL/cm H2O; Females: 35 to 45 mL/cm H2O, up to 100 mL/cm H2O NORMAL RESISTANCE VALUES Unintubated Patient 0.6 to 2.4 cm H2O/(L/s) at 0.5 L/s flow Intubated Patient Approximately 6 cm H2O/(L/s) or higher (airway resistance increases as endotracheal tube size decreases)
- 9. Measuring Airway Resistance PTA = PIP − Pplateau. Raw = (PIP − Pplateau)/flow• STATIC COMPLIANCE is measured when there is no airflow (using plateau pressure – PEEP • STATIC COMPLIANCE = (exhaled tidal volume)/(plateau pressure − EEP) = VT/(Pplateau − EEP) •DYNAMIC COMPLIANCE is measured when airflow is present(using the peak airway pressure- PEEP) • DYNAMIC COMPLIANCE = tidal volume / peak airway pressure- PEEP Measuring Lung Compliance
- 10. CLINICAL CONDITIONS THAT AFFECT THE COMPLIANCE DECREASED COMPLIANCE STATIC DYNAMIC Atelectasis ARDS Pneumothorax Obesity Retained secretions Bronchospasm Kinking of ET tube Airway obstruction INCREASED COMPLIANCE Emphysema Surfactant therapy
- 11. NEGATIVE AND POSITIVE PRESSURE VENTILATION A. NEGATIVE PRESSURE VENTILATION • Negative pressure ventilation creates a transairway pressure gradient by decreasing the alveolar pressures to a level below the airway opening pressure (i. e., below the atmospheric pressure). • Unless airway obstruction is present, negative pressure ventilation does not require an artificial airway. • Two classical devices that provide negative pressure ventilation are the “iron lung” and the chest cuirass or chest shell
- 13. B. POSITIVE PRESSURE VENTILATION • Positive pressure ventilation is achieved by applying positive pressure (a pressure greater than atmospheric pressure) at the airway opening.
- 15. TRIGGER VARIABLE {beginning of inspiration}
- 16. TRIGGERING (INITIATION OF A BREATH) • 1. Patient Triggered or Assisted Ventilation where a mechanical breath results from an inspiratory effort made by the patient.
- 17. • 2. Time Triggered or Controlled Ventilation is a term used when a mechanical breath is generated by a timer allowing delivery of breaths at fixed time intervals. • For example, if the ventilator frequency is preset at 12 breaths per minute (60 sec), the time-triggering interval for each complete breath is 5 sec. • At this time-trigger interval, the ventilator automatically delivers one mechanical breath every 5 sec without regard to the patient’s breathing effort or requirement
- 18. • 3. Triggering can be secondary to a negative pressure generated by the patient (Pressure triggering) or it results when patient removes a specific amount of flow from the circuit during inspiratory effort (Flow triggering).
- 19. • For example, if the sensitivity for pressure triggering is set at -3 cm H2O, then the patient must generate a pressure of -3 cm H2O at the airway opening to trigger the ventilator into inspiration. • If the sensitivity for pressure triggering is changed from -3 to -5 cm H2O, the ventilator becomes less sensitive to the patient’s inspiratory effort as more effort is needed to trigger the ventilator into inspiration. • Changing the sensitivity from -3 to -5 cm H2O is decreasing the sensitivity setting on the ventilator
- 20. • If the ventilator is made more sensitive to the patient’s efforts (pressure, flow, or volume), it is easier for the patient to trigger a breath. The converse is also true.
- 21. • 4. Flow-Triggered. Some ventilators are able to measure inspiratory and expiratory flows. When the patient’s inspiratory flow reaches a specific value, a ventilator-supported breath is delivered. Flow triggering has been shown to be more sensitive and responsive to a patient’s efforts than pressure triggering. • How hard the patient must work to initiate or trigger a breath is termed the ventilator sensitivity.
- 22. LIMIT VARIABLE (Safety) • During a ventilator-supported breath, volume pressure and inspiratory flow all rise above their respective baseline values. • Inspiratory time is defined as the time interval between the start of inspiratory flow and the beginning of expiratory flow. • If one or more variables (pressure, flow, or volume) is not allowed to rise above a preset value during the inspiratory time, it is termed a limit variable.
- 23. LIMIT VARIABLE • 1 PRESSURE LIMIT • 2 FLOW LIMIT • 3 VOLUME LIMIT
- 24. CYCLE VARIABLE {Termination of Inspiration}
- 25. • 1. PRESSURE CYCLED Inspiration is terminated when the preset pressure reaches. • 2. VOLUME CYCLED Inspiration is terminated when the preset volume is delivered by the ventilator.
- 26. • 3. Time-Cycled When the preset inspiratory time elapses, inspiration is terminated. • 4. Flow-Cycled: Inspiration is terminated when flow decreases to a system specific flow rate.
- 27. The basic ventilator circuit diagram
- 28. Ventilator Graphics • Scalars • Curves • Loops
- 29. Types of Waveforms Pressure waveforms • • • Square (constant) Exponential rise Sinusoidal Flow waveforms • • • • • Descending ramp Square (constant) Exponential decay Sinusoidal Ascending ramp Volume waveforms • Ascending ramp • Sinusoidal •Sinusoidal waves are seen with spontaneous, unsupported breathing.
- 30. Types of Waveforms Scalars: plot pressure/volume/flow against time… time is the x axis Loops: plot pressure/volume/flow against each other…there is no time component Six basic waveforms: • Square: AKA rectangular or constant wave • Ascending Ramp: AKA accelerating ramp • Descending Ramp: AKA decelerating ramp • Sinusoidal: AKA sine wave • Exponential rising • Exponential decaying •Generally, the ascending/descending ramps are considered the same as the exponential ramps.
- 31. Scalars • Scalars waveform representations of pressure, flow or volume on the y axis vs time on the x axis • Ventilators measure airway pressure and airway flow • Volume is derived from the flow measurement • Pressure and flow provide all the information necessary to explain the physical interaction between ventilator and patient • Volume scalar – tidal volume delivered during inspiration and expiration
- 34. Types of Waveforms Volume Modes Pressure Modes Volume Control/ SIMV (Vol. Control) Pressure Control/ PRVC SIMV (PRVC) SIMV (Press. Control) Pressure Support/ Volume Support Pressur e FlowVolume Pressur e FlowVolume
- 35. Pressure/Time Scalar • In Volume modes, the shape will be an exponential rise or an accelerating ramp for mandatory breaths. In Pressure modes, the shape will be rectangular or square. This means that pressure remains constant throughout the breath cycle. •In Volume modes, adding an inspiratory pause may improve distribution of ventilation.
- 36. Pressure/Time Scalar Can be used to assess: •Air trapping (auto-PEEP) •Airway Obstruction •Bronchodilator Response •Respiratory Mechanics (C/Raw) •Active Exhalation •Breath Type (Pressure vs. Volume) •PIP, Pplat •CPAP, PEEP •Asynchrony •Triggering Effort
- 37. Pressure/Time Scalar A B Inspiratory pause 1 2 = MAP 1=Peak Inspiratory Pressure (PIP) 2=Plateau Pressure(Pplat) A =Airway Resistance (Raw) B=Alveolar DistendingPressure • The area under the entire curve represents the mean airway pressure (MAP).
- 38. Pressure/Time Scalar Decreased Compliance Pplat PIP Pplat Increased Airway Resistance A. PIP B . •A-An increase in airway resistance causes the PIP to increase, but Pplat pressure remains normal. •B-A decrease in lung compliance causes the entire waveform to increase in size. The difference between PIP and Pplat remain normal.
- 39. Pressure-time waveformsusinga ‘squarewave’ flow pattern Normal pressure-time waveform With normal peak pressures ( Ppeak) ; plateau pressures (Pplat )and airway resistance pressures (Pres) time pressure Ppe ak Pr es Ppl at Pr es # 1 Paw = Flow x Resistance + Volume Compliance tim e flow ‘Square wave’ Normal values: Ppeak < 40 cm H2O Pplat < 30 cm H2O Pres < 10 cm H2O
- 40. time pressure Ppe ak Pr es Ppl at Pr es # 2 Increase in peak airway pressure driven by an increase in the airways resistance e.g. ET tube blocka ge Paw = Flow x Resistance + Volume + PEEP Compliance tim e flow ‘Square wave’ flow pattern Nor mal Pressure-timewaveform- obstruction
- 42. time pressure Ppe ak Pr es Ppl at Pr es # 3 Increase in the peak airway pressure driven entirely by an increase in the airways resistance pressure caused by excessive flow rates shortened inspiratory time and high flow e.g. high flow rates tim e flow ‘Square wave’ Nor mal Normal (low) flow rate Pressuretime waveform–highflow
- 44. time pressure Pre s Ppl at Ppeak P re s # 4 Increase in the peak airway pressure is driven entirely by the decrease in the lung compliance e.g. ARDS Paw = Flow x Resistance + Volume + PEEP Compliance Norm al tim e flow ‘Square wave’ Pressuretime waveform–reducedCompliance
- 46. High Raw: COPD Normal High flow: (short Inspiratory time) Low Compli ance : ARDS Nor ma l PI P Nor ma l Ppl at Hi gh PI P Hi gh PI P Hig h Ppl at Norm al Pplat Nor ma l Ppl at Hi gh PI P Comparison
- 47. Stressindex–Pressuretime waveform • At constant flow, the slope of the airway pressure- time curve is proportional to elastance (inversely proportional to resistance) • In passively breathing patients and at constant flow – shape of the pressure time curve provide overview about compliance/recruitable/overdistension • When rate of pressure increase with time is small indicating a recruitable lung (Curve convex upwards) • When rate of pressure change is higher indicating overdistention
- 49. Stressindexcanbeaccurately determined by visualinspection Mie Sun et al Respiratory Care June
- 51. Overdistension • Stress index upward concavity of the pressure time scalar • Increased Ppeak and Pplat • High peak expiratory flow
- 52. Meanairwaypressure • Average pressure over a ventilatory cycle (one inspiration and one expiration) • Area below the pressure-time curve divided by the ventilatory period (inspiratory time plus expiratory time) • Numerically, calculated as the average of many pressure samples taken over the ventilatory period • PaO2 is proportional to mean airway pressure • Cardiac output may be inversely proportional • Increase airway pressure or increases the I:E ratio (increasing inspiratory time or decreasing expiratory time) increases mean airway pressure
- 53. Esophagealpressurecurve • Esophageal pressure is measured by a catheter with a balloon that is placed at the lower end of the esophagus • Estimate the pleural pressure • Passive patient esophageal pressure increases with each mechanical insufflation • Spontaneously breathing patients esophageal pressure becomes negative during insufflation • Positioning is key
- 56. Esophagealwaveformin spontaneously breathingindividuals • Starts decreasing at the onset of the patient’s inspiratory effortand drops to a minimum pressure at the end of the inspiratory effort
- 57. Clinicalapplication • Measuring transpulmonary pressure at end inspiration and expiration • Open lung strategy in ARDS ventilation and prevention of lung injury • End inspiratory transpulmonary pressure≤25(≤20 cm) • End expiratory transpulmonary pressure 0-5 cm • Spontaneously breathing • Inspiratory effort • AutoPEEP • Asynchrony assessment
- 58. Volume/Time Scalar The Volume waveform will generally have a “mountain peak” appearance at the top. It may also have a plateau, or “flattened” area at the peak of the waveform. •There will also be a plateau if an inspiratory pause set or inspiratory hold maneuver is applied to the breath.
- 59. Volume/Time Scalar Can be used to assess: •Air trapping (auto-PEEP) •Leaks •Tidal Volume •Active Exhalation •Asynchrony
- 60. Volume/Time Scalar Inspiratory Tidal Volume Exhaled volume returns to baseline
- 61. Volume/Time Scalar Air-Trapping or Leak •If the exhalation side of the waveform doesn’t return to baseline, it could be from air-trapping or there could be a leak (ETT, vent circuit, chest tube, etc.) Loss of volume
- 62. Flow/Time Scalar In Volume modes, the shape of the waveform will be square or rectangular. This means that flow remains constant throughout the breath cycle. • In Pressure modes, (PC, PS, PRVC) • the shape of the waveform will have a decelerating ramp flow pattern.
- 63. Iyer et al. ATS review: Ventilator waveform
- 64. Iyer et al. ATS review: Ventilator waveform
- 65. Flow/Time Scalar Can be used to assess: •Air trapping (auto-PEEP) •Airway Obstruction •Bronchodilator Response •Active Exhalation •Breath Type (Pressure vs. Volume) •Flow Waveform Shape •Inspiratory Flow •Asynchrony •Triggering Effort
- 67. Flow/Time Scalar •The decelerating flow pattern may be preferred over the constant flow pattern. The same tidal volume is delivered, but with a lower peak pressure.
- 69. Flow/Time Scalar Auto-Peep (air trapping) •If expiratory flow doesn’t return to baseline before the next breath starts, there’s auto- PEEP(air trapping) present , e.g. emphysema. Start of next breath Expiratory flow doesn’t return to baseline =Normal
- 70. AutoPEEP • Expiration is interrupted before its natural end by the next inspiration some un-expired residual gas remains in thorax • Exerts a pressure onto the respiratory circuit • As a result, the alveolar pressure at the end of expiration is higher than zero (atmospheric pressure = 0) • This incomplete emptying is called dynamic hyperinflation, and the positive alveolar pressure is called PEEPi or auto PEEP
- 71. AutoPEEP
- 73. AutoPEEP consequences • Ineffective triggers • Increased WOB • Hypoxia • Barotrauma • Hemodynamic instability
- 74. Auto PEEPDetection • End-expiratory occlusion is used to measure auto PEEP • Pressure in the lungs equilibrates with the pressure ventilator circuit • Pressure measured at the proximal airways is equal to the end- expiratory alveolar pressure • Auto PEEP is the difference between total PEEP and set PEEP
- 76. OvercomingAutoPEEP • Decrease • Insp time • RR • Vt • Resp demand – pain fever anxiety • Bronchodilator use • External PEEP
- 77. Flow/Time Scalar Peak Exp. Flow Improved Peak Exp. Flow •To assess response to bronchodilator therapy, you should see an increase in peak expiratory flow rate. •The expiratory curve should return to baseline sooner. Shorter E-time Longer E-time Bronchodilator Response Pre-Bronchodilator Post-Bronchodilator
- 78. •Notice the area of no flow indicated by the red line. This is known as a “zero-flow state”. •This indicates that I-time is too long for this patient. Zero flow state
- 79. Waveformsobservedin pressure support • Flow or pressure triggered, pressure targeted and flow cycled • Pressure curve may be shaped by a set rise time • Flow curve characteristics determined by Inspiratory time constant (compliance, resistance) and patients effort
- 80. Rise Time & Inspiratory Cycle Off %
- 82. SIMV
- 86. Rise Time •The inspiratory rise time determines the amount of time it takes to reach the desired airway pressure or peak flow rate. •Used to assess if ventilator is meeting patient’s demand in Pressure Support mode. •In SIMV, rise time becomes a % of the breath cycle.
- 87. Rise Time If rise time is too fast, you can get an overshoot in the pressure wave, creating a pressure “spike”. If this occurs, you need to increase the rise time. This makes the flow valve open a bit more slowly. If rise time is too slow, the pressure wave becomes rounded or slanted, when it should be more square. This will decrease Vt delivery and may not meet the patient’s inspiratory demands. If this occurs, you will need to decrease the rise time to open the valve faster Hence rise time is set according to patients demand. too slowtoo fast pressure spike
- 88. Inspiratory Cycle Off •The flow-cycling variable is given different names depending on the type of ventilator. •The inspiratory cycle off determines when the ventilator flow cycles from inspiration to expiration, in Pressure Support mode. Also know as– •Inspiratory flow termination, •Expiratory flow sensitivity, •Inspiratory flow cycle %, •E-cycle etc…
- 89. Inspiratory Cycle Off •The breath ends when the ventilator detects inspiratory flow has dropped to a specific flow value. Inspiration ends pressure flow
- 90. Inspiratory Cycle Off •In the above example, the machine is set to cycle inspiration off at 30%of the patient’s peak inspiratory flow. 100%ofPatient’s Peak Inspiratory FlowFlow 100% 75% 50% 30%
- 91. Inspiratory Cycle Off 60% 10% •A –The cycle off percentage is too high, cycling off too soon. This makes the breath too small. (not enough Vt.) •B–The cycle off percentage is too low, making the breath too long. This forces the patient to actively exhale (increase WOB), creating an exhalation “spike”. Exhalation spike A B 100% 100%
- 93. Identifying Trigger and flow Related problems via scalars
- 94. Early cycling • Flow from ventilator ends but patient still making insp effort • Distortion of flow and pressure wave form at onset of expiration • Abrupt initial reversal of expiratory flow toward zero, indicating patient’s inspiratory effort is prolonged • Exaggeration of same = autotrigger
- 95. Earlycycling
- 96. Ineffectivetrigger • Respiratory muscular effort which is insufficient to initiate mechanical breath • Manifests as a decrease in airway pressure associated with a simultaneous increase in airflow • Ventilator factors– effort not able to meet the set trigger, large pressure drops across smaller tubes • Patient related- Auto PEEP, resp muscle weakness and decreased drive
- 98. Autotrigger • Assisted breaths delivered which were not patient triggered • Cause • Fluid in circuit, leak, cardiac oscillations, low trigger threshhold
- 99. Doubletrigger • Patients inspiration continues after the ventilator inspiration and triggers another breath immediately after the inspiration • High ventilatory demand of the patient (ARDS) • Inappropriate settings ( Low tidal volume, short inspiratory time, high ETS)
- 100. Doubletrigger
- 101. Reverse triggering • Unique type asynchrony in which diaphragmatic muscle contractions triggered by ventilator insufflations constitute a form of patient- ventilator interaction referred to as“entrainment” • In heavily sedated patients it is suggested that patients had entrainment of neural breaths within mandatory breaths. • This entrainment occurred at a ratio of 1:1 up to 1:3. They occur at the transition from the ventilator inspiration to expiration. • Breath stacking , overdistention and VIDD
- 102. Reverse triggering Mechanical ventilation-induced reverse-triggered breaths: a frequently unrecognized form of neuromechanical coupling. Chest. 2013 Apr; 143(4):927-38
- 103. FlowAsynchrony • Causes : • High ventilatory demand (ALI/ARDS) • Low ventilatory settings ( flow rate, Vt, Pramp) • Treatment: • Treat reversible causes (fever, acidosis) • Increase the Vt • Increase the flow rate ( directly, or by decreasing inspiratory time, increasing pause) • Change to pressure control mode with variable flow
- 104. Flowasynchrony Patient with ARDS weaning
- 105. Loops
- 107. Pressure/Volume Loops Volume is plotted on the y-axis, Pressure on the x- axis. Inspiratory curve is upward, Expiratory curve is downward. Spontaneous breaths go clockwise and positive pressure breaths go counterclockwise. The bottom of the loop will be at the set PEEP level. It will be at 0if there’s no PEEP set. If an imaginary line is drawn down the middle of the loop, the area to the right represents inspiratory resistance and the area to the left represents expiratory resistance.
- 109. PV Loop in VCV
- 110. PV Loop in PCV
- 111. PV Loop in CPAP
- 113. 15 305 A A =Inspiratory Resistance/ Resistive WOB B Pressure/Volume Loops Dynamic Compliance (Cdyn) •The top part of the P/V loop represents Dynamic compliance (Cdyn). • Cdyn = Δvolume/Δpressure 500 250 B = Exp. Resistance/ Elastic WOB
- 114. Pressure/Volume Loops Can be used to assess: •Lung Overdistention •Airway Obstruction •Bronchodilator Response •Respiratory Mechanics (C/Raw) •WOB •Flow Starvation •Leaks •Triggering Effort
- 117. 15 305 Pressure/Volume Loops Overdistention “beaking” •Pressure continues to rise with little or no change in volume, creating a “bird beak”. •Fix by reducing amount of tidal volume delivered 500 250
- 118. 15 305 Pressure/Volume Loops Airway Resistance •As airway resistance increases, the loop will become wider. •An increase in expiratory resistance is more commonly seen. Increased inspiratory resistance is usually from a kinked ETT or patient biting. 500 250
- 119. 15 30 250 500 15 30 Pressure/Volume Loops Increased Compliance Decreased Compliance Example: Emphysema, Surfactant Therapy Example: ARDS, CHF, Atelectasis 500 250
- 120. 15 305 Pressure/Volume Loops A Leak •The expiratory portion of the loop doesn’t return to baseline. This indicates a leak. 500 250
- 121. 15 305 Lower Inflection Point •The lower inflection point represents the point of alveolar opening (recruitment). •Some lung protection strategies for treating ARDS, suggest setting PEEPjust above the lower inflection point. Pressure/Volume Loops Inflection Points 250 500
- 122. Point of upper inflection (Ipu) C lt changed later during Vt because of overinflation of the alveoli The reduction in Clt late in inspiratory cycle is called Ipu The appearance of upper shape PAO curve indicating the presence of Ipu is known as duck bill PVC
- 123. Flow/Volume Loops 0 200 400 600 20 40 60 -20 -40 -60
- 124. Flow/Volume Loops Flow is plotted on the y axis and volume on the x axis Flow volume loops used for ventilator graphics are the same as ones used for Pulmonary Function Testing, (usually upside down). Inspiration is above the horizontal line and expiration is below. The shape of the inspiratory curve will match what’s set on the ventilator. The shape of the exp flow curve represents passive exhalation…it’s long and more drawn out in patients with less recoil. Can be used to determine the PIF, PEF,and Vt Looks circular with spontaneous breaths
- 125. Flow/Volume Loops
- 127. 0 Flow/Volume Loops •The shape of the inspiratory curve will match the flow setting on the ventilator. Volume control Pressure Control
- 128. Flow/Volume Loops In positive pressure ventilation(VC) 0 600 20 40 60 -20 -40 -60 PEF Start of Inspiration 200 400 Start of Expiration
- 129. Flow/Volume Loops In positive pressure ventilation(PC)
- 130. Flow/Volume Loops Can be used to assess: •Air trapping •Airway Obstruction •Airway Resistance •Bronchodilator Response •Insp/Exp Flow •Flow Starvation •Leaks •Water or Secretion accumulation •Asynchrony
- 131. Flow/Volume Loops 0 200 400 600 20 40 60 -20 -40 -60 Expiratory portion of loop does not return to starting point, indicating a leak. Air Leak •If there is a leak, the loop will not meet at the starting point where inhalation starts and exhalation ends. It can also occur with air-trapping. =Normal
- 132. Air Leak
- 133. 0 Reduced PEF“scooping” Flow/Volume Loops •The F-V loop appears “upside down” on most ventilators. •The expiratory curve “scoops” with diseases with small airway obstruction (high expiratory resistance). e.g. asthma, emphysema. Airway Obstruction
- 134. Restrictive Lung DiseaseObstructive Lung Disease
- 136. Air Trapping (auto-PEEP) Causes: • • Insufficient expiratory time Early collapse of unstable alveoli/airways during exhalation How to Identify it on the graphics • • Pressure wave: while performing an expiratory hold, the waveform rises above baseline. Flow wave: the expiratory flow doesn’t return to baseline before the next breath begins. • Volume wave: the expiratory portion doesn’t return to baseline. • Flow/Volume Loop: the loop doesn’t meet at the baseline • Pressure/Volume Loop: the loop doesn’t meet at the baseline
- 137. Airway Resistance Changes Causes: • • • • • • Bronchospasm ETT problems (too small, kinked, obstructed, patient biting) High flow rate Secretion build-up Damp or blocked expiratory valve/filter Water in the HME How to Identify it on the graphics • Pressure wave: PIP increases, but the plateau stays the same • Flow wave: it takes longer for the exp side to reach baseline/exp flow rate is reduced • Volume wave: it takes longer for the exp curve to reach the baseline • Pressure/Volume loop: the loop will be wider. Increase Insp. Resistance will cause it to bulge to the right. Exp resistance, bulges to the left. • Flow/Volume loop: decreased exp flow with a scoop in the exp curve How to fix • Give a treatment, suction patient, drain water, change HME, change ETT, add a bite block, reduce PF rate, change exp filter.
- 138. Leaks Causes • • Expiratory leak: ETT cuff leak , chest tube leak, BP fistula, NG tube in trachea Inspiratory leak: loose connections, ventilator malfunction, faulty flow sensor How to ID it • • • • • Pressure wave: Decreased PIP Volume wave: Expiratory side of wave doesn’t return to baseline Flow wave: PEF decreased Pressure/Volume loop: exp side doesn’t return to the baseline Flow/Volume loop: exp side doesn’t return to baseline How to fix it • Check possible causes listed above • Do a leak test and make sure all connections are tight
- 139. Asynchrony Causes (Flow, Rate, or Triggering) • Air hunger (flow starvation) • Neurological Injury • Improperly set sensitivity How to Identify it• • Pressure wave: patient tries to inhale/exhale in the middle of the waveform causing a dip in the pressure Flow wave: patient tries to inhale/exhale in the middle of the waveform, causing erratic flows/dips in the waveform Pressure/Volume loop: patient makes effort to breath causing dips in loop either Insp/Exp. Flow/Volume loop: patient makes effort to breath causing dips in loop.
- 140. Asynchrony Flow Starvation •The inspiratory portion of the pressure wave shows a scooping or “dip”, due to inadequate flow.
- 141. Asynchrony • How to fix it: • Try increasing the flow rate, decreasing the I-time, or increasing the set rate to “capture” the patient. • Change the mode - sometimes changing from partial to full support will solve the problem If neurological, may need paralytic or sedative Adjust sensitivity
- 142. Asynchrony F/V Loop P/V Loop
- 143. Trigger Asynchrony
- 144. thankyou