Waveforms, lecture about mechanical ventilation, by Prof Ahmed Tarek, Prof of Pediatrics, Abu El rich hospital, Cairo university
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Waveforms, lecture about mechanical ventilation, by Prof Ahmed Tarek, Prof of Pediatrics, Abu El rich hospital, Cairo university
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Waveforms, lecture about mechanical ventilation, by Prof Ahmed Tarek, Prof of Pediatrics, Abu El rich hospital, Cairo university
- 1. BASICS OF WAVEFORM INTERPRETATION RET 2284 Principles of Mechanical Ventilation
- 3. Objectives • Identify graphic display options provided by mechanical ventilators. • Describe how to use graphics to more appropriately adjust the patient ventilator interface.
- 4. Introduction Monitoring and analysis of graphic display of curves and loops during mechanical ventilation has become a useful way to determine not only how patient are being ventilated but also a way to assess problems occurring during ventilation.
- 5. Uses of Flow, Volume, and Pressure Graphic Display • Confirm mode functions • Detect auto-PEEP • Determine patient-ventilator synchrony • Assess and adjust trigger levels • Measure the work of breathing • Adjust tidal volume and minimize overdistension • Assess the effect of bronchodilator administration • Detect equipment malfunctions • Determine appropriate PEEP level
- 6. Uses of Flow, Volume, and Pressure Graphic Display • Evaluate adequacy of inspiratory time in pressure control ventilation • Detect the presence and rate of continuous leaks • Assess inspiratory termination criteria during Pressure Support Ventilation • Determine appropriate Rise Time
- 8. Most Commonly Used Waveforms (Scalars) • Pressure vs. Time • Flow vs. Time • Volume vs. Time
- 9. Pressure vs. Time Curve 1 2 3 4 5 6 30 Sec Paw cmH2O A B C PIP Baseline Mean Airway Pressure -10
- 10. Pressure-Time Curve 1 2 3 4 5 6 20 Sec Paw cmH2O Pressure VentilationVolume Ventilation
- 11. Patient Triggering 1 2 3 4 5 6 30 Sec Paw cmH2O -10
- 12. Adequate Flow During Volume-Control Ventilation 30 Time (s) -10 1 2 awP cmH2O Adequate flow 3
- 13. Inadequate Flow During Volume-Control Ventilation 30 Time (s) -10 1 2 awP cmH2O Adequate flow Flow set too low 3
- 14. Patient/Ventilator Synchrony Volume Ventilator Delivering a Preset Flow and Volume Adequate Flow 1 2 3 4 5 6 -20 SecPaw cmH2O
- 15. Patient/Ventilator Synchrony The Patient Outbreathing the Set Flow Air Starvation 1 2 3 4 5 6 -20 SecPaw cmH2O
- 16. Plateau Time Inadequate plateau time -20 1 2 3 4 5 6 30 SEC Paw cmH2O
- 17. Adequate Plateau Time -20 1 2 3 4 5 6 30 SEC Paw cmH2O Plateau Time
- 18. Flow vs.Time Curve 1 2 3 4 5 6 SEC 120 120 EXH INSP V . LPM Inspiration
- 19. Flow vs.Time Curve 1 2 3 4 5 6 SEC 120 120 EXH INSP V . LPM Inspiration Expiration
- 20. Flow vs.Time Curve 1 2 3 4 5 6 SEC 120 120 EXH INSP Inspiration V . LPM Constant Flow Descending Ramp
- 21. Flow-Time Curve 1 2 3 4 5 6 SEC 120 120 EXH INSP Insp. Pause Expiration V . LPM
- 22. Inspiratory Time Short Normal Long
- 23. 1 2 3 4 5 6 SEC 120 -120 V . LPM Expiratory Flow Rate and Changes in Expiratory Resistance
- 24. A Higher Expiratory Flow Rate and a Decreased Expiratory Time Denote a Lower Expiratory Resistance 1 2 3 4 5 6 SEC 120 120 V . LPM
- 25. Obstructed Lung Delayed flow return
- 26. Pressure-Time and Flow-Time Curves 1 2 3 4 5 6 20 Sec Paw cmH2O Expiration V . Volume Ventilation
- 27. Pressure-Time and Flow-Time Curves Different Inspiratory Flow Patterns 1 2 3 4 5 6 20 Sec Paw cmH2O Expiration V . Volume Ventilation Inspiration
- 28. 20 Pressure-Time and Flow-Time Curves 1 2 3 4 5 6 Sec Paw cmH2O V . Pressure Ventilation Inspiratory Time Volume Ventilation
- 29. Rise Time How quickly set pressure is reached
- 30. Time Minimal Pressure Overshoot Pressure Relief Slow rise Moderate rise Fast rise P V . Flow Acceleration Percent Rise Time
- 31. Patient / Ventilator Synchrony Volume Ventilation Delivering a Preset Flow and Volume Adequate Flow 1 2 3 4 5 6 30 -20 SecPaw cmH2O
- 32. Air Starvation 1 2 3 4 5 6 30 -20 SecPaw cmH2O Patient -Ventilator Synchrony The Patient Is Outbreathing the Set Flow
- 33. If Peak Flow Remains the Same, I-Time Increases: Could Cause Asynchrony LPM 1 2 3 4 5 6 SEC 120 -120 V .
- 34. Changing Flow Waveform in Volume Ventilation: Effect on Inspiratory Time 1 2 3 4 5 6 SEC 120 -120 V . LPM
- 35. Increased Peak Flow: Decreased Inspiratory Time 1 2 3 4 5 6 SEC 120 -120 V . LPM
- 36. Note: There can still be pressure in the lung behind airways that are completely obstructed Detecting Auto-PEEP LPM Zero flow at end exhalation indicates equilibration of lung and circuit pressure 1 2 3 4 5 6 SEC 120 -120 V .
- 37. Detecting Auto-PEEP The transition from expiratory to inspiratory occurs without the expiratory flow returning to zero 1 2 3 4 5 6 SEC 120 120 V . LPM
- 38. Volume vs.Time Curve Inspiration SEC 800 ml 2 3 4 5 61 VT
- 39. Volume vs.Time Curve Expiration SEC 800 ml 2 3 4 5 61 VT
- 40. Typical Volume Curve 1 2 3 4 5 6 SEC 1.2 -0.4 VT Liters I-Time E-Time A B A = inspiratory volume B = expiratory volume
- 41. Leaks 1 2 3 4 5 6 SEC 1.2 -0.4 VT Liters A A = exhalation that does not return to zero
- 42. 1 2 3 4 5 6 SEC 1 2 3 4 5 6 VT 600 cc 120 120 SEC . V LPM 0 450 cc Setting Appropriate I-Time
- 43. Setting Appropriate I-Time 500 cc450 cc Lost VT 1 2 3 4 5 6 SEC 1 2 3 4 5 6 VT 600 cc 120 120 SEC . V LPM 0
- 44. Loops • Pressure-Volume Loops • Flow-Volume Loops
- 45. Pressure-Volume Loop 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT
- 46. Mandatory Breath Inspiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT
- 47. Mandatory Breath Expiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O Inspiration VT Counterclockwise
- 48. Spontaneous Breath Inspiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT Clockwise
- 49. Spontaneous Breath Inspiration Expiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT Clockwise
- 50. Work of Breathing 0 20 40 60-20-40-60 0.2 0.4 0.6 LITERS Paw cmH2O VT
- 51. Assisted Breath 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O Assisted Breath VT
- 52. Assisted Breath Inspiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O Assisted Breath VT
- 53. Assisted Breath Inspiration Expiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O Assisted Breath VT Clockwise to Counterclockwise
- 54. Pressure-Volume Loop Changes 0 20 40 60-20-40-60 0.2 0.4 0.6 LITERS Paw cmH2O VT
- 55. Changes in Compliances Indicates a drop in compliance (higher pressure for the same volume) 0 20 40 602040-60 0.2 0.4 0.6 LITERS Paw cmH2O VT
- 56. Overdistension B A 0 20 40 60-20-40-60 0.2 0.4 0.6 LITERS Paw cmH2O C A = inspiratory pressure B = upper inflection point C = lower inflection point VT
- 59. Flow -Volume Loops Volume Control Volume Tidal Volume Inspiration Expiration
- 60. Flow -Volume Loops Volume Control Volume Peak Expiratory Flow Peak Inspiratory Flow Tidal Volume Inspiration Expiration
- 61. ETT or Circuit Leaks
- 65. Bronchodilator Response 2 1 1 2 3 3 V LPS . VT INSP EXH BEFORE AFTER Worse Better 2 1 1 2 3 3 V LPS . 2 1 1 2 3 3 V LPS .
- 66. Remember! Waveforms and loops are graphical representation of the data generated by the ventilator. Typical Tracings Pressure-time, Flow-time, Volume -time Loops Pressure-Volume Flow-Volume Assessment of pressure, flow and volume waveforms is a critical tool in the management of the mechanically ventilated patient.
Hinweis der Redaktion
- A good way to identify an adequate plateau time is to observe the pressure-time curve. This slide shows an inadequate plateau time; no plateau has occurred. This could lead to an inaccurate estimation of plateau pressure.
- Here, we see that a plateau has occurred, as evidenced by the flattening of the pressure curve at the arrow.
- This slide depicts a long expiratory phase. Note the low expiratory flow rate and extended exhalation phase. This could be caused by a number of clinical situations: bronchospasm, COPD, expiratory filter contamination, secretions or water in the tubing. Watching for changes in expiratory flow helps judge the efficacy of any intervention.
- A higher expiratory flow rate and a decreased expiratory time denote a lower expiratory resistance. A decrease in expiratory resistance may also be observed after the patient receives a bronchodilator (e.g. MDI or aerosolized neb tx). Monitoring the duration of the therapy’s effect can help determine the indicated frequency of therapy.
- Exhalation, seen here in yellow, occurs when the tidal volume has been delivered or the high pressure limit has been reached. Flow ceases and exhalation begins. This is a passive process caused by the elastic recoil of the lung.
- Let’s take a look at the pressure curve resulting from a volume-based breath with a decelerating flow pattern. As you can see in green here, pressure increases more rapidly from the PEEP level when the decelerating flow curve is used. This pressure curve is starting to look more like a pressure-based breath.
- In pressure-based ventilation, once the Pinsp has been reached, the pressure then remains constant for the Tinsp set on the ventilator. Flow decelerates towards end inspiration and then remains at or near zero base line until the set inspiratory time is met. Note the pressure curves are similar. The difference is in the ventilators response to changes in resistance, compliance, or patient demand.
- Did anybody say rise time or flow acceleration percent? Literature suggests that inappropriate flow rate, too high or too low at any time during the inspiratory phase in PCV or PSV, may result in increased inspiratory muscle effort or work of breathing. It can also increase the likelihood of patient discomfort and patient/ventilator asynchrony. FAP allows the clinician to sculpt the shape of the rise to pressure to meet patient demand or comfort. Slow, moderate, and aggressive rise to pressure curves are shown. What is happening at the two arrows? On the pressure-time curve, it is a minimal pressure overshoot caused by an aggressive rise to pressure. On the flow curve, it is a pressure relief that occurs with an active exhalation valve. What happens when there isn’t an active exhalation valve?
- All right, now let’s get on with the fun stuff: detecting abnormalities on waveforms. When your patient begins to fight the ventilator and becomes asynchronous, your job as a clinician is to determine why. We all know that many things can cause the patient to become out of synch. It could be caused by pain, frustration from trying to communicate, or their spouse may have just told them they are filing for divorce. But on a more serious note, patient ventilator dysychrony can be caused when the patient outstrips the peak flow set on the ventilator. Let’s take a look at this. This is a normal pressure curve in volume ventilation with an adequate setting for peak flow.
- What we see here is a patient’s inspiratory flow demand greater than the peak flow set on the ventilator, which can lead to patient/ventilator dysynchrony. What are we going to do to amend this situation?
- However, remember what we talked about earlier. If the peak flow is left at the same setting when we switch to a decelerating flow pattern, the inspiratory time will increase. A decreased expiratory time may have the potential to cause patient/ventilator dysynchrony in and of itself. Perhaps a different mode of ventilatory support may be more appropriate, such as PCV or PS.
- As we discussed earlier, both square and decelerating flow patterns are commonly used in clinical practice. We will not debate the clinical application of these flow patterns, but will point out the impact of changing from a square to decelerating flow curve in volume ventilation without changing the set peak flow. Note the increase in inspiratory time with the decelerating flow pattern.
- If the goal is to maintain a similar inspiratory time, this can be accomplished by increasing peak flow to approximate the same inspiratory time with the decelerating flow pattern that existed with the square wave pattern. This could decrease the potential for developing Auto-PEEP.
- We can look at our flow-time curve. If there is zero flow at the end of exhalation, it would indicate an equilibration of the lung and circuit pressure. Note: There can still be pressure in the lungs behind airways that are completely obstructed.
- On the other hand, if the transition from exhalation to inspiration occurs without the expiratory flow returning to zero, you have Auto-PEEP present.
- The volume-time curve shows the gradual changes in the volume that is delivered during inspiration. Volume is typically measured in milliliters. Pictured in green is the inspiratory phase, in which volume increases continuously until the set tidal volume is achieved or the high pressure alarm limit has been reached, or I-Time has expired.
- During expiration, seen in yellow here, the transferred volume decreases, again due to the passive recoil of the lung. Generally, what goes in comes out, unless you have a leak in the patient circuit or the patient, or gas is trapped in the lung.
- Using both the volume- and flow-time curves provides insight to set the appropriate PIP and I-Time in PCV. For example, the physician orders PCV and tells you that he wants a VT of 500 cc. PCV is initiated with a PIP of 20 cm, resulting in a VT of 450 cc. Before increasing the inspiratory pressure to obtain additional VT, maximize inspiratory time. As shown here at the arrow, inspiratory flow does not return to zero before cycling into expiration. This could result in a lesser delivered volume.
- Pictured in blue here is potentially lost VT. Increasing inspiratory time to allow the flow to return to baseline may increase VT without increasing PIP.
- We have reviewed the normal components of the three standard time curves: Flow, Pressure, and Volume. Now, let’s investigate the normal components of the pressure-volume loop. Instead of plotting one parameter against time, the pressure-volume loop plots the interaction between pressure, on the horizontal axis, and volume, on the vertical axis.
- On a ventilator-initiated mandatory breath, or VIM, the movement of the PV Loop is counterclockwise, starting with inspiration, shown here in green. During inspiration, the lung begins to fill and normally there is a simultaneous increase in both pressure and volume.
- When the inspiration criteria are met, exhalation begins as pictured in yellow here. Normally, this curve resembles a football.
- During a spontaneous, non-pressure-supported breath, the rotation is clockwise; inspiration and then expiration.
- During a spontaneous, non-pressure-supported breath, the rotation is clockwise; inspiration and then expiration.
- The arrow indicates patient work of breathing. Inspiratory effort to the left of the vertical axis translates into increased inspiratory workload for the patient. This is commonly addressed by instituting flow triggering.
- When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
- When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
- When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
- The pressure-volume loop changes, flattening out and moving to the right. What could cause this to happen?
- Did anybody say decrease in compliance? The difference between the white arrow and the red arrow represents a change in compliance as indicated by an increase in pressure without a corresponding increase in tidal volume.
- Overdistention is caused by a combination of PEEP and too much volume or pressure. A is the peak inspiratory pressure; B is the upper inflection point; C is the lower inflection point. The lower inflection point identifies the level of PEEP where the lung is more compliant. This is also referred to as critical opening pressure. The upper inflection point indicates where the lung becomes less compliant and illustrates where overdistension starts to occur. Decreasing the volume or pressure may help avoid barotrauma in this situation.
- This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response.
- This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response.
- This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response.