1. Ventilator waveform analysis: often ignored bedside assessment
Dr. Tang Kam Shing
ICU, Tuen Mun Hospital

2. Introduction Basic parameters measured by ventilator
Pressure
Flow
Volume (as an integration of flow)
Time
From these parameters, basically 5 types of curves commonly available from ventilators
Pressure-time curve
Flow-time curve
Volume-time curve
Pressure-volume curve
Flow-volume curve

3. Introduction
The curves are basically the result of the mechanical interaction between the ventilator and the respiratory system
Important to know the setting on the ventilator before you try to make sense of the waveforms
Volume control or pressure control?
What is the cycling variable?
Important to know whether the patient is relaxed and sedated or actively breathing
Major impact on the interpretation of waveforms

4. Use of waveforms Measurement of:
Peak insp. Pressure
plateau pressure
Auto-PEEP
Detection of over-inflation or gas trapping
Serial change in resistance and compliance
Patient-ventilator synchrony

5. Flow-time curve For VCV For PCV
Basically the TV, Ti and flow waveform you set determine the insp. pattern of flow-time curve in VCV in most cases
Expiratory pattern more useful
For PCV
Both insp. and exp. flow depend on the driving pressure and resp. mechanics

6. VCV
Normal flow-time curve

7. PCV
Normal Flow-time curve

8. Compliance or resistance?
PCV in sedated patient
What is the problem?
Compliance or resistance?
↑ resistance
↓ compliance

9. Flow-time curve PCV What is the abnormality? Any other possibilities?
Patient with ↑ resp drive, insp when exhalation not complete yet

10. Active expiration
After NMB

11. Blue tracing conventional ventilator tracing
Red tracing at tip of OETT
What is the cause of the spike of A? (artefact ∵ not shown at ET tip pressure)
What is the cause of the spike of C?

12. What is the problem?
What is the reason of the spike?

13. Asynchrony:
Double triggering

14. VCV
Flow starvation
Too low flow rate

15. PCV ventilation
What is the abnromalities?
What can we do?

16. What is this?
What is this?

17. Pressure-time curve of VCV

18. Pressure-time curve in VCV
Which is increased resistance?
Which is decreased compliance?

19. Measuring AutoPEEP
Waterfall effect

20. PV loop after treatment
What is the problem?
Compliance or resistance?
Normal lung compliance: 50ml/cmH2O
Initial PV loop

21. PV loop after treatment
What is the problem?
Compliance or resistance?
Initial PV loop