Ventilator waveform analysis often ignored bedside assessment Dr

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

Introduction n Basic parameters measured by ventilator • • n 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

Introduction n n 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 n Major impact on the interpretation of waveforms

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

Flow-time curve n For VCV • 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 n For PCV • Both insp. and exp. flow depend on the driving pressure and resp. mechanics

VCV Normal flow-time curve

PCV Normal Flow-time curve

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

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

Active expiration After NMB

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?

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

Asynchrony: Double triggering

VCV Flow starvation Too low flow rate

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

What is this?

Pressure-time curve of VCV

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

Measuring Auto. PEEP Waterfall effect

PV loop after treatment What is the problem? Compliance or resistance? Initial PV loop Normal lung compliance: 50 ml/cm. H 2 O

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