Start with the airway pressure screen Step 1….determine the CPAP level This is the baseline position from which there is a downward deflection on, at least, beginning of inspiration, and to which the airway pressure returns at the end of expiration.

Step 2…. is the patient triggering? There will be a negative deflection into the CPAP line just before inspiration.

Step 3: what is the shape of the pressure wave?. If the curve has a flat top, then the breath is pressure limited, if it has a triangular or shark’s fin top, then it is a volume breath

Look at the flow screen: Step 3…what is the flow pattern? – If it is constant flow (square shaped) this must be volume controlled, If decelerating, it can be any mode.

Step 3 cont….Is the patient gas trapping? – Expiratory flow does not return to baseline before inspiration commences (i.e. gas is trapped in the airways at end-expiration).

Step 4: the patient is triggering – is this a pressure supported or SIMV breath? This is easy, the pressure supported breath looks completely differently than the volume control or synchronized breath: the PS breath has a decelerating flow pattern, and has a flat topped airway pressure wave. The synchronized breath has a triangular shaped pressure wave. Flow terminated

Step 5: patient is triggering, is this pressure support or pressure control? The fundamental difference between PS and PC is the length of the breath – In PC, the vent determine the inspired time and all breaths have an equal “i” time. In PS, the pt determined the duration of inspiration, which varies from breath to breath and flow termination seen as per setting.

Step 6.. is the patient synchronizing with the ventilator? Each time the ventilator is triggered a breath should be delivered. If the number of triggering episodes is greater than the number of breaths, the patient is asynchronous with the ventilator. Further, if the peak flow rate of the ventilator is inadequate, then the inspiratory flow will be "scooped" inwards, and the patient appears to be fighting the ventilator.

SPONTANEOUS BREATH Time (sec) P V F

SOME BASIC CONCEPTS….. Effects of Changes in Ventilator settings on Waveforms…………… 1.How RR changes Cycle time thereby iTime and eTime 2.How Flow Rate changes iTime and eTime

A post-operative pt brought to PICU And placed on VENT……With following settings…… Tidal volume………… 750 ml..(0.75 L) Resp rate ……………. 15 / min Insp flow rate ……….. 30 L / min Airways resistance …. 10 cm H2O/L//sec Compliance …………… 0.05 L/cm H2O (50 ml/cm H2O) Mode ……………………. CMV

CMV ……. (VOLUME VENTILATION) Preset V T Volume Cycling Dependent on C L & R aw Time (sec) Flow (L/m) Press (cm H 2 O ) Vol (mL) Preset Peak Flow Time triggered, Flow limited, Volume cycled Ventilation

ASSISTED MODE………… (VOLUME CONTROL VENTILATION) Time (sec) Flow (L/m) Pressure (cm H 2 O) Volume (mL) Preset V T Volume Cycling Patient triggered, Flow limited, Volume cycled Ventilation

SIMV…… (VOLUME CONTROL VENTILATION) Spontaneous Breaths Flow (L/m ) Pressure (cm H 2 O) Volume (mL)

Flow Pressure Volume (L/min) (cm H 2 O) (ml) Set PS level PS Breath Flow-cycled

SIMV+PS + CPAP VOLUME CONTROL VENTILATION F P V Set PS level CPAP level

CONTROLLED MODE (PRESSURE VENTILATION) Pressure Flow Volume (L/min) (cm H 2 O) (ml) Time (sec) Time-Cycled Set PC level

ASSISTED MODE ….. (PRESSURE VENTILATION) Pressure Flow Volume (L/min) (cm H 2 O) (ml) Set PC level Time (sec) Time-Cycled Patient Triggered, Pressure Limited, Time Cycled Ventilation

P F V Set PC level Time Spontaneous Breath

P F V SIMV + PS …….. Pressure control Ventilation PS Breath Set PS level Set PC level Time Time-Cycled Flow-Cycled

P F V Set PC level Time SIMV + PS + CPAP……. Pressure control Ventilation Set PS level CPAP level Triggering ? ??

Time (sec) F P V Flow Cycling Set PS level Patient Triggered, Pressure limited, Insp Flow Cycled

Time CPAP level F P V

Set PS level CPAP levelTime F P V Flow Cycling

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