"Signals come out of the patient, go into the ventilator, and pop up on the screen"                                                                                     Warren Sanborn
Ventilator graphics gives us insight of patient’s respiratory dynamics.
Graphics are considered as a area of superspecialist, but every pg who ventilates and monitor ventilated babies should be well verse with these, otherwise ventilation will become a blind procedure…just monitoring pressures, volume,  fio2  is not sufficient … 

Understanding graphics by heart cannot be achieved just by reading this post, it requires thorough knowledge of lung mechanics and machine characteristics and this post is no way a short cut to that.

I have just tried to provide simple handy hand sketched VENTILATOR Graphics that illustrates common problems with ventilation that I face in our unit. In this post only few pressure volume loops are illustrated.
  Normal pressure volume  loop looks like this........

Normal pressure volume loop diagram in ventilator graphics
PV loop displays volume on Y axis and pressure on X axis, TV is tidal volume, PIP is peak inspiratory pressure , ER is expiratory resistance, IR is inspiratory pressure, A is resistive work, B is elastic work CDYN is dynamic compliance = change in volume/change in pressure 

Decreased Lung Compliance
Pressure volume loop showing decrease lung compliance in ventilator graphics

There is slow rising inspiratory limb.Change in volume is liitle as compared to change in pressure that is dynamic compliance is less.
simply look at PV loop it looks like a falling leaf i.e. loop lays more horizontal
Suspect: RDS ARDS, pneumothorax, abdominal distention
Manage: Identify cause and fix it, surfactant, increase PEEP 
                                 Elevated Inspiratory Resistance 
Pressure volume loop showing elevated inspiratory resistance in ventilator graphics

PV loop bulges to the right, it’s insp resistance

Suspect:  Decreased compliance, ETT problems
 (too small, kinked, obstructed, patient biting), mucous 
plug causing insp obstruction

Manage: Identify cause and fix it,

Elevated Expiratory Resistance
Pressure volume loop showing elevated expiratory resistance in ventilator graphics

PV loop bulges to the left, it’s exp resistance

Flow volume loop: Note slow decay of expiratory curve 

Flow volume loop showing elevated expiratory resistance in ventilator graphics
Suspect: ETT problems (too small, kinked, obstructed, mucous plug), bronchospasm, expiratory valve blocked, high flow, water in tubing

Manage: Identify cause and fix itdrain water, change ETT, add a bite block, change exp filter, bronchoscopy for mucous plug, decrease flow, Increase PEEP (stent airways)Adjust cycle time (↓Ti or ↑Te)

Pressure volume loop showing over distention of alveoli in ventilator graphics

PV loop shows bird beak at the top of the loop

Suspect: Vt set too high (vol vent), Pressure set too high (press vent)
Manage: Reduce Vt (vol vent),Reduce pressure (Press vent)
Pressure volume loop showing hyperinflation of lung in ventilator graphics

Observe flat portion of volume change in inspiratory limb 

Suspect: High PEEP, Increase expiratory resistance, Peumothorax

Manage: Decrease PEEP, manage accordingly

Air Hunger

Pressure volume loop showing air hunger in ventilator graphics

Little separation between inflation and deflation limbs of P-V loop “Figure Eight” appearance at end-inspiration

Suspect: low minute volume,  inadequate flow, less Ti, trigger set too high

Manage:  identify above and insure minute volume as per weight

                                    Increase Work of Breathing
Pressure volume loop showing increase work of breathing in ventilator graphics

figure of eight at expiration or A pig tail at the bottom indicates patient triggering. The bigger the pig tail, the higher the patient WOB to trigger the breath

Suspect: Trigger set too high, too high rise time

Manage: accordingly

Air leak

Pressure volume loop showing air leak in ventilator graphics

Pressure-volume loop fails to close, Tidal volume waveform does not reach baseline at end-expiration

Flow volume loop showing air leak in ventilator graphics
Flow volume loop: expiratory
 part doesn’t return to baseline

Suspect: ET leak (small size, wrong placement), tubings detached, water seal detached, sensor not in place
(anything left open in circuit)

Manage: Identify leak and manage accordingly


This causes a “noisy” signal on both waveforms and loops

Suspect: Airway Secretions, Water in the Circuit

Manage: accordingly

                                                   Air Trapping (Auto-PEEP)
Flow volume loop showing air trapping or auto PEEP in ventilator graphics
Suspect: Extrinsic factors like Increased exp resistance in the circuit (small ET tube, excessive secretions) ,high minute ventilation, insufficient expiratory time or intrinsic factors like early collapse of unstable alveoli / airways during exhalation, acute or chronic airflow limitation(Ashtama)

Manage: Identify cause and resolve (suction, ETT size, reduce tube length), decrease Inspiratory time, increase expiratory time, decrease minute ventilation either by decreasing TV or RR (MV=TV x RR), decrease inspiratory flow (If you put less air into the lungs each minute, the patient has to exhale less air and, therefore, there is less potential for air-trapping. Second, you can provide more time for the patient to exhale). add PEEP (do not decrease set peep ! considering there is auto PEEP it is a pathological entity, so we need to overcome it)

Finally, all you have to do is  to draw these and paste them near ventilators, so that they come in  daily use for everybody...

by Ajay Agade
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