Understanding ventilator waveforms—and how to use them in patient care

Ventilator waveform interpretation in mechanically ventilated small animals

“…During expiration, the exhalation valve of the ventilator opens and volume decreases to baseline as shown in the volume‐time scalar labeled A . Typically an air leak in the expiratory circuit of the ventilator, a bronchopleural fistula, or gas trapping in the lung (ie, auto‐PEEP) is responsible when the expiratory limb of the tracing does not return to baseline as shown in the volume‐time scalar labeled B . A drop of the expiratory limb of the curve below the baseline, represented by the volume‐time scalar labeled C indicates active patient exhalation or flow transducer malfunction.…”

“…The starting point of the loop depends on the amount of PEEP applied. Both the inspiratory and expiratory portion of the loop are on the right side of the y ‐axis . The maximum pressure reached on the x ‐axis is the PIP and the maximum volume reached on the y ‐axis is the V T…”

“…In Figure , the expiratory limb of the PV loop does not return to baseline indicating that more volume is delivered during inspiration than returned during expiration. This loss of volume can be quantified by identifying the end point of the expiratory limb of the PV loop (ie, 300 mL) …”

“…When compliance remains constant and R aw increases the amount of pressure needed to overcome R aw increases. In Figure , the widening or bowing of the PV loop is suggestive of increased R aw (solid line) . The size and shape of the bowing depend on different variables including ventilation mode, for example, pressure‐ or volume‐controlled ventilation, an increase in predominantly inspiratory or expiratory resistance, as well as respiratory system compliance…”

“…The PV loop may exhibit a lower inflection point (LIP) and an upper inflection point (UIP) during the inspiratory phase as shown in Figure . An inflection point is the point where the slope of a line changes .…”