Graphical Assessment of Respiratory System

Graphical Assessment of Respiratory System Mechanics and Ventilator Operations
Neil MacIntyre MD
1. PRESSURE, FLOW, VOLUME AND TIME GRAPHICAL DISPLAYS
The four parameters commonly monitored during mechanical ventilatory support are
pressure, flow, volume and time. Pressure is usually measured in the ventilator circuit and
is taken as a reflection of patient airway pressure (Paw). However, pressure can also be
measured in the mid esophagus (Pes) where it is taken as a reflection of pleural pressure.
Flow (V) and volume (V) are commonly measured in the ventilator circuit. These
measurements can be displayed in a variety of ways but are most commonly plotted as
pressure, flow and volume over time. Figure 1 depicts a typical pressure/flow/volume
display over time during a ventilator controlled breath.
FIGURE 1 EXERCISES
Identify by letter and quantify:
Peak airway pressure (peakPaw) ___________________
Plateau airway pressure (platPaw) __________________
End expiratory airway pressure (EEP) _______________
Peak inspiratory flow (insp V)_______________________
Peak expiratory flow (exp V)________________________
Inspiratory time (Ti) ______________________________
Expiratory time (Te) ______________________________
Inspiratory flow time______________________________
Inspiratory hold time _____________________________
Tidal volume (V) _________________________________
End inspiratory esophageal pressure (insp Pes) _______
End expiratory esophageal pressure (exp Pes) ________
Another common way to graphically display these parameters
is to plot pressure and flow over volume (Figure 2).
FIGURE 2 EXERCISES
Identify and quantify:
Peak airway pressure (peakPaw) ___________________
Plateau airway pressure (platPaw) __________________
End expiratory pressure (EEP) _____________________
Peak inspiratory flow (insp V)_______________________
Peak expiratory flow (exp V) _______________________
Tidal volume (Vt) ________________________________
End inspiratory esophageal pressure (insp Pes) _______
End expiratory esophageal pressure (exp Pes) ________