Page 383 - Clinical Application of Mechanical Ventilation

Ventilator Waveform Analysis 349

make it easier to breathe initially, relaxing the patient and satisfying what appeared
to be an inadequate peak flow or V setting. Experience suggests that all three
T
methods should be attempted. No research shows that there is only one way to
satisfy a particular dyssynchronous waveform pattern. These suggestions are based
on knowledge, experience, and research. Sometimes only a change in mode from
VCV to pressure-controlled ventilation will provide patient-ventilator synchrony.
Adjusting the peak flow, In some patients, the breathing patterns can be so erratic that little can be done
sensitivity, tidal volume;
changing the mode of ventila- to provide synchronous ventilation. Pain, neurologic damage, psychologic stress,
tion; or sedating the patient or unknown reasons may be causing erratic patterns of breathing that cannot be
may restore patient-ventilator
synchrony. matched by today’s ventilators. Patients may have to be sedated for periods of rest
under such circumstances.

Dyssynchrony during Descending Ramp
Flow Ventilation

Figure 11-29 presents the same dyssynchronous conditions depicted in Figure 11-28
except that DRFWs are being utilized. The dashed lines show the ideal pressure-
time waveforms. Example a suggests a higher peak flow setting to meet initially

120
V (L/min)

1 2 3 4 5 6 7

P (cm H 2 O) 2120

60
a b

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22
1 2 3 4 5 6 7
Time (sec)
Figure 11-29 Descending ramp flow and pressure-time waveforms showing dyssynchro-
nous ventilation as a result of a, inadequate initial peak flow, or b, inadequate mechanical tidal
volume to meet patient demand.

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