Page 374 - Clinical Application of Mechanical Ventilation

340 Chapter 11

Based on research, auto-PEEP should be avoided if possible, and external PEEP
applied instead. A valuable advantage of having graphics is that auto-PEEP can be
readily observed and prevented whenever lung conditions have changed or ventila-
Graphics can be used to
titrate and increase the T I to tor settings have been altered. Graphics can be used to titrate and increase the T
I
an appropriate inverse-ratio to an appropriate inverse-ratio level without causing gas trapping or auto-PEEP.
level without causing gas
trapping or auto-PEEP. This management technique serves to increase mean P ALV and improve oxygenation
at lower peak P ALV to reduce the potential of barotraumas.

PRESSURE SUPPORT AND SPONTANEOUS
VENTILATION

Pressure Support Ventilation (PSV)
In PSV, only the pressure
support level is preset. The V T
depends on the PS level, in- Figure 11-22 shows different features of pressure support ventilation (PSV). The
spiratory effort, and patient’s
lung/airway characteristics. first set of waveforms shows the patterns that develop for a relaxed patient breath-
ing synchronously with the ventilator, a concave flow- and square pressure-time

100
V (L/min) 50 25%

2 4 6 8 10 12

P (cm H 2 O) 2100

20 d e
b c

10
© Cengage Learning 2014

22 a 2 4 6 8 10 12

Time (sec)
Figure 11-22 Characteristics of pressure support ventilation (PSV). The pressure support level
remains constant as long as the inspiratory flow continues and is above the end flow. The inspira-
tory flow and inspiratory time are dependent on the patient’s spontaneous breathing effort. The
arrows show an end flow of 25% of the peak inspiratory flow. When the inspiratory flow reaches
25% of the peak inspiratory flow, pressure support (inspiration) ends and expiration begins.

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