Page 101 - Clinical Application of Mechanical Ventilation

Classification of Mechanical Ventilators 67

c d
Pressure

a b e

© Cengage Learning 2014

f g
h
Time
Figure 3-14 A pressure-time scalar in pressure-controlled mode. A pressure-time scalar in
pressure-controlled mode. a: beginning inspiration, b: end-expiration/beginning inspiration,
c to d: pressure plateau, d: end-inspiration/beginning expiration, e: end-expiration, f: inspiratory
time, g: expiratory time, h: total cycle time.

Intermittent Mandatory Ventilation (IMV)

Intermittent mandatory ventilation (IMV) allows the patient to spontaneously
breathe between time-triggered ventilator breaths, which may be volume- or
pressure-controlled. The patient is able to breathe gas at the same F O and base-
2
I
line pressure, without triggering a mandatory breath (ventilator breath). Spontane-
ous breaths may also be augmented using pressure support to increase the patient’s
spontaneous tidal volume and to reduce some of the inspiratory work associated
with the endotracheal tube’s resistance. Figure 3-15 illustrates the IMV mode.

Pressure Support

Pressure support is a variation of the spontaneous mode of ventilation that augments
a patient’s spontaneous effort with positive pressure. It is a spontaneous ventilation
mode in which the patient must trigger each breath (pressure- or flow-triggered).
This mode augments spontaneous ventilation, increasing tidal volume with the ap-
plication of adjustable pressure. On initiation of a breath, a constant pressure (preset)
is delivered until the flow rate reaches between 10% to 40% of the peak inspiratory
flow; then, expiration begins. In this mode, flow is variable, and flow will increase
to a level needed to maintain the desired pressure support level. This mode assures
that the patient’s spontaneous breaths are large enough to maintain adequate blood

10 m

3 s © Cengage Learning 2014
0
23
Figure 3-15 A scalar presentation of intermittent mandatory ventilation (IMV).
m = mechanical breath; s = spontaneous breath

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