Page 100 - Clinical Application of Mechanical Ventilation

66 Chapter 3

TERMINOLOGY OF VENTILATION MODES

A mechanical ventilation mode is defined as “a specific combination of breathing
pattern, control type, and operational algorithms” (Chatburn, 2007). With the ad-
vent of microprocessor-controlled ventilators, the variety and complexity of modes
has dramatically increased (Branson et al., 2004). It is important to understand
mechanical ventilation modes in order to match breath delivery to specific clinical
application and patient needs. This section provides the terminology of basic ven-
tilation modes. Chapter 4 will discuss the clinical application of commonly used
modes of ventilation along with the respective waveforms.

Volume-Controlled Ventilation

Volume-controlled ventilation allows the clinician to set the volume to delivered
with each breath (Campbell et al., 2002). With volume delivery fixed, pressure will
vary, depending upon the patient’s pulmonary compliance and airway resistance
(Figure 3-13). Volume will remain constant in spite of changes in the patient’s
condition. The advantage of volume control is the ability to regulate both tidal vol-
ume and minute ventilation (a product of tidal volume and frequency).
Pressure-Controlled Ventilation

The pressure-controlled mode allows the clinician to set a peak inspiratory pres-
sure for each mechanical breath (Campbell et al., 2002). Since pressure remains
constant, volume and minute ventilation will vary with changes in the patient’s
pulmonary compliance or airway resistance (Figure 3-14). Should the patient’s
compliance worsen or airway resistance increase, the peak inspiratory pressure ter-
minates soon and the tidal volume and minute ventilation decreases. The advantage
of the pressure-controlled mode is that the lungs can be protected from excessive
pressures, preventing ventilator-induced lung injury (VILI).

c
Volume

b d
a

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e f
g
Time
Figure 3-13 A volume-time scalar in pressure-controlled mode. a: beginning inspiration,
b: end-expiration/beginning inspiration, c: end-inspiration/beginning expiration,
d: end-expiration, e: inspiratory time, f: expiratory time, g: total cycle time.

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