Biomedical Engineering Reference
In-Depth Information
need oxygen-enriched air or a slightly elevated airway pressure. When the ventilator as-
sists a patient who is capable of breathing, the ventilator delivers spontaneous breaths and
operates in spontaneous mode.
9.8.4 Controlled Mandatory Ventilation
Controlled mandatory ventilation (CMV) may be divided into two distinct approaches:
volume controlled and pressure controlled. Volume-controlled ventilation delivers a
specific tidal volume to the patient during the inspiratory phase. Pressure-controlled ven-
tilation raises the airway pressure to an adjustable set level during the inspiratory period.
9.8.5 Volume-Controlled Mandatory Ventilation
In this mode, the ventilator delivers a specific tidal volume to the patient during the inspi-
ratory phase. However, at the end of the expiration phase, as shown in Figure 9-42, the
airway pressure may not end at atmospheric pressure. This PEEP is sometimes maintained
to keep alveoli from collapsing during expiration. The increased lung volume increases the
surface area available for oxygen diffusion and reduces the volume of poorly oxygenated
blood returning to the left atrium. PEEP therapy is also effective in improving lung com-
pliance with the partially inflated lung, requiring less volume and energy to return to full
inflation than a completely deflated lung.
The clinician specifies the following parameters on the ventilator:
•
Respiration rate (breaths/min)
•
Flow waveform
•
Tidal volume
•
Delivered oxygen concentration
•
Peak flow
•
PEEP
FIGURE 9-42
Inspiratory flow for
volume-controlled
ventilation. [Adapted
from (Bronzino
2006).]
