624074/07 C-17
C.3.3 Lung-protective rules strategy
Not all combinations of Vt and f shown in Figure C-7 are safe
for the patient. The high tidal volumes will over distend the
lungs and the small tidal volumes cannot produce alveolar ven-
tilation at all. Another risk lies in inadequate respiratory rates.
High rates can lead to dynamic hyperinflation or breath stack-
ing, and thus inadvertent PEEP. Low rates can lead to hypoven-
tilation and apnea. Therefore, it necessary to limit the number
of possible combinations of Vt and f. When limits are imposed
on the possible combinations of Vt and f, then ASV uses
a double strategy:
• The operator input for ASV determines the absolute bound-
aries.
• Internal calculations based on patient measurements fur-
ther narrow the limits to counteract possible operator errors
and to follow changes of respiratory system mechanics.
The effect of the strategy is shown in Figure C-8 and explained
in the subsequent subsections.
Figure C-8. Lung-protective rules strategy to avoid high
tidal volumes and pressures (A), low alveolar ventilation
(B), dynamic hyperinflation or breath stacking (C), and
apnea (D)
To Next Page
Loading...