Page 260 - Clinical Application of Mechanical Ventilation

226 Chapter 8

TABLE 8-9 Effects of Flow Rate Change on I Time, E Time, and I:E Ratio

Parameter Change I Time E Time I:E Ratio

Increase flow rate Decrease Increase Increase

Decrease flow rate Increase Decrease Decrease
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Other Ventilator Controls That Affect the I:E Ratio. Besides the flow rate control, other
settings available on some ventilators may also alter the I:E ratio. Table 8-10 shows
the effect tidal volume change on the I:E ratio, and Table 8-11 shows the effect
of frequency change on the I time, E time, and I:E ratio.
Changing the I:E Ratio. Since the I:E ratio may be changed by altering different set-
tings available on selected ventilators, different methods to obtain a desired I:E ratio
are provided as follows (Chang, 2011).

Example 1 Using Flow to Change the I:E Ratio
The calculated flow in
Example 1 is the minimum Given: Minute Volume 5 12 L/min
flow rate required for this I:E
ratio. It is usually set 10 L/min Desired I:E Ratio 5 1: 3
higher to meet changing
minute volume requirements.
Calculate: The flow rate for an I:E ratio of 1: 3
Solution: Flow 5 Minute Volume 3 Sum of I:E Ratio
5 12 L/min 3 (1 1 3)

5 12 L/min 3 4
5 48 L/min

TABLE 8-10 Effects of V T Change on I Time, E Time, and I:E Ratio

Parameter Change I Time E Time I:E Ratio
Increase tidal volume Increase Decrease Decrease

Decrease tidal volume Decrease Increase Increase
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TABLE 8-11 Effects of Frequency Change on I Time, E Time, and I:E Ratio

Parameter Change I Time E Time I:E Ratio

Increase f Minimal change Decrease Decrease
Decrease f Minimal change Increase Increase
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