50/.06 = 833 ml/sec
Then divide the tidal volume by the flow rate.
750/833 = .9 seconds.
Add pause time to the inspiratory time.
.9 + .3 = 1.2 seconds. You should also be able to find the I:E ratio now.
Next, find the plateau pressure if the volume were 650 ml. 650 / 46 = 14 cm H2O.
Then add the pressure due to resistance to the new plateau pressure. 14 + 7 = 21 cm H2O. This assumes you will not change the peak flow during the test breath.
To test the volume, set the sigh volume at 650 ml and the sigh high pressure limit at 25 cm H2O.
Deliver the 'sigh' breath and find the plateau pressure.
If the patient's compliance does not change at the new volume, the sigh high pressure limit will not alarm when the breath is delivered. If compliance equals 46 ml/cm H2O at a volume of 650 ml, the patient is not over-inflated. Try and do this quickly to prove your point before the patient's PaCO2 climbs to 80 torr. 650 x 40 = 325 x ?
? = 80 torr
? = 24 BPM. The patient obviously didn't like a PaCO2 of 80 torr. No surprise there.
RC Ed WebMaster