I recently picked up an adjunct clinical instructor position for a local RT school at the hospital where I'm on staff full time. In going over vent theory, however, I had a hard time explaining the vent's Ecycle & Rise time features. I myself know basics about them and adjust them frequently, but I want to make sure I'm giving the students correct information when I explain how they work & when to change them, etc. - Can someone help? Thanks for your time...

For rise time I've used this analogy.

Imagine a feline (go big, jaguar or leopard) which has the goal of jumping up and landing on a platform a certain distance up in the air. Just like a pressure target in a pressure mode in which rise time would be used or set. Now if the cat jumps straight up, ninety degrees, that is like a rise time of zero, or 100% on 840. What is moving ahead is time. So if the angle is 45 degrees that might mean a 0.4 second rise time.

To calibrate what to set rise time at. I use the analogy of a patient breathing in as fast and deep as he can. Rise Time 0.0 seconds or 100%. But if it's an intubated little old lady with a number 6 ET tube in and she's breathing very slowly, then a rise time as previous would mean that early pressure target aquisition would terminate the breath before enough VT was delivered (and why I don't like to use PS for that "stable and non fatiguing mode")

For E cycle, used in Pressure Support only, I want to instill in the students that it's not Pressure or Volume Control and have them internally ponder "what causes the breath to end?". What starts by flow now will end by flow (getting into preacher mode). And then to appreciate how both rise time and exp flow sensitivity can work together for either good or bad effect.

I then also make some aside about ...if you're worried about insp time and want to use a purely pressure mode, why not use PC and just set it yourself? You can watch the patient and look at waveforms. Just set it. And if you're worried about PS not delivering the VT so are pulling back on Risetime...why not just dial in the VT with PRVC/VC+/Autoflow?

Thought of another method I use. When someone is on Bipap don't use the waveforms but instead the bar graph. Adjust scales so they capture it right. Then do risetime from lowest to highest and see impact on VT, flow etc. I usually set the risetime that give me the largest VT for the settings. I also set the backup Ti pretty long. 1.4 seconds at least. IF the patient doesn't assist or trigger you'll want a longer Ti so that VT has a better chance to get to a patient.

Also on a vent setup a bag and a fairly small ET tube, and alternate with larger one. Show the extremes of setting both Rise Time and Exp Sens and how it impact each (use PC).

Patient breathing like a locomotive on meth----shortest RT and low Exp Flow Termination. Patient breathing slow and low, opposite.

Try this site for that little extra help.

http://www.ventworld.com/education/wp_educational_TeEqu.asp