can somebody explain to me regarding the combination of simv + autoflow and wath will be the out come of this two?

In SIMV when you turn autoflow on the machine or mandatory breaths will change from VC style to PRVC style. Meaning that the flow waveform will go from square to decelerating, the flow its self will go from constant to variable. The pressure waveform will go from accelerating to square. Your mandatory volumes will go from being constant to being slightly variable. The vent will increase or decrease pressure to maintain the volume goal you have set. The autoflow also activates the active exhalation valve allowing the patient to inhale or exhale when ever they want.

Hope this helps, if not let me know and I will try to reword.

light,

thank you for your responds now i understand them very clearly.

It will do the same in CMV mode (Assist Control if Triggering turned on, otherwise really as the patient isn't locked out).

Also in CMV mode one has the option of using Sighs per every 100 breaths the Peep will increase by selected amount. When I was last a Drager user (pre XL) this was only available in CMV mode.

Another option on Drager vents not considered enough (where I've seen it used) is when a patient is on ARDSnet protocol. In PRVC/Autoflow type breaths with low VT IF the patient pulls over the set VT the pressure target (and hence flow) will be reduced in a vicious cycle. To a degree turning on ATC can ameliorate this. But another thing to consider is instead of Autoflow to use the Pmax option. This way one can set a pressure "limit" in which a set initally high flow rate will sense that limit and (without alarming) ramp flow down as it "hugs" that limit---going from square to decelerating. Say you have someone on VT 500 and set Pmax to 35, Ti to 0.8 and flowrate at 120 in CMV mode (ARDSnet calls for A/C not SIMV). So when a breath is triggered (via time or patient effort) flow "jumps out of the gate at 120 L/M UNTIL a pressure of 35 is reached. Then flow decays as pressure stays at 35 UNTIL the VT is delivered. If the VT goes in by 0.6 seconds there is a 0.2 second insp. pause. If by 0.8 seconds the VT hasn't been delivered the breath still ends and an alarm will sound (say patient needs suction, etc. & why setting Ti is important and may need to vary as patient is more actively triggering the vent vs. sedated or paralyzed).

That way a more solid foundation of flow can be established which won't decay if the patient occasionally draws in larger VT's.

I know many here are APRV advocates as opposed to ARDSnet. Without debating this issue the fact remains that many RT's practice in settings where ARDSnet is ordered. Using PRVC/Autoflow/VC+ breaths can be a recipe for flow starvation, whereas setting high flow and short Ti in flow controlled A/C can at least provide foundation which won't decay per the PRVC routine.

First sentence should read

quote:

It will do the same in CMV mode (Assist Control if Triggering turned on, otherwise IMV really as the patient isn't locked out).

jeffwhitnack,

thank you for your responds the problem is your explination is to deep beyond my knowledge. can you explain it in simple as posibble because im new in the field of Respiratory. thank you!

I'll try to simplify.

When Autoflow is selected it turns all volume targeted breaths (in SIMV, CMV, or MMV) into really Pressure Control breaths. You dial in an insp time and a risetime, just as with regular Pressure Control. BUT the volume target then creates a situation analogous as if there was a RT standing there and (super fast) adjusting the Pressure Control pressure target such that the desired or dialed in VT is returned. It only goes up or down from 1-3 cwp per breath. This is essentially the same as PRVC on Servo Vents or VC+ on Puritan Bennett. And since it's Pressure Control then you also get the exhalation valve which allows "free breathing" as the time at the high pressure is really akin to a higher Peep level (say Ti is 4 seconds the patient can breath atop it as if that pressure were just CPAP).

The problem arises when a patient starts to then demand more VT than is set. A good example is when ARDSnet VT's are selected. I'm 6 ft. 2 in. and my ARDSnet VT is 493ml. So imagine that I'm intubated in the field (post trauma) with a number 6 ET nasally cuz they were lucky to get anything in. Further imagine that due to BP concerns (or fad of not sedatinng too much) I'm not given adequate sedation. Major pain, major fear, temp up to 40. But VT in Autoflow is 490 cuz I have low PaO2 on 70% O2, bl contusions, etc. so ARDSnet protocol in place. But I'm consistently drawing in VT's over 1000 cc's. So then Autoflow (or imaginary Quckdraw RT) just drops the PC insp pressure to basically nothing. But I'm in need of support and basically suck in so much I put myself into pulmonary edema.

If the VT overshoot isn't too much, or too often, then turning on Automatic Tube Compensation can help because then the targeted (VT goal based) airway PIP is projected to the calculated carinal--based on VT dialed in, ET tube size, and insp flow demand of patient. So even if the targeted PC insp pressure is only 1 cwp above PEEP, if ATC is on and my flowrate demand is 60 L/M and I've got a number 6 ET tube then the pressure at the proximal airway may be elevated enough to help unload me---though it still may not be enough.

And if the disparity isn't too great or relentless between dialed in VT and desired then going to a high initial flowrate (turning off Autoflow) and using the Pmax might do the trick.

Or otherwise you have to sedate (and possibly paralyze), or increase VT or......I hear an APRV refrain.

thank you jeffwhitnack,

one more thing.i have a patient in cmv with autoflow there is alarm that always come out. volume not constant, pressure limitted. what may be the cause of this alarm?

What that alarm means is that....

given the VT you've dialed in, the upper pressure limit (alarm) selected, the inspiratory time and risetime......and given the lung compliance and resistance of the patient....


The ventilator is unable to deliver the dialed in VT.

Solutions?

Maybe the patient needs suction? Maybe the patient is agitated, and/or has increased edema.

So unless you can fix something with the patient you can solve the alarm (not necessarily the problem) by doing one of a combination of...

Decreasing set VT

Increasing pressure limit

Increasing insp time (especially if flow doesn't terminate by end of current insp. time)

If rise time is set to some high level decrease it to something like zero to 0.2 (I've seen people dial in over 0.4 seconds and the supposed decelerating waveform is actually a sine wave). That way during the set insp time the rise to pressure will be faster (and therefore more likely to get set VT within any set insp time).

quote:

Originally posted by JeffWhitnack:
Using PRVC/Autoflow/VC+ breaths can be a recipe for flow starvation, whereas setting high flow and short Ti in flow controlled A/C can at least provide foundation which won't decay per the PRVC routine.

Wouldn't pressure starvation be a better term here? Given the example you gave the vent will respond to the higher volumes pulled by the patient by dropping the inspiratory pressure. The patient can still breath in what ever inspiratory flow they want, they will just have to do it more on their own.
I agree with what you are saying, many RCP's will forget this part of PRVC/autoflow and I have seen it have detrimental effects on a patients PaO2 since you are lowering the mean airway pressure. In these case I will look more at just going to PCV+assist (pressure control for those that do not use the Drager). This will allow me to select the pressure I want to deliver and just let the patient go with what ever volume they want. I know this goes in the face of ARDSnet 6 cc/kg, but I feel the pressure aspect of ARDSnet is more useful that just the 6 cc/kg.