What vent mode is best?

[Clipper1]

Sensitivity is not the issue here: in A/C you can provide assisted breath however they are not in synch to patient own respiratory effort. That means if awake patients triggers A/C for an extra breath and ventilator provides it and the next scheduled A/C breath falls right after it timing wise the patient will get breath stacked. SIMV accounts for that and adjusts the timing hence more preferred for awake patients. SIMV does not just mean weaning trial mode.

Hence why S in SIMV stands for synchronized. There is no synchrony in A/C.

The S in SIMV came out about 35 years ago after older ventilators were only IMV.

Here is a better chapter with pictures of graph patterns. This is Hess' book which you did not provide the full text from your quotes.

http://samples.jbpub.com/9781449655594/60038_CH22_462_500.pdf

 

[Clipper1]

Sensitivity is not the issue here: in A/C you can provide assisted breath however they are not in synch to patient own respiratory effort. That means if awake patients triggers A/C for an extra breath and ventilator provides it and the next scheduled A/C breath falls right after it timing wise the patient will get breath stacked. SIMV accounts for that and adjusts the timing hence more preferred for awake patients. SIMV does not just mean weaning trial mode.

Hence why S in SIMV stands for synchronized. There is no synchrony in A/C.

I forgot to mention: Sensitivity is how you set the resistance to triggering the ventilator in either flow or pressure triggered. If you are stacking your check the triggering, fixed flow rate and termination flow. Sometimes on the transport ventilators flow is determined by I-time. Sensitivity is an issue everytime unless the patient is on a paralytic.

 

[Ecgg]

I forgot to mention: Sensitivity is how you set the resistance to triggering the ventilator in either flow or pressure triggered. If you are stacking your check the triggering, fixed flow rate and termination flow. Sometimes on the transport ventilators flow is determined by I-time. Sensitivity is an issue everytime unless the patient is on a paralytic.

That is a great pdf, thank you for the link. Although I was using a different book it's title is Essentials of Mechanical Ventilation.

If you adjust the triggering all that does is either allow an easier trigger or more effort on patient part to trigger a breath.

Let me type it out, maybe this will be more clear.


For example we set the ventilator
A/C RR: 10, Tv: 500ml
Patient will get mandatory breath every 6 seconds with 500ml TV no matter what. However, if the patient wants to take his own breath at second 4-5 the ventilator gives him full 500ml breath and gives another scheduled one on second 6 mark with 500ml. Thus the patient just received 2 breaths back to back and he may not have even fully exhaled the first breath. Ie breath stacked. This is what happens when the patient is fully awake, not sedated on A/C.

SIMV RR 10 Tv: 500ml PS 10
Patient will get mandatory breath every 6 seconds with 500ml TV no matter what. However if the patient wants to take his own breath at second 4-5 the ventilator gives him the breath and adjust the next scheduled mandatory breath further away from just given breath. Thus the patient gets to fully exhale and less chance he will get breath stacked.

 

[Clipper1]

You will note that is the same author as the book you quoted. I just included one whole chapter rather than a few sentences which can be taken out of context of a broader explanation. Also, this was chapter 22. That means there are at least 21 other chapters leading up to this one chapter. There are more discussing much more about patient comfort and therapies on a ventilator. The section on the indepth use different gases had still not be reached.

For example we set the ventilator
A/C RR: 10, Tv: 500ml
Patient will get mandatory breath every 6 seconds with 500ml TV no matter what. However, if the patient wants to take his own breath at second 4-5 the ventilator gives him full 500ml breath and gives another scheduled one on second 6 mark with 500ml. Thus the patient just received 2 breaths back to back and he may not have even fully exhaled the first breath. Ie breath stacked. This is what happens when the patient is fully awake, not sedated on A/C.

This is where your understanding of AC either in Pressure or Volume is faulty.
This is the definition of IMV which is the original form of CMV (Controlled Mandatory Ventilation). In AC (VAC or PAC) the patient wants 16 breaths instead of 10, they will get 16 breaths all delivered at the same consistent volume or pressure and flow unless it is an ICU machine which has the ability to predetermine the flow to meet patient's demands or compliance issues.

Probably the purpose of that example is to teach the basics of a ventilatory cycle so you understand I:E ratios. Beyond that the material progresses to how ventilators actually deliver breaths to a patient. This is just a basic calculation. The only time you will see a static I:E ratio like that will be on a dead or paralyzed (pharmacology or some physical reason).

A few of the ATVs which ambulances carry might be CMV but many are also Assist Control with a demand trigger.

ASSIST means just that. Every breath initiated with be given a set VT or Pressure anytime the patient wants it. That is the control part. Yes the sensitivity to trigger that ventilator is very, very important. You do not want the patient to struggle.

The other major factor to consider on a transport is safety. Compliance can change. PSV is not the mode that you can readily identify that on many transport ventilators. Delivering an acidotic patient to the ICU from hypoventilation or fatigue is not good.

This is why experience in critical care watching at least 2 patients for 8 or 12 hours every worked shift is of great value. Many CC RNs will have over 60 ventilator patient hours every week if they only work 12 hour shift. Even with that it is recommended they have at least 2 - 5 years of experience seeing all they can in the various different units since every type of patient will require a different clinical pathway for ventilation and sedation. Then to have the ability to translate this to a single limb transport ventilator, which they do probably every shift taking the patient to procedures, is yet another educational process.

 

[truetiger]

So how is this better than SIMV w/PSV? In a/c you'll get your mandatory rate and be allowed to over breathe the vent, however the vent will deliver the extra breathes with the full tidal volume, out of sync. In SIMV you'll still get your mandatory rate at minimum and can over breathe the vent as well, however; the ventilator will sync with your breaths and deliver adjusted tidal volumes.

 

[Aidey]

I have move the ventilator discussion from the central line thread here. Please keep the discussion of vents out of the central line thread.

 

[Clipper1]

Maybe a critical care discussion should be more appropriate.

What types of lines and meds do you have available? This discussion was started in the Central Line topic but the two are also related. When these same topics are discussed on critical care forums involving many different professionals, a broader range of issues are presented so that the "best mode" is applied to what suits the patient.

I do see in part this being the problem with overview courses which introduce topics but are too short to dive into much depth or discuss the actual management of a patient from all aspects of care which must all be considered. This includes disease process, medications, lines, acute and chronic issues including renal, cardiac and pulmonary failure.

 

[Aidey]

No one is saying you can't have a multi-topic discussion on critical care issues. I'm just saying you can't have it in the central line thread. If you want to discuss multiple critical care issues in the same thread, start it yourself.

 

[Clipper1]

So how is this better than SIMV w/PSV? In a/c you'll get your mandatory rate and be allowed to over breathe the vent, however the vent will deliver the extra breathes with the full tidal volume, out of sync. In SIMV you'll still get your mandatory rate at minimum and can over breathe the vent as well, however; the ventilator will sync with your breaths and deliver adjusted tidal volumes.

Nothing is out of synch when the breath is delivered when the patient initates the ventilator.

For SIMV, especially for transport ventilators, you have a mandatory breath which is given at a fixed flow and a declerating waveform. For PSV you have more of a square way with a rapid acceleration which might terminate quicker or even be prolonged (which can cause air trapping). The PSV breath might only provide 100 ml of VT when the patient wants and needs 500 ml. Compliance and secretions will play a big factor. If the patient wants 10 L of MV but can only get 5 because of the PSV variations in VT delivery, you will get much more asynchony from a hypoventilated patient.

Please look at the chapter on ventilators I posted you will see all of this graphically illustrated.

 

[Ecgg]

Clipper all I read in your post is that “my understanding is faulty” and how much experience you have as a nurse in ICU. Yet you seem not to acknowledge the difference between A/C and SIMV which I have outlined for you.


In SIMV with Pressure Support, I can identify issues just as well as I set appropriate low minute volume alarms based on patient minute volume. Thus you can identify if the pressure supported breaths are not delivering adequate TV.

 

[truetiger]

Both A/C and SIMV allow the patient to initiate a breath. SIMV compensates for rate and tidal volume. A/C compensates for nothing.

Lets say you want to make sure the patient gets 12 breaths a minute at 500ml. On A/C you are guaranteed 12 at 500. If the patient wants more, they can initiate the vent. So you're going to get a breath every 5 sec at 500. Lets say the patient takes a small breath (100ml), at the 4 sec mark that'll trigger the vent initiating the 500ml tidal volume. Now before than can exhale that breath, the vent is going to deliver another 500ml at the 5 sec mark. This will cause breath stacking if it keeps up.

Now lets look at SIMV. Once again you want 12 at 500. You set your back up rate 12 and your tidal volume. You're guaranteed 12 at 500. Now lets say your patient wants a breath at the 4 sec mark, (100ml again.) The vent will assist the other 400ml and now space out the next breath to synchronize with the patient's respiratory effort to avoid breath stacking. SIMV can also be used in weaning by adding PSV and using a low back up rate.

A/C works great if you're patient is paralyzed (just after RSI) or heavily sedated and does not have a good respiratory drive. Ideal if you're trying to give the respiratory muscles a break. If you're patient has a decent respiratory drive (and you want that) you're going to need to use SIMV to avoid breath stacking.

I can't tell you have many times when we've gone in for a transfer and the patient is under sedated and on A/C. The patient was RSI'd 2 hours earlier and hasn't received anything for analgesia since. These patient's are obviously hurting. They open their eyes, are lacrimating, bucking the tube, and have a sympathetic response.

 

[shfd739]

Both A/C and SIMV allow the patient to initiate a breath. SIMV compensates for rate and tidal volume. A/C compensates for nothing.

Lets say you want to make sure the patient gets 12 breaths a minute at 500ml. On A/C you are guaranteed 12 at 500. If the patient wants more, they can initiate the vent. So you're going to get a breath every 5 sec at 500. Lets say the patient takes a small breath (100ml), at the 4 sec mark that'll trigger the vent initiating the 500ml tidal volume. Now before than can exhale that breath, the vent is going to deliver another 500ml at the 5 sec mark. This will cause breath stacking if it keeps up.

Now lets look at SIMV. Once again you want 12 at 500. You set your back up rate 12 and your tidal volume. You're guaranteed 12 at 500. Now lets say your patient wants a breath at the 4 sec mark, (100ml again.) The vent will assist the other 400ml and now space out the next breath to synchronize with the patient's respiratory effort to avoid breath stacking. SIMV can also be used in weaning by adding PSV and using a low back up rate.

A/C works great if you're patient is paralyzed (just after RSI) or heavily sedated and does not have a good respiratory drive. Ideal if you're trying to give the respiratory muscles a break. If you're patient has a decent respiratory drive (and you want that) you're going to need to use SIMV to avoid breath stacking.

I can't tell you have many times when we've gone in for a transfer and the patient is under sedated and on A/C. The patient was RSI'd 2 hours earlier and hasn't received anything for analgesia since. These patient's are obviously hurting. They open their eyes, are lacrimating, bucking the tube, and have a sympathetic response.

Most of us set all of our vent pt's on SIMV, even the sedated ones that are normally A/C. They get the breaths they are supposed to and if they have a light sedation and trigger one they wont get one stacked right behind it. Our CCT medical director is okay with this and suggested this to us.

We also have to do a fair bit of resedation here as well. Almost exclusively with ER transfers. The pt gets RSI'd then no more sedation or paralytics. I also had one recently that was a larger male, on a moderate amount of Propofol and the staff didnt want to increase it and didnt get why he was fighting, lacrimating etc. Guy was a heavy drinker and nearly 300lbs; its gonna take alot of Propofol to keep him down; or try something different. Soon as we got him loaded the Propofol went up, added Versed and once he relaxed gave more Vec.

The wife said he looked comfortable for the first time in 12 hours.

 

[truetiger]

What's even more disturbing is that we have a band aid station that doesn't even consider doing blood gasses in ventilated patients.

 

[Clipper1]

Clipper all I read in your post is that “my understanding is faulty” and how much experience you have as a nurse in ICU. Yet you seem not to acknowledge the difference between A/C and SIMV which I have outlined for you.


In SIMV with Pressure Support, I can identify issues just as well as I set appropriate low minute volume alarms based on patient minute volume. Thus you can identify if the pressure supported breaths are not delivering adequate TV.

Low MV alarm? Tell me this is just a joke. That might be okay on a pure PSV mode in the ICU with the CR monitor. If the VT is hitting your low MV then you have hypoventilated the patient. At what percentage of your set VT is your target PSV VT? How do you determine Low MV? With just the set VT and then what percentage? What about the spontaneous breaths?

You reasoning that a patient in AC will only receive the amount of breaths set is not correct. Every breath will be at the set VT or PC depending upon VAC or PAC mode.

 

[Clipper1]

Both A/C and SIMV allow the patient to initiate a breath. SIMV compensates for rate and tidal volume. A/C compensates for nothing.

Lets say you want to make sure the patient gets 12 breaths a minute at 500ml. On A/C you are guaranteed 12 at 500. If the patient wants more, they can initiate the vent. So you're going to get a breath every 5 sec at 500. Lets say the patient takes a small breath (100ml), at the 4 sec mark that'll trigger the vent initiating the 500ml tidal volume. Now before than can exhale that breath, the vent is going to deliver another 500ml at the 5 sec mark. This will cause breath stacking if it keeps up.

Incorrect. If you please read the link provided earlier or a decent ventilator book you will see that AC is no longer IMV. All modern ventilators (for the past 25 years) will synch with a delivered breath unless you have failed to set the other parameters correctly such as sensitivity, flow and termination percentages. The set rate is not fixed to be delivered exactly as you have text book calculated the rate.

Now lets look at SIMV. Once again you want 12 at 500. You set your back up rate 12 and your tidal volume. You're guaranteed 12 at 500. Now lets say your patient wants a breath at the 4 sec mark, (100ml again.) The vent will assist the other 400ml and now space out the next breath to synchronize with the patient's respiratory effort to avoid breath stacking. SIMV can also be used in weaning by adding PSV and using a low back up rate.

A/C works great if you're patient is paralyzed (just after RSI) or heavily sedated and does not have a good respiratory drive. Ideal if you're trying to give the respiratory muscles a break. If you're patient has a decent respiratory drive (and you want that) you're going to need to use SIMV to avoid breath stacking.

I can't tell you have many times when we've gone in for a transfer and the patient is under sedated and on A/C. The patient was RSI'd 2 hours earlier and hasn't received anything for analgesia since. These patient's are obviously hurting. They open their eyes, are lacrimating, bucking the tube, and have a sympathetic response.

Again look at the flow patterns. Every ventilator text book will explain the differences to you.

The example you have posted about RSI is just criminal. If this is your patient please, please learn more about ventilator management.

If you RSI a patient, you really should NOT alloow the patient to just wake up abruptly. With any paralytic you should also be sedating. If the patient is bad enough to require RSI, you need to keep that tube and this means keeping adquate sedation. There is absolutely no reason for a patient to ever become wide awake after intubation in an emergent situation.

I have to ask, where are you getting your ventilator training from?

 

[Clipper1]

Most of us set all of our vent pt's on SIMV, even the sedated ones that are normally A/C.

If the patient has a plateau pressure over 34 or even just secretions, what do you think that PSV breath is going to do. There is a reason why come patients are on AC.

I also hope everyone here realizes AC (Asist Control) applies to both Volume and Pressure modes.

 

[Clipper1]

What if you have a patient at the hospital on AC? Would you automatically just change to SIMV because YOU like it better?

What about patients who are on HFOV, HJV or APRV? Is SIMV also going to be your mode of choice?

 

[shfd739]

If the patient has a plateau pressure over 34 or even just secretions, what do you think that PSV breath is going to do. There is a reason why come patients are on AC.

I also hope everyone here realizes AC (Asist Control) applies to both Volume and Pressure modes.

Im thinking by PSV you mean pressure support?

We rarely have pressure support patients.

 

[shfd739]

What about patients who are on HFOV, HJV or APRV? Is SIMV also going to be your mode of choice?

Ive never heard of or seen these in use.

 

[Ecgg]

Clipper I think you are misinterpreting what is being said. We are discussing pure mode A/C and SIMV and what you are giving an example of is actually PRVC

Modern ventilators can combine various parameters and modes together, however that is no longer what we are discussing here. Certainly a hospital ventilator will be much more sophisticated than a transport ventilator. However as I stated we are looking what pure A/C mode and SIMV mode.

The definitions provided are very sound. Perhaps you can do a consult with RTT about this.