# Autovent 4000 I:E Question



## 18G (Aug 10, 2012)

On the Autovent 4000, the Inspiratory Time has a setting of 1 sec for a child and 2 sec for adult as labeled. This is confusing me. 

A normal I:E time is usually 1:2 which is inspiration occurs over 1 sec. So why does the Autovent specify an adult receives its volume with an Inspiratory Time over 2 secs versus the usual 1 sec? And further why is a child receiving it's volume over 2 secs versus 1 sec?

I am seeing that the "Adult" and "Child" labels can really confuse the operator. If I am understanding correctly, the Autovent Inspiratory Time control needs adjusted appropriately based on the desired VT to be delivered. Such as an adult can be ventilated on the "Child" setting as this is just a specific Inspiratory Time. A 1 sec Inspiratory Time is generally considered appropriate unless a specific need for longer Inspiratory Time is indicated, correct? So, most of the time we should have the Inspiratory Time control on "Child" which is 1 sec?

For example, per the Autovent manual, 200 - 600mL can be delivered over 1 sec and 400 - 1200 delivered over 2 secs. 

So last question is, is it best to just ignore and adult and child labels and just be aware of the VT that is delivered with each of the two Inspiratory Time settings?


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## Merck (Aug 10, 2012)

An Autovent is a bit of a simplistic vent.  A Ti of 2 seconds for an adult is quite long, especially for lower volumes.  This results in a very low flow which can be extremely uncomfortable for a patient.  Also, volumes of 1200 are huge in the vent world and could easily lead to volu- and barotrauma.

With kids one also has to be quite careful as the younger they are the more likely I am to use a pressure setting over volume.  A Ti of 1 second might also be inappropriate there as well.


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## 18G (Aug 10, 2012)

Merk... thank you for your reply. This is what I was thinking too but wanted to seek clarification and some added explanation.

So for an adult patient with a VT to be delivered of say 450mL, the Inspiratory Time of 1sec should be used even though it is indicated as "child" on the vent?


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## Merck (Aug 10, 2012)

Always tricky to give absolutes with a vent as there are so many factors.  In general if you were delivering a Vt of 450 like you say an I time of 2 seconds would be very long leading to crazy low flow.  However, the underlying pathology and reason for ventilation in the first place must be taken into account.  Also, as we don't use the autovent anymore and I haven't used it personally I don't know if there are other built-in things that go along with placing it into Child mode.

It's a lot easier to achieve dysynchrony on a venilator than synchrony and unfortunately the options on the autovent seem to push one into having to heavily sedate any patient.  If you're looking for numbers to compare usually 6-8 ml/kg for a Vt and flow rates should generally be around 40-60 l/min.  I times of around 0.7 to 1.2 are kind of the range I operate in for a patient on volume ventilation.  There's as many variations as there are patients though so don't get locked in to absolutes.

And note the disclaimer that I don't use the Autovent so don't take my word as gospel - I'm more chatting generally about basic vent stuff.  Happy to talk about it though.


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## MSDeltaFlt (Aug 10, 2012)

18G said:


> On the Autovent 4000, the Inspiratory Time has a setting of 1 sec for a child and 2 sec for adult as labeled. This is confusing me.
> 
> A normal I:E time is usually 1:2 which is inspiration occurs over 1 sec. So why does the Autovent specify an adult receives its volume with an Inspiratory Time over 2 secs versus the usual 1 sec? And further why is a child receiving it's volume over 2 secs versus 1 sec?
> 
> ...



An I:E ratio is in no way governed by seconds.  It merely says that your pt's expirations are twice as long as their inspirations. 
Let's look at how that ends up being relating to time if you kept the Ti at 1 sec. 

A RR of 20 with a Ti of 1sec will give you an I:E ratio of 1:2

A RR of 15 will give you an I:E of 1:3.

A RR of 12 will be 1:4.

These numbers have absolutely nothing to do with volume, flow, and if you're setting ratios, Ti.


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## Merck (Aug 10, 2012)

Fine point MS, should of made that clear, sorry


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## 18G (Aug 10, 2012)

With exception of a patient with Auto-PEEP which would require a longer expiratory time, is the I:E important to consider then with the Autovent 4000? 

The only way to cause a longer expiratory time is by lowering the RR?

A 1:2 is said to be a normal physiologic I:E ratio yet with a typical RR on a vent of say 10, the I:E is like 1:5. Is this an important consideration? If so, how?


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## JakeEMTP (Aug 10, 2012)

18G said:


> With exception of a patient with Auto-PEEP which would require a longer expiratory time, is the I:E important to consider then with the Autovent 4000?



With this "automatic BVM" you would have to determine the actual intrinsic PEEP or to appropriately adjust for it since you do not have a graphics or even a decent manometer.  Auto PEEP comes in at least 3 different forms and does not always result in hyperinflation. Adjusting the inspiratory or expiratory times may not always be the answer and may worsen the situation for some patients. This ventilator should only be used on the dead, almost dead with little to no response and on a very, very stable patient that is used to a ventilator and can give you feedback.  I would hope you never put this on a CCT truck. 

Only if someone is very experienced in manipulating ventilators and very confident in assessment of a patient receiving mechanical ventilation should the machine ever be used on complex patients. 

I also suggest you get another inservice from the rep before using on a live patient if you are planning to use it at all.


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## Merck (Aug 11, 2012)

Well put.  LTV 1200 ftw


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## DrankTheKoolaid (Aug 11, 2012)

Merck said:


> Well put.  LTV 1200 ftw



That, I initially trained on this and thankfully we have 2 for our CCT's.  Rest seem like toys after using it


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## 18G (Aug 11, 2012)

In the state I am stationed the Autovent 4000 is the only ventilator approved by the state. However, in the other state I practice we do have the LTV1200. 

I would much rather have the Autovent for controlled ventilation than no vent at all. And the 4000 does CPAP as well. 

I agree that up to this point training has been light. That is what I am tasked with to change hopefully by getting the respiratory dept to provide the training. 

But the vents are deployed now so I'm doing the best I can to start elevating staff knowledge regarding vent management.


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## MSDeltaFlt (Aug 11, 2012)

18G said:


> In the state I am stationed the Autovent 4000 is the only ventilator approved by the state. However, in the other state I practice we do have the LTV1200.
> 
> I would much rather have the Autovent for controlled ventilation than no vent at all. And the 4000 does CPAP as well.
> 
> ...



The LTV 1200 is good. Bulky and knobby, but good.  I prefer the LTV ReVel. Smaller, lighter, easier to use, but not cheap unfortunately.


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## 18G (Aug 11, 2012)

Can someone say specifically what the inspiratory time should be on the Autovent? 

Vent settings of say RR of 12 and VT of 450mL. Should this be over the 1sec or 2sec? And why?


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## usalsfyre (Aug 11, 2012)

18G said:


> Can someone say specifically what the inspiratory time should be on the Autovent?
> 
> Vent settings of say RR of 12 and VT of 450mL. Should this be over the 1sec or 2sec? And why?



The problem is it's patient to patient dependent. You can't blanket say "use an I time of x"


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## 18G (Aug 11, 2012)

usalsfyre said:


> The problem is it's patient to patient dependent. You can't blanket say "use an I time of x"



I get that its not a blanket answer. I'm simply asking the question to start with a basic understanding and then go from there. In other words I'm trying to validate what I believe to be true. 

The Autovent has two inspiratory time settings. Give examples of which setting should be used for certain patient types. Hopefully that is a little more clear with what I am asking. 

Or how about this way. A patient with "normal" lungs.... should this patient receive inspiration with a physiological 1sec or 2secs?


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## MSDeltaFlt (Aug 11, 2012)

18G said:


> I get that its not a blanket answer. I'm simply asking the question to start with a basic understanding and then go from there. In other words I'm trying to validate what I believe to be true.
> 
> The Autovent has two inspiratory time settings. Give examples of which setting should be used for certain patient types. Hopefully that is a little more clear with what I am asking.
> 
> Or how about this way. A patient with "normal" lungs.... should this patient receive inspiration with a physiological 1sec or 2secs?



We're not trying to be difficult here.  It literally is completely dependent upon the pt.  Maybe this will help.

If you are wanting your pt on a rate of 20 and you also want an I:E ratio of 1:2 then you will end up having your Ti at 1 sec.  If you want your pt on a rate of 12 and still a ratio of 1:2 then you will end up having your Ti at 2 secs.

Does this help out any at all?


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## 18G (Aug 11, 2012)

MSDeltaFlt said:


> We're not trying to be difficult here.  It literally is completely dependent upon the pt.  Maybe this will help.
> 
> If you are wanting your pt on a rate of 20 and you also want an I:E ratio of 1:2 then you will end up having your Ti at 1 sec.  If you want your pt on a rate of 12 and still a ratio of 1:2 then you will end up having your Ti at 2 secs.
> 
> Does this help out any at all?



Yes, thank you! That does help a lot. So my next question is... should a 1:2 ratio be maintained unless something indicates other wise since a 1:2 is considered physiologic? And a 1:2 is more comfortable for the patient generally speaking?

Granted, when we are using the Autovent, the patient is seriously injured or ill (ie SAH, massive MI, overdose, etc) and the patient is sedated and sometimes paralyzed. So the patient isn't aware of the vent but again just want to be clear.


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## JakeEMTP (Aug 11, 2012)

18G said:


> Yes, thank you! That does help a lot. So my next question is... should a 1:2 ratio be maintained unless something indicates other wise since a 1:2 is considered physiologic? And a 1:2 is more comfortable for the patient generally speaking?



"Normal" often only applies to textbooks and leaves out the real world. If you observe people, not just patients, of many types you will find they breathe at many different rates and depths. People who are obese or have a restrictive disease will breathe more rapid and shallower with more like a 1:1 with an average rate of 26 - 30 but that is their norm. When lying flat or just supine people will alter their respiratory rate since that position may not be what they are used to. Having a piece of plastic that is only 7 mm in diameter also alters "normal".  For this reason you will have to try to match the ventilator with what the patient is doing especially with something like this AutoVent which is not a "smart" vent with limited sensitivity  and will not adjust to the patient. The textbook norms might only apply to a completely sedated, paralyzed or almost dead patient. Even then you will have to adjust your settings for the patient but then an Autovent won't give you much feed back on how much it is stuggling to ventilate the patient.


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## MSDeltaFlt (Aug 11, 2012)

18G said:


> Yes, thank you! That does help a lot. So my next question is... should a 1:2 ratio be maintained unless something indicates other wise since a 1:2 is considered physiologic? And a 1:2 is more comfortable for the patient generally speaking?
> 
> Granted, when we are using the Autovent, the patient is seriously injured or ill (ie SAH, massive MI, overdose, etc) and the patient is sedated and sometimes paralyzed. So the patient isn't aware of the vent but again just want to be clear.



Without overthinking this, yes.  Generally speaking 1:2 is considered normal.  This is how I manage my vents.  Vt = 5-10 CC/kg of ideal body weight.  RR = 12-20... ish.  FiO2 to SpO2 > 94%.  Keeping RR and I:E to maintain EtCO2 35-45 with as efficient as possible to keep optimal PIP without any inverse I:E ratios.


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## 18G (Aug 11, 2012)

MSDeltaFlt said:


> Without overthinking this, yes.  Generally speaking 1:2 is considered normal.  This is how I manage my vents.  Vt = 5-10 CC/kg of ideal body weight.  RR = 12-20... ish.  FiO2 to SpO2 > 94%.  Keeping RR and I:E to maintain EtCO2 35-45 with as efficient as possible to keep optimal PIP without any inverse I:E ratios.



This is what I do too actually. Perhaps I am over thinking the whole I:E ratio. I just wanted to make sure I was understanding correctly so when people choose the inspiratory time on the Autovent they are not falsely locked into a particular  setting based on the adult and child label on the dial. 

Thanks for explaining.


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## Merck (Aug 11, 2012)

Mechanical ventilation is probably the most subtle thing to get your head around.  For me the concepts where much more difficult when learning than any pharmacology, etc.  It really pays to get a good base of knowledge starting with anatomy and physiology and then applying the changes wrought by various disease states.  Inappropriate vent settings are the best way to increase morbidity/mortality IMO.

Grab a used copy of 'Mechanical Ventilation' by Pilbeam.  Dryest read ever but good information.


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