Mechanical Ventilation- what's the difference between settings?

XingtheBBB, BSN, RN · Feb 4, 2010

Easiest question/ shortest answer first- FiO2 is the amount of oxygen mixed into the room air. Tidal volume Vt is the amount of air filling the lungs with each breath.

For modes- start with this video-

sunnycalifRN · Feb 4, 2010

a good place to start is http://www.icufaqs.org

after that, talk with one of the experienced RT's in your ICU when you have a patient on a vent. explanations make more sense when they're about your patient

detroitdano · Feb 4, 2010

Find a trustworthy RT and have them explain things to you when you have a vented patient. Like was mentioned already, it's much easier to understand everything when you can see hard numbers and real machinery at work.

I'm just curious as to why basic things like the differences between modes is something you're not comfortable with yet. My orientation program drilled us hard on vents and understanding ABG's, etc. Did your orientation not really cover any of that? If so, I'd be asking for some extra education sessions because you're likely not the only new RN in your hospital's system that didn't get enough education on vents.

dmc_rrt · Feb 5, 2010

Quick Version:

Volume A/C=pt triggers breath, and ventilator delivers set tidal volume or Pt cannot trigger breath (due to decreased resp drive) and ventilator delivers set Resp rate and tidal volume.

Pressure A/C=pt triggers breath, and ventilator delivers set Inspiratory Pressure or Pt cannot trigger breath and ventilator delivers set Resp rate and Inspiratory Pressure.

SIMV=A/C, but also, pt can make Pressure Support breaths between set Resp rate.

Hope this makes a little sense.

fiveofpeep · Feb 5, 2010

my problem is that I understand the concepts but I cant figure out a way for me to remember the names. I end up having to look it up every time I have a patient until it sticks.

XingtheBBB, BSN, RN · Feb 5, 2010

my problem is that I understand the concepts but I cant figure out a way for me to remember the names. I end up having to look it up every time I have a patient until it sticks.

A-C ASSISTS each breath to a CONTROLLED volume.

SIMV SYNCHRONIZES (not every but) INTERMITTENT breaths to a MANDATORY Volume- other breaths can be as small or big as the patient's respiratory effort allows.

Maybe that helps?

fiveofpeep · Feb 5, 2010

it definitely does. thanks thats what I was looking for :)

RTpupil · Jun 27, 2013

A/C and SIMV will both ventilate the patient so either mode is good. A/C mode will assist/ control meaning it will give the patient a breath, it will pick up on the pt trying to take a breath and give the patient that breath. Simv mode will give the pt the set rate (f) and let the pt take a breath on their own. no need to worry about breath stacking the machine synchronizes the breaths. A/C is good for initial setting, SIMV is good for weaning. incase there is some Raw in SIMV mode just add pressure support :)

TraumaSurfer · Jul 5, 2013

A/C and SIMV will both ventilate the patient so either mode is good. A/C mode will assist/ control meaning it will give the patient a breath, it will pick up on the pt trying to take a breath and give the patient that breath. Simv mode will give the pt the set rate (f) and let the pt take a breath on their own. no need to worry about breath stacking the machine synchronizes the breaths. A/C is good for initial setting, SIMV is good for weaning. incase there is some Raw in SIMV mode just add pressure support :)

Both modes can be either Volume or Pressure.

Both modes allow for spontaneous breathing. However, AC allows for more synchrony with each breath being delivered more consistently. SIMV has "a big" breath and then a "little pressure supported" breath both with variations in flow leaving the patient feeling like "what's up" trying to keep up with the different flows and tidal volumes. Usually when people set the pressure supported breath they just pull a number out of the air like 5 or 10 cmH2O and don't really understand why. You see this a lot on IFT transports because "someone told them SIMV was best and 5 or 10 is per protocol". SIMV is also the mode where you are more likely to get breath stacking because of the differences in flow patterns and the volume of the PS breath being woefully inadequate.

incase there is some Raw in SIMV mode just add pressure support.

With this comment you have taken ventilation back to the 1970s. Refer to the photos of the MA1 on another discussion. That is called IMV and torture. Why would you not support a patient's breath? This would only lead to asynchrony and fatigue faster.

SIMV is also the slow boat for weaning and luckily by now most physicians and RTs have realized this. AC to straight PSV or VSV is the way to go without the "decrease by one breath today" and get an ABG in the morning SIMV mentality. SIMV was great in the 1980s also serves a purpose in neonates, especially preemies, due to their breathing already being rather asynchronous but not for the adults unless they are in a SubAcute and have years to wean.

Also most modern ventilators are sensitive to detect a spontaneous breath or have the technology for a skilled RN or RT to make adjustments to prevent it. Breath stacking comes from inappropriate setting or a need for medications to be adjusted.

This is one good purpose for SIMV but only temporarily and that is for hiccups. It is a bandaid fix for the hiccup to be with the PSV breath so they won't set off the high pressure alarm.

To the OP:

For whatever ventilator you are using there is probably a manual lying around somewhere or you can download it and see just how the ventilator delivers a breath in each mode. Most will also have great diagrams for easy visual understanding.

Example:

Drager

http://www.draeger.net/media/10/07/76/10077601/rsp_new_nomenclature_ventilation_modes_ICU_booklet_9066477_en.pdf

Also, look at the graphics while assessing the patient and you will see and hear the difference.