Vent settings? - page 2

What do these vent settings really mean?? VT (tidal volume) AC Peep F02... Read More

  1. by   NRSKarenRN
    Check out our thread: Vent Information
  2. by   ethelbsnrn
    I got another "wrinkle" in my brain.....thanks.

  3. by   HawaiiRRTRN
    Quote from papawjohn
    Hey Raindrop

    Simple answers mostly. Tidal Volume: When the machine cycles it is set to give a specific amount of air (well--gas, since it meters in a certain Oxygen content, but think of it as air for now.) Say we set the vent for a TV of 800ml. Then every breath given by the vent is--you guessed it!!--800ml.

    AC: Assist Control. There are two really 'normal' or 'popular' ways of using the vent. One is to set the machine so that every breath gets the FULL TIDAL VOLUME. This means that say we set the vent to give 8 breaths per minute and 800ml/breath and it set on ASSIST CONTROL. OK? The very least the patient's gonna get is 8 full breaths/min. What if the pt is awake and takes a couple of breaths more than 8/min? (We say--he 'breaths over' the vent.) Well, the vent senses his breath and gives him the FULL TIDAL VOLUME of 800ml with each breath whether or not there's much of a breathing effort on his part.

    Constrast this with IMV (Intermittent Mechanical Ventilation). Imagine the same breaths/min are programmed into the vent: 8/min and the same volume of 800ml. But we're on IMV mode istead. He gets 8breaths/min of 800ml. But this setting means that his own spontaneous breaths are ONLY AS BIG AS HE CAN BREATH.

    Usually the pt in crisis gets put on AC, then is 'weaned' from the vent through the IMV settings--because that requires him to work harder on his own.

    PEEP: Positive End-Expiratory Pressure. Remember that air is pulled by the lungs into tiny little air sacs called 'alveolus'. These are very very small little balloons where the blood swooshs around the outside--giving up its CO2, absorbing O2. You know they're wet inside. You know the coughing and suctioning and mucous production of the chest can collapse these balloons. Yes? It's not hard to imagine a sick persons chest has lots of aveoli that are collapsed like shriveled up little balloons.

    Now if your kid (nephew, neighbors kid) brings this poor very wet shriveled up balloon to you and says: Blow up my balloon! You're going to have to puff very hard to get the walls of the wet balloon to seperate so you can blow it up. OK? You've had that experience? Well, why? The answer is 'surface tension' which means the fluid in the balloon clings to the walls of the balloon.

    Same thing happens inside the alveoli. The wet walls cling together and make the alveolus resistant to re-opening. (Therefore the importance in non-vented pts of 'turn, DEEP BREATH, and cough.')

    PEEP is a constant elevation of the pressure inside the pt's lungs that minimizes the collapse of the alveolus. Since the lowest pressure in the lungs is at the 'end of expiration' (DUH!!)--we apply--you guessed it "POSITIVE END-EXPIRATORY PRESSURE".

    Little hint: the lungs are soft and actually expand a little bit when we 'blow them full' by using PEEP. And what else is in the chest? THE HEART!! So PEEP can lower the cardiac output and lower the blood pressure.

    FiO2: "Fraction Inspired Oxygen". It's the oxygen setting on the vent.

    Pressure Support: It is an extra 'push' of pressure delivered with each breath above the minimum needed to get the pre-set volume in. So each breath is bigger than it would ordinarily be. It's less important when your pt's on AC mode. It increases the volume of breaths and works with PEEP to increase the number of full alveoli--and since pressure helps the Oxygen in the 'air' dissolve through the interstitial fluid into the blood--you get higher pO2 levels and higher Sats.

    AG: Don't use that abbreviation except for 'attorney general' (on political websites).

    Hope this helps
    Papaw John
    Papaw John,

    Excellent explaination of the vent abbreviations! Would like to add one small clarification....Pressure Support only works in SIMV and Spontaneous modes of ventilation and then only on spontaneously generated breaths. It's main purpose is to allow the patient to overcome the resistance created by the artificial airway by providing that extra "push". It can also improve ventilation (lower PCO2) as well as increase oxygenation (PO2). Also, never heard of AG in relation to the vent.

  4. by   papawjohn
    Hey Hawaii

    You are of course correct that there are subtle ways that Pressure Support and Peep and such interact with the AC mode and SIMV mode. Actually, I've had to pass that test and if pressed, could draw graphs on a piece of paper and explain it "KINDA". It has to do with the way the vent keeps the Pt from having to create negative pressure (suction) through the vent tubing. Yes?
    Because the vent 'senses' the negative pressure and instantly compensates.

    Anyhow--I'm finished a long string of nights of work--am behind a couple of rum drinks--can't straighten this out right now.

    But the important things all happen in the alveolus. All the subtle and interesting things we can talk about and analyse--they don't make much difference if the O2 goes in and the CO2 comes out. That is a function of volume and pressure in the smallest airways.

    If new nurses can listen to their Pt's bases and look at the pressures on the vent and see the ABGs and put all that together---what more can we want?

    Keeping the target in the bullseye--
    Papaw John

    So many years ago--took the RedCross Life Guard course to work as a life guard at swimming pools. Maybe 1959? This was before CPR-can you belief it?

    We were s'posed to lay a near-drowning victim prone on the side of the pool, squat at his head, and rhythmically raise his elbows up in the air and compress them against his chest. (This was s'posed to save his life!! Can you imagine?)

    The rhythm for this was set by the reciting of the words:
    OUT goes the bad air....
    IN comes the good air....

    Well. The technique of course was unbelievably stupid from the viewpoint of 2005. But the idea: OUT goes the bad air---IN comes the good air. Never has lost it's logic.

    P- J-
    Last edit by papawjohn on Oct 19, '05
  5. by   breatheasy
    Quote from raindrop
    What do these vent settings really mean??

    VT (tidal volume) the amount of air moved during one cycle of respiration. Inspiration + Expiration

    AC Assist Control-a mode of ventilation whereas the patient triggers breaths but has a set volume delivered with each breath.

    Peep positive end-expiratory pressure- pressure applied at end-expiration to splint open collapsed alveoli

    F02 actually FIO2. Fraction of inspired oxygen. The amount of ozygen in room air is approximately 21%

    PS (pressure support) Pressure applied at inspiration to help lower the resistance of artificial airways (ETT, Trach)

    ABG? arterial blood gas?
  6. by   PageRespiratory!
    Pressure support is deactivated during assist control. It seems you're confusing PS with the trigger variable, which could be pressure or flow generated. PS is generally considered a ventilatory function (Vt) as oppsed to oxygenation. PEEP is not only used to prevent atelectasis but to increase oxygenation, and usually higher levels are used to push that pulmonary edema back were it belongs! In fact, you and I are walking around with 3-5 cmH2O of "physiologic peep". Some would say a mechanically ventilated Pt. without any peep set is, well, cruel. Your explanation of surface tension is, a little less tham accurate. Don't forget LaPlaces law!
    Last edit by sirI on Oct 19, '07 : Reason: unnecessary input
  7. by   Dinith88
    I wonder how the Aussies get along in critical care?... respiratory therapists dont even exist there. They probably dont use ventilators down under i'd bet...because there arent any RT's to educate them.

    It is a poor nurse (speaking soley of ICU nurses) who doesnt have a handle on vents, vent-settings, running the vent, ABG's and all the rest. I get really frustrated with nurses who just 'page respiratory' because they're lazy, dumb, or both. Respiratory therapists are important but remain an ancillary or 'supplemental' aspect of care. Nurses are responsible for their patients...and all of their systems..including the repsiratory system.

    (Also (for anyone who cares) there was a recent article in the Journal of Critical Care regarding Australian ICU-nurses guiding patient ventilator-weaning and extubation. The nurses got very good scores...a good read for anyone interested)
    Last edit by sirI on Oct 19, '07 : Reason: quoted and referred to edited post
  8. by   PageRespiratory!
    Holy Jeez, you're right I don't even know how I was suscribed to this thread! I now see how ancient threads get resurected. Aussie nurses do just fine because they get the training a therapist gets stateside. It's true RT's are not the primary caregiver, but "supplemental" I think not. At the the hospital where I work , the order usually reads: vent settings as per RT, wean to extubate as per RT. And so on and so on. Therapist driven protocols. Many institutions view RT's as physician extenders. I'm not trying to start a pissing contest, I have a great deal of respect for a lot of nurses as well as therapists. An ICU nurse with 20 years of experience probably has a pretty damned good idea about vents and such. The same could be said for an RT about "nursing duties". That being said, most people who've done both (I Know quite a few) will agree RT school is WAY more, lets say challenging. Be honest, during your first RN degree how lond did you spend studying things like the alveolar air equation, shunt equation, Henderson-Hasselbalch equation, the oxygen content equation,gas laws, air entrainment ratios, and even surface tension (pulmonary surfactant). In my class we had 2 RN's and an MBA, and all 3 failed out. And yes, one can get an MS in respiratory.
    Unfortunately we don't have the proffessional advocacy that you guys have (much younger proffession) and therefore, have less clinical advancement. In Canada, a lot of therapists' go on to practice anesthesia. Much like the CRNA's here. Again, I'm not trying to start a contest here. If you were my co-worker, I bet you'd have a whole new respect for us, and would never hesitate to "page respiratory". I'm sure there are a lot of things from a nursing standpoint you could educate me about, and I bet there are a number of things from a respiratory standpoint I could educate you about. We play for the same team.
    Last edit by sirI on Oct 19, '07 : Reason: referred to edited post
  9. by   RN1980
    pawpaw john, i enjoyed you using the "wet balloon" variable in explaning surface tension. it has been explained to me in a very similair way in many lectures. glad to see that there are folks that can easily explain something that would require others to break open a physics book that would lead to this law or that law..but anyway i like the way you broke it down to a very simplistic form for someone who very well may be just now trying to grasp the concept of surface tension,surfactant and compliance.
  10. by   panamabrt
    Way to say it 'page respiratory'...!!! For some reason it seems to be a constant challenge b/t the two. I am an RRT and a BSN and to be honest RRT was extremely difficult but then nursing was difficult in a different way.

    As the nurse learns about the systems (Heart, Lung, Liver, Bladder etc...) The RRT must learn how these systems affect ventilation which include very detailed information. Our field is more about precise measurments of how ventilation occurs, nursing hits just the main topics.

    So really if we all learn to love what we have learned in school and expand our knowledge base and work as a team, we can all be an integral, interdisciplinary team player for the patient

    With friends like us...who needs enemas !!!
  11. by   danissa
    With friends like us...who needs enemas !!![/QUOTE]

    LOVE That!!! You Clever thing you!!!
  12. by   panamabrt
    why thank you danissa

    Have a good day and write back some time !
  13. by   bibbles5
    thanks....this has helped alot!!