[alem-tsahai]

That was an AWESOME explanation! I learned something myself, and I WORK in a pulmonary unit!

[Sarah, RNBScN]

Originally Posted by 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

Thanks so much. Why didn't I have a person like you during my ICU orientation. Many thanks.

Sarah

[darkblack]

Originally Posted by NRSKarenRN

Check out: http://www.icufaqs.org/ website--loads of CCU info!

Vents and ABGs updated 2/5/04!

Hi everyone, i'm new here, does anyone know of other websites that cover ventilator system and settings like the one above. Thanks in advance.

[NRSKarenRN]

Check out our thread: Vent Information

[ethelbsnrn]

I got another "wrinkle" in my brain.....thanks.

Ethel

[HawaiiRRTRN]

Originally Posted by 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.

HawaiiRRTRN

[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-

[breatheasy]

Originally Posted by 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)

AG

ABG? arterial blood gas?

[PageRespiratory!]

PapaJohn,
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!

[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)