Book on Mechanical Ventilation

[NontradICUdoc]

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Do any of you guys have a recommendation for a good book on mechanical ventilation as an adjunct to the practical education given in the unit?

 

[secants]

The ventilator book by Owens is a good primer from what I've heard

 

[Hernandez]

If you're a CC fellow, you should read Tobins.

 

[jdh71]

Lol. Tobin. Best technical tome to be sure, but I think I'd rather eat glass.

I didn't learn vents from a book. I didn't even learn vents sitting at the feet of one of the greats. I learned vents by adjusting them myself at the bedside.

 

[Hernandez]

Oh I agree it's tedious but there is a ton of golden info in it that I have used repeatedly. Especially as he goes into detail of the older studies and has many charts and graphs to explain differences on how lungs react to different adjustments to flow shape and then it picky differences between volume control and pressure control. I agree much of the vent management comes from close observation of patient vent interaction and adjusting from there but my personal bias is if you're to be a subject matter expect you should be at least acquainted with the default text and had read some of it. Granted I'm also the guy in fellowship who read all of Murray/nadels & fishmans and a large chunk of Parre.

 

[NontradICUdoc]

Thanks for the responses. I do a lot of learning at the bedside with the vents, but also wants to ensure I have a good foundation

 

[Cytarabine]

Just going to tag on to this thread. Does anyone know of a concise source explaining the physiology of high frequency ventilation? I think I get the general principles but get a little lost in getting the vent adjustments to make sense

 

[jdh71]

Just going to tag on to this thread. Does anyone know of a concise source explaining the physiology of high frequency ventilation? I think I get the general principles but get a little lost in getting the vent adjustments to make sense

You mean adjusting to "thigh wiggle" seems odd???

 

[Cytarabine]

You mean adjusting to "thigh wiggle" seems odd???

Well that bit is just downright logical

 

[jdh71]

Well that bit is just downright logical

Basically HFOV works by increasing mean airway pressure above other modalities.

 

[Cytarabine]

Basically HFOV works by increasing mean airway pressure above other modalities.

So the gist is you get a higher mean airway pressure over other modalities because you're essentially at near constant volume / pressure, and you don't have peak pressures that vary significantly from your mean pressure. You keep alveoli inflated with that mean pressure and maintain oxygenation/ventilation by having a constant mixing of air by essentially agitating the air in the whole closed system while steadily introducing fresh air mixed to whatever desired fio2. So, adjust mean airway pressure and fio2 for oxygenation. For ventilation, you have frequency and driving pressure which are inversely related. Do you have modes like pressure control vs volume control that you have with traditional mechanical ventilation where you adjust either frequency or driving pressure? Or are they both adjustable?

 

[jdh71]

So the gist is you get a higher mean airway pressure over other modalities because you're essentially at near constant volume / pressure, and you don't have peak pressures that vary significantly from your mean pressure. You keep alveoli inflated with that mean pressure and maintain oxygenation/ventilation by having a constant mixing of air by essentially agitating the air in the whole closed system while steadily introducing fresh air mixed to whatever desired fio2. So, adjust mean airway pressure and fio2 for oxygenation. For ventilation, you have frequency and driving pressure which are inversely related. Do you have modes like pressure control vs volume control that you have with traditional mechanical ventilation where you adjust either frequency or driving pressure? Or are they both adjustable?

Yup.

And you adjust frequency or driving pressure. Usually frequency to help with ventilation.

 

[engineeredout]

I second the ventilator book by Owens. Relatively short, breaks things down. Is actually an easy read but gives you all the fundamentals, plus quick troubleshooting tips when things are going wrong. Usually end up rereading it on all my ICU blocks as a refresher

 

[Mad Jack]

Yup.

And you adjust frequency or driving pressure. Usually frequency to help with ventilation.

We'd usually adjust the amplitude for ventilation in our patients- adjusting the frequency outside of its optimal range (which is variable in each patient based on their age and lung mechanics) in HFOV can be detrimental to good CO2 control, as you can fall out of the resonance range. Adults would generally all get thrown on 6 Hz, barring unusual pathologies like pulmonary fibrosis.

Explaining this is kind of difficult and has to do with the bizarre nature of HFOV as a highly fluid-dynamic dependent form of mechanical ventilation- where tissue resonance is highly important, and where you're working with extremely small expansion times and a lot of backflow of gas every time the piston releases for expiration. Fair warning, I'm terrible at describing things, but that's the best I can do- it's really something you have to see visually drawn out to get, or at least that's how it clicked for me. The net result of this is basically that there is a multiplier on your amplitude's (and thus tidal volume's) effect on ventilation- the commonly accepted equation for this is Ve=f x Vt^(1.5 to 2.5, depending on other variables, such as Hz and %Ti), as compared to the traditional Ve=f x Vt, and that amplitude increases are far more effective than frequency increases in your HFOV patients.

So the gist is you get a higher mean airway pressure over other modalities because you're essentially at near constant volume / pressure, and you don't have peak pressures that vary significantly from your mean pressure. You keep alveoli inflated with that mean pressure and maintain oxygenation/ventilation by having a constant mixing of air by essentially agitating the air in the whole closed system while steadily introducing fresh air mixed to whatever desired fio2. So, adjust mean airway pressure and fio2 for oxygenation. For ventilation, you have frequency and driving pressure which are inversely related. Do you have modes like pressure control vs volume control that you have with traditional mechanical ventilation where you adjust either frequency or driving pressure? Or are they both adjustable?

Here's a great powerpoint on HFOV that can explain things way better than I could manage on here, at least without digging up a bunch of pictures to demonstrate things: Emory HFOV Powerpoint

 

[jdh71]

We'd usually adjust the amplitude for ventilation in our patients- adjusting the frequency outside of its optimal range (which is variable in each patient based on their age and lung mechanics) in HFOV can be detrimental to good CO2 control, as you can fall out of the resonance range. Adults would generally all get thrown on 6 Hz, barring unusual pathologies like pulmonary fibrosis.

Explaining this is kind of difficult and has to do with the bizarre nature of HFOV as a highly fluid-dynamic dependent form of mechanical ventilation- where tissue resonance is highly important, and where you're working with extremely small expansion times and a lot of backflow of gas every time the piston releases for expiration. Fair warning, I'm terrible at describing things, but that's the best I can do- it's really something you have to see visually drawn out to get, or at least that's how it clicked for me. The net result of this is basically that there is a multiplier on your amplitude's (and thus tidal volume's) effect on ventilation- the commonly accepted equation for this is Ve=f x Vt^(1.5 to 2.5, depending on other variables, such as Hz and %Ti), as compared to the traditional Ve=f x Vt, and that amplitude increases are far more effective than frequency increases in your HFOV patients.

Here's a great powerpoint on HFOV that can explain things way better than I could manage on here, at least without digging up a bunch of pictures to demonstrate things: Emory HFOV Powerpoint

It's too bad it probably actually kills some people.

Even it comes to hfov these days we might as well we talking about iron lungs and real negative pressure ventilation.

 

[Mad Jack]

It's too bad it probably actually kills some people.

Even it comes to hfov these days we might as well we talking about iron lungs and real negative pressure ventilation.

I don't think HFOV kills people- I think they're already dead, so we try it as a last resort because nothing else is working, and then they die.

HFOV works great on neonates and peds patients, but I think I've seen a grand total of two adults survive a ride on the oscillator, one back during the swine flu thing a few years ago, one with a bad case of ARDS. I don't think it's a good mode of ventilation in adults- I much prefer APRV (or bilevel ventilation for the sticklers about not using brand names out there) in the adult population if you need a low shearing, high MAP mode of ventilation. It's more predictable and the mechanics are just better overall for the physiology of sick adult lungs (and hearts), which tend to throw too many wrenches in the works for a mode as finicky as HFOV.

 

[jdh71]

I don't think HFOV kills people- I think they're already dead, so we try it as a last resort because nothing else is working, and then they die.

HFOV works great on neonates and peds patients, but I think I've seen a grand total of two adults survive a ride on the oscillator, one back during the swine flu thing a few years ago, one with a bad case of ARDS. I don't think it's a good mode of ventilation in adults- I much prefer APRV (or bilevel ventilation for the sticklers about not using brand names out there) in the adult population if you need a low shearing, high MAP mode of ventilation. It's more predictable and the mechanics are just better overall for the physiology of sick adult lungs (and hearts), which tend to throw too many wrenches in the works for a mode as finicky as HFOV.

Ah. Yet. That's sort of what the data showed. It killed some people. The independent variable was hfov vs other modes in the same all comers messed up lungs patient population. You get enough numbers a signal comes through the noise. Hfov killed people. No other explanation makes sense.

 

[Mad Jack]

Ah. Yet. That's sort of what the data showed. It killed some people. The independent variable was hfov vs other modes in the same all comers messed up lungs patient population. You get enough numbers a signal comes through the noise. Hfov killed people. No other explanation makes sense.

I believe it. I mostly used HFOV in neonates, where there was a proven, small but statistically significant benefit versus conventional mechanical ventilation, but the data on adults fits what I'd seen anecdotally.

 

[jdh71]

I believe it. I mostly used HFOV in neonates, where there was a proven, small but statistically significant benefit versus conventional mechanical ventilation, but the data on adults fits what I'd seen anecdotally.

You can believe the sky is green. Maybe you took acid and it looked that way once. The data don't support your belief. You can reconcile that however you need. Anecdotes are always interesting without data with data contrary though you're just masturbating with a confirmation bias.

 

[Mad Jack]

You can believe the sky is green. Maybe you took acid and it looked that way once. The data don't support your belief. You can reconcile that however you need. Anecdotes are always interesting without data with data contrary though you're just masturbating with a confirmation bias.

We could go back and forth about it for a while- there's data pointing both ways. In our primary HFOV population, extremely premature, very low birth weight infants, the data is so close that it is hard to call. It's a fairly hotly debated topic overall.

http://adc.bmj.com/content/88/9/833.full

"We extracted data from the Cochrane systematic review (Henderson-Smart et al) for the trials comparing HFOV using high volume strategy versus CV and combined that with the data from the trials by Johnson et al and Courtney et al. The resulting meta-analysis (seven trials and 2069 infants) showed a borderline statistically significant reduction in the incidence of CLD or death in the HFOV group (summary RR 0.90, 95% CI 0.83 to 0.98; NNT 20, 95% CI 11 to 100). There was no evidence of difference in the incidence of grade 3 or 4 IVH (summary RR 0.97, 95% CI 0.78 to 1.19) or pulmonary airleaks (summary RR 1.04, 95% CI 0.87 to 1.25)."

That's some data.

I think HFOV is a bad call in adults- but then again, I'd only see the mention of pulling out the B model when we were throwing the kitchen sink at a tanking patient. I still don't buy it as a viable strategy in adults, as you need far too much sedation, the lung mechanics aren't optimal for the volumes being delivered with each oscillation, you have to allow for some pretty extreme hypercarbia that isn't conducive to surviving the sort of illness that lands someone on the 3100 in the first place, etc. But if it were my 24 weeker? I'd favor the oscillator if they were having trouble on CMV. It's extremely good for getting premies through the rough patches after the honeymoon period, especially if the neo team knows what they're doing.

At worst, there is no difference- novel optimal volume ventilation has been found to have similar outcomes to HFOV in some later studies:

http://www.nature.com/jp/journal/v28/n1s/full/jp200849a.html

"High-frequency and conventional ventilatory techniques have been extensively evaluated in the management of RDS in preterm infants. When an optimal lung volume strategy is employed, there does not appear to be any significant difference between these two modalities."

So, as with many things in the mechanical ventilation arena, it comes down to what you're comfortable with, which studies you believe had better methodology, and which strategies you feel are optimal for a given patient. HFOV certainly hasn't killed babies left and right (at least when it's being used by the right hands, but that's another story...) as you seemed to imply.

 

[jdh71]

We could go back and forth about it for a while- there's data pointing both ways. In our primary HFOV population, extremely premature, very low birth weight infants, the data is so close that it is hard to call. It's a fairly hotly debated topic overall.

http://adc.bmj.com/content/88/9/833.full

"We extracted data from the Cochrane systematic review (Henderson-Smart et al) for the trials comparing HFOV using high volume strategy versus CV and combined that with the data from the trials by Johnson et al and Courtney et al. The resulting meta-analysis (seven trials and 2069 infants) showed a borderline statistically significant reduction in the incidence of CLD or death in the HFOV group (summary RR 0.90, 95% CI 0.83 to 0.98; NNT 20, 95% CI 11 to 100). There was no evidence of difference in the incidence of grade 3 or 4 IVH (summary RR 0.97, 95% CI 0.78 to 1.19) or pulmonary airleaks (summary RR 1.04, 95% CI 0.87 to 1.25)."

That's some data.

I think HFOV is a bad call in adults- but then again, I'd only see the mention of pulling out the B model when we were throwing the kitchen sink at a tanking patient. I still don't buy it as a viable strategy in adults, as you need far too much sedation, the lung mechanics aren't optimal for the volumes being delivered with each oscillation, you have to allow for some pretty extreme hypercarbia that isn't conducive to surviving the sort of illness that lands someone on the 3100 in the first place, etc. But if it were my 24 weeker? I'd favor the oscillator if they were having trouble on CMV. It's extremely good for getting premies through the rough patches after the honeymoon period, especially if the neo team knows what they're doing.

At worst, there is no difference- novel optimal volume ventilation has been found to have similar outcomes to HFOV in some later studies:

http://www.nature.com/jp/journal/v28/n1s/full/jp200849a.html

"High-frequency and conventional ventilatory techniques have been extensively evaluated in the management of RDS in preterm infants. When an optimal lung volume strategy is employed, there does not appear to be any significant difference between these two modalities."

So, as with many things in the mechanical ventilation arena, it comes down to what you're comfortable with, which studies you believe had better methodology, and which strategies you feel are optimal for a given patient. HFOV certainly hasn't killed babies left and right (at least when it's being used by the right hands, but that's another story...) as you seemed to imply.

You're moving the goal posts. I was never talking about neonates.

 

[Mad Jack]

You're moving the goal posts. I was never talking about neonates.

When did I ever defend the use of HFOV in adults?

I believe it. I mostly used HFOV in neonates, where there was a proven, small but statistically significant benefit versus conventional mechanical ventilation, but the data on adults fits what I'd seen anecdotally.

The data I was referring to was your data, which fit the anecdote I had referred to previously:

I think I've seen a grand total of two adults survive a ride on the oscillator, one back during the swine flu thing a few years ago, one with a bad case of ARDS. I don't think it's a good mode of ventilation in adults

I stated that I didn't think HFOV kills adults, but that most of them I've seen on it had died. Their condition when starting HFOV made it difficult to determine whether it was the ventilation that killed them or their existing condition. You said the data showed that the vent killed them. I said that that data fits what I'd seen anecdotally, which was a lot of dead adults.

I brought up neonates because I figured you were saying it killed neonates, since I had just agreed with you that your data fit my observations in adult patients, so that couldn't have been the point of contention in your next post.

 

[Mad Jack]

Let this be a lesson- even agreeing with jdh can't get you out of debating with jdh 😉

 

[jdh71]

When did I ever defend the use of HFOV in adults?

The data I was referring to was your data, which fit the anecdote I had referred to previously:

I stated that I didn't think HFOV kills adults, but that most of them I've seen on it had died. Their condition when starting HFOV made it difficult to determine whether it was the ventilation that killed them or their existing condition. You said the data showed that the vent killed them. I said that that data fits what I'd seen anecdotally, which was a lot of dead adults.

I brought up neonates because I figured you were saying it killed neonates, since I had just agreed with you that your data fit my observations in adult patients, so that couldn't have been the point of contention in your next post.

This apparently has been one big misunderstanding.