High Frequency Oscillatory Ventilation

[Schumz]

Hi Guys, I would like an opinion on HFOV, HFOV+VG as a mode of ventilation for extremely preterm infants.

Case:  24 weeks, 600g baby (day2-3) past honeymoon period, on 2x inotropes just maintaining borderline BP. Ventilation: HFOV+VG, Hertz 6, VG:3.3mls/kg. Blood gas was reasonable. The baby was put on this mode as there were apparently issues with CO2 clearance. My experience with this mode is (...use it when nothing works!) limited. I have used it comfortably in term or near-term infants but in an extremely preterm infant, I was a bit shaky. Anyhow, I thought gases are stable and the baby seems to be coping well... let's not rock the boat!

Unfortunately, the VG started to play up as the ventilator kept beeping (...volume not being delivered) so I took off the VG... then didn't quite know whether to put the Hertz up (from 6 to ???? how much? or to just leave it) because now we were only HFOV minus VG. Repeat gas wasn't as good. In the middle of the night, the safest thing to do was to switch the baby over to conventional which I did and it worked for the baby.

I couldn't comprehend the reasoning for the initial ventilator settings ...so started reading about strategies in preterm infants as I do not have enough experience with this mode in extremely preterm ELBW babies and thought I'll get some useful information. But I was totally confused and felt blank especially after reading what was available (not much, I have to say).  Therefore I thought I shall bring my dilemma here ...for expert opinions and comments. I do not seem to find any standards or reasonable guidance on the following:

1. What should the starting frequency be (especially in babies <1000 g)? Should we be using this mode for these babies in the first place? 

2. What about the VG mode? What kind of frequency do you use in your practice for extremely preterm ELBW babies? Is it ok to go down to 6hz in a baby ~600g on VG mode? Is there any evidence? Is it just experience-dependent? 

3. Any useful literature or guidance on the strategies, safety, outcomes etc in this population to share, please?  

I would appreciate your input and comments. 

[Dr. Saad Ahmed Seth]

Your are setting high tidal volumes on HFOV. Usual TV on HFOV is between 1.5 -2.5 ml/kg.

As a recommendation for very small babies you start with frequency of 12-15. In VG mode changing the Hz is not going to make any meaningful difference as your tidal volume is already guaranteed. 

there are studies about safety and Benefits of HFOV in preterm population. 

https://clinicaltrials.gov/ct2/bye/rQoPWwoRrXS9-i-wudNgpQDxudhWudNzlXNiZip9Ei7ym67VZR0R-g0VOg08A6h9Ei4L3BUgWwNG0it.

[thx3]

Hello!

1. We have used HFO + VG for some years in our unit. We very often use HFO from start in extremely preterm and not as rescue-treatment. Our experience is good and they tolerate HFO well. I find it easier to control pCO2 with mild permissive hypercapnia in HFO+VG compared to HFO or CV. I think it is definitely an option to use HFO in the first place. But you should make sure that you and the rest of the staff is on the same level there and do some reading first. The frequency in extremely premature babies should be 10-15. We usually start at 10 and probably beneficial to the smallest children to have higher frequencies.  Initial setting of ΔP should be around 20-25cm H20 in a newborn ELBW, or titrate until you se discrete chest wall vibration. You would need higher amplitudes when using HFO as rescue. 

2. The volumes usually are 1.5-3ml/kg but depend on Hz (higher volumes for lower Hz and vice versa). I find the easiest way to apply VG is to "lock" the volume when you have a blood gas with pCO2 with mild permissive hypercapnia. Set the ΔPmax about 5cmH20 above the setting that you had with VG turned off. The reason why the ventilator starts beeping is that the ΔP is not high enough to allow for the volume requested. So for the patient you describe I would set Hz to 10-12 and the volume should be around 2/kg. Hz in the area 5-10 you should reserve for patients with meconium aspiration syndrome, PPHN and other term babies.

3. Dräger has a brochure on HFO that I find quite good, that covers the theoretical background of HFO and settings, and practical tips. It is available to download. We don´t have Dräger in our unit but their brochure is good. 

[rajnandyal]

Hello,

I agree with Dr. SAS. To start with, I rarely use HFOV for ELBW babies (less than 1000 grams), either from the start or as a rescue mode. If I use HFOV, I start with frequency like 10 to 12 Hz. If I have to choose one of the high frequency vents, I usually prefer Jet ventilation (HFJV) over Oscillator (HFOV) for tiny babies. The reasons for that are, I want to have more control on PIP, PEEP (indirectly delta P), the rate, and to avoid/decrease the over distension of lungs (to decrease barotrauma and volutrauma).

Nowadays in our unit, the number of babies who are still on ET ventilation is smaller beyond 2 days of age, when compared to those who are on non-invasive (nasal) ventilation (NIV). Our unit is big on early extubation within 24 to 48 hours (or even within 6 to 12 hours), after loading with caffeine, and use NIV. Some our neonatal fellows are admitting babies on HFJV for night admissions. They invariably end up on higher doses of medications like fentanyl, morphine or midazolam. One of the strong reasons for the heavy sedation is, night nurses' preference. Those babies tend to stay on ET HFJV for longer period. In day time, when the baby gets admitted on conventional ventilator, we load them with caffeine, give surfactant (only some babies get it), and extubate to NIV, all within a 4 to 6 hours.

For ELBW babies, I personally use HFJV mainly as a rescue mode, when they require on conventional respirator MAPs of 10 to 12 (to maintain arterial PO2s 50 to 65 range and pCO2s in 45 to 55 range) either on PC/PS mode or PRVC mode, or if the chest X-rays show early s/o PIE. Based on the evidence (medical literature), and cumulative experience of 30 plus years, I strongly feel early extubation, tolerance to reasonable permissive hypercapnia, and the early use of NIV will decrease the incidence of BPD.

Those are my two cents. Hopefully, this discussion is helpful,

 

[Schumz]

7 hours ago, Dr. Saad Ahmed Seth said:

Your are setting high tidal volumes on HFOV. Usual TV on HFOV is between 1.5 -2.5 ml/kg.

As a recommendation for very small babies you start with frequency of 12-15. In VG mode changing the Hz is not going to make any meaningful difference as your tidal volume is already guaranteed. 

there are studies about safety and Benefits of HFOV in preterm population. 

https://clinicaltrials.gov/ct2/bye/rQoPWwoRrXS9-i-wudNgpQDxudhWudNzlXNiZip9Ei7ym67VZR0R-g0VOg08A6h9Ei4L3BUgWwNG0it.

Thank you for your comments. Very helpful. 

 

7 hours ago, thx3 said:

Hello!

1. We have used HFO + VG for some years in our unit. We very often use HFO from start in extremely preterm and not as rescue-treatment. Our experience is good and they tolerate HFO well. I find it easier to control pCO2 with mild permissive hypercapnia in HFO+VG compared to HFO or CV. I think it is definitely an option to use HFO in the first place. But you should make sure that you and the rest of the staff is on the same level there and do some reading first. The frequency in extremely premature babies should be 10-15. We usually start at 10 and probably beneficial to the smallest children to have higher frequencies.  Initial setting of ΔP should be around 20-25cm H20 in a newborn ELBW, or titrate until you se discrete chest wall vibration. You would need higher amplitudes when using HFO as rescue. 

2. The volumes usually are 1.5-3ml/kg but depend on Hz (higher volumes for lower Hz and vice versa). I find the easiest way to apply VG is to "lock" the volume when you have a blood gas with pCO2 with mild permissive hypercapnia. Set the ΔPmax about 5cmH20 above the setting that you had with VG turned off. The reason why the ventilator starts beeping is that the ΔP is not high enough to allow for the volume requested. So for the patient you describe I would set Hz to 10-12 and the volume should be around 2/kg. Hz in the area 5-10 you should reserve for patients with meconium aspiration syndrome, PPHN and other term babies.

3. Dräger has a brochure on HFO that I find quite good, that covers the theoretical background of HFO and settings, and practical tips. It is available to download. We don´t have Dräger in our unit but their brochure is good. 

Thank you for the above explanation. I did read the Drager brochure and found that very helpful and that was when I got a bit confused. Because the baby in the unit was on a very low frequency, whereas, in Drager they recommend babies to be started on a frequency of 12-15 and on VG 10 Hz, hence I brought it up.  I understand the lower frequency strategy for meconium babies etc but it was difficult to understand the lower frequency strategy in extremely preterm ELBW baby. I guess the aim was to increase VG but couldn't find a real explanation! Maybe frequency doesn't make any sense in VG as Dr SAS suggested so it was reasonable to go lower down in above case? I always thought it is the amplitude that you don't have to fiddle with when on VG mode, as the ventilator decides that. 

But overall I feel more in context with the use of VG in extremely preterm infants. I perhaps need more time and reading to try it one day.  

[Schumz]

2 hours ago, rajnandyal said:

Hello,

I agree with Dr. SAS. To start with, I rarely use HFOV for ELBW babies (less than 1000 grams), either from the start or as a rescue mode. If I use HFOV, I start with frequency like 10 to 12 Hz. If I have to choose one of the high frequency vents, I usually prefer Jet ventilation (HFJV) over Oscillator (HFOV) for tiny babies. The reasons for that are, I want to have more control on PIP, PEEP (indirectly delta P), the rate, and to avoid/decrease the over distension of lungs (to decrease barotrauma and volutrauma).

Nowadays in our unit, the number of babies who are still on ET ventilation is smaller beyond 2 days of age, when compared to those who are on non-invasive (nasal) ventilation (NIV). Our unit is big on early extubation within 24 to 48 hours (or even within 6 to 12 hours), after loading with caffeine, and use NIV. Some our neonatal fellows are admitting babies on HFJV for night admissions. They invariably end up on higher doses of medications like fentanyl, morphine or midazolam. One of the strong reasons for the heavy sedation is, night nurses' preference. Those babies tend to stay on ET HFJV for longer period. In day time, when the baby gets admitted on conventional ventilator, we load them with caffeine, give surfactant (only some babies get it), and extubate to NIV, all within a 4 to 6 hours.

For ELBW babies, I personally use HFJV mainly as a rescue mode, when they require on conventional respirator MAPs of 10 to 12 (to maintain arterial PO2s 50 to 65 range and pCO2s in 45 to 55 range) either on PC/PS mode or PRVC mode, or if the chest X-rays show early s/o PIE. Based on the evidence (medical literature), and cumulative experience of 30 plus years, I strongly feel early extubation, tolerance to reasonable permissive hypercapnia, and the early use of NIV will decrease the incidence of BPD.

Those are my two cents. Hopefully, this discussion is helpful,

 

Thank you very helpful discussion indeed. My personal practice and training have been as above, therefore, nothing made sense to me in the above case. I agree Conventional +VG is the only strategy that has shown to improve BPD or quick transition to NIV.

But I would not disagree with @thx3 on the accepted use in preterms, but need to have a clear understanding before starting to do something new in this vulnerable population. He is right, the staff and everyone else should be on the same page. 

[rajnandyal]

I also want to emphasize what previous discussants already mentioned,  that the entire team should be on the same page. I am sure that all of you often heard this comment before- "baby failed HFJV". In most of those cases (with due credit to the clinicians), I feel that WE failed (not the baby) to choose the correct strategy, or manage the ventilation/oxygenation, or unable to wait for a strategy to work, based on our bias, bad habits or our past experience. I encourage our fellows to contact the HELP team of HFJV in difficult situations. Contacting that RT team is very productive and educational. Please let us know, if there is any such "on-call personnel" for other vendors. We all will benefit. Thanks. 

[Tanyah]

Dear All 

As the application specialist for Dräger in Neonatal Ventilation in South Africa, perhaps if I could suggest Prof. Jane Pillow’s book on HFOV where the A-Z on HFOV is addressed. There are also various online webinars where Prof. Jane Pillow discusses HFOV including HFOV + VG. 

 

Extremely important with HFOV is that the set Amplitude is achieved at patient end which can only be measured if using the proximal flow sensor during HFOV. The monitored patient values should include the patient realized Delta Pressure if the set amplitude and measured delta pressure are not equal, blood gas result will reflect minimal changes in response to  hertz changes, and in the event of VG it is highly likely that tidal volumes will also not be achieved. The hertz and I:E of HFO (or Ti) need to be adjusted until delta pressure is achieved at patient. This will influence tidal volume and thus CO2. VG regulates the the amplitude according to changes in lung compliance and or resistance changes. Compliance changes will directly influence the tidal volume and hence the set TV may not be achieved and the ventilator will give the message that tidal volume is then not achieved. Trouble shooting would include eliminating reason for a change in lung compliance and/ or resistance and if possible increase amplitude max or changing I:E ratio and hertz. Monitoring  of the DCO2 value gives additional information with regards to CO2. The DCO2 is a calculated value and is inversely proportionate to CO2, hence if CO2 is on the increase the DCO2 value will drop, and visa versa.

I hope this will be of assistance in the future during HFOV. 

Best Regards 

 

 

[pHred]

Agree that 6 hz is too slow. Appropriate MAP is key to successfully ventilating and oxygenating.

Axiom #1: The best ventilator is the one you have the most expertise with. New (to the user) forms of ventilation open the door for errors of inexperience.

Axiom #2:  HFOV has a checkered past in many studies. Sun et al demonstrated strongly positive results in VLBW infants receiving HFOV vs pressure support ventilation. Why the discrepancy? Consider the adjunct care. 

Hypothesis: Whenever an infant is disconnected from an oscillating device, the lungs instantly deflate. Consider that extremely premature infants have little, if any, alveolar surface area.Temporary ventilation is usually provided by a manual resuscitation device that cannot match the oscillator. This act in itself likely contributes to barotrauma and subsequent CLD. Terminal bronchioles are “bubbled up” by attempts to mimic the ventilation we see in term infants. Evidence includes the observation that it can take a half hour after reconnecting the infant to HFOV  to fully achieve reinflation. Thus, any interruption in oscillatory MAP can be considered iatrogenic.

Axiom#3: The role of manual resuscitation in the development of CLD has not been adequately studied (almost completely ignored). Disconnection from high MAP ventilation is rarely a point of focus. These omissions skew most of the observations and conclusions in neonatal ventilation studies.

ref: Sun et al ClinicalTrials.govNCT01496508

Respiratory Care Feb 2014, 59(2) 159- 169

[Christian Heiring]

The praxis described by Thx3 is very sensible and similar to what we use in my unit. We use HFO on VN500 either as primary mode or rescue mode. 

In RDS you can often start at 10Hz and VG around 1,5-2 ml/kg and then adjust VG upwards or downwards depending on pCO2 (assuming the lung is adequately recruited by using appropriate MAP) or start without VG and adjust amplitude based on chest wiggle and pCO2 trend, and when you have the right number you lock the VtHf by adding VG / but remember to allow the maximum amplitude to be set well above the avarage needed to achieve the set VtHf.

The VN500 delivers a very consistent and stable Vt in VG mode - the Mve trend line becomes completely flat and you don’t see many surprising pCO2 changes once you have the right VG. Also in my view you can theoretically archive more gentle ventilation by going up on frequency with a constant VtHf and thus keeping VtHf below dead space volume rather than using lower frequency to achieve higher Vt (with out VG).

However still not much litterateur to support but Jane Pillow and Manuel Lucnas groups have done clinical studies on HFO-VG