Hi everybody,

I would like to ask about the I:E ratio in an HFO-VG setting in case of ELGANs.

Do you use an I:E ratio of 1:1 or 1:2 in HFO-VG on the VN800 for ELGANs 22-23 wks below 500g BW?

Also would you worry of causing atelectasis using an I:E ratio of 1:2 when the infant is on low MAPs like 8 or 9 cmH2O, Frequency of 12Hz at DOL10 ?

Edited March 14Mar 14 by Hamed
Added additional information of the Ventilator setting (Frequency of 12Hz)

Hi,

I think it also depends on which frequency you are using. I would refer to these publications:

Sanchez-Luna M, Gonzalez-Pacheco N, Santos-Gonzalez M, Tendillo-Cortijo F. High-frequency Ventilation. Clin Perinatol. 2021;48(4):855-68. https://www.ncbi.nlm.nih.gov/pubmed/34774213

Also helpful in this aspect (Hibberd et al 2024): https://www.ncbi.nlm.nih.gov/pubmed/37726160

On I:E ratio:

The I:E impacts both inspiratory and expiratory VT, with ratios of 1:2 (inspiratory time half as long as expiratory time at any given frequency) or 1:1 (inspiratory and expiratory time equal) most commonly used. At any given frequency, I:E of 1:2 will deliver a lower VT, and PAW, than an I:E of 1:1 and introduces a variable PAW drop of 2–4 cmH2O between the airway opening and the lung, which may enhance gas transport (online supplemental figure S2).52 Clinical data on the setting of I:E ratio are lacking, but preclinical and bench studies provide a rationale to use a ratio of 1:2 when gas trapping is present.

IMHO I personally would not be to worried about more atelectasis solely because of IE-ratio if you are using volume-guarantee. But probably there are smarter people out there who know more about HFO and may be able to help better.

My ten cents to the discussion are... given a normal ventilation, the Stockholm strategy would probably be 10Hz and a 1:1 IE ratio.

@Martin.Keszler and @Padkaer - what's your advice?

2 hours ago, Francesco Cardona said:

Hi,

I think it also depends on which frequency you are using. I would refer to these publications:

Sanchez-Luna M, Gonzalez-Pacheco N, Santos-Gonzalez M, Tendillo-Cortijo F. High-frequency Ventilation. Clin Perinatol. 2021;48(4):855-68. https://www.ncbi.nlm.nih.gov/pubmed/34774213

Also helpful in this aspect (Hibberd et al 2024): https://www.ncbi.nlm.nih.gov/pubmed/37726160

On I:E ratio:

The I:E impacts both inspiratory and expiratory VT, with ratios of 1:2 (inspiratory time half as long as expiratory time at any given frequency) or 1:1 (inspiratory and expiratory time equal) most commonly used. At any given frequency, I:E of 1:2 will deliver a lower VT, and PAW, than an I:E of 1:1 and introduces a variable PAW drop of 2–4 cmH2O between the airway opening and the lung, which may enhance gas transport (online supplemental figure S2).52 Clinical data on the setting of I:E ratio are lacking, but preclinical and bench studies provide a rationale to use a ratio of 1:2 when gas trapping is present.

IMHO I personally would not be to worried about more atelectasis solely because of IE-ratio if you are using volume-guarantee. But probably there are smarter people out there who know more about HFO and may be able to help better.

Thanks a lot @Francesco Cardona

True, the freqency is 12Hz.

I am with you on not to worry about developing atelectasis, hyperinflation could be a higher risk, and using Sighs could ptobably prevent atelectasis.

Yes, you are correct the infant is on volume-guarantee.

1 hour ago, Stefan Johansson said:

My ten cents to the discussion are... given a normal ventilation, the Stockholm strategy would probably be 10Hz and a 1:1 IE ratio.

@Martin.Keszler and @Padkaer - what's your advice?

Thanks @Stefan Johansson that is close to what we are on 1:1 at 12Hz.

11 minutes ago, Hamed said:

Thanks a lot @Francesco Cardona

True, the freqency is 12Hz.

I am with you on not to worry about developing atelectasis, hyperinflation could be a higher risk, and using Sighs could ptobably prevent atelectasis.

Yes, you are correct the infant is on volume-guarantee.

Thanks @Stefan Johansson that is close to what we are on 1:1 at 12Hz.

Maybe using lower than 12Hz to 10 could improve the ecpiration on reduce the hyper-inflation.

Hi, Actually, the volume guarantee does just affect ventilation, which means CO2 elimination. The tidal volume in HFOV is completely different from the conventional ventilations tidal volume which means how much the lungs should be inflated. To prevent from atelectasis, it is most important to keep adequate mean airway pressure. It is very much up to the Dead Space if you keep normal ventilation to those tiny bebis. I have never used MAP less than 9 cm because of trends of atelectasis, especially due to the small diameter of the ETT.

Where I do my Level-4 rotation (Queen Silvias in Gothenburg) they implemented a strategy for the first few days of ventilating ELGANs with RDS aiming at higher frequency to minimize tidal volumes. After the acute phase of RDS is over and lung compliance is improved, a change of strategy is warranted (at latest at 5-7 days of age). But they start at:

Setting Start Target

MAP 10 – 12 cmH2O 8 – 10 cmH2O

Amplitude (ΔP) 40 cm H2O (Max amplitude) 15 – 25 cm H2O (by ventilator)

Frequency 15 Hz 16 – 17 Hz

Volume 1,7 ml/kg as low as possible, normocapnea

I:E 1:1 1:1

If normocapnia (pCO2 5.0 – 6.0 kPa) Note DCO2; increase Hz 1 – 2 and decrease volume 0,1 – 0,2 ml/kg – target equal DCO2

If hypocapnia (pCO2 < 5.0 kPa) Only decrease volume 0,1 – 0,2 ml/kg

If hypercapnia (pCO2 > 6.0 kPa) Only increase frequency by 1 – 2 Hz

The rationale behind using 1:1 is that if frequency >14 Hz with I:E 1:2 the ventilator will not be able to provide sufficient tidal volumes.

After the first few days the HFO-strategy (if you choose to continue with HFO) will change to ventilating at a lower frequency and aiming at 10-12 Hz with the tiniest infants. This might require somewhat increased volumes but with reduced amplitudes. At this stage, in cases that would require longer expiration and where increasing MAP is contraindicated (pulmonary interstitial emphysema, overdistension), I:E of 1:1,5 can be considered.

The strategy is compiled by Juliús Kristjansson, he did an amazing work with this. I have only cited the PM.

As for the I:E reasoning he cited another Sanchez-Luna article than mentioned above:

PubMed

Effect of the I/E ratio on CO2 removal during high-freque...

•The tidal volume on HFOV is determinant in CO 2 removal, and this is generated by delta pressure and the length of the inspiratory time. What is New: •HFOV combined with VG, an I/E ratio of 1:2 is...

aswell as

https://pubmed.ncbi.nlm.nih.gov/35136198/

and

https://www.draeger.com/Content/Documents/Content/jane-pillow-hfov-br-9102693-en.pdf

I hope this could help you in your reasoning, I'm not very knowledgeable in this myself, but it's at least something.