I want a Guarantee.

Enomoto M, et al. Effect of Volume Guarantee in Preterm Infants on High-Frequency Oscillatory Ventilation: A Pilot Study. American journal of perinatology. 2016(EFirst).

One of the things that really bugs me (and there are many, as my gentle readers will know by now) is that new ventilator technology can be introduced with no actual evidence that it is safe, effective or improves outcomes. The same can be said of most medical devices (I am talking about Canada, but I think this applies in Europe also, and probably in most parts of the world), but assisted ventilation is the most invasive and potentially life-threatening intervention we perform on a daily basis; so a new trick on a ventilator holds a huge risk of creating more lung injury, and more mortality; but also potentially improving outcomes.

Shouldn’t we require phase 1 (proof of concept) trials, followed by small phase 2 trials (for efficacy), and then by large phase 3 trials, for safety and comparison with current best practice, when a ventilator manufacturer adds a new way of ventilating a critically ill baby to their machine?

When we took delivery of our Drager VN500 ventilators we found that they had a new mode of ventilation, High-frequency volume guarantee ventilation. The ventilator can be set to deliver a particular volume on high-frequency, and then will adjust the amplitude of the pressure excursions to maintain the same volume.

What a great idea!

(I am not being sarcastic, I actually do think its a great idea)

But. Shouldn’t there be some evaluation of whether it actually works in the real world, and not just in the engineers hangar? Some evidence that it actually improves stability of blood gases, without a major increase in potential markers of lung injury? And then some evidence that babies are actually better off (or at least not worse off) when using this technology compared to standard high frequency ventilation?

If someone introduced a new drug: “Lungprotecticon”: to improve pulmonary outcomes in premies we would ask for nothing less. But when we hook their lungs up directly to a machine capable of delivering enormously damaging pressures/volumes we accept that it is just a new tweak to an already evidence-poor part of neonatology.

This has to change.

Lets get back to the article at the top of this post.

In a tiny sample of 6 very small babies, (under 24 weeks gestation), these authors found that periods of time spent on volume guarantee high frequency had less fluctuation of measured minute volume, and less fluctuation of DCO2, and less desaturation. However, the minute ventilation is measured by the ventilator itself, and without independent validation I am not 100% sure that the numbers are reliable. The DCO2 is calculated by the ventilator based on Alison Froese’s equation that estimated that CO2 elimination is proportional to the tidal volume squared multiplied by the frequency; as the tidal volume is being measured by the ventilator, it really is the same result as the minute ventilation result.

Although the authors state that trans-cutaneous PCO2 was used in all the babies, I don’t see any result of those data. Was PCO2 more stable? I would guess that with only 6 babies the answer is likely no. So this is very limited phase 1 type data, which I think needs more phase 1 data before going on to phase 2 trials, but at least it is a start.


About Keith Barrington

I am a neonatologist and clinical researcher at Sainte Justine University Health Center in Montréal
This entry was posted in Neonatal Research and tagged , . Bookmark the permalink.

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