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This question is addressed to Dr Bancalari about the increasing use of high-flow nasal cannula systems. In your presentation, you steadfastly stuck to data and avoided mentioning a practice that is very widespread – high-flow nasal cannula ‘Vapotherm.’ This is basically the standard treatment in many nurseries on the West Coast, although there is very little data. Can you comment on it?
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Dr Bancalari: In our unit, we often have babies on nasal cannulas and it makes sense because it allows them to move. A few trials have shown that it produces some continuous distending airway pressure. However, I have significant concerns with the use of high-flow nasal cannulas. The system essentially is connected to the wall and there is no pop-off valve. If you are you using it as a flow generator just to give additional oxygen, it is fine. But I have found in many of our small infants, the cannulas fit relatively tightly in the nostrils. If you have a tight fit, the only escape valve is the mouth. I have stuck a needle in the cannulas on a few babies and found pressures of nothing if the cannula is a little bit out. With the cannulas pushed in, we have measured pressures of 26 cm of water, continuous distending pressure. I think it is an extremely dangerous system that should not be used unless you are absolutely sure the cannulas will not obstruct the nostrils. Otherwise, you do not have any idea what pressures you are generating.
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Nurseries will convert to this approach because it is so easy. Some see a slight increase in pneumothoraces when they introduce it and maybe then they become a little more cautious. The next question addressed to Dr Soll focuses on high-frequency ventilation. The high-frequency studies were carried out over a variety of times, which is a problem. Also, they were done before widespread use of prenatal steroids. Basically, it was used to convince perinatologists or obstetricians to give steroids because so few of them were doing it. Do you think there is a relationship between this and some of the intraventricular hemorrhage (IVH) results?
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Dr Soll: I have concerns about the IVH issue from other trials. Even in the most recent trials, in populations that are very similar to those we treat today, there is no mortality benefit suggested. Although I recognize that throwing in some older trials in which we took very different approaches may not seem relevant, there is still some concern. With the high-frequency jet issues, we are concerned if we do not use a high-volume strategy.
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During the trial, the transported babies had the highest incidence of IVH, although it did not turn out to be significant in both groups. In the early days of high-frequency use, I remember taking a few of the babies who were very unstable hemodynamically and putting them on high mean airway pressure settings and seeing them go white from obstruction of cardiac output. Caution is always warranted with high-frequency ventilation. Even the most recent French trial showed a nonsignificant increase in IVH without any pulmonary benefits.
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Most of the pneumothoraces, we see in our unit are those 35- to 36-week white males on nasal continuous positive airway pressure (nasal CPAP). We try to be noninvasive and the next thing we know, they blow a pneumothorax. It is difficult to do a large study with the small numbers, but has anyone else seen this? It seemed to me it would make sense to intubate, use surfactant, and put them back on nasal CPAP, but I have not seen any evidence for that.
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Dr Soll: Yes, part of the explanation may be that we are keeping sicker babies on nasal CPAP when they are large because they are able to breathe and that may explain why they have a higher incidence of pneumothorax. The other more likely explanation is that bigger babies do not like to have things stuck on their noses and many of them fight the cannulas vigorously. This may be why they develop a pneumothorax. In theory, a pressure of 4, 5, or 6 cm of water should not do much in terms of rupturing the lung. It is probably the fact that the babies are generating a much larger effort on their own when they fight.
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Four or five studies have looked at whether bigger, spontaneously breathing babies do any better if we electively intubate, give surfactant, and rapidly extubate to CPAP support. I would include Verder's first study in that group. The Texas Group also has carried out such a study and the Vermont Oxford Network completed a study, which has been presented but not published. There is a consistent trend throughout these studies of decreasing pneumothorax with surfactant treatment, and the meta-analysis by Stevens and co-workers that was presented at the SPR suggested that may be the case.
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Dr Soll: There is some interesting data in the Vermont Oxford study. The effects were seen mostly in infants who were enrolled between 12 and 24 h, which seems counterintuitive because every time I speak about surfactants, I talk about earlier treatment being better. It may be that this is a heterogenous group of infants who have some respiratory insufficiency in the first 12 h. The ones who persist in having it may be the infants who truly are surfactant deficient. In our nursery, if that group of infants is still on CPAP with an oxygen requirement at 12 h of age, we intubate, give surfactant, and extubate as soon as we can.
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Recently, I had the opportunity to view other units and I noticed a trend of giving nasal cannula flow at 2 l per minute. The nurses swear that it helps. Could you comment on that?
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Dr Bancalari: I am sure it helps because it generates pressure, so we can apply positive airway pressure with a nasal cannula. However, we do not have any idea how much pressure we are applying. It all depends on the relationship between the size of the cannulas and the nostrils, and how tight that seal is and how much flow there is. I believe it works and we also have several attending physicians who use it. If we want to apply nasal CPAP, we need to know how much pressure we are applying. Otherwise, we are going in blind and may cause damage. Proper monitoring systems are very expensive. We cannot afford them in our hospital, so we use a system in which the humidification and the heating of the gas are inadequate. This means there are essentially two detrimental effects: we do not know what pressure we are using and we are using gas that is not properly heated and humidified. I suspect many units use the cannulas without good humidification. If the cannula is small and leaves sufficient space to vent out, the risk is much lower. We do not know how much pressure we are using, although it is unlikely to be excessive because everything is leaking out. It is also not humidified. They are using the conventional low-flow cannula as a high-flow cannula without humidification. We have seen many babies develop severe nasal erosions and obstruction because of that. For all of my discussion of evidence-based medicine, the idea of putting babies on high-flow cannulas even swept through my unit. The nurses find it very attractive because it is so easy.
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There were a lot of questions and concerns raised during the discussion about using high flow nasal cannulas and the potential dangers and lack of well-controlled studies with these devices. This question relating to the use of high flow nasal cannulas and generation of CPAP is addressed to Dr Bancalari. My unit acquired 10 Vapotherm devices about two weeks ago after lobbying for months. I always felt like it produced some CPAP but I did not realize it was that high, up to 26 cm of water. So my first question is when you measured the positive end-expiratory pressure (PEEP), where did you measure it and how did you measure it? The idea is to keep the mouth open, which is the opposite of CPAP, in which we want the mouth to be closed to have the effective PEEP. My second question is it seemed like Vapotherm was successful because of the humidification. Is there less secretion and is the cannula patent all the time?
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Dr Bancalari: If you are going to use nasal cannulas, Vapotherm is ideal because at least you know it is heated and humidified. If you think a baby needs nasal CPAP because of apnea or low functional residual capacity (FRC), use a nasal CPAP device to know exactly what CPAP you are giving. If you want to use supplemental oxygen, using the nasal cannula is okay. You still will not know how much oxygen the baby is getting though, because the cannula is loose-fitting and the baby is inhaling gas around the cannula. From a safety point of view, if you make sure it is not tight, it is okay to use it to give supplemental oxygen. My concern is when people use it for the positive pressure without knowing how much positive pressure they are using.
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Where would you measure the pressure?
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Dr Bancalari: I stick a needle in the prongs in the tube that fits in front of the nose and I start moving the cannula in and out. If you have a small cannula and a big nose, there is no problem. You will not achieve any pressure. But if you have a relatively large cannula in a very small baby, you can get a real range, depending on how much the baby opens its mouth.
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How about the posterior pharynx?
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Dr Bancalari: We have not measured in the posterior pharynx, but there should not be any gradient. This is the end expiratory pressure. If the baby is exhaling through the nose, which does not happen all the time, the pressure should be the same as in the pharynx. The only escape is when the baby opens its mouth, so it releases the pressure.
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When you measured the pressure, what was the flow? Was there a big difference between the flows or is it just related to nostrils and a tight fit?
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Dr Bancalari: The pressure again depends on the flow. We were using low flows and two liters is standard. The lower the flow, the less risk you have.
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I have a problem with claiming that the pressure you measure in the tubing necessarily tells you what is happening in the lungs because you may have obstruction in the nose and your pressure may be up. The pressure you measure in the tubing does not necessarily equate to the pressure in the lungs. It is worrisome because maybe there is some blockage to the flow in the nose itself and the pressure is not going to get into the lungs and you also have the opening of the mouth. We do not know what pressure we actually transmit into the lungs and this is of concern. One of the ways we may deal with this is to cut the prongs off and only have the holes. Put the cannula in front of the nose and then you can be sure those safety issues are addressed. We still do not know how much pressure we are delivering but there is an escape. This question is addressed to Dr Bancalari. Is it better to extubate babies early to CPAP, nasal CPAP, or nasal intermittent mechanical ventilation (IMV) rather than keeping them intubated because they are not gaining weight?
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Dr Bancalari: We should not intubate any baby who does not need intubation and we should not continue intubation in any baby who can be extubated. The trick is to know which baby needs intubation and when is the right time to extubate. Many trials have tried to develop criteria for successful extubation, but there are no data that you can apply to all patients. The idea of not intubating everybody and allowing the babies who show sufficient respiratory effort to breathe spontaneously with nasal CPAP is very good. It is absurd to intubate everybody. There are many babies under 1 kg who could sustain ventilation with nasal CPAP. Very few babies over 1 kg would require intubation. I think the strategy proposed by Linder and many others of not intubating everybody but observing the baby, is right. It is a fight I have every morning with our fellows and the first question I ask is ‘Why is this baby on a ventilator?’ Usually they have a good reason, but I do not accept that the baby was intubated because he was too small, unless we are talking about 24 weeks and under 600 g. But for others, I require a reason. Then there is the more complicated question of extubation. Some of our attendings say they want to keep babies on a ventilator so they grow. I ask them, ‘Until they grow what, Pseudomonas or Klebsiella?’
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This question is addressed to Dr Soll about the use of elective versus rescue high frequency ventilation. Elective high-frequency ventilation is not beneficial so we are left with rescuing babies who fail conventional ventilation, given that there are not many studies on rescue high-frequency ventilation and outcome. In fact, one of your studies showed that might not be good. What are our options if a baby fails conventional ventilation?
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Dr Soll: Let me go back to your original statement because I think Frank Mannino, MD was alluding to the fact that it is possible that we are not doing any harm with these therapies. My take-home point is that I am surprised that everyone is so seduced by this therapy and everyone is increasing its utilization. Whatever you are comfortable with in terms of maintaining FRC with CPAP, high-frequency oscillator, or some more conventional approaches, you know that is going to be the winning strategy. I would not just dismiss elective high-frequency ventilation if that was your policy. I do not know if you are doing any harm with it. You asked about rescue and I would argue that there are no data really, although you would think that would be the most appealing approach. From the questionnaire, it seems to be that most people are using rescue high frequency ventilation. It probably warrants further trials, but I would also use it in a child who is failing conventional ventilation.
This question is addressed to Dr Bancalari about the increasing use of high-flow nasal cannula systems. In your presentation, you steadfastly stuck to data and avoided mentioning a practice that is very widespread – high-flow nasal cannula ‘Vapotherm.’ This is basically the standard treatment in many nurseries on the West Coast, although there is very little data. Can you comment on it?