When I began my career in Neonatology we initially ventilated primarily with pressure limited time cycled modes of ventilation and only supported some of the breaths as in SIMV modes. With time and emerging research a movement to using set volumes came about and in many centres supporting every breath using an assist control mode or similar version. Although I don’t have access to it in my centre, ventilators such as the Avea also allow for automated FiO2 control in addition to having a choice of two different volume targeting modes. The difference between the modes is the subject of a study entitled Comparison of volume guarantee and volume-controlled ventilation both using closed loop inspired oxygen in preterm infants: a randomised crossover study (CLIO-VG study). I suppose it shouldn’t be a big surprise that as technology advances and we fine tune practice, different modes for volume targeting would arise.
What’s the difference?
Volume Controlled Ventilation (VCV) – flow based on a set volume and measurement of the PIP every 2 ms. Next breath is given the greater of PEEP+2 cm H2O or PIP-2 cmH2O. The ventilator at the end of each breath is able to determine if the baby is still demanding flow and continues providing flow but stops when inspiratory flow is <25% of peak set flow. There is constant inspiratory flow and peak volumes.
Volume Guarantee (VG)- inspiratory pressure is adjusted breath to breath. These breaths have a decelerating flow instead of a fixed flow as in VCV.
Using automated FiO2 control for both groups the study design was a crossover one. The concept was that better ventilation would help to keep O2 saturations more reliably in a target range of 90-95% and that one of these modes might be superior than the other in doing so. Infants in the study were born at 23+0 – 36+6 weeks and had to be intubated and on >21% FiO2 to be part of the study. Each group spent 12 hours in each arm with the starting mode randomly chosen before switching over to the other mode.
Based on a power calculation in which the authors selected looking for a 5% difference they determined they needed 19 patients in the study overall. The median GA of the infants was 25 weeks (IQR 24-28) with a BW of 685g.
On a personal note, I use only VG in my centre so I am pleased to see there is really no difference in the primary outcome but the trend in the secondary outcomes at least puts a slight smile on my face as well!
I have written a lot over the years on the topic of BPD. It isn’t by chance as it is a condition that Neonatologists have put a lot of weight on. In many ways it is a benchmark that is often the go to condition when comparing one unit to another. When two Neonatologists get together their first question isn’t what’s your rate of ROP or severe developmental delay but more often comparing rates of BPD. We like to compare this as a metric as it’s something we can see as compared to say rates of late onset sepsis. You can see a patient on a ventilator or on CPAP at 36 weeks but you can’t see bacteria coursing through veins.
Not all BPD is the same though. in 2000 the NIH produced a new consensus definition of BPD as shown below.
What stands out for the babies <32 weeks is how severe BPD is defined. Babies who are ventilated are classified in the same severity group as those who are on CPAP. Somehow that doesn’t seem quite right intuitively but alas that is what they decided at the time.
Type 1 sBPD: patients on nasal cannula or noninvasive positive pressure support (i.e., high flow nasal cannula (HFNC), nasal continuous positive airway pressure (nCPAP), noninvasive intermittent positive pressure ventilation (nIPPV)) Type 2 sBPD: infants receiving iMV
The authors then looked at a sample of 564 patients from 2015-2019 in the BPD collaborative registry and subdivided them into 429 (76%) Type 1 vs 135 (24%) Type 2 sBPD and compared outcomes between the two. The differences between the two types of BPD are quite significant and shown in Table I. Babies who went on to develop sBPD as Type 2 were younger and smaller than those with Type 1. Medication use within the NICU and after discharge was markedly different as were the total ventilator days which is likely not surprising since by definition they were still intubated at 36 weeks. Importantly if you were still intubated at 36 weeks PMA almost one quarter of the patients went on to receive a tracheostomy.
Looking at it another way using relative risks the signifance of having Type 2 sBPD is impactful.
Taking Meaning From This
You might be quick to say, Michael this is absolutely no surprise. On the other hand if you have read this blog for some time you may remember this piece The New BPD That Matters. This study looked at what gestational age really mattered when looking at long term pulmonary outcomes in a Canadian cohort. When you take all comers it was 40 weeks and not 36 weeks that really mattered. The likely differernce here though is that by selecting out only the severe patients in this current study it is indeed the 36 week mark that still has relevance. I actually think the two papers together are not contradictory but rather additive.
What I think one takes away from the current study is that failure to extubate by 36 weeks does in fact carry with it significant long term risk to the patient. It would be easy enough to say that these babies should be extubated but as you see from table I it isn’t that they didn’t try. From a medication standpoint it would appear that they ” threw the kitchen sink” at these babies. The only thing I find a little surprising is that only 47% of babies in the collaborative with type 2 sBPD received systemic steroids. If they were that sick I would have expected it to be higher although that also may just be a reflection of my own practice.
One thing that I think will be a hot topic moving forward is the use of higher levels of CPAP than what many units are accustomed to. This has also been recently discussed in High CPAP vs NIPPV. Is there a winner? There may be a reluctance by some units to use CPAP levels in the +9-12 cm H2O range but when looking at these downstream complications for patients who remain ventilated at 36 weeks I think people need to seriously consider their biases and whether they are based on science or what they were taught. I can’t help but think of the oft used expression absence of evidence is not evidence of absence and think that if we can all be a little humble who knows what we may discover that can help this population.
Who doesn’t love a good match up?! Supporting neonates in need of resuscitation after delivery has been the subject of many studies over the years. The movement has certainly been to non-invasive support with CPAP or NIPPV but some babies need some degree of support with PPV after delivery when they simply won’t breathe. Prior to intubation the rise of the t-piece resuscitator has meant that practitioners can set a PIP and PEEP and with only a finger press to deliver a tidal volume at set pressure and with the finger released provide CPAP through the same device. The only problem potentially with use of these devices is the imposed work of breathing (iWOB) which has been measured in other studies. Any device I have used has provided ventilation through a mask so imagine my surprise to come across a new device called rPAP using prongs from the original infant flow design. From the manufacturers website the company claims that their design used with either a mask or nasal prongs reduces iWOB by 92% compared to other comparable machines! Imagine my greater surprise to see a head to head RCT comparing this new device to standard t-piece resuscitators with a mask.
The intervention was completed with one of three outcomes were met.
Stable and breathing on method of support after a minimum of 10 minutes of support.
At 30 minutes when respiratory support could continue as decided by the clinician without crossover allowed.
Looking at the appendices for the trial it appears that one could use either device to administer PPV or CPAP but the point of the trial was that the devices would be used to support the infants until one of the three above criteria were met. If the claims about reduced iWOB were true compared to other devices in use then one might expect to see a difference in the primary outcome of incidence of intubation or death within 30 minutes of birth.
In total there were 250 infants recruited with 127 assigned to the rPAP and the other 123 to t-piece resuscitation. The mean GA in the trial was 24.8 weeks and the baseline characteristics between groups were similar although the group randomized to the rPAP has more c-sections and more general anesthetic exposure compared to the t-piece group. Lastly, humidification of gases during resuscitation was similar between the two groups.
How Did They Compare?
It just might be that the claims of decreased iWOB might have merit. In Figure 2 below the Kaplan-Meier curves show a difference favouring the rPAP device when looking at the primary outcome. This difference was significant with 41 of 124 infants (33.1%) in the rPAP group and in 55 of 122 infants (45.1%) in the T-piece group having the primary outcome of intubation or death within the first 30 minutes of life. Moreover when looking at the adjusted odds ratio it was still significant at 0.53; 95% CI, 0.30-0.94. The incidence of intubation and death in the first 72 hours although trending towards favouring the new system did not reach statistical significance.
Finally, none of the secondary outcomes reached statistical significance which included such things as death in the delivery room, use of surfactant, or PPV in the DR.
Does it make sense?
If you had asked me to tell you prior to the study whether resuscitation with nasal prongs vs a mask would be different I would have said a mask would be better due to less leak. Turns out based on this data that I would be wrong in that guess. A look at the website though for the rPAP device indicates that it can be used with a mask or nasal prongs. It would have been nice in the study presented here to have used a mask as a third arm with the rPAP device as it leaves me wondering a bit whether it was the interface that mattered more than the type of driver used? Maybe I am wrong and by using prongs it allows the infant to have less iWOB than with a mask over the mouth and nose? Could it be that it has more to do with that that the type of driver whether it is a traditional t-piece resuscitator or the new rPAP device? Regardless, I have a suspicion that these results will resonate with people. A posting of the abstract alone has garnered a lot of attention on twitter this week so clearly this is of interest.
I don’t think there is much fault to find in this study other than my question of why they didn’t choose to have a head to head comparison with masks as well but perhaps that is for another study. I imagine we will see this approach adopted in many centres around the world as they replace their traditional t-piece resuscitators in need of replacement. I also suspect there will be many that will want a larger study before adopting this strategy to look more closely with come faith in the results at secondary outcomes in particular having to do with safety.
One thing is for certain. There will be more studies to come!
If there is a country that leads this site in terms of mentions it has to be Sweden. This isn’t just because I happen to know some Neonatologists from there who are fine people but because of the fantastic research that spills forth from their national registry of births. Surfactant is one of the oldest treatments we have in Neonatology and we know that in babies with RDS giving it early within 2 hours has benefits such as reduction in pneumothorax. The reality though is that as we have become familiar with the therapy its use has spilled over to other conditions. Years ago use of surfactant in meconium aspiration syndrome was shown to reduce need for ECMO. It has also been shown to imrove clinical condition in babies with pneumonia. Interestingly as a fellow I was criticised one call night for wanting to give a three day old baby with a history of RDS and high FiO2 requirements a repeat dose of surfactant. That was in 2001 and at that time no one could believe I was suggesting such an odd thing to give a dose after 48 hours yet now this is commonplace. Again as we have become more comfortable with surfactant such “off label” use spreads. I am not being critical of my colleagues back in 2001 as that was what the “conventional wisdom” was with respect to surfactant but that was then and this is now.
Looking at their registry data for 97377 infants born from 2009-2018 they found 7980 surfactant administrations to 5209 infants. The reasons for surfactant administration are shown in the table 1 below from the paper. Clearly and not surprisingly the bulk of surfactant administration is for RDS especially as gestational age declines. Given that so few preterm infants will pass meconium in-utero it also is understandable why MAS clusters in the more mature babies.
When it comes to multiple surfactant administrations they found 59.2% received 1 administration, 25.8% received 2, 7.3% had 3, and 2.8% had 4 or more administrations. Not surprisingly the more immature infants were more likely to receive multiple administrations. I have to say at this point that I feel vindicated with that suggestion for late surfactant administration all those years ago as these extra doses would have been given up to days after the first dosing.
Now Here Comes The Interesting Part
Much like previous work before this study, delivery of surfactant within the first 2 hours of age was associated with a reduction in very important outcomes of pneumothorax, IVH and need for ventilation beyond 7 days.. In short, improving compliance has a lot of benefits! The surprise was the in-hospital survival which favoured giving surfactant late. Put another way, if you receive surfactant in the first two hours you are more likely to die in hospital.
How can that possibly be if provision of surfactant has all those benefits outlined in table 3? More on that in a bit.
The next table addresses another question which is what if you don’t get surfactant at all? Interestinly the in-hospital survival is better for that group as well. On the other hand no difference exists for pneumothorax or IVH and ventilation beyong 7 days is improved with no surfactant at all!
The Difference Between Association and Causation
Ultimately that is what I think is at play here. You could look at the information quickly and conclude that giving surfactant late or not at all improves your chances of survival! Maybe aggressive use of surfactant isn’t such a good thing after all. I think you would be wrong there though based on prospective randomized trials. What is happening here is that the baseline characteristics are not likely equal and you are really looking at three different groups of patients.
Group 1 – These are the ones who get surfactant early within 2 hours of life. My suspicion is that the number of babies in this group that are really sick who may also have other comorbid issues is higher. There might be some babies with servere IUGR, pulmonary hypoplasia, meconium aspiration or pleural effusions that made the resuscitating team so nervous that they in advance of delivery had surfactant thawing and ready to go. Yes overall this group might benefit from better compliance and have less pneumothoraces for example but their comorbid conditions put them at higher risk of death.
Group 2 – Surfactant given after 2 hours of age. These are likely babies who are not as sick as group 1. Maybe they are babies initially managed with CPAP or NIPPV who due to escalating FiO2 requirements get surfactant. Much less likely to die.
Group 3 – No surfactant needed at all. The reason there might not be a difference in the major morbidities is that while they have RDS, TTN or MAS they are mild in nature. Clearly very low risk of death here and for that matter complications.
It might have been helpful to have some meaures of acuity documented such as SNAPPE-II (Score for Neonatal Acute Physiology with Perinatal Extension-II) used as it would help us in figuring out such differences.
Overall I think the message remains the same. Give surfactant early for those with significant lung disease. What I think it adds is an awareness that repeat dosing even if off-label is being done in Neonatology. The next question will be whether this repeat dosing makes the babies better or just us!
Giving bronchodilators to preemies on a ventilator has certainly been tried before. The major issue to contend with is getting the drug to where it is supposed to be. Anyone reading who has a child with asthma knows that you should use an aerochamber when taking a puff to help with better distribution to the lung. Giving a puff or two without it largely ends up on the back of the throat. Similarly, giving puffs through an endotracheal tuberaises questions about how much of the medication winds up on the plastic tube rather than the smooth muscle of the airways where the medication is intended to be. This has been looked at in a cochrane review as well entitled Bronchodilators for the prevention and treatment of chronic lung disease in preterm infants
Can Albuterol Save The Day?
Albuterol is a beta agonist much like ventolin that can act on the smooth muscle of airways to achieve bronchodilation. Considering that preemies with immature lungs may have issues with both resistance and compliance, Raffay TM et al in their paper Response to first dose of inhaled albuterol in mechanically ventilated preterm infants chose to examine responsiveness in a group of 33 infants (all < 30 weeks at birth) to albuterol. Ideally, responsiveness would be done by pulmonary function testing but given that this was not possible in these infants they chose to examine other indicators of impact. After giving two puffs of 90 mcg of albeterol via a metered dose inhaler without an aerochamber the authors looked at changes in FiO2 as well as compliance and resistance measurements on the ventilator as a means of determining responsiveness. Ultimately, could they get drug into the distal airway in patients who were ventilated at about a month of age as shown in table 1 along with other baseline characteristics?
What makes this different than other studies I suppose is the use of the ventilator measurements and their use of histogram data on oxygen saturation to ascertain responsiveness to treatment. This was an observational study based on a secondary analysis of a previous study so we don’t have sham controls to compare to. Having said that by administering the medication and seeing what happens immediately afterwards it is possibile to get a sense of whether the drug had an effect.
So What if Any Effect Did It Have?
From the figure in the paper the answer is some effect. Overall, post albuterol resistance for the 33 patients overall was found to decrease. Compliance and FiO2 (not shown in the graphs below) did not change though. What did change however was the percentage of time spent below 80 and 85% respectively comparing a 4 hour window pre and a 4 hour window post with respect to histograms from the patient monitor.
Putting it together
Ok so this isn’t a gold standard RCT looking at placebo treatments vs albuterol. It is hypothesis generating though as if resistance was decreased by albuterol one could expect improved delivery of O2 to the distal alveoli and therefore better oxygenation which is what is seen here. Should we be surprised that no difference in compliance is seen with albuterol therapy? I don’t think so as the effect of the drug is not on the distal alveoli and parenchyma but rather the more proximal branching airways. SInce airway resistance is governed by Poiseuille’s Law (you thought physics was over in high school?!) you can see that resistance (R) is directly proportional to the viscosity (n) and length (l) of the airway but inversely affected by the radius (r) to the 4th power. In other words if the radius of the airway after albuterol increases by 25% that effect is amplified to the 4th power in terms of reducing resistance.
I suppose I am buying what they are selling here but again the key is finding a method of getting the drug to deposit not in the trachea or proximal bronchi but to the lower airways. I can’t help but wonder if use of high frequency jet ventilation which carries flow down the centre of the airway might be a very effective way of getting such puffs further into the lung. Speculation of course but perhaps someone a little more creative than I can figure out how to do that and test deposition.
Should we use this routinely? Probably not as an everyday approach but it does make me wonder about those babies who are having a bad day so to speak. If one can glean from the ventilator that resistance has increased from one day to another might this be something worth trying? The authors found that the first treatment was effective but second and third not so much so to me this may just be a “hail mary” that is worth trying when nothing else seems to be working to reduce FiO2 in the presence of increased resistance.
If anyone is doing this routinely I would be curious in hearing your own experiences.