I know how to bag a baby. At least I think I do. Providing PPV with a bag-valve mask is something that you are taught in NRP and is likely one of the first skills you learned in the NICU. We are told to squeeze the bag at a rate of 40-60 breaths a minute. According to the Laerdal website, the volume of the preterm silicone bag that we typically use is 240 mL. Imagine then that you are wanting to ventilate a baby who is 1 kg. How much should you compress the bag if you wish to delivery 5 mL/kg. Five ml out of a 240 mL bag is not a lot of squeeze is it? Think about that the next time you find yourself squeezing one. You might then say but what about a t-piece resuscitator? A good choice option as well but how much volume are you delivering if you set the initial pressures at 20/5 for example? That would depend on the compliance of the lung of course. The greater the compliance the more volume would go in. Would it be 5 mL, 10 ml or even 2.5 mL based on the initial setting? Hard to say as it really depends on your seal and the compliance of the lung at the pressure you have chosen. If only we had a device that could deliver a preset volume just like on a ventilator with a volume guarantee setting!
Why is this holy grail so important?
It has been over 30 years since the importance of volutrauma was demonstrated in a rabbit model. Hernandez LA et al published Chest wall restriction limits high airway pressure-induced lung injury in young rabbits. The study used three models to demonstrate the impact of volume as opposed to pressure on injuring the lung of preterm rabbits. Group 1 were rabbit ventilated at pressures of 15/30/45 cm H2O for one hour, group 2 rabbits with a cast around their thorax to limit volume expansion and group 3 sets of excised lungs with no restriction to distension based on the applied pressures. As you might expect, limitation of over distension by the plaster cast led the greatest reduction in injury (measured as microvascular permeability) with the excised lungs being the worst. In doing this study the authors demonstrated the importance of over distension and made the case for controlling volume more than pressure when delivering breaths to avoid excessive tidal volume and resultant lung injury.
The “Next Step” Volume Ventilator BVM
Perhaps I am becoming a fan of the Edmonton group. In 2015 they published A Novel Prototype Neonatal Resuscitator That Controls Tidal Volume and Ventilation Rate: A Comparative Study of Mask Ventilation in a Newborn Manikin. The device is tablet based and as described, rather than setting a PIP to deliver a Vt, a rate is set along with a volume to be delivered with a peep in this case set at +5. This study compared 5 different methods of delivering PPV to a 1 kg preterm manikin. The first was a standard self inflating bag, the next three different t-piece resuscitators and then the Next Step. For the first four the goal was to deliver a pressure of 20/5 at a rate of 40-60 breaths per minute. A test lung was connected to the manikin such that each device was used for a one minute period at three different levels of compliance (0.5 ml/cmH2O, 1.0 ml/cmH2O and then 2.0 ml/cm H2O representing increasing compliance. The goal of the study was to compare the methods in terms of delivering a volume of 5 mL to this 1 kg model lung. The order in which the devices were used was randomized for the 25 participants in the study who were all certified in NRP and included some Neonatologists.
Some Concerning Findings
As I said at the beginning, we all like to think we know how to ventilate a newborn with BVM. The results though suggest that as compliance increases our ability to control how much volume we deliver to a lung based on a best guess for pressures needed is lacking. One caveat here is that the pressures set on the t-piece resucitators were unchanged during the 1 minute trials but then again how often during one minute would we change settings from a starting point of 20/5?
Without putting in all the confidence intervals I can tell you that the Next Step was the tightest. What you notice immediately (or at least I did) was that no matter what the compliance, the self inflating bag delivers quite an excessive volume even in experienced hands regardless of compliance. At low compliance the t-piece resuscitators do an admirable job as 5-6 ml/kg of delivered Vt is reasonable but as compliance improves the volumes increase substantially. It is worth pointing out that at low compliance the Next Step was unable to deliver the prescribed Vt but knowing that if you had a baby who wasn’t responding to ventilation I would imagine you would then try a setting of 6 ml/kg to compensate much like you would increase the pressure on a typical device. How might these devices do in a 29 week infant for example with better compliance than say a 24 week infant? You can’t help but wonder how many babies are given minutes of excessive Vt after birth during PPV with the traditional pressure limited BVM setup and then down the road how many have BPD in part because of that exposure.
I wanted to share this piece as I think volume resuscitation will be the future. This is just a prototype or at least back then it was. Interestingly in terms of satisfaction of use, the Next Step was rated by the participants in the study as being the easiest and most comfortable to use of all the devices studied. Adding this finding to the accuracy of the delivered volume and I think we could have a winner.
This is becoming “all the rage” as they say. I first heard about the strategy of feeding while on CPAP from colleagues in Calgary. They had created the SINC * (Safe Individualized Feeding Competence) program to provide an approach to safely introducing feeding to those who were still requiring CPAP. As news of this approach spread a great deal of excitement ensued as one can only imagine that in these days when attainment of oral feeding is a common reason for delaying discharge, could getting an early start shorten hospital stay? I could describe what they found with the implementation of this strategy but I couldn’t do it the same justice as the presenter of the data did at a recent conference in Winnipeg. For the slide set you can find them here. As you can imagine, in this experience out of Calgary though they did indeed find that wonderful accomplishment of shorter hospital stays in the SINC group. We have been so impressed with the results and the sensibility of it all that we in fact have embraced the concept and introduced it here in both of our units. The protocol for providing this approach is the following.
I have to admit, while I have only experienced this approach for a short time the results do seem to be impressive. Although anecdotal a parent even commented the other day that she felt that SINC was instrumental in getting her baby’s feeding going! With all this excitement around this technique I was thrown a little off kilter when a paper came out suggesting we should put a full stop to feeding on CPAP!
What caused my spirits to dampen? This study enrolled preterm infants who were still on CPAP at ≥ 34 weeks PMA and were taking over 50% of required feeding volumes by NG feeding. The goal was to look at 15 patients who were being fed on CPAP +5 and with a mean FiO2 of 25% (21-37%) using video fluoroscopic swallowing studies to determine whether such patients aspirate when being fed. The researchers became concerned when each of the first seven patients demonstrated abnormalities of swallowing function indicating varying degrees of aspiration. As such they took each patient off CPAP in the radiology suite and replaced it with 1 l/min NP to achieve acceptable oxygen saturations and repeated the study again. The results of the two swallow studies showed remarkable differences in risk to the patient and as such the recruitment of further patients was stopped due to concerns of safety and a firm recommendation of avoiding feeding while on CPAP was made.
|Table 2. Percentage of all swallows identified with swallowing dysfunction
|Variable Mean ± s.d.
||Mean ± s.d.
||Mean ± s.d.
|Mild pen. %
|Deep pen. %
|| 25 (18.2–32)
|Nasopharyngeal reflux %
Taking these results at face value it would seem that we should put an abrupt halt to feeding while on CPAP but as the saying goes the devil is in the details…
CPAP Using Ram Cannulae
Let me start off by saying that I don’t have any particular fight to pick with the RAM cannulae. They serve a purpose and that is they allow CPAP to be delivered with a very simple set of prongs and avoid the hats, straps and such of more traditional CPAP devices. We have used them as temporary CPAP delivery when moving a patient from one area to another. As the authors state the prongs are sized in order to ensure the presence of a leak. This has to do with the need to provide a way for the patient to exhale when nasal breathing. Prongs that are too loose have a large leak and may not deliver adequate pressure while those that are too tight may inadvertently deliver high pressure and therefore impose significant work of breathing on the patient. Even with appropriate sizing these prongs do not allow one to exhale against a low pressure or flow as is seen with the “fluidic flip” employed with the infant flow interface. With the fluidic flip, exhalation occurs against very little resistance thereby reducing work of breathing which is not present with the use of the RAM cannula.
A comparison of the often used “bubble CPAP” to a variable flow device also showed lower work of breathing when variable flow is used.
The Bottom Line
Trying to feed an infant who is working against a constant flow as delivered by the RAM cannulae is bound to cause problems. I don’t think it should be a surprise to find that trying to feed while struggling to breathe increases the risk of aspiration. Similarly, under treating a patient by placing them on nasal prongs would lead to increased work of breathing as while you may provide the needed O2 it is at lower lung volumes. Increasing work of breathing places infants at increased risk of aspiration. That is what I would take from this study. Interestingly, looking at the slide set from Calgary they did in fact use CPAP with the fluidic flip. Smart people they are. It would be too easy to embrace the results of this study and turn your nose to the SINC approach to feeding on CPAP. Perhaps somewhere out there someone will read this and think twice about abandoning the SINC approach and a baby will be better for it.
* SINC algorithm and picture of the fluidic flip courtesy of Stacey Dalgleish and the continued work of Alberta Health Services
This may sound familiar as I wrote about this topic in the last year but the previous post was restricted to infants who were under 1000g. High Flow Nasal Cannula be careful out there had a main message that suggested the combined outcome of BPD or death was more prevalent when HFNC is used alone or with CPAP than when CPAP is used alone. The question remains though whether this applies to larger infants. Without looking at the evidence for that combined outcome most people would say there is unlikely to be a difference. Larger more mature babies have a much lower risk of BPD or death so proponents of HFNC would say it is simpler to use and helps prevent nasal breakdown as well. The question remains as to whether all outcomes are the same in larger infants and that is the point of this post.
A Non-Inferiority Trial
First off it is important to understand what this type of trial is. The first requirement is that the two treatments have both been compared to a placebo and found to be both effective. Once you establish that you have a choice between two treatment options then you eliminate the placebo and compare them head to head. What you are looking for in this type of trial is to determine not whether one is better than the other but that there is no difference in a clinical outcome of interest. If you find no difference then the next step is to look at other outcomes that might be of interest and see if there are any benefits to picking one versus the other. In the case of CPAP vs HNFC, if a non-inferiority trial showed no difference in an important outcome such as length of stay but nasal breakdown was less with HFNC it might lead a unit to use HFNC for their infants. Okay, now that we have that cleared up we can move on to an actual study examining this very subject.
This was an interesting study with a great name (The HIPSTER trial) that enrolled infants > 28 weeks and 0 days with none of the infants receiving surfactant but either being randomized to HFNC or CPAP after delivery. These infants were your typical modern day cohort of babies who may avoid intubation and surfactant by establishing FRC early with positive pressure applied to the nose through one of these devices. The end point for the study was treatment failure within 72 hours. If an infant failed in the HFNC they could have a trial of CPAP whereas in the CPAP group they were intubated. For each infant in the HFNC group flow was set from 6-8 l/min and for CPAP 6-8 cmH2O.
Treatment was considered to have failed if an infant receiving maximal support (high-flow therapy at a gas flow of 8 liters per minute or CPAP at a pressure of 8 cm of water) met one or more of the following criteria:
- FiO2 of 0.4 or higher
- Arterial or free flowing cap gas with a pH of 7.2 or less plus a pCO2 > 60 mm Hg obtained at least 1 hour after starting treatment
- Two or more episodes of apnea requiring positive-pressure ventilation within a 24-hour period or six or more episodes requiring any intervention within a 6-hour period.
- Infants with an urgent need for intubation and mechanical ventilation.
So what happened?
The trial randomized 583 infants (278 HFNC, 286 CPAP) but was halted by the data and safety monitoring committee after an analysis of the first 515 revealed that the outcome was worse in the HFNC group (25.5% failure rate vs 13.3 for CPAP). Interestingly treatment failures were more common in babies below and above 32 weeks so it was not just the smallest infants who failed.
Another interesting finding was that the most common reason for treatment failure was criteria 1 (FiO2 > 40%) while intubation was higher for all infants but did not reach statistical significance. Curiously what did reach a significant difference was criteria #4 (18.4% urgent intubations in the CPAP group vs 5.6% in the HFNC group). You might be tempted to therefore ponder which is worse, a little O2 or being intubated but you need to recall the trial design which was set up to provide this kind of result. If you failed HFNC you were placed on CPAP whereas if you failed CPAP you were intubated. In the HFNC group, 78 infants were deemed to have failed but 28 of them were in fact “rescued by CPAP”. It therefore isn’t a fair comparison when it comes to urgent intubation since if you failed CPAP there wasn’t another option.
Not a total loss
Nasal trauma was indeed much lower in the HFNC group, occurring only 8.3% vs 18.5% of the time with CPAP. Pneumothorax was also found to be significantly different with none of the patients in the HFNC group having that complication vs 2.1% in the CPAP group. What this study tells us is that as a primary modality to treat newborns with RDS who have not received surfactant it is preferable to use CPAP in the first 72 hours. Some of you may say it might not say that at all but consider the impact of having more babies exposed to high FiO2. We know from other studies that high FiO2 can be quite damaging to preterm infants and this study was certainly not powered to look at all those important outcomes such as ROP, PVL and BPD. The authors report them and found no difference but without adequate power to show a difference I wouldn’t take much comfort in those findings.
I think were things may settle out though is what to do in more mature infants. There is no question that for those on chronic respiratory support there is some risk of nasal breakdown. Although I don’t have much experience with HFNC I would think that for the older patient who either already has BPD at 36 weeks or is close to that point but reliant on +4 or +5 CPAP that HFNC might help “give them a break”. As such I don’t see this as a total loss but rather an option to try when CPAP for whatever reason is not tolerated.
As a primary therapy for non-invasive management RDS I will keep my CPAP for all babies thank you.
What follows is a local news story that I had the pleasure of being involved in. I am posting on the blog not to show off in the least but rather highlight how true collaboration between professionals (who on the surface might not seem to be related) can accomplish incredible things. The strategy employed in this case had not been described before in the literature and thus it is my hope that this post may be shared at your local institutions and in the event a child with a cleft lip and palate is born and needs CPAP this appliance could be utilized.
If you would like further information on this approach please email me at [email protected] and I would be happy to provide you with assistance. The link to obtain the abstract and from there if you have personal or facility access to the full article can be found here: http://www.ncbi.nlm.nih.gov/pubmed/25794910
Within the last year a team of professionals from Dentistry, Neonatology and Respiratory Therapy came together to solve an unusual problem. A baby had been born prematurely at 26 weeks gestational age and less than 2 lbs and relied on a ventilator to help her breathe. As many of these children age, their reliance on a ventilator becomes less and they are changed to a non-invasive level of support called CPAP (continuous positive airway pressure). This consists of a mask put over the nose, which passes air into the lung thereby keeping a babies lungs inflated while we wait for continued development of their lungs. In this case however this premature infant had been born with a complete unilateral cleft lip and palate. Having this cleft created a leak, which makes the use of CPAP very challenging. The flow of air leaks out through the cleft instead of getting to the lungs to keep them inflated. One day, one of our respiratory therapists John Minski asked the Neonatologist on service (Dr. Michael Narvey) whether we could use a 3D scanning and printing technology to create an appliance that would seal the palate and allow pressure to be maintained in the lungs through the flow of air in the nose. Dr. Narvey had not heard of such a strategy being employed before but consulted Dr. Igor Pesun from the Faculty of Dentistry for an opinion and what came out of this discussion was a novel concept that we believe is the first of its kind.
A dental obturator was created to seal the palatal defect. A child who is as small as Michaela, made the use of current intra oral scanning technology not possible. An impression using conventional dental materials was used to record the anatomy of the palate. A model was made and used to fabricate the obturator that was connected to the CPAP tubing.
Over a period of 4 days the obturator was used to maintain a palatal seal and allowed for sufficient pressure to be maintained to manage the child off the ventilator. After this point she was deemed ready to transition to being off CPAP.
The collaboration between these services was instrumental in taking an idea from concept to reality. We were able to demonstrate that a premature infant, who previously would have been forced to remain on a ventilator until they were ready to come off breathing support completely, could be managed with a novel airway appliance. This type of approach has never been tried before in the literature and exemplifies some of the creative and innovative collaborative work happening at the Health Sciences Centre. Finally it serves as a shining example of how different seemingly unrelated specialties can come together within the Faculty of Health Sciences at the University of Manitoba.