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.
I would consider myself fairly open minded when it comes to care in the NICU. I wouldn’t call myself a maverick or careless but I certainly am open to new techniques or technologies that may offer a better level of care for the babies in our unit. When it comes to “non-Western” concepts though such as therapeutic touch, chiropractic manipulations of infants and acupuncture (needle or otherwise) I have generally been a skeptic. I have written about such topics before with the most popular post being Laser acupuncture for neonatal abstinence syndrome. My conclusion there was that I was not a fan of the strategy but perhaps I could be more open to non traditional therapies.
This would appear to be the newest and perhaps strangest (to me at least) approach to pain relief that I have seen. I do love name of this study; the MAGNIFIC trial consisted of a pilot study on the use of auricular magnetic acupuncture to alleviate pain in the NICU from heel lances. The study was published in Acta Paediatrica this month; Magnetic Non-Invasive Acupuncture for Infant Comfort (MAGNIFIC) – A single-blinded randomized controlled pilot trial. The goal here was to measure pain scores using the PIPP scoring system for pain in the neonate before during and after a painful experience (heel lance) in the NICU. Being a pilot study it was small with only 20 needed per arm based on the power calculation to detect a 20% difference in scores. The intervention used small magnets placed at specific locations on the ear of the infant at least two hours before the heel lance was to occur. Before I get into the results, the authors of the study provide references to explain how the therapy works. Looking at the references I have to admit I was not able to obtain complete papers but the evidence is generally it would appear from adult patients. The explanation has to do with the magnetic field increasing blood flow to the area the magnet is applied to and in addition another reference suggests that there are affects the orbitofrontal and limbic regions which then impacts neurohormonal responses as seen in functional MRI. The evidence to support this is I would have thought would be pretty sparse but I was surprised to find a literature review on the subject that looked at 42 studies on the topic. The finding was that 88% of the studies reported a therapeutic effect. The conclusion though of the review was that the quality of the included studies was a bit sketchy for the most part so was not able to find that this should be a recommended therapy.
So what were the results?
Despite my clear skepticism what this study did well was that aside from the magnets, the intervention was the same. Twenty one babies received the magnetic treatments vs 19 placebo. There was a difference in the gestational ages of the babies with the magnet treated infants being about two weeks older (35 vs 33 weeks). What difference that might in and of itself have on the PIPPs scoring I am not sure. The stickers were applied to the ears with and without magnets in a randomized fashion and the nurses instructed to score them using the PIPP scoring system. Interestingly, as per their unit policy all babies received sucrose as well before the intervention of a heel lance so I suppose the information gleaned here would be the use of magnets as an adjunctive treatment. No difference was noted in the two groups before and after the heel lance but during the procedure the magnet treated infants had a difference in means (SD): 5.9 (3.7) v 8.3 (4.7), p=0.04). No differences were found in secondary measures such as HR or saturation and no adverse effects were noted. The authors conclusions were that it was feasible and appears safe and as with most pilot studies warrants further larger studies to verify the results.
Should we run out and buy it?
One of the issues I have with the study is that in the introduction they mention that this treatment might be useful where kangaroo care (KC) is not such as a critically ill infant. Having placed infants who are quite sick in KC and watched wonderful stability arise I am not sure if the unit in question under utilizes this important modality for comfort.
The second and perhaps biggest issue I have here is that although the primary outcome was reached it does seem that there was some fishing going on here. By that I mean there were three PIPP scores examined (before, during and after) and one barely reached statistical significance. My hunch is that indeed this was reached by chance rather than it being a real difference.
The last concern is that while the intervention was done in a blinded and randomized fashion, the evidence supporting the use of this in the first place is not strong. Taking this into account and adding the previous concern in as well and I have strong doubts that this is indeed “for real”. I doubt this will be the last we will hear about it and while my skepticism continues I have to admit if a larger study is produced I will be willing and interested to read it.
A debate broke out recently at one of our rounds when someone asked whether a recent case of NEC was possibly related to a transfusion that a baby received. Much has been written about Transfusion Associated Necrotizing Enterocolitis (TANEC) with the pendulum swinging back and forth between it existing as a real entity or simply being an association that is not causative in the least. Using one of my favourite sources, a retrospective analysis of the Canadian Neonatal Network database found no difference in mortality or morbidities for those who had a transfusion and NEC vs those without. Despite this we continue to see those who “hold feeds” for a few hours prior to transfusion and then resume them a few hours later. Why does this happen?
Risk vs Benefit
Those who hold feeds argue that in Neonatology we hold feeds for far less. Furthermore, what is the harm? If a baby develops NEC within 24 hours of a transfusion and we held the feeds we feel we have done all we could. If a baby is fed and develops NEC we are left asking “what if?”. The purists out there would argue the contrary though, that the evidence is not strong enough to support the practice and may require the insertion of an IV which is a painful procedure and places the infant at risk of infection from one or more skin breaks. Additionally, does the interruption of feeds potentially alter the microbiome of the patient and with it risk potential downstream consequences. In case you are wondering, I have tended to sit on the side of holding a feed although more often when I am asked about it than ordering it upfront. The fact is I just don’t know. The evidence has never been solid in this regard but it is hard to ignore the possibility when you have been bitten once or twice before (whether it was causative or not!). I doubt it really exists but then again what if there is something there?
It May Not Be The Transfusion But Anemia Itself
A recent paper Association of Red Blood Cell Transfusion, Anemia, and Necrotizing Enterocolitis in Very Low-Birth-Weight Infants may have found a possible explanation to the ongoing debate. Research papers associating transfusions with NEC may all have one thing in common in that they have not been able to prove causation. When you have many papers finding the same thing it leads medical teams to begin to believe there is causation. Something else may be at play at this paper suggests another association which again may not be causative but at least in my mind is perhaps biologically plausible. It may be that those patients who are transfused when their hemoglobin is below a threshold of 80 g/L are at increased risk of developing NEC rather than all patients transfused.
This study was a secondary analysis of a prospective study on transfusion transmission of cytomegalovirus in preterm infants < 1500g. The authors chose 80 g/L as a cutoff based on previous studies suggesting this threshold as an important one for transfusion practices. Forty eight out of 60 eligible infants developed NEC and it is from this 48 that multivariable analysis sought to identify factors predisposing to the outcome in question of NEC. The factor with the greatest hazard risk for NEC was severe anemia in a given week with an approximate 6 fold risk (range 2 – 18) while receiving an RBC transfusion in a given week of life did not meet statistical significance.
What does this mean?
Before embracing the result and concluding we have the answer we have to acknowledge the authors have gone on a fishing expedition of sorts. Any secondary analysis of a study that is done carries with it some words of warning. There may be variables that were not controlled for that are affecting the results. As well when looking at many many variables it could be by chance that something or several things come up by chance. Lastly it may be that again there is nothing more than an association here at play. Having said that, there is some biologic plausibility at least here.
- Delivery of oxygen to the tissues is dependent on HgB level. The oxygen content of blood is described by: O2 content = (gm Hbg)(1.34 ml O2/gm Hbg)(% sat) + 0.003(pO2) = ml O2/dL.
- Oxygen delivery = cardiac output X O2 concentration (or content)
- Could RBCs become less deformable and increase viscosity in low O2 environments? This could be the case when the HgB declines below 80 g/L. Such changes to deformability have been demonstrated at mild levels of hypoxia as might exist in low pO2 conditions at the tissue level with anemia.
So imagine we have fewer RBCs carrying as much oxygen as they can but eventually you cross a threshold where there is not enough O2 being delivered at the tissue level and the RBCs become lodged or perhaps sluggish as they move through capillaries of the intestines. Add to this that NEC occurs in watershed areas most commonly and you have the potential setup for NEC.
Can we use the results of this study?
I suppose statistical purists out there will argue that it is merely an association. The fact remains that there are many people who are holding feeds for varying amounts of time despite the lack of conclusive evidence that TANEC exists. I wonder if a middle ground might be to be more cautious and restrict such practice to those with low HgB values below 80 g/L as the authors here have found. To me at least there is biologic plausibility as outlined above. It would seem to me that to hold feeds for all babies is excessive and likely without evidence but could the threshold actually matter which it comes to oxygen content. Given that NEC is a condition related to ischemia, the authors here have provided another association that makes me at the very least scratch my head.
I have written about respectful communication before in Kill them with kindness.
The importance of collaborating in a respectful manner cannot be overemphasized, as a calm and well prepared team can handle just about anything thrown their way. This past week I finally had the opportunity to take the 7th ed NRP instructor course. What struck me most about the new version of the course was not the approach to the actual resuscitation but the preparation that was emphasized before you even start! It only takes 30 seconds to establish who is doing what in a resuscitation and while it would seem logical to divide up the roles each will take on it is something that has not been consistently done (at least in our institution). When a baby is born and responds to PPV quickly, this may not seem that important but in a situation where a team is performing chest compressions, placing an emergency UVC and moving on to epinephrine administration it certainly is nice to know in advance who is doing what.
The Golden Hour
We and many other centres have adopted this approach to resuscitation and at least here developed a checklist to ensure that everyone is prepared for a high risk delivery. While teams may think they have all the bases covered, when heart rates are racing it may surprise you to see how many times crucial bits of information or planning is missed. As I told you in another post I will be releasing a series of videos that I hope others will find useful. The video in this case is of a team readying itself for the delivery of a preterm infant that they anticipate will have respiratory distress. Ask yourself as you watch the film whether your team is preparing to this degree or not. Preparing in such a fashion certainly reduces the risk of errors caused by assumptions about who is doing what or what risk factors are present.
As you can tell I am a big fan of simulation in helping to create high functioning teams! More of these videos can be accessed on my Youtube channel at
All Things Neonatal YouTube
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Lastly a big thank you to NS, RH and GS without whom none of this would have been possible!
Positive pressure ventilation puts infants at risk of developing chronic lung disease (CLD). Chronic lung disease in turn has been linked many times over, as a risk for long term impacts on development. So if one could reduce the amount of positive pressure breaths administered to a neonate over the course of their hospital stay, that should reduce the risk of CLD and by extension developmental impairment. At least that is the theory. Around the start of my career in Neonatology one publication that carried a lot of weight in academic circles was the Randomized Trial of Permissive Hypercapnia in Preterm Infants which randomized 49 surfactant treated infants to either a low (35-45) or high (45-55) PCO2 target with the thought being that allowing for a higher pCO2 should mean that lower settings can be used. Lower settings on a ventilator would lead to less lung damage and therefore less CLD and in turn better outcomes. The study in question did show that the primary outcome was indeed different with almost a 75% reduction in days of ventilation and with that the era of permissive hypercapnia was born.
The Cochrane Weigh in
In 2001 a systematic review including this and another study concluded that there was insufficient evidence to support the strategy in terms of a benefit to death or chronic lung disease. Despite this lack of evidence and a recommendation from the Cochrane group that permissive hypercapnia be used only in the context of well designed trials the practice persisted and does so to this day in many places. A little lost in this discussion is that while the end point above was not different there may still be a benefit of shorter term ventilation.
A modern cohort
It would be unwise to ignore at this point that the babies of the late 90s are different that the ones in the current era. Surfactant and antenatal steroid use are much more prevalent now. Ventilation strategies have shifted to volume as opposed to pressure modes in many centres with a shift to early use of modalities such as high frequency ventilation to spare infants the potential harm of either baro or volutrauma. Back in 2015 the results of the PHELBI trial were reported Permissive hypercapnia in extremely low birthweight infants (PHELBI): a randomised controlled multicentre trial. This large trial of 359 patients randomized to a high or low target pCO2 again failed to show any difference in outcomes in terms of the big ones “death or BPD, mortality alone, ROP, or severe IVH”. What was interesting about this study was that they did not pick one unified target for pCO2 but rather set different targets as time went on reflecting that with time HCO3 rises so what matters more is maintaining a minimum pH rather than targeting a pCO2 alone which als0 reflects at least our own centre’s practice. There is a fly in the ointment here though and that is that the control group has a fault (at least in my eyes)
|Day of life
In the original studies of permissive hypercapnia the comparison was of a persistent attempt to keep normal pCO2 vs allowing the pCO2 to drift higher. Although I may get some argument on this point, what was done in this study was to compare two permissive hypercapnia ranges to each other. If it is generally accepted that a normal pCO2 is 35-45 mmHg then none of these ranges in the low target were that at all.
How did these babies do in the long run?
The two year follow-up for this study was published in the last month; Neurodevelopmental outcomes of extremely low birthweight infants randomised to different PCO2 targets: the PHELBI follow-up study. At the risk of sounding repetitive the results of Bayley III developmental testing found no benefit to developmental outcome. So what can we say? There is no difference between two strategies of permissive hypercapnia with one using a higher and the other a lower threshold for pCO2. It doesn’t however address the issue well of whether targeting a normal pCO2 is better or worse although the authors conclude that it is the short term outcomes of shorter number of days on ventilation that may matter the most.
The Truth is Out There
I want to believe that permissive hypercapnia makes a difference. I have been using the strategy for 15 or so years already and I would like to think it wasn’t poor strategy. I continue to think it makes sense but have to admit that the impact for the average baby is likely not what it once was. Except for the smallest of infants many babies these days born at 27 or more weeks of gestation due to the benefits of antenatal steroids, surfactant and modern ventilation techniques spend few hours to days on the ventilator. Meanwhile the number of factors such chorioamniotitis, early and late onset sepsis and genetic predisposition affect the risks for CLD to a great degree in the modern era. Not that they weren’t at play before but their influence in a period of more gentle ventilation may have a greater impact now. That so many factors contribute to the development of CLD the actual effect of permissive hypercapnia may in fact not be what it once was.
What is not disputed though is that the amount of time on a ventilator when needed is less when the strategy is used. Let us not discount the impact of that benefit as ask any parent if that outcome is of importance to them and you will have your answer.
So has permissive hypercapnia failed to deliver? The answer in terms of the long term outcomes that hospitals use to benchmark against one and other may be yes. The answer from the perspective of the baby and family and at least this Neonatologist is no.
A strange title perhaps but not when you consider that both are in much need of increasing muscle mass. Muscle takes protein to build and a global market exists in the adult world to achieve this goal. For the preterm infant human milk fortifiers provide added protein and when the amounts remain suboptimal there are either powdered or liquid protein fortifiers that can be added to the strategy to achieve growth. When it comes to the preterm infant we rely on nutritional science to guide us. How much is enough? The European Society For Pediatric Gastroenterology, Hepatology and Nutrition published recommendations in 2010 based on consensus and concluded:
“We therefore recommend aiming at 4.0 to 4.5 g/kg/day protein intake for infants up to 1000 g, and 3.5 to 4.0 g/kg/day for infants from 1000 to 1800 g that will meet the needs of most preterm infants. Protein intake can be reduced towards discharge if the infant’s growth pattern allows for this. The recommended range of protein intake is therefore 3.5 to 4.5 g/kg/day.”
These recommendations are from six years ago though and are based on evidence that preceded their working group so one would hope that the evidence still supports such practice. It may not be as concrete though as one would hope.
Let’s Jump To 2012
Miller et al published an RCT on the subject entitled Effect of increasing protein content of human milk fortifier on growth in preterm infants born at <31 wk gestation: a randomized controlled trial. This trial is quite relevant in that it involved 92 infants (mean GA 27-28 weeks and about 1000g on average at the start), 43 of whom received a standard amount of protein 3.6 g/kg/day vs 4.2 g/kg/d in the high protein group. This was commenced once fortification was started and carried through till discharge with energy intakes and volume of feeds being the same in both groups. The authors used a milk analyzer to ensure consistency in the total content of nutrition given the known variability in human milk nutritional content. The results didn’t show much to write home about. There were no differences in weight gain or any measurements but the weight at discharge was a little higher in the high protein group. The length of stay trended towards a higher number of days in the high protein group so that may account for some of the difference. All in all though 3.6 or 4.2 g/kg/d of protein didn’t seem to do much to enhance growth.
Now let’s jump to 2016
This past month Maas C et al published an interesting trial on protein supplementation entitled Effect of Increased Enteral Protein Intake on Growth in Human Milk-Fed Preterm Infants: A Randomized Clinical Trial. This modern day study had an interesting question to answer. How would growth compare if infants who were fed human milk were supplemented with one of three protein contents based on current recommendations. The first group of 30 infants all < 32 weeks received standard protein intake of 3.5 g/kg/d while the second group of 30 were given an average intake of 4.1 g/kg/d. The second group of 30 were divided though into an empiric group in which the protein content of maternal or donor milk was assumed to be a standard amount while the second 15 had their protein additive customized based on an analysis of the human milk being provided. Whether the higher intake group was estimated or customized resulted in no difference in protein intake on average although variability between infants in actual intake was reduced. Importantly, energy intake was no different between the high and low groups so if any difference in growth was found it would presumably be related to the added protein.
Does it make a difference?
The results of this study failed to show any benefit to head circumference, length or weight between the two groups. The authors in their discussion postulate that there is a ceiling effect when it comes to protein and I would tend to agree. There is no question that if one removes protein from the diet an infant cannot grow as they would begin to break down muscle to survive. At some point the minimum threshold is met and as one increases protein and energy intake desired growth rates ensue. What this study suggests though is that there comes a point where more protein does not equal more growth. It is possible to increase energy intakes further as well but then we run the risk of increasing adiposity in these patients.
I suppose it would be a good time to express what I am not saying! Protein is needed for the growing preterm infant so I am not jumping on the bandwagon of suggesting that we should question the use of protein fortification. I believe though that the “ceiling” for protein use lies somewhere between 3.5 – 4 g/kg/d of protein intake. We don’t really know if it is at 3.5, 3.7, 3.8 or 3.9 but it likely is sitting somewhere in those numbers. It seems reasonable to me to aim for this range but follow urea (something outside of renal failure I have personally not paid much attention to). If the urea begins rising at a higher protein intake approaching 4 g/kg/d perhaps that is the bodies way of saying enough!
Lastly this study also raises a question in my mind about the utility of milk analyzers. At least for protein content knowing precisely how much is in breastmilk may not be that important in the end. Then again that raises the whole question of the accuracy of such devices but I imagine that could be the source of a post for another day.