More about Prebiotics

I don’t know if there is an “official” definition of prebiotics, but I think of them as molecules present in the diet that promote the growth of probiotic organisms. I believe that originally the term was applied only to molecules that are not digested by humans (or I guess another animal being studied) and are only digested by commensal organisms, including those that have a positive health benefit. I have seen the term used more widely however to include such molecules as lactoferrin which is partially degraded by humans to produce lactoferricin, and which can be absorbed and have direct impacts on health. It also is not, I believe digested by any probiotic organisms.

Although lactoferrin is a very interesting molecule, it probably shouldn’t be considered a prebiotic, the most interesting prebiotic molecules are in fact carbohydrates, including a number of oligosaccharides.

Even though the Human Milk Oligosaccharides (HMOs) are not digested and have no direct nutritional benefit for human babies, they together form the 3rd most abundant component of breast milk, after lactose and lipids. There are very many of them which appear to have importance for the growth of probiotic bacteria.

To get much further into biochemistry than I am really qualified for, the HMOs are a group of compounds which consist of various combinations of glucose, galactose, fucose, N-acetylglucosamine and N-acetyl neuraminic acid. The last mouthful in that sentence is one of a group of molecules, sugars with 9 carbon atoms, which are collectively known as sialic acid; N-acetyl neuraminic acid is also sometimes itself referred to as sialic acid, just to make it a bit more confusing.

This is a wordy preamble to introduce the fact that there is one of the HMOs which looks like it might be extremely important in the pathophysiology of NEC, or rather in the prevention of NEC and that is a molecule known as…. take a deep breath…. Disialyllacto-N-tetraose

Here is schematic of what it looks like

The purple diamonds are the N-acetyl neuraminic acid residues, the blue circle is glucose, the yellow circles are galactose, and the blue square is N-acetylglucosamine. A few years ago now the idea that this particular HMO might be very important arose from a number of studies including an animal model of NEC. (Autran CA, et al. Sialylated galacto-oligosaccharides and 2′-fucosyllactose reduce necrotising enterocolitis in neonatal rats. Br J Nutr. 2016;116(2):294-9), which was followed by a multicentre cohort study (Autran CA, et al. Human milk oligosaccharide composition predicts risk of necrotising enterocolitis in preterm infants. Gut. 2018;67(6):1064-70) showing that among mothers who were provding breast milk to their babies, the infants who nevertheless developed NEC had much lower concentrations of that particular HMO in the breast milk they were receiving.

The figure on the left shows cases with Bell stage 3 NEC in red squares, Bell stage 2 as yellow circles and the other grey dots are the matched controls.

This has just been confirmed in an independent cohort, (Masi AC, et al. Human milk oligosaccharide DSLNT and gut microbiome in preterm infants predicts necrotising enterocolitis. Gut. 2020) which again showed much lower DSLNT concentrations in the breast milk of babies who went on to develop NEC. In this study they also analyzed the intestinal microbiome and showed that babies who developed NEC had lower Bifidobacterium longum concentrations.

This work has a number of implications, for one, I wonder whether screening donor mother’s milk for the concentration of DSLNT would be feasible, and whether selecting milk with higher concentrations might enhance the protection that donor milk provides to babies whose mothers cannot produce all the milk they need.

Of course, the question of whether supplementation of the infants’ diet with DSLNT might prevent NEC is going to be the next issue. It appears that it can be synthesised, but I have no idea about the potential cost of synthetic DSLNT or whether it could be extracted from human breast milk.

Prebiotics have actually been tested in clinical trials for NEC prevention, but here you have to be very careful, and realize that not everything that has been tested are actually prebiotics according to the definitions above, and none of the studies have tested any of the most likely effective HMOs, such as DSLNT.

A new network meta-analysis, for example, (Chi C, et al. Effects of Probiotics in Preterm Infants: A Network Meta-analysis. Pediatrics. 2021;147(1)) includes 5 articles that they state studied a prebiotic. One of the studies did not actually include a prebiotic, one of the studies included a group receiving lactoferrin, and the 2 others that are easily available studied inulin. The 5th studied a “fructo-oligosaccharide” which I think is also inulin. None of these molecules are the prebiotics that we need to be studying. This network meta-analysis did, however, report, based on 45 publications including over 12,000 participants, findings that confirm those of other reviews that NEC is reduced by probiotic supplementation and that combination preparations appear to be more effective.

I think the next stage ought to be a trial of babies receiving breast milk (either maternal or donor) and a multi-strain probiotic mixture including B. longum subsp infantis which randomizes the infants to prebiotic or placebo. The prebiotic could either be a mixture of HMOs, or DSLNT, how we can obtain these I am quite unsure.

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When should we transfuse preterm babies, and why? Redux.

The TOP trial has just been published in the FPNEJM (Kirpalani H, et al. Higher or Lower Hemoglobin Transfusion Thresholds for Preterm Infants. N Engl J Med. 2020;383(27):2639-51). It was a multicenter, non-masked RCT among 1800 babies of less than 1 kg birthweight, between 22 weeks and <29 weeks and <48 hours of age. They had not had a previous red cell transfusion unless they had needed an emergency transfusion before 6 hours of age (which happened in about 5%). The infants were randomized to a higher or lower transfusion threshold, and the primary outcome was survival without Neurological impairment or developmental delay at about 2 years corrected age.

The study was therefore almost twice as large as the ETTNO trial that I posted about earlier this year, with similar entry criteria, except that in ETTNO babies could be enrolled up to 72 hours of age, and 25% of them had already had at least one transfusion. The average difference in haematocrit between the 2 groups in ETTNO was about 3% from week 3 to week 10, equivalent to about a haemoglobin difference of 1.1 g/100mL. This was a smaller haemoglobin separation between groups than TOP (average 1.9 g/100mL)

The primary outcome of TOP was not different between higher and lower transfusion threshold groups, and no part of the primary was different. Important, pre-specified secondary outcomes were also all just about identical between the 2 groups. This included brain injury as diagnosed on ultrasound, bronchopulmonary dysplasia (very slightly more frequent in the group transfused at a higher threshold, 59% vs 56%) and necrotising enterocolitis, 10% in each group.

The other trials with similar treatment comparisons are the aforementioned ETTNO, and PINT, as well as the Iowa transfusion trial. The Iowa trial was a little different in that it included babies up to 1300 gr (just up to 1 kg in the other trials) and had the same transfusion thresholds throughout the study, depending only on respiratory status and not changing with postnatal age. Here are the thresholds for the 4 trials, converted where necessary into Haemoglobins (g/100mL) and rounded to the nearest 0.5:

Or presented as Haematocrit, rounded to the nearest 1%.

The definition of “Sick” and “Not Sick” are somewhat different between the studies. For TOP it was entirely respiratory they used “a higher threshold when respiratory support was warranted. Respiratory support was defined as mechanical ventilation, continuous positive airway pressure, a fraction of inspired oxygen (Fio2) greater than 0.35, or delivery of oxygen or room air by nasal cannula at a flow of 1 liter per minute or more).”

In EttNO being sick meant “having at least 1 of the following criteria: invasive mechanical ventilation, continuous positive airway pressure with fraction of inspired oxygen >0.25 for >12 hours per 24 hours, treatment for patent ductus arteriosus, acute sepsis or necrotizing enterocolitis with circulatory failure requiring inotropic/vasopressor support, >6 nurse-documented apneas requiring intervention per 24 hours, or >4 intermittent hypoxemic episodes with pulse oximetry oxygen saturation <60%”

In PINT it was just respiratory support “assisted ventilation, continuous positive airway pressure, or supplemental oxygen” without further specification.

As I have ranted on about before, this makes no sense. Why do we think that a preterm infant with a saturation of 92% in 30% oxygen needs to have a higher haemoglobin than a baby with this saturation in 21% oxygen? Or if they are intubated? Maybe if they are intubated on high-frequency ventilation with a very high mean airway pressure there might be enough impact on their cardiac function to limit tissue oxygen delivery, but in the majority of patients, moderate respiratory disease or respiratory support should have no impact on tissue oxygenation or transfusion needs.

Infants with a limited cardiac output might need to have a higher haemoglobin to maintain oxygen delivery to the tissues, but I actually think that is unlikely to be a common problem; perhaps in septic shock, or with a cardiomyopathy, but most babies can probably increase their cardiac output to respond down to quite low haemoglobin concentrations. The ETTNO trial inclusion of needing cardiovascular support makes much more sense than the other criteria for demanding a higher threshold.

As you may know, the PINT outcome study showed no major difference in long term development between the high and low threshold groups, but, there were some minor differences in Bayley Scores, which appeared to favour the high threshold group, the proportion of survivors with a Bayley II MDI less than 70 was 18% in the high group vs 24% in the low group, so being extra careful they also analysed the proportion of survivors who had an MDI <85, which looked different between groups, 34% high threshold vs 45% low threshold. As a result, there remained a concern that perhaps a higher threshold would be preferable, these 2 new studies demonstrate that is not the case. Transfusion thresholds in the low columns above are consistent with good practice, and will lead to fewer babies being transfused without measurable adverse effects.

One other thing that I noticed is that the Iowa trial showed some differences in apneas between the groups, with the babies who received fewer transfusions having more apneas, and more severe apneas.

In both TOP and ETTNO, with the difficulty in clinical research of accurately quantifying apnea, the only data point they give that is relevant is when the caffeine was finally stopped (with nearly 100% of these babies having received caffeine) in the 2 trials caffeine was stopped at about the same time in the groups, suggesting that persistent apnea is not more common if you let the haemoglobin fall to these levels.

In these 2 linked blog posts I have tried to answer the question of when to transfuse, and have avoided the question of “why?”

The “why” should surely be to prevent complications or improve outcomes. The “why” on a physiologic basis is to improve oxygen-carrying capacity, when that oxygen-carrying capacity is too low to allow adequate oxygen delivery and when this leads to tissue hypoxia. There is no sign from these new data, when analyzed together with the older information, that transfusing above the Low Transfusion Thresholds is of any benefit, and I think we are way above the threshold where tissue hypoxia becomes an issue, further data of clinical situations where a transfusion is necessary would be really helpful (Do babies in shock benefit from a transfusion?). There is also, of course, no clear evidence of any harm from an approach to transfusion which follows either the high or low thresholds, or something in between!

With delayed cord clamping, initial blood work done on whatever blood is left in the placenta when possible, and restricted blood sampling throughout hospitalisation, we should be able to dramatically reduce transfusion requirements. Then we should ask the parents of infants at-risk of needing a transfusion whether they would prefer that their infant receives erythropoietin (or darbepoetin) in order to reduce the probability even further. We can ask them that while still reassuring them that blood transfusion is extremely safe.

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Should all asphyxiated babies have MR spectroscopy?

MRI post-asphyxia, and post-rewarming, seems to be more predictive of long term outcomes than MRI at term for preterm infants. Imaging and analysis of the Apparent Diffusion Coefficient in the PLIC (posterior Limb of the Internal Capsule), for example, has reasonably good predictive value, and I like the fact that it is relatively objective, I can look at an MRI on a hospital computer, put my cursor on the PLIC and the software gives me a number; the lower the number the worse the outcome, in simple terms. I am not any good at interpreting MRIs by looking at the images, so getting a nice clear number appeals to me (and usually confirms what I think clinically). I can’t say it has ever really helped me in the clinical care of a baby.

We haven’t always been getting spectroscopy with our MRIs, but the new framework for practice from the British Association of Perinatal Medicine recommends the following

Where possible, Proton (1H) MRS Lactate/N acetyl aspartate (Lac/NAA) of the basal ganglia and thalamus should be performed with the MRI at 5-15 days after birth. This is the most accurate predictor of outcome in babies who have undergone TH therapeutic hypothermia.

The two references they give for that statement are 2 of the only three studies I am currently aware of. Mitra S, et al. Proton magnetic resonance spectroscopy lactate/N-acetylaspartate within 2 weeks of birth accurately predicts 2-year motor, cognitive and language outcomes in neonatal encephalopathy after therapeutic hypothermia. Arch Dis Child Fetal Neonatal Ed. 2019;104(4):F424-F32 and Lally PJ, et al. Magnetic resonance spectroscopy assessment of brain injury after moderate hypothermia in neonatal encephalopathy: a prospective multicentre cohort study. Lancet Neurol. 2019;18(1):35-45. The third one being Barta H, et al. Prognostic value of early, conventional proton magnetic resonance spectroscopy in cooled asphyxiated infants. BMC Pediatr. 2018;18(1):302.

This figure shows basically what we are discussing, placing the voxel of interest in the thalamus, and then looking at the proton spectrum.

According to the framework for practice, the lactate to NAA ratio is highly predictive of adverse outcomes. Mitra et al (from where I took that image) refers to the Lac+Thr/tNAA (total NAA) which I think is the same thing as what Lally et al call the Lactate-NAA ratio. Barta et al also report that they calculated the Lac/NAA ratio, but that it was not one of the 3 ratios that adequately discriminated between the “good and poor outcome groups”.

The study by Lally defined an adverse outcome as death (I think there was only 1 death in this cohort) or a score on the Bayley 3 language or composite of <85 or cerebral palsy (GMFCS 2 or worse), seizure disorder or deafness, and has this figure :

Which shows a number of interesting things: firstly there are only 12 babies with an “adverse” outcome for the NAA concentration data (probably because it takes substantially longer to get this result, and perhaps because it is not available everywhere), there are about 26 adverse outcomes for the metabolite ratios; secondly, all of the measurements and calculated ratios show an overlap between the “normal” and “adverse” outcome babies. According to this study, the sensitivity of a Lactate-NAA ratio >0.22 is 88% and the specificity is 90% with the area under the ROC curve being 0.94. According to the same trial, an absolute NAA concentration <5.6 mmol/kg brain wet weight has a sensitivity of 100% and a specificity of 97% with an ROC curve area of 0.99.

If we look in detail at the results of Mitra et al, they included 55 infants with 16 deaths and 20 with an abnormal motor outcome, 19 with an abnormal cognitive outcome and 21 with abnormal language outcome by 2 years of age. By abnormal outcome they mean either death or a score on the Bayley3 composite of <85. They show this figure which I just can’t understand; if death or a low Bayley score on the cognitive composite was abnormal, then there should be 35 red dots, and 20 green dots, but there aren’t. There are actually more green dots than red, and even though it is difficult to count them there are more than 20 green dots.

In addition, the dot colours are the wrong way round for the language outcome. More importantly, the cut off they use for determining what is abnormal is different to the threshold used by Lally et al, a Log10 of -0.4 is a Lac+Thr/tNAA ratio of about 0.4. The ratio used as the threshold value by Lally et all (0.22) gives a Log10 value of -0.65, which, looking at these figures, if you used the threshold that Lally et al used for these babies in the Mitra study, it would classify many of their normal babies in the abnormal group.

Looking at these data I really do not see that there is enough data to support performing MR spectroscopy on all babies with HIE.

  1. We can with some degree of confidence, based on about 45 babies, state that if the Lac/NAA ratio is low, then outcomes are probably going to be worse than if they are higher. But what threshold ratio we should use to make this determination is not clear, and it doesn’t seem to work in Hungary.
  2. Does it really matter if a Bayley 3 score is <85? I think that dividing babies up into the “normal” and “abnormal” is unhelpful, and creating a category that includes 16% of the non-asphyxiated population and calling them “abnormal” is questionable. Dichotomizing the richness of human development should be avoided.
  3. What is the clinical value to an individual or their family that is added by performing MR spectroscopy? Does knowing the Lac/NAA ratio help the family in some way? Does it help them to access services, or prepare for the future, or is there some other benefit?
  4. Does MR spectroscopy adequately differentiate between the babies with very severely abnormal outcomes (such as an inability, or very restricted ability, to communicate) and babies who have no, minor, or moderate disability?

As far as I can see currently, perhaps spectroscopy can help us to perform asphyxia intervention studies with shorter follow up. If we can confirm that interventions that have no impact on spectroscopy have little or no clinical benefit, then MR spectroscopy as a biomarker for research might be very valuable to screen out things that are unlikely to improve outcomes.

The absolute NAA concentration, based on a very small sample, might be a better biomarker, but it currently takes an extra 25 minutes in the magnet, if you have the right 3T magnet and the software.

As for clinical use as a routine after HIE, the data regarding NAA concentration or the metabolite ratios are based on very small numbers of babies, with outcomes that are not very important.

If future studies can focus on extremely adversely affected babies, and if they use the same thresholds to classify studies as abnormal or not, then we might in the future have enough data to support using routine spectroscopy as a clinical tool.

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Diuretics as Anticonvulsants?

In recent years there has been a lot of interest in neonatal seizures and how to treat them. Older studies confirmed that phenobarbitone (or phenobarbital, I never know these days) appears effective, but with limits; many babies have a partial response, and many more continue to have electrical seizures even after they stop clinical convulsions. Other agents have limited efficacy, phenytoin is not as effective as a second line agent compared to giving more phenobarb and levetiracetam appears not to be living up to the initial hope that it would be a valuable neonatal agent.

Neonatal neurones are different.

In contrast with the adult brain, immature neurons actively accumulate chloride via the electroneutral NaK2Cl transporter known as NKCC1. Under these conditions, GABAA receptor activation results in a net efflux of negatively charged chloride ions, which depolarizes the membrane. The size of the chloride flux is important, and smaller anion effluxes may not trigger action potentials. However, if the membrane is depolarized sufficiently to trigger action potentials and open voltage-gated calcium channels, GABA action is clearly excitatory. Under both conditions, GABAA receptor activation may still be inhibitory by virtue of strongly depolarizing glutamate-mediated activity. The importance of the shunting effect of GABA is well established by the finding that when all GABAA receptors are blocked, the net effect is proconvulsant in the neonatal brain. Thus, synaptically released GABA has a dual action, both excitatory and inhibitory, in the immature nervous system.

That paragraph is (slightly) adapted from Dzhala VI, et al. Bumetanide enhances phenobarbital efficacy in a neonatal seizure model. Ann Neurol. 2008;63(2):222-35. The title of which reveals what this post is all about. Loop diuretics work by inhibition of the NK2Cl cotransporters in the thick ascending limb of the loop of Henle. All of them work on this ion pump but with differing affinity. Bumetanide has the highest affinity and thus requires the lowest dosage; in terms of clinical efficacy there is not much to choose between the agents, toxicities may differ depending on other possible effects, ethacrynic acid, for example, is hepatotoxic and may well cause more deafness. I always wondered, in oliguric babies, whether the fact that you need to excrete fewer millimoles of bumetanide than of furosemide might make it more effective, as the ion pump is only on the luminal side so you have to excrete the molecule before it can work (Oliveros MMD, et al. The use of bumetanide for oliguric acute renal failure in preterm infants. Pediatr Crit Care Med. 2011;12(2):210-40). In any case, it was previously thought that bumetanide might be more selective for the NKCC2, but that is probably not the case. The choice of bumetanide rather than furosemide for anticonvulsant effects might just have been an arbitrary choice at first, but most of the animal studies have been with this molecule.

Including the study by Dzhala et al; in that study, isolated slices of neonatal rat hippocampus and intact neonatal rat hippocampal preparations were induced to have convulsions by perfusing them with very low magnesium. That preparation leads to electrical phenomena which are identical to seizures. They then “treated” their preparations with drug combinations.

Phenobarbital failed to abolish or depress recurrent seizures in 70% of hippocampi. In contrast, phenobarbital in combination with bumetanide abolished seizures in 70% of hippocampi and significantly reduced the frequency, duration, and power of seizures in the remaining 30%

I am aware of 2 studies examining the effect of bumetanide on human neonatal seizures. The new one is the stimulus for this blog post (Soul JS, et al. A Pilot Randomized, Controlled, Double-Blind Trial of Bumetanide to Treat Neonatal Seizures. Ann Neurol. 2020). In this study, a diverse group of 43 term and late preterm newborns with seizures, (about half HIE, the remainder with strokes, intracranial haemorrhage or “other”) who had already received at least 20 and less than 40 mg/kg of phenobarb and were being continuously monitored with video-EEG were randomized to receive either a further 5-10 mg/kg of phenobarb and a placebo or the phenobarb plus a dose of bumetanide (increasing doses 0.1, 0.2 or 0.3 mg/kg). This was considered to be a pilot trial, and therefore the outcomes of interest are to do with the feasibility of a full trial, in this instance the safety and kinetics of bumetanide, with an exploratory outcome of the effects of bumetanide at the 3 doses on seizure burden.

There were 27 babies who received bumetanide and 16 controls, there was some baseline imbalance with all the stroke babies being in the bumetanide group. Also by chance, there was a higher seizure burden among the bumetanide babies than the controls, mean of 2.5 minutes of seizures per hour compared to 1.1 at baseline; 3.3 compared to 1.6 during the last 2 hours prior to drug administration.

That baseline imbalance means that we should be careful analyzing the data. The phenomenon of regression to the mean implies that we should expect a larger reduction in seizure burden among the bumetanide babies than the controls, just because they started with a higher burden. At first glance, that seems to be what they showed, seizure burden decreased by 1.2 with bumetanide and by 0.1 in controls during the first 4 hours after the study drug. When they looked at the second half of that 4 hour period, the controls had no improvement in seizure burden compared to pre-treatment, whereas the bumetanide babies had a decrease. When analyzed by dose, the higher dose of bumetanide looks more effective.


With the proviso of small numbers, in a situation where the natural history is very variable, and the baseline imbalance, this pilot suggests a potential role for bumetanide in neonatal seizures. The animal model I referred to above is of questionable relevance, I just did a quick search for other models which are potentially more relevant to the babies we see, by which I mean an intact neonatal mammal with an asphyxial injury. The two articles I found have differing results; Cleary RT, et al. Bumetanide enhances phenobarbital efficacy in a rat model of hypoxic neonatal seizures. PLoS One. 2013;8(3):e57148. this study gave phenobarb and then bumetanide to neonatal rats before a hypoxic insult that normally causes seizures (95% of the rats had at least 5 seizures). Bumetanide alone had an impact on seizure numbers but only at 0.3 mg/kg, phenobarb alone had an impact, phenobarb plus either dose of bumetanide had an additive impact in reducing seizures.

In the other study (Johne M, et al. Phenobarbital and midazolam suppress neonatal seizures in a noninvasive rat model of birth asphyxia, whereas bumetanide is ineffective. Epilepsia. 2020) phenobarb worked when given before the asphyxia, but not afterwards, and bumetanide did not improve the efficacy of phenobarb when given either before or after the asphyxia. However, that study outcome was the proportion of animals with seizures, which was about 100% with phenobarb or phenobarb+bumetanide. Midazolam, given after asphyxia, did decrease the proportion of rats with seizures.

In fact, these two studies aren’t necessarily in conflict, both showed that close to 100% of rats have seizures after asphyxia which doesn’t change when pretreated with either phenobarb or phenobarb+bumetanide. The Johne study doesn’t report the numbers of seizures.

To return to human beings, the other trial of bumetanide was terminated very early, it was a dose-finding trial which only included babies with asphyxia and seizures who had received 20 mg/kg of phenobarb, (Pressler RM, et al. Bumetanide for the treatment of seizures in newborn babies with hypoxic ischaemic encephalopathy (NEMO): an open-label, dose finding, and feasibility phase 1/2 trial. Lancet Neurol. 2015;14(5):469-77). The trial was stopped after 14 babies were enrolled, because they did not reach efficacy and because of some hearing loss. Of note, all the babies except one also had an aminoglycoside and several did not have seizures during the 2 hours baseline recording prior to receiving the bumetanide with an extra 10 mg/kg of phenobarb.

If you actually look at the results in detail, all of the babies who had the higher doses of bumetanide of 0.2 (n=6) or 0.3 (n=1) mg/kg of bumetanide, and who had seizures during the baseline period, had a major reduction (>50%) in seizure burden during the subsequent 4 hours, only 1 of them (who was having 16 minutes of seizures per hour) had another drug (midazolam) during that period. As has been pointed out by Marianne Thoresen (Thoresen M, Sabir H. Epilepsy: Neonatal seizures still lack safe and effective treatment. Nat Rev Neurol. 2015;11(6):311-2), that looks to me like a signal for efficacy. In the NEMO trial, 3 babies of the 11 survivors had hearing loss. In the new trial, there were 2 of 26. In many studies, around 10% of babies who survive therapeutic hypothermia for HIE have hearing loss. The frequency of hearing loss in NEMO is not enormously different.

Putting all this together, I think there remains a major possibility that bumetanide (or potentially other loop diuretics if they penetrate the brain) is a useful additive to therapeutic phenobar levels in the neonate. Particularly in HIE and perhaps in srtoke patients.

Adverse effects of diuretics are few and relatively easy to treat, in infants with asphyxial oliguria in my experience (I don’t like to say “in my experience”, but there seems to be very little data) they don’t seem to cause significant diuresis and I don’t use them for that indication. If we can avoid treating asphyxia with antibiotics, and particularly aminoglycosides, then we can probably significantly reduce the chance of hearing loss with loop diuretics.

More trials please.

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Do Sub-Ependymal Haemorrhages cause cerebral palsy?

The germinal matrix is a region in the immature brain where a large proportion of cortical neurones are formed before they migrate out to form the neo-cortex. It is intensely metabolically active as it is producing hundreds of thousands of neurones per minute. It has a very high blood flow as a result and large fragile vessels that bleed easily. Such germinal matrix/sub-ependymal haemorrhages are associated in most studies with no discernable effects on long term neurological, developmental or functional problems. This has always fascinated me, how can such a critical region of the developing brain be severely damaged in a way which is clearly visible on head ultrasound, without much effect on brain development? The plasticity of the newborn and especially the preterm brain is remarkable.

A new publication from the amazing group in Melbourne (Hollebrandse NL, et al. School-age outcomes following intraventricular haemorrhage in infants born extremely preterm. Arch Dis Child Fetal Neonatal Ed. 2020) suggests that such bleeds might indeed have impacts. Using data accumulated over many years they present the outcomes at years of age of 499 babies born at <28 weeks. The results are drawn from 3 cohorts that the group of studied from Victoria state in Australia, from 1991, 1997 and 2005.

The high-quality follow-up has been maintained over those time periods and includes IQ testing, academic achievement and executive function evaluation, motor function tests, and examination for cerebral palsy. The authors note that there was no appreciable difference in the results between the 3 time periods.

There were decreasing trends with worsening grade of IVH for multiple birth and antenatal corticosteroid treatment, and increasing trends for male sex, receiving surgery, postnatal corticosteroids, bronchopulmonary dysplasia and cystic PVL

In terms of IQ, academic achievement and executive function there was no apparent difference between babies with grade 1 or 2 IVH and control babies without IVH.

Babies with grade 3 or 4 IVH had a higher proportion of babies with IQ scores <-2SD, 22% and 42% respectively compared to 12% without IVH, and many more with at least one academic skill below the term norms. (There are only 23 babies with grade 3 and 12 with grade 4 IVH in these cohorts).

Executive function did not change with grade of IVH.

Although the methods mention the term-born controls on 2 or 3 occasions, they don’t present any comparisons between the term controls and the preterm babies. I think they mention the term controls (always one of the strengths of the publications from this programme) mostly as they are the source of the standardized scores for IQ and academic achievement.

The main finding of the study, to my mind, is the association between low grades of IVH and motor abnormalities, that is: any motor dysfunction, cerebral palsy, or a low MABC score. All are more frequent with grade 1 and in particular grade 2 IVH than among babies without a haemorrhage.

This is consistent with some other studies, but not all. As in all observational studies, we cannot be sure that this association is causative. The analysis was not adjusted for many complications of neonatal care that are known to be associated with poorer outcomes, such as postnatal steroids, BPD, late-onset sepsis, NEC, sex, or surgery. There was however a similar proportion of boys in the no IVH, grade 1 and grade 2 groups, so it would probably make no difference to adjust for sex. There was more BPD (44% controls, 56% grade 1 and 2 combined) and postnatal steroids (32% vs 46%), however, in those 2 groups, both of which are themselves associated with CP and could possibly account for these findings. One of the other studies that examined this issue (Payne AH, et al. Neurodevelopmental outcomes of extremely low-gestational-age neonates with low-grade periventricular-intraventricular hemorrhage. JAMA Pediatr. 2013;167(5):451-9) examined 1472 infants <27 weeks in the NICHD network. They did not show an impact of low-grade IVH on motor outcomes and had a much smaller difference in BPD between the grade 1 and 2 babies (53% with BPD) and the controls without IVH (47%), and no difference in postnatal steroid use (14% in each group). In other studies (EPIPAGE for example) grade 2 but not grade 1 haemorrhages were associated with CP in adjusted analyses.

My evaluation of all this is that it appears that low grade IVH may have an association with motor dysfunction in some cohorts, but it is not clear at all to me that it is causative. It could well be that babies who are somewhat more unstable in the first 3 days are more likely to have low-grade haemorrhage and more likely to develop BPD, more likely to have received postnatal steroids, and probably at somewhat greater risk of white matter injury. All of which may predispose them to develop motor problems. Low-grade IVH could be considered a potential marker for infants that require extra effort to ensure they get followed up and are evaluated repeatedly to see if they need intervention.

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Does intravitreal bevacizumab adversely affect long term development? Two simultaneous systematic reviews say yes, or no.

A reliable answer to the above question would require a large multicentre RCT comparing intravitreal bevacizumab (IVB) to laser, powered for long term outcomes. Such a trial does not currently exist.

As a result, 2 groups have just published systematic reviews of the observational studies that have compared outcomes of non-randomized cohorts with bevacizumab compared to either no treatment or to laser therapy.

The 2 reviews come to opposite conclusions!

Kaushal M, et al. Neurodevelopmental outcomes following bevacizumab treatment for retinopathy of prematurity: a systematic review and meta-analysis. J Perinatol. 2020, state “Bevacizumab treatment for severe ROP is associated with increased risk of cognitive impairment and lower cognitive and language scores in preterm infants”.

Tsai CY, et al. Neurodevelopmental Outcomes After Bevacizumab Treatment for Retinopathy of Prematurity-A Meta-Analysis. Ophthalmology. 2020. on the other hand state “severe NeuroDevelopmental Impairment risk was not increased in ROP patients after IVB treatment. Bayley-III scores were similar in the IVB and control groups, except for a minor difference in motor performance”.

In addition to cohort comparisons there is a small amount of data (n=16) from one of the centres involved in the BEAT-RoP RCT. All of the other studies reviewed were comparisons of non-randomized cohorts.

Such studies are fraught with potential bias. In our centre, for example, we were at first only using IVB for babies with BPD who were extubated and fragile and who we really didn’t want to re-intubate for laser surgery. They were therefore higher risk than laser treated babies. We also were using IVB mostly for babies with posterior disease who are not necessarily comparable to babies with zone 2 retinopathy.

Why would 2 almost simultaneous systematic reviews produce diametrically opposite results?

The first thing I did was to look at the tables with the included studies. Kaushal et al includes 13 studies, whereas Tsai has 8, three of which are not in Kaushal.

The discrepancies seem to be because Tsai included 2 studies that compared outcomes of babies who received IVB to babies with no treatment, and in one of those cases to a second control group of babies without retinopathy. You would think that such studies would show a difference in outcomes between IVB and control but in fact they showed very little. Those studies were not eligible for the review of Kaushal et al.

Kaushal includes 2 studies only reported as abstracts, which were not in Tsai’s publication list, and included 2 studies published in 2020 which may have appeared after Tsai finished their literature review. In addition 2 of the studies in Kaushal’s review only supplied mortality data, and one other does not appear to have supplied any data used in their analyses. The main difference in data sources, therefore, seems to be that Kaushal included Zayek et al and Arima et al from 2020, whereas Tsai included the above-mentioned studies with untreated controls.

As for the results, the definitions of “Severe Neurodevelopmental Impairment” are similar in the 2 reviews, and both reviews conclude that the 95% CI include an RR of 1.0, but Tsai’s analysis includes 5 studies and an RR of 1.52 (95% CI 0.91, 2.54) whereas Kaushal includes 3 studies (only 2 of which are in the Tsai analysis) and an RR of 1.33 (95% CI 0.74, 2.39).

As for the scores on the cognitive composite of the Bayley 3 evaluation, the Kaushal review, based on 6 studies, shows that cognitive scores are 1.8 points less with IVB than laser (the figure axis title wrongly states that this result “favours IVB”) 95% CI -3.5, -0.1; whereas Tsai et al also have 6 studies of IVB vs laser (only 3 of the studies are in both reviews) and a difference in cognitive scores of 1.69, 95% CI -4.9, +1.6. The 2 studies in Tsai’s review that compared laser to no treatment are calculated separately as showing little difference with wide confidence intervals (-2.6, 95% CI -8.2, +3).

In a similar way, but with a more marked difference, the scores on the Bayley 3 language composite are lower in the Kaushal review, 5.4 points less with IVB than laser (95% CI -9.2, -1.6), but in the Tsai review the difference in scores is only 1.36, (95% CI -5.5, +2.8).

What does this all mean? Basically, I don’t think you can rely on the results of these SRs to give an answer to the question. Systematic reviews of observational studies suffer from the same problems as the observational studies they are based on. Differences in characteristics of the babies treated with either therapy are likely, and, no matter how the data are adjusted, such biases remain.

Long-term visual outcomes are clearly better with IVB, with much lower rates of severe myopia. I think all that you can say about long term developmental and neurological outcomes is that there remains a concern that there could be adverse impacts of IVB, but the data collected so far are conflicting. I think we should give parents a choice when retinopathy treatment is required, informing them that for aggressive or posterior disease there are advantages of IVB, and also major unknowns for the long term. Of course the ophthalmologists treating the babies have to agree to that also!

Clearly, the large multicentre RCT, powered for long term outcomes, that I mentioned at the beginning of this post, is needed. These systematic reviews suggest that such a trial should be powered to find a 5 point difference in cognitive scores on the Bayley version 3, which would need close to 150 patients per group, or alternatively a 10% difference in the proportion of children with neurological impairment or developmental delay, in this high-risk group that would need somewhere in the region of 200 babies per group, depending on what the hypothesized baseline rate is. Those sample sizes seem achievable to me without too much difficulty, and I think this should be considered a priority for our community.

Type 1 RoP with plus disease (A) and after laser surgery (B). Hwang CK, et al. Outcomes after Intravitreal Bevacizumab versus Laser Photocoagulation for Retinopathy of Prematurity: A 5-Year Retrospective Analysis. Ophthalmology. 2015;122(5):1008-15.

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Three trials with null results, how should we respond?

These 3 articles have just been published, all show no difference in long term outcomes between the randomized groups. What does that mean for the impact on therapeutic decision-making?

Natalucci G, et al. Neurodevelopmental Outcomes at Age 5 Years After Prophylactic Early High-Dose Recombinant Human Erythropoietin for Neuroprotection in Very Preterm Infants. JAMA. 2020;324(22):2324-7.

Rozé J-C, et al. Effect of Early Targeted Treatment of Ductus Arteriosus with Ibuprofen on Survival Without Cerebral Palsy at 2 years in Infants with Extreme Prematurity: A Randomized Clinical Trial. The Journal of Pediatrics. 2020.

Tauzin M, et al. Neurodevelopmental Outcomes after Premedication with Atropine/Propofol versus Atropine/Atracurium/Sufentanil for Neonatal Intubation: 2 Year Follow Up of a Randomized Clinical Trial. The Journal of Pediatrics. 2020.

The first of them, Natalucci et al is a longer-term follow up of a trial that already reported their 2-year primary outcomes. It was an RCT of infants of 26 weeks gestation or more and less than 32 weeks, who received either 3000 iu of erythropoietin at < 3 hours of age and then 2 other doses at 12 to 18 hours and 36 to 42 hours. There was no impact on the Bayley MDI at 2 years, and now they have shown in the 77% of children left in the trial (total n= 345) that there was no difference between groups on a test of cognition, or in cerebral palsy, disabling CP, or hearing or visual problems. This study complements the PENUT trial which included babies down to 24 weeks gestation (up to < 28 weeks) and gave a dose of 1000 iu/kg every 48 hours for 6 doses and then 400 iu/kg 3 times a week until 33 weeks. That study also showed no benefit on long term outcomes.

The next study, Roze et al TRIOCAPI , randomized babies born between 24 and <28 weeks who did not have an IVH on initial head ultrasound. They had a screening cardiac ultrasound at 12 to 24 hours of age and, if the ductus was “large” (calculated as > 2.26 – (0.078 x postnatal age in hours) mm), they received either ibuprofen or placebo. The primary outcome was survival without cerebral palsy at 2 years of age; among the 228 babies randomized in the 2 groups, this outcome was not different by treatment group, at just over 71%. This was double what they were expecting in the control group, as outcomes have improved dramatically in France for these very immature babies, so they were somewhat underpowered. They did show a decrease in pulmonary haemorrhages in the first 3 days (those requiring an increase in FiO2 > 20% or an increase in mean airway pressure > 2cmH2O) from 8% to just under 2% with ibuprofen; at 3 days of age, they were much more likely to have closed the PDA (66% vs 17%). There were a large proportion of the babies, 62% of controls and 17% of the ibuprofen group, who received open-label ibuprofen after the first 3 days.

The third of these studies Tauzin et al, PRETTINEO is the first, I think, controlled trial of premedication for neonatal intubation that has published long term follow up and has a sample size large enough to have reasonable power. The drug regimes compared for non-emergency intubations in the NICU are mentioned in the title. Atropine at 15 microg1kg was given to everyone, followed by either propofol (2.5 mg/kg for babies >1kg, and 1 mg/kg <1kg) or atracurium 0.3 mg/kg and sufentanil (0.2 microg/kg >1kg and 0.1 microg/kg <1kg). The initial publication of the acute results showed about the same incidence of the primary outcome, prolonged desaturation, in the two groups. The propofol group required many more extra doses of medication to achieve “adequate anaesthesia”; they were also less well sedated and required a longer time to be intubated. However, they started to breathe again more quickly, the atracurium sufentanil group taking a median of 33 minutes compared to 14 with propofol. The follow-up data are mostly from the Ages and Stages Questionnaire, and showed no difference between the groups. However, of the 166 babies included in the follow-up only 118 had data from the ASQ included, the others haveing their data imputed, many more in the propofol group (40%) than the atracurium/sufentanil group (19%). With this limitation in mind, all of the ASQ scores were basically identical between groups.

What should we do when we have results like these 3 trials, showing no difference in the long term outcomes or mortality between two treatment approaches? I don’t thin kit necessarily means you should throw the treatment out of the door, if there are really no differences in long term outcomes between 2 treatments then there are a few questions we should ask:

How reliable are the results?

What differences between groups are compatible with the results?

How applicable is this to my practice?

What are the short term impacts of the treatment?

What are parents likely to prefer?

How reliable are the results? Is the trial likely to be unbiased? Or are there potential sources of bias in the trial design or reporting of the results? This is a huge subject, but some things can improve your confidence that there really is no difference between the groups, such as a trial with masked allocation (and masked intervention, if possible) funded by an independent source that was registered before the trial started and reports the same primary (and a limited number of secondary) outcomes as are in the registration documents.

What differences between groups are compatible with the results? A trial may be called a null trial because the results did not reach a threshold of “p<0.05” but the confidence limits of the trial should be examined, a small to moderate size trial may still be compatible with a large, clinically important, difference in the treatments.

How applicable are these results to my practice? If the comparison group is not managed as they are managed in my practice, if the eligibility criteria eliminate many babies that I look after, or if control group outcomes are dramatically different to my patients, then the applicability to my practice may be very limited.

What are the short term impacts? We have become so focused on long term outcomes, very often survival without disability, that the impacts of short term outcomes may get lost. So a treatment that doesn’t impact survival or long term outcomes might well have advantages that are worthwhile. Such as reducing severe IVH despite no change in developmental progress or reducing the need for retinopathy therapy despite no final impact on blindness. If those short term benefits are achieved without short term adverse effects, that might be an indication for using a treatment.

What are parents likely to prefer? Outcomes which are important to parents should be a major part of our considerations, even if long term benefits are few or unproven. To return to the example above, would a parent prefer that their baby does not have a severe IVH, even if that doesn’t necessarily improve their long term outcome? If so, then prophylactic indomethacin should be considered, especially as the large, high-quality trials (Ment Indo IVH Prevention Trial and TIPP) showed no substantial difference in adverse events.

To apply these question to our three new null publications.

How reliable are the results?

For the trial of Natalucci, I would say that I can’t find any important potential bias in this trial design, a multicentre double-masked trial with the primary outcome as initially specified.

The TRIOCAPI trial is also well done, again a multicentre masked RCT with a pre-specified primary outcome.

For the PRETTINEO trial, the low rate of follow up and the reliance on the imputed outcomes makes me rather hesitant, especially with the very low rate of follow up in the propofol group.

What differences between groups are compatible with the results? This is, of course, a consideration of power and of confidence intervals.

For the Natalucci trial the primary cognitive score was almost identical in the 2 groups, and the results were compatible with a true difference between groups of a 3 point decrease in scores to a 2 point increase (approx), and therefore very little chance of a significant adverse impact of Erythropoietin.

The results of TRIOCAPI showed, again, almost identical rates of the primary outcome, but, as a smaller trial, the results are compatible with a 17% relative reduction or a 16% increase in the outcome of survival without cerebral palsy. The absolute risk difference in CP between groups was about 5% and the 95% limits of the absolute difference are between about a 9% lower frequency with indomethacin and a 6% higher frequency. The differences in disabling CP (GMFCS >2) were tiny (3 patients in the placebo and 2 in the indomethacin groups).

For PRETTINEO, the confidence intervals for the difference in “survival without neurodevelopmental delay” are very different if you include the imputed values or not, and therefore I would say that you can’t really rely on the confidence intervals.

How applicable is this to my practice?

The Natalucci trial is relatively applicable, but it excluded the highest risk babies of under 26 weeks. Survival and other outcomes among enrolled babies are not very dissimilar to mine.

TRIOCAPI again excluded the most immature babies <24 weeks, but included 24 week infants (French NICUs have a higher rate of comfort care in the delivery room at 24 weeks than we do, so the proportion of enrolled 24 week infants is somewhat lower), the main thing that makes me concerned about applicability is the very high rate of early PDA treatment among placebo group babies, which is much more, I guess, than a similar group of babies in my NICU. But, whether that would have an impact on the rate of CP or other developmental delays, I doubt.

PRETTINEO compared propofol premedication to a regime that is somewhat similar to what I use, which is atropine/succinylcholine/fentanyl. Succinylcholine has a much shorter duration of action than atracurium, so the babies start breathing gain much faster (sometimes it is too fast and we have to give a second dose), so I would say somewhat relevant.

What are the short term impacts?

Natalucci’s trial showed no adverse effects; the PENUT trial also showed no evidence of any adverse effect, the previous concern about a possible increase in retinopathy with some regimes is not born out by this new data. I can’t find a report of transfusion requirements in the Nataluci trial publications, but PENUT showed that the proportion of babies who never needed a transfusion increased from 13% to 28% with their erythropoietin regime and the median number of transfusions decreased from 4 to 2.

TRIOCAPI also showed little in the way of adverse impacts of early targeted ibuprofen treatment. There were a lot fewer pulmonary haemorrhages 2% vs 8% in the first 3 days of life, but somewhat more GI perforations, 8.8% vs 3.5%. The Cochrane review of prophylactic ibuprofen (not exactly the same I know, but ibuprofen given in very early life, also shows more GI perforations compared to no treatment, but is only based on 2 small trials with a total of 167randomized babies and 14 events, the confidence intervals are very wide and include no difference. GI bleeding is also more common in the Cochrane review, although that is supposed to be “statistically significant” it is largely based on 2 very small Thai trials that had enormous rates of GI bleeding.

PRETTINEO in their initial publication showed a high frequency of hypotension after propofol, which received treatment on 2 occasions, No other major difference in short term impacts was shown, the proportion desaturating during intubation was similar. There were many more intubations on the first attempt in the atracurium/sufentanil group.

What does mean for the clinical implications of these null studies?

Early Erythropoietin, doesn’t seem to offer any neuroprotection when you put it into the context of other trials. It does seem to reduce the proportion of babies who receive a transfusion and the total volume of blood transfused, without any adverse effects. I think that is an impact that might be valuable to some parents, and that therefore it would be reasonable to offer it as an option to parents with babies at risk of being transfused. If we couple it with delayed cord clamping and greater efforts to reduce blood losses, by taking initial blood work from the blood left in the placenta for example, we could probably do even better to reduce transfusions, which I know are extremely safe these days, but still not as safe as not having a transfusion!

Early targeted ibuprofen was something that we introduced into our unit as a pilot after the Kluckow trial, partly because we had been through a phase of having quite a lot of pulmonary haemorrhages. This trial means, I think that we should rethink that approach. It confirms that there are fewer pulmonary haemorrhages leading to respiratory deterioration with this approach, but there may be an increase in GI perforation. Is there a better way to target those at risk of pulmonary haemorrhage to change the risk:benefit ratio?

The PRETTINEO trial confirms to me that propofol is not a good idea, even though there was no adverse long term impact (with the limitations already mentioned) intubation took longer and more attempts and there was more hypotension. Maintaining the use of a regime with a short acting muscle relaxant seems to me optimal, as long as a potent analgesic is also used.

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What role for High Flow Nasal Cannulae?

There are a few new publications which might help us to answer the question posed in the title of this post.

When heated, humidified, high flow nasal cannulae were first being spoken about I remembered an old study using standard cannulae but with flow rates up to 2 litres per minute. In 13 infants with an average body weight of about 1500g, the authors measured intra-oesophageal pressures, using either 0.2 or 0.3 cm diameter prongs. (Locke RG, et al. Inadvertent administration of positive end-distending pressure during nasal cannula flow. Pediatrics. 1993;91(1):135-8).

As you can see from this figure you can get very high oesophageal pressures with 2 litres per minute of flow if you have tight-fitting nasal prongs. The average was 9.8 cmH2O, and the error bars are SEM, which means the SD was 3.6, so the upper limit of pressures generated could easily be 9.8+2SD= 17cmH2O! The lower limit would be about 2 cmH2O with a 2 litre flow, and as you can see a pressure of 0 when the smaller prongs were used. You can see from the title of the article that the PEEP delivered, at that time, was considered “inadvertent”!

Since then the use of heated humidified gases and systems specifically designed for high flow have been introduced. Unfortunately, the initial introduction of HFNC was without good trials evaluating risks and benefits. I, for one, was reticent to use them for quite a while. The only advantage I could see was that they seemed to be more comfortable for larger, more mature, kids, although the trials evaluating pain scales are contradictory. There does, however, seem to be less nasal trauma when they are used for younger preterm infants (<28 wk PMA), and parents generally prefer them, perhaps because it is easier to interact and play with their babies with HFNC than CPAP.

We started using them for older babies with mild to moderate BPD who still needed CPAP when they were getting to be over 34 weeks. One of the features of our unit is that babies on HFNC can be transferred to the intermediate care section of the unit, whereas if on CPAP they have to stay in an intensive cot. When we were short of beds we sometimes switched a baby from CPAP to HFNC to make room for a new admission. So the use of HFNC gradually crept up, which made us review our practices and ask a couple of questions based on more recent data than the article from 1993.

In terms of the impact of HFNC on the respiratory system, they do generate PEEP under certain circumstances, but it is variable from baby to baby, and from minute to minute. It depends on how tight they fit in the nostrils of the baby. and the flow rate and whether the mouth is open or not.

And here I can’t help myself, but I must insist: NARE IS NOT A WORD! Sometimes the nostrils are referred to as the “nares” (pronounced naireez) which is a Latin word occasionally used in English to refer to the two nostrils. One nostril in Latin is “naris”, so, if you wanted to, you could refer to a naris, but I would insist that the whole sentence is in Latin! Quid magnum naris! (what a big nostril!) We have a perfectly functional English word for the nostril, let’s use it!

As another aside, one thing I find cute in a French-speaking NICU is that nasal flaring is referred to as “flapping the wings of the nose” (battement des ailes du nez).

To return to medicine…

A recent article on the physiological impacts of HFNC has, for the first time in preterm babies, I believe, tried to actually measure one of the supposed mechanisms of action, that is, dead space washout. (Liew Z, et al. Physiological effects of high-flow nasal cannula therapy in preterm infants. Arch Dis Child Fetal Neonatal Ed. 2020;105(1):87-93) They did this in 44 low birth weight babies (500 to 1900g), testing different flow rates and comparing to nCPAP at 6 cmH2O.
Normally, when you inspire, you at first pull into your gas exchange sacs (terminal sacs or alveoli depending on GA) the gas that you just expired, from the tracheobronchial tree then the upper airways, before getting fresh atmospheric gas (there is, of course, a gradual mixing during inspiration). The idea of dead space washout with HFNC is that a high flow of gas into the pharynx, much higher than the infant’s minute ventilation, will wash out the pharynx with a fresh gas flow (21% oxygen or more and 0% CO2) and thus decrease the effective dead space. To measure this you could look at the moment by moment gas composition of the gas in the pharynx during the respiratory cycle, and determine the inspiratory concentrations of CO2 and O2. This group did almost exactly that, but taking into account the mixing of gases and the turbulence caused by the HFNC in the pharynx, they decided to measure the peak, end-tidal CO2. Which dropped progressively as gas flow increased.

As you can see the pEECO2, or end-tidal CO2, expressed as a percentage dropped from 2.3% at a flow of 2 to 0.9% at 8 litres per minute, confirming that there was indeed a wash-out of the dead space. In addition, minute ventilation fell, although not as consistently, as flows increased, which is what you would expect; if you wash out CO2, then PCO2 will fall, leading to a decrease in respiratory drive and then in minute ventilation until PCO2 comes back up to where it was, this is confirmed by the stability of the transcutaneous CO2 (about 46 mmHg in old units). This might mean that a baby who has a high work of breathing associated with BPD will have a reduction in their respiratory effort as flows increase, which is in fact what we sometimes see in the NICU.

As another aside, babies (and indeed adults) with chronically raised CO2 have intact CO2 responses. This has clearly been shown in adults with COPD who do NOT become “dependent on hypoxic drive” as stated in some texts, which has led in the past to restricted oxygen administration. Newborns also remain responsive to CO2, even when chronically hypercapnic. I studied this back when I was a fellow, in the last century, giving 2% CO2 to a few babies with BPD and chronic hypercapnia, they increased their minute ventilation, just as you would expect.

The pharyngeal pressures as shown in the table don’t clearly show the variability in the pressures obtained, which are better demonstrated in their graph:

A flow of 8 lpm/kg produced pressures between 2 and 14 cmH2O, at 2 lpm/kg pressures were between close to 0 and 7 cmH2O.

Are there any advantages to HFNC compared to CPAP? What are the disadvantages?

As mentioned above parents seem to prefer them, they also state that their child prefers them. In this randomized cross-over trial (Klingenberg C, et al. Patient comfort during treatment with heated humidified high flow nasal cannulae versus nasal continuous positive airway pressure: a randomised cross-over trial. Arch Dis Child Fetal Neonatal Ed. 2014;99(2):F134-7) parents rated their child’s “satisfaction” as an average of 8.6/10 compared to 6.9 for nasal CPAP, even though the PIPP scores were just about identical between the two groups.

That, I think, is an important difference, but must be offset by the fact that initial use of HFNC for early respiratory distress is more likely to fail than CPAP (Roberts CT, et al. Nasal High-Flow Therapy for Primary Respiratory Support in Preterm Infants. N Engl J Med. 2016;375(12):1142-51), and infants are more likely to fail extubation if they receive HFNC rather than CPAP (Uchiyama A, et al. Randomized Controlled Trial of High-Flow Nasal Cannula in Preterm Infants After Extubation. Pediatrics. 2020:e20201101. Manley BJ, et al. High-flow nasal cannulae in very preterm infants after extubation. N Engl J Med. 2013;369(15):1425-33).

This may not matter too much if you have CPAP available as a backup, but in some circumstances, failure of the HFNC might be associated with substantial pulmonary de-recruitment, and difficulty stabilising with CPAP.

In addition, we may be drowning the babies! (Reiner E, et al. Using heated humidified high-flow nasal cannulas for premature infants may result in an underestimated amount of water reaching the airways. Acta Paediatr. 2020), this was a study in an in vitro model so it is of limited applicability in terms of the actual numbers compared to the complex dynamics of a newborn’s upper airway, but a Heated humidified HFNC system deposited up to 44 mL of water over a 24 hour period in a feeding bottle being used as the model for the upper airway. A CPAP system with a heater wire in the inspiratory limb may well lead to less water deposition, but I don’t know that for sure and it would be interesting to know.

All of which leads to a few studies suggesting from several centres that when they started using more HFNC they had worsening pulmonary outcomes. Heath Jeffery RC, et al. Increased use of heated humidified high flow nasal cannula is associated with longer oxygen requirements. J Paediatr Child Health. 2017;53(12):1215-9. Hoffman SB, et al. Impact of High-Flow Nasal Cannula Use on Neonatal Respiratory Support Patterns and Length of Stay. Respir Care. 2016;61(10):1299-304. Multicentre databases have reported the same thing. Taha DK, et al. High Flow Nasal Cannula Use Is Associated with Increased Morbidity and Length of Hospitalization in Extremely Low Birth Weight Infants. J Pediatr. 2016;173:50-5 e1.

I actually wonder whether that may be because of the increased ease of use and apparent comfort of the babies on HFNC, which makes us less pressed to wean their support so we end up weaning more slowly and the babies are exposed to more positive pressure, potentially more oxygen, and maybe even more water droplets in the airway(?). The Cochrane review did not find any evidence of worse pulmonary outcomes with HFNC, but there really aren’t many trials comparing the long-term use over several weeks during the recovery phase of preterm lung disease compared to CPAP, so the Cochrane review doesn’t really cover that kind of usage. This small trial found no advantage of prolonged HFNC compared to CPAP for babies recovering from their RDS in terms of learning to feed Glackin SJ, et al. High flow nasal cannula versus NCPAP, duration to full oral feeds in preterm infants: a randomised controlled trial. Arch Dis Child Fetal Neonatal Ed. 2017;102(4):F329-F32.

So what are the indications for HFNC today?

  1. Initial respiratory support of the preterm infant? I think that very preterm babies (<32 weeks) are at higher risk of failing compared to CPAP and, as such babies are usually in a tertiary NICU with CPAP available, that should be their initial support. 32 to 35 week babies in a level 2 nursery could be managed initially with HFNC if CPAP is not easily available, but early contact with a referral centre should be instituted, in case of failure.
  2. Post-extubation support? This should be either CPAP for larger preterm babies or nIMV for smaller preterm babies. I don’t think HFNC is a good option for any baby immediately after extubation.
  3. Prolonged respiratory support? This is the one place where I think there may be a role for HFNC, parents prefer it and they see that their infants are more comfortable. I think that for the baby approaching 36 weeks, who is starting to be more interactive, if CPAP can’t be weaned off, then HFNC could be considered. The caveat is that we should have a protocol for weaning, with frequent evaluation of the baby and attempts at weaning, the dead space washout might reduce respiratory efforts in babies with low compliance or high resistance lungs, and they may therefore have less retractions and their nose wings might flap less (!), but beware being complacent about the baby who is stuck on HFNC, you may end up with more of them having respiratory support for longer.
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Probiotics and NEC, the latest answer?

The updated Cochrane review of probiotics for prevention of NEC, sepsis and mortality has been published.

Meta-analysis showed that probiotics may reduce the risk of NEC: RR 0.54, 95% CI 0.45 to 0.65 (54 trials, 10,604 infants; I2 = 17%); RD -0.03, 95% CI -0.04 to -0.02; number needed to treat for an additional beneficial outcome (NNTB) 33, 95% CI 25 to 50. Evidence was assessed as low certainty because of the limitations in trials design, and the presence of funnel plot asymmetry consistent with publication bias. Sensitivity meta-analysis of trials at low risk of bias showed a reduced risk of NEC: RR 0.70, 95% CI 0.55 to 0.89 (16 trials, 4597 infants; I2 = 25%); RD -0.02, 95% CI -0.03 to -0.01; NNTB 50, 95% CI 33 to 100. Meta-analyses showed that probiotics probably reduce mortality (RR 0.76, 95% CI 0.65 to 0.89; (51 trials, 10,170 infants; I2 = 0%); RD -0.02, 95% CI -0.02 to -0.01; NNTB 50, 95% CI 50 to 100), and late-onset invasive infection (RR 0.89, 95% CI 0.82 to 0.97; (47 trials, 9762 infants; I2 = 19%); RD -0.02, 95% CI -0.03 to -0.01; NNTB 50, 95% CI 33 to 100). Evidence was assessed as moderate certainty for both these outcomes because of the limitations in trials design. Sensitivity meta-analyses of 16 trials (4597 infants) at low risk of bias did not show an effect on mortality or infection.

I find this extremely interesting, but also somewhat concerning. The recent network meta-analysis that I posted about ( found the following:

Compared with placebo, a combination of 1 or more Lactobacillus species (spp) and 1 or more Bifidobacterium spp was the only intervention with moderate- or high-quality evidence of reduced all-cause mortality (odds ratio [OR], 0.56; 95% confidence interval [CI], 0.39-0.80). Among interventions with moderate- or high-quality evidence for efficacy compared with placebo, combinations of 1 or more Lactobacillus spp and 1 or more Bifidobacterium spp, Bifidobacterium animalis subspecies lactis, Lactobacillus reuteri, or Lactobacillus rhamnosus significantly reduced severe NEC (OR, 0.35 [95% CI, 0.20-0.59]; OR, 0.31 [95% CI, 0.13-0.74]; OR, 0.55 [95% CI, 0.34-0.91]; and OR, 0.44 [95% CI, 0.21-0.90], respectively).

The differences between the reviews, and between the interpretations of the evidence are fascinating. The Cochrane review did not include 12 trials which are included in the Network Meta-Analysis (NMA), with a total of 3580 subjects; most of those trials are listed in the excluded trials table as having been excluded because “most participants were not very preterm or VLBW”. Three of the trials in the NMA are not listed as excluded in the Cochrane review, one of them has 174 participants, and a mean GA of 29.5 weeks, and is probably eligible for inclusion in the Cochrane review, but has only been published as an abstract in conference proceedings, so may not have been found by their literature search. The other 2 trials, one large (n=524) and one small (n=62) appeared to be mostly larger preterm infants, so probably would have been excluded anyway.

The Cochrane review included 9 trials not in the NMA, it is not clear why they weren’t included, but those trials enrolled a total of 765 infants. Most are limited to VLBW infants, and many are not difficult to find (in JPGEN and PLOS1, for example).

The interpretation of the quality of the data are divergent, the NMA referring to moderate to high-quality data, while the Cochrane review refers to evidence of low certainty. In part, this is based on an analysis of the funnel plot, which looks a bit asymmetric and the statistical test for missing data was just below p=0.05. It is, of course, impossible to be sure if there is missing data or not, if you knew about it it wouldn’t be missing! The statistical test used has been evaluated by using simulations, which is I guess the only way to test such tests, but makes me a little uncertain how reliable it is.

The divergence of opinion also points out that there is some degree of subjectivity in deciding on the quality of the evidence.

Where I start to have concerns about the Cochrane review is that, when restricting the analysis to high-quality trials, there remains a major reduction in NEC, those trials number 16 with 4,597 infants enrolled. Also when analyzing mortality in only trials with a low risk of bias, they state that there was no difference, in fact, the mortality with probiotics was 5.9% and with placebo was 7%, which are 2 different numbers unless I am mistaken. You could say they are not statistically significantly different, or that there is a small difference which may be due to chance, the weighted RR from the meta-analysis is 0.86 (95% CI 0.69, 1.07).

I guess the main issue is : how confident do you have to be to introduce an intervention which has next to no risk, is very cheap, does not prevent you from introducing other interventions to reduce NEC risk, and which decreases NEC in a meta-analysis of high-quality trials? Even though the reductions in mortality and in invasive infection are not below a p-value of 0.05, the differences are in the right direction in the high quality trials.

When you add to the RCTs the real-world experience of introducing probiotics in multiple studies, from large databases in Germany, the USA, and Canada, and individual hospital experiences like ours, and Toronto and Norwich, I think it is hard to avoid the fact that probiotics are almost certainly effective in reducing NEC, and that large enough high-quality studies would likely show a decrease in mortality, which is already evident when the lower quality studies are included in the analysis. It seems likely to me that Bifidobacterium longum Subsp Infantis in a mixture with a Lactobacillus or another Bifido-may be the best, but that is less certain.

Do we really want to spend the next 2 million dollar grant for an RCT comparing probiotics to placebo? Surely cluster randomized trials comparing different preparations could be much more cost-efficient and could quickly give us much larger sample sizes, and would permit an answer to the question of which preparations are most effective.

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Quality of life cannot be predicted from a brain scan

…either ultrasound or MRI, or by EEG, or neurological examination, or even during follow-up by screening for disabilities.

That title is from a recently published editorial (Fayed N, et al. Quality of life cannot be predicted from a brain scan. Dev Med Child Neurol. 2020;62(4):412) which is available full-text open access, and which includes this pearl:

Even though levels of cognitive and motor problems can often be  based on magnetic resonance imaging results, abnormal electroencephalogram findings, and a neonate’s hospital course, the happiness and acceptance a child will achieve in their families and communities cannot.

I actually would argue that none of those 3 methods can be used to identify cognitive or motor problems with any reliable degree of certainty. The PPV of disabling cerebral palsy, for example, based on white matter injury shown on the MRI, is LESS THAN 50%.

Even if pre-discharge imagery were perfectly predictive of impairments, which is far from being the case, being impaired does not imply a poor quality of life. There is very little correlation between a life of quality and whether or not an individual is impaired. As these authors note:

disability severity has little relationship to life quality. Instead, emotional well-being, peer interactions, parental adaptation, and community support are much more powerful predictors of whether a child is likely to grow up to have a good life. When conveying a prognosis of severe disability and its consequences to child and family, the solution is a simple one. Refrain from confounding the concept of a good QoL with the prognosis of cognitive or physical disability.

We perform many investigations to try and predict the outcomes of our patients, sometimes with the idea that we should change the intensity of our care based on the results.

When you state the issue as clearly as these authors did in the title of their article it becomes almost self-evident; of course you cannot predict quality of life by looking at the brain. And if you cannot, then why are we doing so many scans?

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