ARDS is a fairly common problem in the adult and the paediatric ICU; following trauma, or systemic sepsis, or other extrapulmonary insults, usually inflammatory in nature, or as a complication of direct pulmonary insults, such as pneumonia or aspiration of gastric contents. It is characterised by acute respiratory distress, diffuse pulmonary infiltrates on the x-ray, without signs of cardiac compromise, an oxygenation defect, and a major decrease in lung compliance. Various definitions have been proposed, none of which are entirely satisfactory, but many cases in the PICU are fairly clear.
It also occurs in newborn infants; many of us will have seen, for example, an infant with systemic sepsis who develops a secondary respiratory deterioration within the first day or so, with a “white-out” on the xray, and a serious deficit in oxygenation, with very stiff lungs. One question then is, how to define the entity, ARDS in the newborn (nARDS)? The consensus definition from Montreux is shown below

As with any definition there are some problems with this. For example, that publication also states that “the mandatory criteria for diagnosis of RDS are respiratory distress appearing within the first 24 h of life, with complete, sustained, and prompt response to surfactant or lung recruitment or both”. Which suggests that almost any infant who has a partial response to surfactant could then be defined as nARDS.
I am also unsure, for some problems, if it helps to have this diagnosis. As one example, the document above discusses meconium aspiration syndrome as a cause of nARDS. I am sure that many of the pathophysiologic processes of MAS and nARDS do indeed overlap, but there are also very specific features of MAS. With meconium in the airways and distal lung, leading to surfactant displacement and inactivation and chemical pneumonitis, in association with frequent asphyxial impacts on the circulation and lung, there are management approaches which may be very different to other causes of nARDS. Trials of treatment in MAS will not necessarily be extrapolatable to other causes of nARDS, and vice versa. For example, lung lavage with diluted surfactant might be an appropriate option for MAS, but is unlikely to be helpful for other causes of nARDS.
Similarly for pulmonary haemorrhage, it is clear that surfactant dysfunction is common in clinically important haemorrhages, (in the lab, haemoglobin and fibrinogen are very useful to inhibit surfactant function) and surfactant replacement therapy often leads to acute improvements in clinical status. Should trials of therapy for nARDS include PH, or enrol them as a separate subgroup?
The reason for discussing these issues is the appearance of a new RCT comparing conventional ventilation to high frequency oscillation. (Li J, et al. High-Frequency Oscillation vs Mechanical Ventilation for Neonatal Acute Respiratory Distress Syndrome: A Randomized Clinical Trial. JAMA Netw Open. 92026. p. e260268). This is a single centre study from Chongqing in China, infants from 25 to <36 weeks were eligible if they were diagnosed with nARDS and were then randomized, to either be switched from the CMV to HFOV, or to remain on CMV. The primary outcome was “overall BPD”.
There are a huge number of problems with this publication. One good point is that the study was prospectively registered prior to commencing the study, as has been the required standard since 2005. Many studies are still being published that do not follow this simple rule, more on this soon.
In the first version of the registration documents this was a multi-centre trial with a sample size of 1000 infants. Shortly after that the sample size was reduced to 600, but there are about 30 different centres listed (perhaps this was just a “wish list”), the final publication had 386 infants included from a single centre. The sample size calculation was based on an effect size of 17% difference in BPD between groups, leading to a calculated need for 160 subjects per group. The actual mean GA of the participants was 31 weeks.
The published primary outcome of the trial, BPD, is presented with 2 different definitions, the NICHD 2001 definition, and the Jensen et al definition from 2019, both of which are analysed and presented. In the registration documents, however, only the NICHD definition is used. But whichever definition is used these only apply to infants of <32 weeks gestation. In other words nearly half of the babies in this study could not have BPD by either definition! This is not just semantics, defining BPD at 36 weeks GA is already problematic enough, but diagnosing it at 1 week of age in a 35 week GA infant is nonsensical. The authors themselves state in the discussion “it makes no sense to look for BPD in neonates born after 28 weeks”! This sounds to me like a quotation of a comment from one of the reviewers, but the authors have simply included that phrase in their discussion without otherwise discussing the implications for their study.
We only know the mean GA in each group, 31 weeks as noted above, so the proportion of infants <32 weeks isn’t precisely clear, but probably somewhere around half.
The fact that JAMA allowed the authors to add a second definition of BPD, and report both of them as if they were both the primary outcome of the study is extremely disappointing. In addition, BPD is calculated as the proportion of enrolled infants, even though there was significant mortality (19% with HFOV, 16% with CMV). We don’t know if the infants died before or after they reached 36 weeks, so we can’t even calculate the rate of BPD among surviving infants, which given the GA range of the babies in this study is not such a big deal!
Infants were screened and enrolled in the trial at an average of 4.8 hours, which is well before they had a diagnosis of nARDS. According to the CONSORT flow diagram, there were 632 infants of <34 weeks GA during the study period. 180 had RDS, and 12 did not meet criteria, with another 23 “unavailable”, 24 parents didn’t consent, Leaving 386 infants enrolled in the study who were randomized. All the randomized infants (except 11 CMV infants who “did not receive CMV”, not explained why) entered one of the treatment arms. I would guess that many babies enrolled (at 5 hours of age) never developed nARDS, what on earth happened to them?
This means that the incidence of nARDS in the centre reporting this study is enormously high, orders of magnitude higher than any previous report. Previous epidemiologic reports (De Luca D, et al. Epidemiology of Neonatal Acute Respiratory Distress Syndrome: Prospective, Multicenter, International Cohort Study. Pediatr Crit Care Med. 232022. p. 524–34. Chen L, et al. Clinical characteristics and outcomes in neonates with perinatal acute respiratory distress syndrome in China: A national, multicentre, cross-sectional study. EClinicalMedicine. 552023. p. 101739.) show a rate of about 1.5% of NICU admissions. One of those epidemiologic studies’ first authors was an author of this new trial.
I certainly do not understand how the incidence of nARDS can be more than double that of RDS among preterm infants. About 60% of each group are stated to have had early onset sepsis, which is also an enormously high proportion, but no diagnostic criteria are given.
The publication states that the study was masked to investigators and parents, which is clearly nonsense, unless parents were not allowed to visit, and the investigators had to stay outside of the NICU. Like almost all mechanical respiratory support interventions it is impossible to blind the intervention. This doesn’t really matter, masking of the randomisation process, so that the group assignment is unknown at the time of enrolment, is far more important anyway
There were 11 babies, analysed in the CMV group, who had been randomized to HFOV but treated with CMV because of lack of equipment. Again I can’t understand why JAMA would allow this, those infants should either have been included in the HFOV group, according to intention to treat principles, or just eliminated from the trial (which would have been quite reasonable).
Babies were allowed to be crossed over if they were not doing well, and they were appropriately analysed in the randomised group. The criteria for failure were different between groups, however, requiring persistent life-threatening hypoxia in the HFOV group (<50% saturation for more than 3 hours) compared to modest desaturation (<90% for >3h) in the CMV group. In either group persistent PCO2 >60 was also a criterion.
There are several other strange features of this study, the average mean airway pressure (MAP) at enrolment was >11 cmH2O, but the starting MAP in both of the groups was reduced to 8. The CMV group also have both a mandatory starting pip (16 cmH2O) and a set tidal volume (5 mL/kg). The copy-editor clearly didn’t do their job either, there are numerous weird phrases such as “Only pressure-regulated volume control is provided by any type of neonatal ventilator.” I think that means that any neonatal ventilator was allowed in the CMV group, and I don’t think they really mean PRVC. But I don’t know if they were using volume-targeted ventilation or pressure controlled.
I know I am being even more picky that usual with this study! It is easy to be critical, and much harder to do prospective research. One reason for focusing on this study, though, is that I have seen it quoted approvingly in a few places, as if it gave evidence supporting the use of HFOV in RDS. The authors themselves make many comparisons between their trial and other published research, and meta-analyses, which are all in infants with probable RDS. But this is, supposedly, a different patient group, with a different primary pathophysiology. The available data from trials in preterm infants with acute pulmonary dysfunction (as the Cochrane review puts it) show no advantage to initiating assisted ventilation with HFOV over CMV.
How to treat nARDS is an important issue, unfortunately this trial just muddies the waters. With uncertainties over the diagnosis, the outcomes, some suboptimal features of the design and the interventions, it doesn’t help me at all in a choice of ventilatory strategy for a baby with nARDS.
































































