When Air Escapes From a Newborn's Lung

Four studies from Japan and the United States, published between April 2025 and January 2026, on what makes a collapsed lung more likely in the smallest babies — and how doctors decide whether it needs to be drained

A pneumothorax happens when air leaks out of a baby's lung and becomes trapped between the lung and the chest wall. It affects one or two of every hundred babies in newborn intensive care, and most recover with nothing more than close watching — but it is far more common, and far more dangerous, in babies born extremely early.

Four studies published over the past year look at the problem from two directions. Three ask what makes the air leak happen in the tiniest babies, and one asks how doctors should decide, once it has happened, whether to put in a tube to let the trapped air out.

The problem, and why it has been hard to solve

Every baby's first breaths are unusually forceful, because the lungs have to open for the first time. Doctors recognised more than sixty years ago that this effort alone could tear a small hole in a newborn's lung [1]. When machines that push air into the lungs came into use in the 1970s, they saved the lives of babies who could not breathe well enough on their own — but they also created a new way for lungs to tear, because the pressure has to come from somewhere [2].

Since then, a series of advances have made air leaks much less common. Steroid injections given to mothers before an early birth help the baby's lungs mature. Surfactant, a slippery substance that keeps the tiny air sacs from sticking shut, is given directly into the lungs after birth. And gentler forms of breathing support, delivered through soft prongs in the nose rather than a tube in the windpipe, have replaced many machine breaths [3]. Families of babies born today are far less likely to hear the word "pneumothorax" than families were a generation ago.

The improvement has not reached everyone equally. Among babies born at 23 to 28 weeks of pregnancy, about 9 in every 100 have an air leak in the first three days [4]. At 22 to 23 weeks — the very edge of what is survivable — one Japanese hospital found the figure was about 14 in every 100, and that babies who had one were several times more likely to die [5]. Larger studies across whole countries have found the same pattern: the earlier the birth, the higher the risk, and the more it matters [6][7].

That leaves doctors with two separate questions, and until recently neither had good answers. For the smallest babies, the air leak happens so fast that preventing it matters far more than treating it — but nobody had carefully worked out which of the things doctors do in those first few hours make it more or less likely. For bigger babies, the air leak is usually survivable, but someone has to decide whether to put a tube in the chest, and that decision has mostly been made on experience and instinct rather than any measurement.

Three things that seem to change the risk in the smallest babies

Three of the four studies come from the same hospital: Kagoshima City Hospital in Japan, the only specialist newborn centre in its region, which means it cares for essentially every extremely early baby born there. All three looked back through years of records rather than testing anything on new patients, which is an important limitation to keep in mind.

The first study looked at a breathing manoeuvre called a "sigh breath." Babies on a particular kind of ventilator — one that delivers many very small, very fast puffs of air rather than full breaths — sometimes have parts of the lung that stay collapsed. A sigh breath is a single larger push, delivered a few times a minute, meant to reopen those areas. Among 64 babies born at 22 to 25 weeks who needed this ventilator in their first hours, 10 developed a serious air leak. Seven of those 10 had been given sigh breaths, compared with only 9 of the 54 who did not have an air leak — a difference unlikely to be chance [8]. The authors could not prove the sigh breaths caused the problem, because the babies given them already had the sicker-looking lungs. But the finding is a real caution, and other research had already shown that this particular ventilator carries a somewhat higher risk of air leaks than gentler alternatives [9].

The second study looked at the pressure setting on the ventilator itself. Following 12 of the very smallest babies minute by minute, the researchers found that the average pressure had already been creeping upwards in the hours before the lung tore, and suggested that once it reaches a certain level, doctors should look hard for any way to bring it down [10]. That fits with earlier work in slightly bigger babies pointing to a similar pressure threshold [11].

The third study looked at pain and sedation medicine. Extremely early babies on ventilators are sometimes given a low, steady dose of fentanyl, a strong painkiller, to keep them comfortable. Among 138 babies born at 22 to 23 weeks, only 1 of the 54 who received fentanyl had a serious air leak, compared with 15 of the 84 who did not [12]. The suggested explanation is straightforward: a baby who is uncomfortable fights against the ventilator, and a breath taken against a machine breath generates far more force inside the lung than either would alone. This is a promising idea rather than a settled fact — it rests on a single case among the treated babies, and an older, more rigorous study in slightly larger babies found no such benefit [13]. It is not a reason for families to ask that their baby be sedated, but it is a good reason for researchers to test the question properly [14].

What an air leak does to a baby, and what happens after it is treated

The most detailed of the four studies followed the vital signs of 12 extremely premature babies through the whole episode. Air leaks tended to happen about a day after birth. At the moment the leak was found, the pressure in the large vein returning blood to the heart had risen sharply, blood pressure had dropped, oxygen levels had fallen, and the amount of extra oxygen the baby needed had risen substantially [10]. Trapped air presses on the lung and on the heart, so blood cannot return properly — which explains all of these changes at once.

One detail is worth knowing. In these very small babies the heart rate went down, not up. In older children and adults, the heart usually races in this situation. Knowing to expect the opposite in a 23-week baby helps the team recognise what is happening sooner.

Another finding may reassure families. After the trapped air was drained, the babies improved — but not immediately or completely. Blood pressure in particular took time to come back [10]. A baby who still looks unwell for some hours after a drain is placed is not necessarily a sign that the procedure failed.

Deciding whether to drain, and a simple way to measure

The fourth study comes from Rainbow Babies & Children's Hospital in Cleveland, in the United States, and looked at a very different group: 62 babies who were mostly born at or near their due date. The researchers took each baby's chest X-ray and measured how wide the pocket of trapped air was, then divided that by how wide the chest was at the same level. This gives a simple number describing what fraction of the chest the air occupies [15].

The number turned out to predict the decision remarkably well. Two thirds of these babies — 41 of 62 — never needed a procedure at all; watching and giving oxygen was enough. Among those whose air pocket took up less than about a tenth of the chest width, not a single baby needed draining. Among those whose air pocket took up more than about a fifth, every baby did. In between, it was roughly a coin flip, and the decision came down to how the baby looked and behaved [15].

Used sensibly, this is less a rule than a way of getting ready. A small measurement supports a decision to wait; a large one tells the team to call the right person early, so that if a tube is needed it can be placed calmly rather than in an emergency. The study has real limits — the measurements were made by one person, so it is not yet known whether different doctors would get the same number, and almost all the babies were born close to term, so the same figures may not apply to a very premature baby. Ultrasound at the cot side is more accurate than an X-ray for spotting an air leak, and is increasingly used alongside it [16].

The same study also found that many air leaks treated first with a needle — a quicker, less invasive way to remove trapped air — went on to need a proper chest tube anyway [15]. Other research has found this too, though less often [17][18]. It does not mean the needle is useless; it is often the fastest way to relieve a baby in trouble. It does mean that a needle is frequently a first step rather than the whole treatment, and parents told that a needle procedure will be tried should also be told that a tube may follow.

What this means for families, and what comes next

If your baby has had a pneumothorax, the most likely outcome by a wide margin is recovery. In babies born at or near term, most never need anything beyond observation, and those who need a drain generally do well. In babies born extremely early the picture is more serious, and the honest figure is that fewer than a third of babies born at 22 to 23 weeks who had a serious air leak survived to go home [12] — a reminder that in those births the air leak is one part of a much larger struggle.

The most useful thing these four studies do is turn a sudden emergency into something partly foreseeable. Researchers are now working on which ventilator settings and comfort measures reduce the risk in the first place, on whether the pressure in a baby's veins can be used as an early warning sign hours before anything visible happens, and on whether the simple X-ray measurement works in other hospitals and in smaller babies. Each of those questions needs a proper trial, and each is being planned. Families who want to understand more about the care of the smallest babies may find the companion In[Neo]Sight article on survival at 22 and 23 weeks across 61 Korean newborn units helpful. If your baby is affected, it is entirely reasonable to ask the team what they saw on the X-ray, how large the air pocket was, and what would make them decide to place a drain.

References

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