PEEP, or positive end-expiratory pressure, helps newborns by keeping their lungs partially inflated between breaths. This prevents the tiny air sacs in the lungs from collapsing completely during exhalation, which is especially critical for premature babies whose lungs are underdeveloped and lack enough natural surfactant (the slippery coating that keeps air sacs open). The pressure is gentle, typically starting at 3 to 5 cmH₂O, and it serves as the foundation of nearly all breathing support given to newborns in distress.
How PEEP Keeps Newborn Lungs Open
A newborn’s first challenge outside the womb is clearing fluid from the lungs and filling them with air for the first time. Once air enters, the lungs need to hold onto a baseline volume of gas even after the baby exhales. This baseline is called functional residual capacity, or FRC, and it’s what keeps the air sacs from sticking shut between breaths. Without it, the baby’s lungs would need to fully re-inflate with every single breath, which takes enormous effort for a tiny body.
PEEP maintains a small amount of air pressure in the lungs at the end of each breath, acting like a doorstop that prevents the air sacs from closing all the way. In premature infants, there is a strong link between the absence of this baseline lung volume and the later development of serious breathing problems that require a ventilator. By establishing and maintaining FRC, PEEP addresses the root mechanical problem in a struggling newborn’s lungs rather than just pushing more air in.
Protecting Fragile Lung Tissue
When air sacs repeatedly collapse and reopen with each breath cycle, the tissue lining those sacs gets damaged by shear forces, similar to the wear you’d see from folding and unfolding a piece of paper along the same crease. This repetitive opening and closing also breaks down whatever surfactant the baby does have, making the problem progressively worse. In animal studies, ventilation without PEEP leads to significantly more protein leaking into the air sacs, a sign of tissue injury, compared to ventilation with PEEP.
PEEP breaks this cycle. By keeping air sacs at least partially open, it eliminates the mechanical stress of constant collapse and re-expansion. Research in preterm animal models shows that using PEEP from the very first breaths reduces the formation of hyaline membranes (the waxy deposits that characterize severe respiratory distress), preserves surfactant function, and reduces inflammatory markers in the lungs. The protection starts immediately, which is why PEEP is now applied in the delivery room during resuscitation rather than waiting until the baby reaches the intensive care unit.
Improving Oxygen Levels
When large portions of a newborn’s lungs are collapsed, blood flows past those deflated areas without picking up oxygen. This mismatch between airflow and blood flow is one of the main reasons a sick newborn’s oxygen levels drop. PEEP recruits collapsed air sacs back into service, opening up more surface area for oxygen exchange and reducing the amount of blood that passes through the lungs without being oxygenated.
In very preterm lambs, applying PEEP during resuscitation cut oxygen requirements in half within ten minutes. A recent study of late preterm and term newborns with respiratory distress syndrome found that those managed with higher PEEP levels needed a lower concentration of supplemental oxygen at 24 hours after birth. Their oxygenation index, a measure of how efficiently the lungs are working, was also significantly better compared to the group receiving standard lower pressures.
Working Together With Surfactant
Surfactant therapy and PEEP are complementary, but research suggests PEEP may actually be the more important factor in getting a newborn’s lungs to hold air. Studies in premature rabbits found that PEEP was more important than surfactant alone in recruiting functional lung volume. When both were used together, the combination produced better lung compliance and more even distribution of air throughout the lungs than either intervention alone.
This makes physiological sense. Surfactant lowers the surface tension inside air sacs so they don’t stick shut as easily, but it can only do its job if those air sacs are open in the first place. PEEP provides the mechanical scaffolding that keeps air sacs expanded, giving surfactant a stable environment to coat. Without PEEP, surfactant gets squeezed out of collapsing air sacs and loses its effectiveness. Without surfactant, higher pressures would be needed to achieve the same result, increasing the risk of overdistending healthy parts of the lung.
Reducing Time on the Ventilator
One of the most practical benefits of optimized PEEP is that it can shorten how long a newborn needs mechanical breathing support. In a study comparing higher PEEP to standard levels in newborns with respiratory distress syndrome, the higher PEEP group spent an average of 60 hours on the ventilator compared to 83 hours in the standard group. The higher PEEP group also needed zero additional hours of supplemental oxygen after coming off the ventilator, while the standard group averaged about 11 more hours.
The mechanism behind this is straightforward. When PEEP is too low, parts of the lung remain collapsed, and the air that does get delivered is unevenly distributed. The baby has to work harder to compensate for this inefficiency. Optimal PEEP recruits more air sacs into active duty, spreads incoming air more evenly, and reduces the areas of both collapse and overinflation. The lungs simply work better, so the baby can take over sooner.
How PEEP Is Delivered
PEEP can be delivered through several methods depending on how much support the baby needs. The least invasive approach is CPAP (continuous positive airway pressure), where constant pressure, usually 5 to 7 cmH₂O, is delivered through small nasal prongs. In this setup, the baby breathes on their own while the pressure simply keeps the lungs from deflating too much. One low-tech version called bubble CPAP creates this pressure by submerging the outflow tube in water so the baby exhales against the resistance of the water’s depth.
For babies who need more support, PEEP is built into mechanical ventilators as one component of the breathing cycle. The ventilator delivers a pressurized breath during inhalation, then maintains PEEP between breaths. If a baby on CPAP starts requiring higher oxygen concentrations or higher pressures, that’s a signal the medical team may need to move to full ventilator support.
Risks of Too Much PEEP
While PEEP is essential, more is not always better. Excessive pressure can overdistend air sacs that are already healthy, potentially causing air leaks where gas escapes from the lung into surrounding spaces. High PEEP also increases pressure inside the chest cavity, which can squeeze the heart and reduce how much blood it pumps with each beat. This effect on cardiac output is more pronounced when the lungs are relatively healthy and compliant, because more of that pressure gets transmitted to the heart rather than being absorbed by stiff lung tissue.
In practice, this means the sickest lungs (which are stiff and collapsed) tolerate higher PEEP levels well, while healthier lungs are more sensitive to the cardiovascular side effects. Earlier studies from the 1970s and 1980s raised concerns about PEEP reducing blood flow, though this was most common in babies who were already low on fluid volume and could often be managed with careful fluid support. The clinical team balances PEEP levels by monitoring oxygen levels, lung compliance, and blood pressure, adjusting up or down as the baby’s condition changes.