What Does PEEP Help Achieve in NRP?

PEEP (positive end-expiratory pressure) is a small pressure kept in a baby’s airway after each breath during resuscitation, so the lungs never fully empty. Its main job in NRP is to help a newborn’s lungs switch from holding fluid to holding air, and then stay open. That makes it less about pushing air in and more about keeping what each breath gains from being lost before the next one. It works best at the right level, because the same pressure that holds the lungs open can, in excess, overstretch them and slow blood flow through them.

How PEEP Helps a Newborn’s Lungs Fill With Air and Stay Open

Before birth, a baby’s lungs are filled with liquid, not air. The first breaths, or the first assisted breaths, have to push that liquid out of the airways and into the lung tissue. Once air is in, the lungs need a cushion of it left over at the end of each breath out. That cushion is the resting air volume. In ventilated preterm newborn animals, a steady end-breath pressure was needed both to create that resting air volume and to keep it.¹

The first push to open stuck, wet air sacs takes the most effort. PEEP keeps each sac slightly open, so the next breath needs less effort. Without it, the lung goes back to flat after every breath and has to start again.

PEEP may not be enough on its own to keep pushing liquid down the airways.² It does appear to stop liquid from flooding back into the airways between breaths.³ In preterm newborn rabbits given breaths with no PEEP, air moved in and out but no resting air volume formed at all.⁴ With PEEP, the resting air volume grew with every breath, though not evenly across the lung.⁵ That resting volume gives oxygen a constant surface to pass into the blood, even between breaths, so oxygen levels stay steadier.

A long first inflation is another way to open the lungs. A single long opening breath built more resting air volume in the first minute, but PEEP kept the resting volume larger throughout the first seven minutes.⁶ Combining them worked best, yet PEEP had the greatest influence on how much and how evenly the lungs filled.⁷

At the bedside, a breath without PEEP can look fine: the chest rises with each squeeze and falls back fully on release, even though little air stays behind. The cue to watch is the baby’s response, especially a rising heart rate along with rising oxygen saturation, not chest rise on a single breath.

Protecting Fragile Lungs From Injury

Breathing for a baby at low lung volumes causes injury from air sacs collapsing and reopening over and over.⁸ Each time they snap open, shear forces act on delicate tissue.⁹ Very preterm babies are at high risk because they struggle to keep their upper airway open and to hold a resting air volume.¹⁰ Assisted breaths with too little PEEP leave too little air behind, no resting volume forms, and parts of the lung collapse.¹¹

Preterm lungs make less of their own surfactant, so air sacs collapse more easily. Their chest walls are soft and pull inward, letting the lung shrink, and their airways can close on their own. PEEP stands in for some of what a mature lung does naturally.

Surfactant is a slippery coating in the air sacs that lowers surface tension so they don’t stick shut. Repeated collapse also damages it.¹² In surfactant-treated preterm lambs, PEEP improved oxygen levels and lung stretchiness compared with no PEEP.¹³ PEEP also kept three to four times more surfactant in its working form.¹⁴ In preterm rabbits, mechanical breathing reduced how well given surfactant stuck to the lung compared with breathing on their own.¹⁵

Better Oxygen Levels and Steadier Breathing

During mechanical breathing, PEEP helps keep air sacs stable and holds the resting air volume.¹⁶ It also steadies the chest wall and upper airway, lowers resistance to airflow and reduces fluid in the air sacs.¹⁷ Breaths become larger and oxygen levels improve, with less lung collapse and fewer pauses from a blocked airway.¹⁸ In late preterm and term newborns with breathing distress, higher PEEP shortened time on a ventilator.¹⁹

Oxygen only enters the blood where open air sacs sit next to flowing blood vessels, so both have to line up. Blood passing collapsed sacs picks up almost no oxygen, and that poorly oxygenated blood mixes back into the rest of the circulation. Opening those sacs with PEEP lets more of the blood flow past air, so the oxygen level in the blood rises. This matching of air and blood flow is why PEEP can raise oxygen even when the oxygen concentration being given stays the same. Extra oxygen can’t reach the blood through collapsed air sacs, so teams adjust pressure to oxygen needs to avoid unneeded high pressures.²⁰

When PEEP is working, the baby’s oxygen reading on the pulse oximeter rises toward target. Chest movement becomes more even and less effort is needed. A rising heart rate is the most important sign that ventilation is working, and these signs guide whether to adjust support.

The gain from fine-tuning is modest. In babies on long-term ventilation, setting PEEP at an individually tested best level raised oxygen saturation by about 2 points on average, though not consistently.²¹

Does PEEP Save Lives, and for Which Babies

Across resuscitation studies, giving PEEP was linked to about 40% lower odds of death in preterm babies.²² The quality of that evidence is low to moderate.²³ It supports PEEP as standard for preterm babies without proving it is the only cause of better survival.

Resuscitation is hard to study, since babies cannot be randomly assigned to go without breathing support, so the evidence often comes from observational studies. Those can be affected by differences between babies who did and did not get PEEP, which is why the certainty is rated lower. Even so, the result agrees with how PEEP works in the lungs, so the biology and the data point the same way.

For term babies, no link between PEEP and death rates was found, and the evidence is limited.²⁴ PEEP is still commonly used when term babies need assisted breaths.

Many units start breathing support with CPAP in the delivery room for babies who are breathing and have a heart rate above 100.²⁵ This aims to avoid placing a breathing tube when possible.

How PEEP Is Delivered in Resuscitation

A T-piece resuscitator is a device where the clinician covers a hole to give a breath and a set pressure stays in the airway between breaths. A self-inflating bag refills on its own and needs an added valve to give PEEP. During real resuscitation, the T-piece delivered more PEEP and steadier breath pressures than the bag.²⁶

Using a T-piece, the team connects it to a gas supply and sets the peak inspiratory pressure and PEEP before the baby needs it. The clinician seals the mask on the baby’s face and covers the opening on the cap to deliver a breath, then lifts the finger to let the pressure fall back to the PEEP level. Because the gas keeps flowing, the set PEEP is held at the end of each breath, as long as the mask seal is good. The pressure gauge lets the team see what they are delivering, so settings can be checked rather than assumed.

Bag valves are far less dependable. In bench testing:

In a low-resource setting, switching to T-pieces for preterm babies cut delivery room intubations, surfactant use by about a third and air leaks by more than half.³¹ It did not significantly change death rates in very low birth weight babies.³²

For providers, the practical points are to know which device your unit uses and its PEEP limits. If you use a bag with a valve, don’t assume the dial equals what the baby gets, and check the manometer during breaths when one is available. A T-piece is preferred when PEEP matters most, as in preterm babies. A self-inflating bag is still kept nearby as a backup because it works without a gas supply.

When PEEP Becomes Too Much

The right PEEP can open lungs, improve oxygen and lower resistance in lung blood vessels without hurting circulation.³³ Too much pressure overstretches air sacs, raising that resistance and cutting blood returning to the left side of the heart.³⁴ In 50 ventilated newborns, raising PEEP reduced the output of the right side of the heart by about 17 ml per kilo per minute.³⁵ So clinicians aim for a middle ground, since more pressure is not better.³⁶

High pressure inside the lungs can squeeze the blood vessels running through them. That makes it harder for the right side of the heart to push blood through, so less blood returns to the left side and less is pumped to the body, which can lower blood pressure. Excessive pressure or inappropriate use can also overdistend the lungs and cause air leaks such as a collapsed lung.³⁷

Several signs suggest pressure may be too high. Oxygen levels stop improving or fall despite support, and heart rate or blood pressure may drop. One side of the chest may move less, a possible air leak. The team then rechecks the pressure and the baby’s chest.

Mask Leaks and Other Things That Undercut PEEP

Face mask leak and clinician skill both vary, making steady pressure hard to keep during stabilisation.³⁸ With a bag, making up for leak depends on bag size, squeeze and operator skill.³⁹ A good mask seal is therefore essential during assisted breathing.⁴⁰

PEEP depends on a closed system. When air escapes around the mask, the pressure inside the airway falls toward the outside air pressure, so a leak can cancel the benefit of a correctly set valve or T-piece.

To improve the seal, choose a mask that covers the mouth and nose but not the eyes. Use a firm, even grip and lift the jaw into the mask. If the chest doesn’t rise, reposition the head and mask, and watch the pressure gauge for drops that signal a leak.

Showing a breathing-function monitor during resuscitation lowered mask leak in some trials but not the largest.⁴¹ It reduced overly large breaths in two of three trials.⁴² It has not been shown to change air leak rates.⁴³