Bradycardia and Apnea in Premature Babies

In premature babies, apnea and bradycardia often occur together, along with low blood oxygen levels. Apnea is a period when breathing briefly stops. It often triggers bradycardia, which is a slow heartbeat.

First, apnea occurs and the baby will stop breathing. Because the baby isn’t breathing, blood oxygen levels will fall. The heart slows down in response to the low blood oxygen levels.

Apnea and bradycardia are often called “the As and Bs” or "spells." Understandably, the condition can be nerve-racking for parents who are already anxious over having a baby born at 37 weeks or less.

This article explains apnea and bradycardia, their respective causes, the long-term effects, and the available treatment options.

Oxygen Saturation

Oxygen saturation measures the amount of oxygen-carrying hemoglobin in the blood. The blood of a full-term baby, like that of a child or adult, should be 95% to 100% saturated with oxygen.

The blood of a premature baby receiving extra oxygen is usually maintained between about 88% and 94% saturation, not higher, to prevent retinopathy of prematurity, a serious eye condition.

In the hospital, pulse oximetry is used to measure the amount of oxygen in the blood. When the blood does not have enough oxygen, it is called a desaturation. Desaturations can cause a bluish tint to the lips or skin and cause a baby to lose tone, becoming “floppy.”

Apnea

Apnea means a period in which breathing stops. In premature babies, apnea is any pause in breathing that lasts longer than 20 seconds, causing bradycardia, or a drop in the baby’s blood oxygen level. 

If the pause lasts longer than 20 seconds, the premature baby (already hooked up to a monitor) may need a "reminder" to start breathing. In this case, the monitor will trip an alarm. If the alarm doesn't inspire the baby to breathe, a nurse will gently jostle the baby or rub their back until the baby breathes on their own. This is standard operating procedure in most neonatal intensive care units (NICU).

Bradycardia

Bradycardia usually results from a baby having apnea. Bradycardia means a slower than normal heart rhythm. In newborns, a heart rate is deemed to be bradycardia if it falls below 100 beats per minute in a baby less than 1,250 grams (or 2 pounds, 12 ounces) or to less than 80 beats per minute in a bigger baby. 

Neonatal nurses are usually well-trained to deal with the As and Bs. For example, they take note of how often these events occur, how long they last, and how much stimulation a baby needs to resume breathing.

Causes

Usually, there's a simple reason why apnea and bradycardia are common in premature babies: Their nervous system hasn't finished developing. And without the full resources of the brain's respiratory center, the lungs aren't "notified" to take regular breaths. Nearly half of babies that weigh less than 5 ½ pounds are prone to have some apnea. 

Apnea occurs because the process in the brain that tells the baby to breathe fails. As a result, the baby stops breathing repeatedly, which is called central sleep apnea. If the baby’s immature muscular system isn't strong enough to keep the airway open, the condition is called obstructive sleep apnea.

The As and Bs can be traced to other causes, too, such as an infection, anemia, and neurological problems. But by far the most likely culprit is what's called the "apnea and bradycardia of prematurity." As a baby's gestational age increases, the severity of the condition decreases. Put another way, the more time a baby's central nervous system has to develop, the less likely they will be born with the As and Bs.

Long-Term Effects

Doctors aren’t sure what the long-term effects of apnea and bradycardia are. They know that bradycardia causes a temporary reduction in the brain’s blood and oxygen levels. They also know that premature infants who had more days with recorded episodes of apnea have lower scores at age 3 on tests that measure developmental and neurological outcomes. However, they can’t say for certain that apnea and bradycardia cause the lower scores.

One thing that doctors do know is that apnea and bradycardia do not directly cause sudden infant death syndrome (SIDS), though it's possible that these infants could face a higher risk. Says the Emory University School of Medicine: "While apnea of prematurity and SIDS are different problems, some babies who need NICU care may have a slight increased risk of later SIDS. We cannot predict which infants are at risk; there is no guarantee that a baby will not develop SIDS later. But the vast majority of infants will not be at risk and will not need monitors."

Treatment

If the baby has only occasional episodes that respond to gentle stimulation—a rub on the back, a jiggling of the hand—no further treatment may be needed except to monitor the baby until the episodes stop. If the baby shows a change in color—by turning pale or blue—a nurse may give the baby extra oxygen.

If the events are due to infection or other problems, then treating the problem will often cause the episodes to stop, too.

Babies who have frequent bouts of apnea may be placed on continuous positive airway pressure (CPAP) to help them breathe. Medication can also be used to treat apnea (and bradycardia) of prematurity. Caffeine is a relatively new treatment for apnea that has few side effects and has been largely successful.

Preventing Further Spells

Knowing what triggers episodes of apnea and bradycardia can help nurses and parents minimize the number of spells that premature babies experience. Apnea and bradycardia tend to occur during transitions out of deep sleep, so prenatal nurses know that it's important to indulge babies with long periods of deep sleep.

As a parent, you may wish to coordinate your visits to the NICU with feeding and assessment times. And use an "indoor voice" if you're visiting while your baby is sleeping. Fluctuations in incubator temperatures can also cause As and Bs. So try to maintain a stable temperature in the incubator by keeping incubator doors closed as much as possible.

When Will It Go Away?

The good news for parents? Once a "preemie" matures and is ready to go home (about the time of the baby's due date), the baby is often no longer at risk for the As and Bs. However, some babies mature slower than others and may still experience an occasional event. In this case, a home apnea monitoring system and/or pediatric medication may be necessary.

Remember too that your baby will be eating and drinking and gaining strength with each passing day. When physicians say that the vast majority of babies literally "outgrow" the As and Bs, they genuinely mean it.

Summary

Apnea and bradycardia are called “the As and Bs” because they usually occur together. Apnea is a brief period of time (no longer than 20 seconds) when a baby's breathing stops. This state often triggers bradycardia, which is a low heart rate. There's a simple and straightforward reason why the As and Bs torment the parents of a premature baby: The baby's nervous system hasn't finished developing. And without the complete resources of the brain's respiratory center, the lungs aren't "told" to take regular breaths. So they don't. Most premature babies outgrow the As and Bs by the time they're ready to go home from the hospital.

A Word From Verywell

The As and Bs usually result in a quick and happy ending for the parents of a premature baby. These babies often demonstrate no lasting effects of the condition, either. But there's always a lesson to be learned from a health scare, and physicians might say that parents would be wise to sign up for a cardiopulmonary resuscitation (CPR) class. Arguably, it's a smart move for anyone who is responsible for the life and safety of a human being of any age.