What Is a Blood Gas?
A blood gas is a blood test that helps the NICU team understand how well your baby is breathing and how their body is maintaining its normal chemical balance.
Blood gases are commonly checked in premature babies, especially those who need breathing support.
The results help the healthcare team determine whether your baby's lungs are removing carbon dioxide effectively and whether adjustments to respiratory support may be needed.
A blood gas is one piece of information the NICU team uses to evaluate your baby's condition.
Why Does My Baby Need a Blood Gas?
Your baby may need a blood gas if they:
Are receiving oxygen or respiratory support
Are using CPAP or a ventilator
Have increased work of breathing
Are experiencing frequent desaturations
Have changes in their breathing pattern
Need monitoring after a change in respiratory support
Blood gases may also be checked when the healthcare team is concerned about other medical conditions that can affect the body's acid-base balance.
What Are the Different Types of Blood Gases?
You may hear the NICU team use the terms ABG, CBG, or VBG.
These describe where the blood sample comes from.
ABG — Arterial Blood Gas
Blood collected from an artery.
An arterial blood gas provides information about carbon dioxide, acid-base balance, and oxygen levels in arterial blood.
CBG — Capillary Blood Gas
Blood collected from tiny blood vessels, often through a heel stick.
Capillary blood gases are commonly used to monitor carbon dioxide and acid-base balance. They are less reliable for measuring oxygen levels.
VBG — Venous Blood Gas
Blood collected from a vein.
Venous blood gases can help assess acid-base balance and provide information about carbon dioxide, although the values differ from arterial measurements.
The healthcare team chooses the type of blood gas based on the information needed and your baby's condition.
What Do the Blood Gas Numbers Mean?
Several measurements appear on a blood gas report.
Here are the most important ones explained simply.
pH — Is the Blood Too Acidic or Too Alkaline?
The pH measures the acid-base balance of the blood.
The body works to keep this balance within a healthy range.
Changes in pH may occur when a baby has difficulty breathing or when other medical conditions affect the body's chemistry.
pCO₂ — How Well Is My Baby Removing Carbon Dioxide?
Carbon dioxide (CO₂) is a gas the body produces naturally.
The lungs remove it when we breathe out.
If carbon dioxide builds up, it may mean your baby is not moving enough air in and out of the lungs.
The NICU team uses this measurement to help evaluate breathing and respiratory support.
pO₂ — How Much Oxygen Is Dissolved in the Blood?
This measurement provides information about oxygen in the blood.
It is most useful when measured from an arterial sample.
Capillary and venous pO₂ values cannot be interpreted the same way as arterial oxygen measurements.
Your baby's oxygen saturation monitor also helps the team assess oxygenation.
HCO₃ — Bicarbonate
Bicarbonate helps the body maintain a healthy acid-base balance.
Changes may occur with breathing problems or other medical conditions.
Base Excess
Base excess is another measurement that helps the healthcare team understand the body's acid-base balance.
It provides additional information when evaluating certain medical conditions.
Parents generally do not need to interpret bicarbonate or base excess values independently.
Does an Abnormal Blood Gas Mean Something Is Wrong?
Not necessarily.
Blood gas values can change depending on your baby's gestational age, medical condition, and type of respiratory support.
Some premature babies have blood gas results outside typical adult ranges that are acceptable for their individual situation.
The NICU team looks at the overall pattern rather than focusing on one number.
A blood gas result is not interpreted by itself.
Your baby's breathing, oxygen saturation, physical examination, and other findings are equally important.
How Does a Blood Gas Help With Respiratory Support?
Blood gases can help the NICU team determine whether your baby needs changes in breathing support.
For example, results may help guide adjustments to:
Ventilator settings
CPAP or other respiratory support
The amount of assistance your baby receives with breathing
The team also considers oxygen saturation, work of breathing, and your baby's overall stability.
Not every blood gas result requires a change in treatment.
Will My Baby Need Frequent Blood Gases?
Some babies need blood gases more often than others.
A baby receiving significant ventilator support may require more frequent testing.
As breathing improves and respiratory support decreases, blood gases may become less frequent.
The healthcare team tries to limit unnecessary blood draws, especially in premature babies.
What Can Parents Ask?
If your baby has a blood gas checked, consider asking:
Why was a blood gas needed?
Was the result reassuring?
Is my baby removing carbon dioxide adequately?
Did the results indicate a need to change breathing support?
Will another blood gas be needed?
You do not need to memorize all the numbers to understand your baby's progress.
What Should Parents Know?
Blood gases help the NICU team evaluate breathing and the body's acid-base balance.
They are particularly useful for babies receiving respiratory support.
The two measurements parents may hear discussed most often are pH and carbon dioxide (pCO₂).
Other measurements provide additional information that helps the healthcare team make treatment decisions.
One abnormal number does not necessarily mean your baby is getting worse.
The most important thing is how your baby is doing overall and whether their breathing support is meeting their needs.
