What is a Blood Gas?
A blood gas is a blood test that looks at the acid/base balance and oxygenation level in the blood. Blood gasses are some of the most common blood tests used in the NICU, as they pack a ton of information about a baby's health into just a few drops of blood.
In the NICU, you may hear blood gasses called many different names. A blood gas can be called an "ABG," for arterial blood gas, a "CBG," for capillary blood gas, or just a "gas." Other NICUs may have other terminology - in my NICU, we sometimes call them i-STATs after the brand name of the analysis machine.
NICU staff collects blood for a blood gas in different ways. If your baby has an umbilical artery catheter (UAC), blood can be drawn from the UAC without having to prick your baby. Blood gasses can also be collected with a heel prick or by inserting a needle into one of your baby's arteries or veins.
Understanding Blood Gas Results
When your baby has a blood gas, NICU staff can learn a lot from the results. A blood gas looks at:
- pH: Your baby's acid/base balance is measured by the pH. A low pH means that your baby's blood is acidotic; a high pH means that the blood is alkaline. Both conditions can be dangerous.
- Carbon dioxide: Carbon dioxide builds up in the blood when the baby is not breathing well, and can cause acidosis. Doctors lower carbon dioxide levels by making sure that your baby's airway is open or by increasing respiratory support. For example, a baby with a high carbon dioxide may need to be placed on CPAP or have his or her ventilator settings changed.
- Bicarbonate: Bicarbonate, or bicarb for short, is a measure of your baby's metabolic functioning. A high or low bicarb can have many causes, including sepsis, prolonged lack of oxygen, or problems with the heart, kidneys, or gut.
- Oxygen saturation: An arterial blood gas is an accurate measure of how much oxygen is in your baby's blood. Blood gasses drawn from a vein or from a heel prick are not good measures of oxygenation.
All blood gasses look at the measures listed above. Some tests may look at other measures of your baby's health in the blood sample, including glucose level, electrolytes, and hematocrit.
Why Do Preemies Need So Many Blood Gasses?
When a baby is in the NICU, parents often worry about how many blood tests their baby is getting. Doctors and nurses worry about it too! Too many blood tests can cause anemia, especially in preemies who have less blood to begin with in their tiny bodies.
Frequent blood gasses are common in the NICU, but for good reasons. It's important to make sure that babies are getting the very best respiratory support, especially since preemies are very sensitive to even small changes in ventilator settings and oxygen levels. The blood draws won't hurt your baby if he or she has an umbilical artery catheter or an arterial line. If blood gasses must be drawn via heel stick, NICU staff will be very gentle and will combine blood tests to minimize the number of painful procedures your baby needs.
Newborn Emergency Transport Service. "Blood Gas Interpretation" Neonatal Handbook Retrieved from http://www.netsvic.org.au/nets/handbook/index.cfm?doc_id=449
Karlesen, K. (2006) The S.T.A.B.L.E. Program Learner Manual (5th ed).
UCSF Children's Hospital. (2004) "Acid Base Balance." Intensive Care Nursery House Staff Manual. Retrieved from http://www.ucsfbenioffchildrens.org/pdf/manuals/19_AcidBaseBalance.pdf