Oxygen saturation (SpO2) measures the percentage of hemoglobin in the blood carrying oxygen. Hemoglobin is the protein within red blood cells responsible for binding to oxygen and transporting it to the body’s tissues and organs. Monitoring this level in infants assesses the efficiency of their respiratory and circulatory systems. A low SpO2 can signal a potential problem with a baby’s breathing, lungs, or heart. Caregivers use this measurement as an important sign of a baby’s overall health, especially since oxygen is vital for healthy growth and brain development.
How Oxygen Saturation is Measured
The measurement of SpO2 is typically done non-invasively using a pulse oximeter. This painless test involves placing a soft sensor probe on a baby’s hand, finger, toe, or foot. The sensor shines red and infrared light through the skin. Oxygenated and deoxygenated hemoglobin absorb these light wavelengths differently; by analyzing the absorption ratio, the device calculates the SpO2 percentage and displays the baby’s pulse rate. Accurate readings require the baby to be relatively still and the probe correctly secured.
Normal Oxygen Levels for Infants
For a healthy, full-term infant breathing room air, the normal range for oxygen saturation is between 95% and 100%. The goal is to maintain a saturation level above 95%; a reading below this may warrant further observation. Immediately after birth, a newborn’s SpO2 levels are naturally lower as their lungs adjust to breathing outside the womb. It takes a healthy term newborn approximately five to ten minutes to reach a saturation greater than 90%, with levels stabilizing into the higher expected range after 24 to 48 hours. Preterm infants or babies with pre-existing lung conditions may have different target ranges set by their medical team, often targeting a slightly lower range (e.g., 91% to 95%) to avoid excessive oxygen levels which can be harmful to developing eyes and lungs.
Common Factors Affecting Readings
A pulse oximeter reading that appears low is not always an indication of a true medical problem. Technical errors are frequent, often due to the sensor probe being improperly placed or becoming detached. Cold extremities can significantly reduce blood flow to the sensor area, leading to a falsely low or erratic reading. Movement is a common cause of unreliable readings, as a baby who is squirming, shivering, or crying introduces motion artifacts that interfere with the light absorption analysis. Intense ambient light shining directly on the sensor or residue on the skin from lotions can also affect the results.
Recognizing a Medical Emergency
While temporary low readings can be caused by technical issues, a sustained low oxygen saturation is a serious sign of hypoxemia, or insufficient oxygen in the blood. The threshold for serious concern is typically a reading that remains below 90% to 92% for several minutes, especially if the baby appears unwell; if the reading is consistently below this level, immediate medical attention is necessary. Physical signs of respiratory distress will often accompany a true drop in oxygen saturation, including a bluish discoloration around the mouth, lips, or fingernails (cyanosis). Other observable signs are rapid breathing, flaring of the nostrils, or a grunting sound with each exhale, which is the body’s attempt to keep the air sacs open. Caregivers may also notice retractions, where the skin pulls in sharply between the ribs, under the ribcage, or at the neck as the baby struggles to breathe, along with lethargy or an increased heart rate.