Oxygen saturation (SpO2) is a measurement indicating the percentage of hemoglobin in a child’s red blood cells that is bound to oxygen. Hemoglobin picks up oxygen in the lungs and transports it throughout the body. This measurement offers a quick, non-invasive assessment of how effectively a child’s respiratory system is functioning, signaling if the body is receiving the necessary oxygen. When this percentage drops, it signals that the body is not getting the oxygen it requires, which can affect the heart, brain, and other organs.
Understanding Oxygen Saturation Measurement
The primary way to estimate oxygen saturation outside of a hospital laboratory is through a pulse oximeter, a small device usually clipped onto a child’s finger or toe. This non-invasive device works by shining two specific wavelengths of light, red and infrared, through the skin. Oxygenated and deoxygenated hemoglobin absorb these light wavelengths differently, allowing the oximeter to calculate the SpO2 by measuring the ratio of light absorption.
The pulse oximeter measures peripheral oxygen saturation (SpO2). This method is distinct from an arterial blood gas (ABG) test, which is an accurate but invasive procedure requiring a blood sample drawn from an artery to measure the partial pressure of oxygen (PaO2). The pulse oximeter provides a quick and painless reading that is sufficient for routine monitoring at home or in a clinic.
To ensure an accurate reading, the child must remain still for one to two minutes, allowing the device to stabilize the measurement. The sensor should be placed correctly, typically on the middle or index finger, or the great toe in infants. Fingernail polish or artificial nails must be removed, as these can interfere with the light signals and produce a false reading. Cold hands or poor circulation can also affect the results, sometimes requiring the extremity to be warmed first.
Defining Normal O2 Levels in Children
For a healthy child at sea level, the normal range for oxygen saturation is considered to be between 95% and 100%. Readings within this range indicate that the child’s body is efficiently distributing oxygen from the lungs to the bloodstream. The 95% threshold remains the widely accepted lower limit for general health.
A sustained reading below 95% is typically considered abnormal and warrants further evaluation. However, there are nuances based on the child’s age and environment. For newborns, a saturation level between 90% and 95% may be considered normal during the first few minutes of life, but this should quickly rise to the standard range. In children with chronic heart or lung conditions, a slightly lower level, such as 92% to 94%, may be deemed acceptable by their healthcare provider.
The geographical location can also slightly influence the baseline reading. Children living at high altitudes naturally have a marginally lower oxygen saturation due to the lower atmospheric oxygen content. While a reading slightly below 95% may be expected at very high elevations, a saturation under 92% is still an indication for concern and professional assessment.
Identifying Causes of Low O2 (Hypoxemia)
A low oxygen saturation reading is the primary indicator of hypoxemia. This condition is almost always a symptom of an underlying medical condition or acute event that affects the body’s ability to take in or distribute oxygen, often involving respiratory illnesses that obstruct the airways or damage the lungs.
Acute respiratory infections like pneumonia, bronchiolitis, and severe cases of influenza or COVID-19 can cause inflammation and fluid buildup in the lungs, hindering oxygen exchange. Asthma exacerbations are another frequent cause, where the airways constrict and swell, making it difficult for air to reach the deeper parts of the lungs. A mechanical obstruction, such as choking on a foreign object, can also dramatically and suddenly drop oxygen levels by physically blocking airflow.
In some children, low oxygen is related to structural issues with the heart or lungs. Certain congenital heart defects can cause deoxygenated and oxygenated blood to mix, leading to lower systemic oxygen saturation. Conditions like obstructive sleep apnea, where breathing repeatedly stops or becomes shallow during sleep, can also result in intermittent hypoxemia. Anemia, a low red blood cell count, can also contribute to hypoxemia because there are fewer hemoglobin molecules available to transport oxygen.
When to Seek Immediate Medical Help
If a child’s pulse oximeter reading is consistently below 92%, or if it drops below 90% at any point, immediate medical attention is required. However, the reading alone is not the only factor to consider, as physical signs of respiratory distress can be equally important.
Parents should immediately call emergency services if the child exhibits visual signs of severe breathing difficulty, regardless of the pulse oximeter number. These signs indicate severe oxygen deprivation:
- A bluish discoloration around the lips, tongue, or fingernails.
- Signs that the child is working extremely hard to breathe, such as nasal flaring or retractions (where the skin visibly pulls in between the ribs, above the collarbone, or at the neck).
- An unusually rapid or shallow breathing rate.
- Grunting sounds with each breath out, or an inability to speak in full sentences.
- A change in mental status, such as lethargy, confusion, or difficulty waking up.
A change in mental status is a serious indication of low oxygen affecting the brain. While awaiting medical assistance, keep the child calm and try to reposition them into a comfortable position, often sitting upright, to help maximize lung expansion.