Respiratory Syncytial Virus (RSV) is a highly contagious virus and a frequent cause of lower respiratory tract infection in infants and young children. When RSV spreads into the lungs, it causes bronchiolitis, which is the inflammation of the tiny airways called bronchioles. This inflammation leads to swelling and excessive mucus production, obstructing these small passages. This obstruction interferes with the normal exchange of gases, causing the amount of oxygen reaching the bloodstream to drop, making breathing difficult.
Understanding Oxygen Saturation (SpO2) Measurement
The concentration of oxygen in a baby’s blood is measured using oxygen saturation, or SpO2. This value represents the percentage of hemoglobin molecules in red blood cells that are carrying oxygen. Hemoglobin is the protein that transports oxygen from the lungs to the body’s tissues.
Oxygen saturation is determined non-invasively using a pulse oximeter. This small device is typically clipped onto an infant’s finger, toe, or foot. The oximeter works by shining light through the tissue and measuring how much of that light is absorbed by the blood, which allows it to calculate the ratio of oxygenated to deoxygenated hemoglobin.
For a healthy infant breathing normally, an SpO2 reading of 95% or higher is the expected range. Readings at this level indicate that the vast majority of the hemoglobin is successfully transporting oxygen throughout the body. The pulse oximeter provides a continuous number that helps caregivers and medical professionals assess the efficiency of the infant’s breathing.
Defining the Critical Oxygen Threshold in Infants with RSV
Determining the point at which an oxygen level becomes too low in an infant with RSV is guided by clinical consensus and the child’s overall condition. While a reading above 95% is normal for a healthy baby, a drop into the low 90s for an infant with bronchiolitis signals that the lungs are struggling to keep up with oxygen demand. A consistently low SpO2 indicates hypoxemia, meaning insufficient oxygen is delivered to vital organs like the brain and heart.
The threshold for medical concern and intervention falls between 90% and 92%. Many hospitals use a sustained reading below 90% as the firm point for initiating supplemental oxygen therapy. This number is used because the relationship between oxygen saturation and the partial pressure of oxygen in the blood changes significantly around this point. A small further drop in saturation can lead to a drastic reduction in available oxygen.
For infants hospitalized with RSV who are stable and receiving supportive care, maintaining an SpO2 of 90% or greater is often sufficient. If an infant’s reading drops below 90% and remains there, it is a clear indication that emergency medical attention is necessary. This sustained low reading suggests the body’s compensatory mechanisms are failing and additional respiratory support is needed.
Parents monitoring an infant at home should treat any reading that falls below 92% as a serious warning sign. If the reading drops to 90% or lower and does not immediately improve, or if the infant also shows signs of increased breathing effort, seek emergency care immediately. This limit ensures the infant receives timely intervention to prevent tissue damage from oxygen deprivation.
Recognizing Clinical Signs of Respiratory Distress
Even without a pulse oximeter, parents can recognize several visible and audible signs that an infant’s oxygen level may be low due to RSV. These signs reflect the infant’s intense physical effort to pull enough air into the obstructed airways. One of the clearest indicators is a noticeable change in the rate and depth of breathing.
The infant may begin breathing much faster than normal, or have periods of shallow breathing or temporary pauses known as apnea. Look closely at the chest and neck area for retractions, which appear as the skin sucking in sharply beneath the ribs, above the collarbone, or at the notch of the neck with every breath. These retractions demonstrate the use of accessory muscles to force air in and out of the lungs.
Other visual and audible signs include:
- Nasal flaring: The nostrils spread open wider during inhalation in an attempt to draw in more air.
- Grunting: An audible sign that the infant is trying to keep air sacs in the lungs open by exhaling against a partially closed airway.
When oxygen deprivation is severe, a bluish discoloration, known as cyanosis, may appear around the lips, on the tongue, or beneath the fingernails. Cyanosis is a late and serious symptom requiring immediate emergency care. If these signs of labored breathing are present, especially if they are worsening or combined with lethargy or a significant decrease in feeding, emergency medical help should be sought at once.
Medical Management of Hypoxemia in Infants
When an infant with RSV-related hypoxemia is admitted to the hospital, the primary goal is to provide supportive care until the virus runs its course. The first line of treatment involves delivering supplemental oxygen to raise the SpO2 back to a safe level, typically using a nasal cannula. This helps overcome the reduced gas exchange caused by the inflammation in the bronchioles.
Airway clearance is a component of care, as the virus causes excessive, thick secretions. Nurses use saline drops and gentle suctioning to remove this mucus, which reduces the effort required for breathing. Adequate hydration is maintained, often through intravenous fluids, because the infant may be too fatigued to feed effectively and rapid breathing increases fluid loss.
For infants with significant respiratory compromise, advanced support may be employed. This includes a high-flow nasal cannula (HFNC), which delivers warm, humidified oxygen at a high flow rate. Non-invasive ventilation methods like Continuous Positive Airway Pressure (CPAP) can also be used to keep the airways open. In the most severe cases of respiratory failure, the infant may require intubation and mechanical ventilation to support breathing while the lungs recover.