A pulse oximeter is a non-invasive medical device that measures two indicators of a newborn’s health: the oxygen saturation level (SpO2) and the pulse rate. This monitoring tool works by shining a light through thin tissue, such as a hand or foot, and measuring how much light is absorbed by the oxygen-carrying hemoglobin in the red blood cells. The measurement provides a percentage indicating the amount of oxygen relative to the total hemoglobin present. Accurate oxygen monitoring is important in neonatal care as it helps medical professionals observe the infant’s transition to breathing outside the womb. This simple and painless test is a standard part of newborn screening protocols.
Standard Placement for Newborn Screening
The specific placement of the pulse oximeter on a newborn is determined by the screening protocol for Critical Congenital Heart Disease (CCHD). This screening requires a two-site measurement to compare oxygen levels in two different areas of the infant’s circulation. The first mandatory site is the right hand, which provides the pre-ductal oxygen saturation reading. The second mandatory site is either foot, typically the sole or heel, which provides the post-ductal reading.
These two measurements are taken either simultaneously using two sensors or sequentially to ensure a valid comparison. The overall screening is considered passed if both readings are 95% or higher and the difference between the two sites is 3% or less.
This two-site testing is performed typically after the baby is 24 hours old to allow for the normal physiological transition following birth. Comparing the oxygen saturation between the upper and lower body extremities helps identify specific types of heart defects before the baby leaves the hospital.
Understanding Pre-Ductal and Post-Ductal Flow
The requirement for two distinct measurement sites is rooted in the unique circulatory system of a newborn baby. During fetal development, a temporary vessel called the ductus arteriosus connects the pulmonary artery directly to the aorta, allowing blood to bypass the lungs. This connection usually begins to close shortly after birth as the baby starts breathing air.
The pre-ductal circulation refers to blood flow that branches off the aorta before the ductus arteriosus. Placing the sensor on the right hand measures this pre-ductal blood, which is generally the most oxygenated blood available to the infant’s body. Conversely, the post-ductal circulation is the blood flow that travels through the aorta after the ductus arteriosus connection. The measurement taken from the foot reflects this post-ductal blood, which may be mixed with deoxygenated blood if the ductus arteriosus remains open and abnormal shunting is occurring.
A significant difference between the pre-ductal (right hand) and post-ductal (foot) saturation readings suggests the presence of right-to-left shunting. This shunting indicates that deoxygenated blood from the pulmonary artery is mixing with the oxygenated blood in the aorta through the patent ductus arteriosus. The comparison between the two sites is a powerful way to detect CCHD, where this mixing of blood can cause dangerously low oxygen levels in the lower half of the body.
Techniques for Reliable Readings
Obtaining an accurate pulse oximetry reading on a newborn requires careful attention to the application technique. Specialized neonatal sensors, often soft wraps or sleeves, must be used instead of adult clips, as they are specifically designed for the size and fragile skin of an infant. The sensor should be positioned so the light emitter and the light detector are directly opposite each other on the thin part of the hand or foot.
The sensor must fit snugly against the skin to prevent light leakage but should not be wrapped so tightly that it restricts blood flow, which would lead to an inaccurate reading. Maintaining a warm, calm environment for the infant helps ensure peripheral circulation is adequate, since cold extremities can decrease perfusion and compromise the accuracy of the reading.
Excessive movement, crying, or shivering can also interfere with the signal, so minimizing motion is helpful during the measurement period. Ambient light, such as phototherapy lamps, can sometimes skew the reading, so the sensor is often temporarily turned off or shielded to ensure the device is reading only the light it emits.