A pulse oximeter is a non-invasive device that uses light to estimate oxygen saturation (\(\text{SpO}_2\)) and the patient’s pulse rate. The foot is frequently the preferred application site for infants and neonates because their fingers are often too small for accurate sensor placement, and the foot offers a large, fleshy area for contact. Monitoring the foot provides a post-ductal reading, which is compared to a pre-ductal reading (usually from the right hand) to screen for critical congenital heart disease. Proper placement is important because the device relies on pulsatile blood flow to accurately determine how efficiently oxygen is being delivered to the extremities.
Preparing the Device and Infant
Confirm the pulse oximeter system is designed for pediatric or neonatal use, as adult clip-style sensors are too large and will yield inaccurate results. Select a sensor size, typically a wrap-around or adhesive style, that matches the infant’s foot size to ensure optimal skin contact. Verify the device is charged or properly connected to a power source. If the sensor is reusable, it must be clean according to manufacturer guidelines to avoid errors and infection.
Preparing the infant centers on optimizing blood flow to the measurement site, as poor circulation severely impedes the reading. The baby should be calm and warm, as crying or shivering introduces movement artifact, while cold extremities cause peripheral vasoconstriction. Remove any clothing, socks, or lotions from the foot. Gently warm the foot if it feels cool to the touch, which can be accomplished by swaddling the baby. The skin should be clean and dry before attempting sensor application.
Step-by-Step Sensor Application
The most effective placement site is the fleshy, outer side of the sole, or the side of the foot just below the pinky toe. This location provides sufficient tissue depth for the light to pass through the capillary bed and avoids the bony structure of the heel, which can obstruct the light path and cause scattering. The sensor is comprised of a light emitter and a photodetector, which must be positioned directly opposite each other on the skin. This precise alignment ensures the detector accurately measures the light that has passed through the pulsatile arterial blood.
The wrap-style or adhesive sensor is secured around the foot to hold the emitter and detector in place without any gaps between the sensor and the skin. Use the accompanying disposable wrap or adhesive, ensuring it is snug but not constrictive, which would compromise blood flow and result in a low signal. A good practice is to be able to comfortably slip a finger between the wrap and the baby’s skin. The sensor cable should be routed away from the foot, typically up the ankle and leg, and secured loosely with medical tape to prevent the infant from accidentally dislodging it.
Once secured, ensure the sensor cable connection to the main monitoring unit is firm and free of kinks or tension. The light from the emitter should be visible through the skin if the sensor is correctly placed and functioning. A stable reading should appear within several seconds after a consistent pulse signal is established. The sensor site should be checked regularly, at least every two to four hours during continuous monitoring, to ensure skin integrity and prevent irritation.
Addressing Common Issues for Accurate Readings
Inaccurate or inconsistent readings often stem from a phenomenon called movement artifact, where the baby’s movements interfere with the light-based measurement. If the reading is erratic, check if the infant is crying, fussing, or kicking. Try to stabilize the foot or wait for a period of quiet rest or sleep to obtain a stable signal. Swaddling the baby can help limit movement and promote the calm state necessary for an accurate reading.
Another frequent issue is ambient light interference, where external light sources, such as overhead room lights or a phototherapy lamp, overwhelm the sensor’s photodetector. This interference can be mitigated by lightly covering the sensor and the baby’s foot with a blanket or cloth to block the extraneous light from reaching the sensor.
If the monitor repeatedly displays a “low signal” or “no pulse” message, the first step is to re-evaluate the sensor placement and alignment, confirming the emitter and detector are exactly opposite each other. The second check involves ensuring the foot is warm, as cold reduces the blood flow needed for a reliable signal, and gently rewarming the extremity may resolve the issue. Finally, confirm that the sensor cable is securely plugged into the monitor, as a loose connection can mimic a signal failure.