The Correlation of CO2 Measured by SenTec Transcutaneous Monitoring With Arterial Blood Gas CO2 Levels in Neonates

Background and Significance/Preliminary Studies Carbon dioxide (CO2) measurement is part of the fundamental respiratory evaluation in an ICU, as both high and low values of CO2 can have detrimental effects on neonatal health. The partial pressure of CO2 reflects ventilation, which is the elimination of carbon dioxide. The ABG sample is the clinical tool most commonly used to evaluate acid-base physiology at the bedside. It directly measures the pH, arterial partial pressure of oxygen, and arterial partial pressure of CO2. Though direct measurement of CO2 in the arterial blood is the most accurate way to assess the amount of CO2, it requires blood sampling from the arteries and does not provide continuous monitoring of CO2.

A non-invasive tool for measuring PaCO2, such as the SenTec monitor, can help decrease blood draws, thereby decreasing the incidence of iatrogenic anemia and the need for neonatal blood transfusions. Blood samples are collected through arterial lines, capillary heel sticks, or peripheral arterial punctures which are invasive and can be painful for the patient and may potentially result in injury. Although an ABG in neonates typically only requires 0.3mL-0.5mL of arterial blood, the need for frequent ABG sampling (every two to six hours) may result in a significant amount of iatrogenic blood loss. A newborn has a total blood volume of only 80mL/kg. In addition, the transcutaneous sensor has potential monitoring advantages as measurements are continuous rather than representative of a single point in time, as seen in ABGs. Continuous monitoring can help to avoid fluctuations in CO2 levels which can potentially result in neurologic injury in preterm babies, such as intraventricular hemorrhage and periventricular leukomalacia. One of the most beneficial aspects of the SenTec monitor is that it displays CO2 levels in real time, allowing clinicians to monitor trends and to intervene sooner if needed.

Previous studies have been conducted on transcutaneous monitors in newborns. One such study evaluated the CO-OXSYS Digital Sensor (also known as the V-Sign Digital Sensor) made by SenTec. 25 patients between the ages of 10 months to 79 years of age were studied. Each sensor was placed on the tragus of each patient's ear. An ABG was obtained fifteen minutes after sensor application and TCCO2 measurements were recorded at the same time. ABG samples were analyzed with a Rapidpoint 405 analyzer. A reliable correlation was found between the TCCO2 and the PaCO2 readings (R2-0.61, p=<0.001). It was noted that age and temperature did not affect the accuracy of the CO2 readings. This study concluded that with more sampling, the CO-OXSYS Digital Sensor would be useful in a variety of clinical settings.

A second study was performed assessing the SenTec monitor during neonatal High Frequency Oscillatory Ventilation. Fourteen neonatal patients were studied. The digital sensor was applied to each patient on varying body parts that included the left chest, right chest, and liver. Fifteen minutes after sensor application, an ABG was obtained and the simultaneously displayed TCCO2 measurement was recorded. ABG measurements were subsequently analyzed using a Siemens Rapidpoint 405 analyzer. A clinically acceptable correlation was found between the TCCO2 and PaCO2 readings (R2=0.807, p=<0.001). This study suggested the monitor could certainly be used as an alternative to ABGs.

In 2004 a study reviewed the TOSCA monitor, made by Linde Medical Sensors, which combined pulse oximetry and TCCO2 monitoring. This machine used a single ear sensor which worked at 42 degrees C to enhance blood flow in capillaries below the sensor. This study included 60 neonates who had an ear sensor placed on the right earlobe. Ten minutes after placement, an ABG was performed and compared to the TCCO2 reading. The transcutaneous readings were found to be clinically acceptable when compared to the ABGs. A secondary benefit of the transcutaneous monitoring on the earlobe was a decrease in the head movement of the neonate to aid in maintaining a patent airway. In addition, the sensor did not have to be removed for chest radiographs or while the parent was bonding with his or her infant in their lap (also known as "kangaroo care").