Non-Invasive Monitoring of Partial Pressure of Carbon Dioxide in Mechanically Ventilated Preterm Infants

Background: In mechanically ventilated preterm infants, the ability to monitor carbon dioxide partial pressure (pCO2) values is indispensable. The gold standard for pCO2 measurement is from an arterial blood sample (paCO2). This has two drawbacks: firstly, it requires an arterial line and, secondly, it does not provide the clinicians with a continuous measurement. At present, two alternative pCO2 monitoring systems are available in the field of neonatal intensive care medicine: end-tidal CO2 (etCO2) capnography and transcutaneous CO2 (tcCO2) measurements. Both methods have disadvantages including potential technical errors as well as pathologies that may reduce reliability as a surrogate for blood gas analysis (BGA). In particular, conventional side-stream etCO2 capnography underestimates pCO2 in presence of a tube leakage, which is a common occurrence in ventilated preterm infants where only tubes without cuff are used. Distal etCO2 (detCO2) by means of a double lumen endo-tracheal tube may solve the problem of unreliable etCO2 values in the presence of tube leakage.

Several studies compared etCO2 and tcCO2 to paCO2, simultaneously. A comparison study of etCO2 and tcCO2 in a cohort of critically ill children did not reveal significant differences in the absence of severe pulmonary parenchymal disease. Tobias et al compared etCO2 and tcCO2 in a cohort of pediatric intensive care patients with respiratory failure and found tcCO2 measurements to be more accurate. In a cohort of ventilated newborns, tcCO2 monitoring was generally more precise than etCO2 during neonatal transport to monitor ventilation. In a more recent study restricted to a cohort of postsurgical neonates without lung disease, etCO2 underestimated paCO2 more than tcCO2 but provided greater precision over paCO2, however it was less accurate at smaller tidal volumes. These studies have in common that the adapter of the pCO2 analyzer was attached in-line and proximal to the endotracheal tube.

Aim of the study: The aim of this study is to compare the agreement, precision and repeatability of the distal etCO2-measurement technique described by Kugelman et al. with respect to paCO2 and tcCO2 in mechanically ventilated preterm infants. Since ventilation strategies and pCO2 limits may vary among different centers, this study helps to determine which non-invasive CO2 monitoring system (detCO2 or tcO2) is more suitable in terms of applicability and reliability in preterm infants at our neonatal intensive care units.