June 2002 / Volume 47 / Number 6 / Page 682
Clinical Validation of a Continuous Intravascular Neonatal Blood Gas Sensor Introduced Through an Umbilical Artery Catheter
Arterial blood gas (ABG) values are a necessary diagnostic measurement in the management of critically ill, ventilated patients in the neonatal intensive care unit (NICU). The frequency of blood gas sampling is usually determined by the severity of the condition and clinical practice. A drawback to scheduled ABG sampling is that changing conditions may be missed. The relationship between PaCO2 fluctuations and cerebral blood flow have been well described. Hypercarbia and hypocarbia are both linked to the development of intraventricular hemorrhage and periventricular leukomalacia. Frequent ABG sampling from a neonate results in blood loss that can necessitate transfusions and increase the risk of intravascular contamination. In critical situations the practitioner may have to wait for an ABG sample to be drawn and taken to the laboratory, which may or may not be in close proximity to the NICU. Rapid changes in blood gas values can occur following surfactant administration and during high-frequency ventilation. With the advent of continuous ABG monitoring, treatment modalities can be proactive rather than reactive.
Continuous ABG estimations have been available in a variety of noninvasive forms. Unfortunately, transcutaneous monitoring of carbon dioxide and oxygen levels necessitates frequent site changes and recalibration of the probe, and it is contraindicated in hemodynamically compromised patients because of changes in blood flow to the tissues. Pulse oximetry offers continuous estimation of blood oxygen saturation but gives no information about pH or PaCO2. For the past 2 decades, continuous intra-arterial PaO2 measurement has been available with the use of a Clark electrode with an umbilical artery catheter (UAC). In recent years, advances in fiberoptics have provided continuous monitoring of blood gases in adults by allowing passage of a multivariable sensor through a catheter placed in a peripheral artery. Recently that same technology was adapted to allow sensor placement through the UAC in critically ill newborns.
We evaluated a continuous-readout intravascular blood gas monitoring system (Neotrend, Diametrics Medical, St Paul, Minnesota) in critically ill newborns and compared the values obtained to ABG measurements made in the hospital's clinical laboratory. We also collected data to evaluate duration of sensor function and sensor performance in high UAC position (T8-10) versus low UAC position (L3-4). We hypothesized that the Neotrend intravascular blood gas monitoring system would produce blood gas results with clinically acceptable bias and precision, in comparison to laboratory values, but with no blood loss.