The Science Journal of the American Association for Respiratory Care

Original Contributions

June 2002 / Volume 47 / Number 6 / Page 682

Clinical Validation of a Continuous Intravascular Neonatal Blood Gas Sensor Introduced Through an Umbilical Artery Catheter

Patricia A Meyers RRT, Catherine Worwa CRT, Robert Trusty RRT, and Mark C Mammel MD

INTRODUCTION: Arterial blood gas (ABG) values are a necessary diagnostic measurement in the management of critically ill neonates. We hypothesized that a fiberoptic intravascular blood gas sensor, adapted for use through an umbilical artery catheter, would produce blood gas results with clinically acceptable bias and precision, in comparison to laboratory values, but with no blood loss. METHODS: We evaluated a fiberoptic intravascular blood gas sensor (Neotrend) in 23 consecutive neonates suffering respiratory failure. The sensor was inserted into the descending aorta via a 4.0 or 4.5 French umbilical artery catheter and extended 20 mm beyond the catheter tip. Arterial blood samples were drawn as clinically indicated and analyzed using a standard laboratory analyzer. Sensor measurements were recorded at the time of arterial blood sampling. Additionally, we recorded and evaluated data related to umbilical artery catheter placement (low position [L3-L4] vs high position [T8-T10]), duration of sensor functioning and use, and sensor bias and precision compared to the laboratory analyzer (using Bland-Altman technique and linear regression analysis of pH, PaCO2, and PaO2). RESULTS: Duration of sensor use ranged from 1 to 304 hours (3-304 h in high position and 1-91 h in low position). Nine sensors were used for > 72 h (1 in low position and 8 in high position). Nine sensors were placed in low position, with a placement success rate of 56%. Eighteen sensors were placed in high position, with a placement success rate of 89%. The sensor values for pH, PaCO2, and PaO2 were strongly correlated (p < 0.0001) with the laboratory-determined values. Bias and precision for all values met standards for discrete analyzers for laboratory use. CONCLUSIONS: The Neotrend device was accurate and reliable in the neonatal setting, allowing blood gas assessment with no iatrogenic blood loss. Catheter placement in high position may increase the likelihood of successful sensor placement and sensor duration of function.
Key words: intravascular blood gas sensor, umbilical artery catheter, monitoring, respiratory failure, neonates.
[Respir Care 2002;47(6):682–687]

Introduction

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.

The entire text of this article is available in the printed version of the June 2002 RESPIRATORY CARE.

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