Clinical evaluation of a continuous intra-arterial blood gas system in critically ill patients

Abstract

Objective

To evaluate the clinical performance of a new, continuous intra-arterial blood gas monitoring system (CIABG) in abnormal ranges of blood gases, and during episodes of low blood pressure, in critically ill patients.

Design

Prospective study.

Settings

Medical ICU, University Hospital.

Methods

The CIABG system, based on fluorescent dyes, consists of a fiber-optic sensor introduced through an arterial catheter. Twenty-one sensors were evaluated in 15 acutely ill patients. A high failure rate (6/21) was found, due to the brittleness of the fibers. The bias, between CIABG and standard method, and precision were determined for each fiber and for the overall values. Analysis focused on the data collected in patients with arterial oxygen tension (PaO₂) values below 75 mmHg, pH lower than 7.35 and arterial carbon dioxide partial pressure (PaCO₂) values exceeding 50 mmHg and during episodes of low blood pressure. The accuracy of the CIABG to follow sequential changes in blood gases was studied among the abnormal values.

Results

Measurements with CIABG among the abnormal values showed biases of +2 mmHg, +0.1 mmHg and +0.005 for PaO₂, PaCO₂ and pH, respectively, and precisions of 9.0 mmHg, 3.5 mmHg and 0.027, respectively. Bias and precision were not influenced by hemodynamic instability. A substantial difference in the performance of individual CIABG was observed for PaO₂ analysis, with 30% of the fibers having a much poorer performance than the others. The sensors were kept in place for 5±2 days and the drift rate per day was 0.005 for pH, 0.6 mmHg for PaCO₂ and −1.2 mmHg for PaO₂.

Conclusion

In situations of severe hypoxemia, hypercapnia and acidosis, the agreement between CIABG and arterial blood sampling (ABS) is better for PaCO₂ and pH than for PaO₂, and is not influenced by episodes of low blood pressure.