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

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.

Prospective study.

Medical ICU, University Hospital.

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.

Measurements with CIABG among the abnormal values showed biases of +2mmHg, +0.1mmHg and +0.005 for PaO2, PaCO2 and pH, respectively, and precisions of 9.0mmHg, 3.5mmHg 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, 0.6mmHg for PaCO2 and -1.2mmHg for PaO2.

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.