Intra-arterial blood gas monitoring system: more accurate values can be obtained

To compare values measured by a continuous intra-arterial blood gas monitoring system with those measured by conventional blood gas analyzer for the assessment of the clinical performance of a new device for measurement of PaO2, PaCO2, and arterial pH.

Forty-six patients undergoing cardiopulmonary bypass were enrolled in this study. All patients had a continuous intra-arterial sensor (PB 3300) placed into the radial artery through a 20-gauge catheter. A total of 319 arterial blood gas and pH values were obtained for comparison with a conventional blood gas analyzer. The measurements were performed every 12 hrs after the initial in vitro calibration of the sensor for each patient.

Measurements were made over a range of 12 to 192 hrs. The overall bias and precision determined by the two methods were 4.5 and 17.1 mmHg for PaO2; 4.5 and 6.2 mmHg for PaCO2; and 0.009 and 0.035 for pH, respectively. For the range of PO2 less than 150 mmHg, the bias and precision improved to 4.2 and 9.5 mmHg. The sensor-derived PCO2 value, PCO2 (IABG), increased significantly more than the conventional blood gas analysis value, PCO2(ABG), even within 72 hrs (2.8 and 4.1 mmHg). The relationship between the two measurements can be described as: PCO2(IABG)/PCO2(ABG) = 1 + 0.0026.t where t is the time period of use (in hours). By correcting the PCO2(IABG) value using this formula, the overall bias and precision of the values measured by two methods decreases to -0.4 and 3.6 mmHg.

The PO2 and pH values derived from an intra-arterial blood gas monitoring system agreed well with the values measured by a conventional blood gas analyzer. However, the PCO2 value must be corrected due to an increase of drift, especially with extended use for more than 72 hours.