Clinical trial of an ex vivo arterial blood gas monitor

PURPOSE: The purpose of this study was to test the performance of a patient attached, on demand ex vivo arterial blood gas (ABG) monitor, and to compare the frequency of ABG analysis using the monitor, where the monitor was operated by intensive care unit (ICU) staff on shock trauma and neurosurgical intensive care patients for < or = 6 days, with standard clinical laboratory analysis. MATERIALS AND METHODS: The ABG monitor (SensiCath; Optical Sensors Inc., Minneapolis, MN) incorporates fiber optic pH, PCO2, PO2, and thermistor temperature sensors in a 0.3-mL sensor chamber that attaches in line with the patient's arterial pressure tubing and connects via a fiberoptic cable to a bedside instrument. The monitor and standard clinical laboratory performance were compared following an institutionally approved protocol. Adult ICU patients (n = 30) were studied for whom an arterial cannula was required, the expected ICU stay was > 72 hours, > or = 2 ABG analyses/day were anticipated, and informed consent had been obtained. Paired comparison ABG analyses and quality assurance checks were performed daily. The frequency of ABG analyses in this study, for which monitor values were used for clinical decision making, was compared with the frequency previously reported for the same ICUs, for which the monitor and laboratory results were compared but only the latter were used for clinical decision making. RESULTS: Five hundred ABG analyses, 436 over the first 72 hours, were obtained using the monitor for patient management over 3,248 patient hours (85 +/- 47 hours/patient). Monitor-laboratory comparison ABG analyses (n = 258) indicated stable performance over 6 days: For pH, the range of laboratory measurements was 7.200 to 7.540, accuracy (mean difference between monitor and laboratory measurement) was +0.013, and precision (standard deviation of difference between monitor and laboratory measurements) was +/-0.031. For PCO2, range: 18 to 78.5, accuracy: -0.8, precision: +/-3.4 mm Hg. For PO2, range: 41.0 to 344.0, accuracy: +2.3, precision: +/-12.8 mm Hg. The frequency of ABG analyses obtained using the monitor (ie, 15.0 +/- 11.6 ABGs/patient/72 hours) was significantly greater than that using the clinical laboratory (ie, 8.8 +/- 4.2 ABGs/patient/72 hours) (P = .01). CONCLUSION: The ABG monitor provides performance comparable to standard clinical laboratory analysis for < or = 6 days (< or = 144 hours), consistent with ICU arterial cannula changeout schedules. More frequent ABG analyses are obtained by critical care practitioners using the monitor compared with the clinical laboratory system, suggesting that clinical decision making based on ABG data may be limited by the frequency of ABG analysis.