The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

INACCURACIES IN CO2 MEASUREMENTS OF THE i-STAT BLOOD GAS ANALYZER WHEN COMPARED TO THE AVL OMNI BLOOD GAS ANALYZER

RW Kraemer CRTT, M Siobal BS RRT, RH Kallet MS RRT, JD Marks MD PhD, Department of Anesthesia. Valerie Ng MD, Clinical Laboratories, San Francisco General Hospital, UCSF

Introduction: We report inaccuracies in PaCO2 using the i-STAT Portable Clinical Analyzer with Thermal Control (i-STAT Corp, East Windsor, NJ). During routine weekly comparisons of i-STAT vs. AVL Omni blood gas instrument (AVL Scientific Corp. Roswell, GA), the i-STAT value for PaCO2 was 20 mmHg lower than the AVL Omni value. In the previous month, a PaCO2 discrepancy of 15 mmHg occurred. In both instances, commercial liquid controls performed on the i-STAT were within the accepted range. Because of these discrepancies, we performed a number of i-STAT vs. AVL comparisons in order to determine the extent of the problem.

Methods: First, three levels of liquid controls were performed on all instruments. Then 1.5 - 2.5 ml of blood was drawn from 11 critically ill patients using the SIMS line draw sampling kit (Part # 4043W-2, SIMS Portex, Keene, NH). Analysis of the sample was performed on the AVL Omni. AVL 995, and two i-STAT instruments providing 4 separate measurements for each sample.

Results: Liquid controls performed on all instruments were within the manufacturers acceptable range. In 3 of 11 patient samples (6 of 22 i-STAT vs. Omni comparisons), the i-STAT PaCO2 was > 5 mmHg lower than the AVL with a maximum variance of 11.6 mmHg.

AVL 995 AVL Omni i-STAT #1 i-STAT vs Omni i-STAT #2 i-STAT vs Omni
pH PCO2 pH PCO2 pH PCO2 D pH DPCO2 pH PCO2 D pH DPCO2
- - 7.246 48.4 7.236 49.8 -0.010 1.4 7.227 50.9 -0.019 2.5
7.239 53.7 7.278 50.0 7.275 52.8 -0.003 2.8 7.273 53.2 -0.005 3.2
7.222 51.6 7.243 50.1 7.269 50.5 0.026 0.4 7.272 51.8 0.029 1.7
QNS 49.4 7.251 47.3 7.258 48.8 0.007 1.5 7.256 50.2 0.005 2.9
7.165 48.2 7.211 45.6 7.202 37.7 -0.009 -7.9 7.213 35.0 0.002 -10.6
7.254 34.9 7.292 32.9 7.267 23.4 -0.025 -9.5 7.278 25.2 -0.014 -7.7
7.357 33.3 7.380 32.4 7.385 20.8 0.005 -11.6 7.376 22.5 -0.004 -9.9
7.269 47.6 7.311 45.0 7.322 45.2 0.011 0.2 7.318 45.7 0.007 0.7
7.380 47.8 7.403 45.4 7.427 41.1 0.024 -4.3 7.427 42.8 0.024 -2.6
7.416 36.5 7.433 35.6 7.412 32.4 -0.021 -3.2 7.457 32.7 0.024 -2.9
7.318 51.2 7.349 50.4 7.345 46.0 -0.004 -4.4 7.352
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