Arterial Gas Analyzer and Autoanalyzer Compared for Electrolytes

Electrolyte values are measured in most critically ill intensive care unit (ICU) patients using both an arterial blood gas analyzer (ABG) and a central laboratory autoanalyzer (AA).

Data on sodium and potassium ion concentrations in ICU patients have been examined to see whether the electrolyte levels assessed by the ABG and the AA are equivalent and reliable.

Scientists at the Sevket Yilmaz Education and Research Hospital (Bursa, Turkey) retrospectively studied patients hospitalized in the ICU between July and August 2011. They identified 84 instances, of 1,105 patient blood gas samples analyzed, in which arterial and venous samples were collected simultaneously and sodium (Na+) and (K+) were measured using two methods.

In the ICU, arterial blood samples were collected in heparinized blood-gas syringes and analyzed using the benchtop pHOx Stat Profile Plus L blood–gas analyzer (Nova Biomedical; Waltham MA, USA) which employs direct ion-specific electrode (ISE) technology. Another sample was drawn, at the same time, from the same arterial sampling point, using a vacuum technique featuring clot-activating tubes. These samples were sent, pneumatically sealed, to the central laboratory, where serum Na+ and K+ concentrations were analyzed via indirect ISE on a Modular ISE900 auto-analyzer (Roche Diagnostics; Mannheim, Germany).

The mean sodium concentration was 138.mmol/L (standard deviation, SD ±10.2 mmol/L) using the ABG and 143.0 mmol/L (SD ±10.5 mmol/L) using the AA, which was statistically different. The mean potassium level was 3.5mmol/L (SD ± 0.9 mmol/L) using the ABG and 3.7 mmol/L (SD ± 1.0 mmol/L) using the AA which was also significantly different. The extent of interanalyzer agreement was unacceptable for both K+ and Na+. The between-day imprecision of both instruments (AA and ABG) was small and lacked clinical significance when compared with analytical performance indicators based on biological variation.

The authors concluded that their study illustrates the importance of determining the concordance, for each individual hospital, of electrolyte values obtained by ABG and those obtained in the central laboratory. As instrument type and calibration methods may differ among hospitals, it is important that each center conducts an in-house study as in their study the ABG and AA do not yield equivalent Na+ and K+ data. The study was published on August 3, 2012, in the BioMed Central journal BMC Anesthesiology.

Related Links:
Sevket Yilmaz Education and Research Hospital
Nova Biomedical
Roche