The (in-)validity of volatile POCT parameters from patients beyond normothermia.

BACKGROUND: A common characteristic of all blood gas analyzers on the market is that measurements are processed at 37°C, not at the real patients´ temperature. Subsequently temperature-sensitive parameters can be mathematically corrected (alpha-stat method) or used directly (pH-stat method). National rules in Germany (Rili-BAEK) demand defined accuracy and precision without any restriction to samples´ temperatures or corrections. As consequence in the investigation at hand we tried to find out whether blood gas analyzers can fulfill the regulations for pCO2 and pO2 when normothermia of the matrix is not given. METHODS: Five matrices (blood from intensive care unit (ICU) patients, blood from healthy donors and 3 levels of bovine based quality control material) were tonometered at "high" and "low" partial pressures of O2 and CO2 within the RiLi-BAEK controlled range at 32, 37 and 40°C. One mL material was aspired into each blood gas (BG) syringe and analysis was accomplished immediately after. The procedure was repeated 10-fold for "high" and "low" gas concentrations and run on 4 different analyzers. At 18°C instead to the "high" one a "median" gas (n=10 as well) was employed. Every condition which constitutes of temperature (4), matrix (5), analyzer (4) and level of the partial pressure (2) led to a total of 1600 measurements. RESULTS: At 32°C or 37°C matrix temperature 7.5% to 27.5% of the pCO2(T) and between 14.5% and 28.1% of the pO2(T) results were outside the borders required by the RiLi-BAEK. At 18°C or 40°C the number of results beyond the allowed borders grows up to 82.5% for pCO2(T) and 73% for pO2(T) depending on the partial pressure (PP) level. CONCLUSIONS: High precision in automated quality control (at a constant matrix temperature) is given in modern BGAnalyzers but is counteracted in practice by non normothermic patient's temperature and unavoidable sample handling effects.

Preanalytics: The (in-)stability of volatile POCT parameters and the homogeneity of blood in syringes at the market.

BACKGROUND: In between calibrations, quality controls and so on reduce the availability of blood gas analyzers. Despite the intended urgency of the measurements, these inhibitory circumstances cause delays of measurements. The comparison of changes (primarily PO2 and PCO2, secondarily ctHb) in syringes from different suppliers and the embedding into guideline ranges are the objectives of this study. METHODS: Five matrices were tonometered at two levels within the German guideline (RiLi-BAEK) controlled range. Matrices were aspired into each syringe and blood gas analysis accomplished after 0 to 30min. The procedure was repeated 5 to 8-fold for the gas concentrations and every condition which consisted of syringe type (7), matrices (5) and time delay (7). RESULTS: Syringes produce almost identical effects on partial pressures during the 30min observation period. Initial fast changes arise when partial pressure (PP) differs widely from the atmospheric pressure and are followed by diffusion, gas production or consumption and ctHb depending effects. CONCLUSIONS: Only normal arterial blood gases without "atmospheric pollution" are not affected by the syringe materials within 30min. The homogeneity of a de-aerated and capped ICU-patients' sample is hardly to be provided after more than 10min of resting without mechanical assistance.