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 pCO and pO 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 O and CO 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 pCO(T) and between 14.5% and 28.1% of the pO(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 pCO(T) and 73% for pO(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.