Effectiveness of the Stewart Method in the Evaluation of Blood Gas Parameters
Mustafa Gezer1, Fatih Bulucu2, Kadir Ozturk3, Selim Kilic4, Umit Kaldirim5, Yusuf Emrah Eyi5
1Department of Internal Medicine, Mevki Military Hospital, Ankara, Turkey
2Department of Internal Medicine, Gulhane Military Medical Academy, Ankara, Turkey
3Department of Gastroenterology, Gulhane Military Medical Academy, Ankara, Turkey
4Department of Public Health, Gulhane Military Medical Academy, Ankara, Turkey
5Department of Emergency Medicine, Gulhane Military Medical Academy, Ankara, Turkey
Keywords: Blood gases; Stewart method
In 1981, Peter A. Stewart published a paper describing his concept for employing Strong Ion Difference. In this study we compared the HCO3 levels and Anion Gap (AG) calculated using the classic method and the Stewart method.
Four hundred nine (409) arterial blood gases of 90 patients were collected retrospectively. Some were obtained from the same patients in different times and conditions. All blood samples were evaluated using the same device (ABL 800 Blood Gas Analyzer). HCO3 level and AG were calculated using the Stewart method via the website AcidBase.org. HCO3 levels, AG and strong ion difference (SID) were calculated using the Stewart method, incorporating the parameters of age, serum lactate, glucose, sodium, and pH, etc.
According to classic method, the levels of HCO3 and AG were 22.4±7.2 mEq/L and 20.1±4.1 mEq/L respectively. According to Stewart method, the levels of HCO3 and AG were 22.6±7.4 and 19.9±4.5 mEq/L respectively.
There was strong correlation between the classic method and the Stewart method for calculating HCO3 and AG. The Stewart method may be more effective in the evaluation of complex metabolic acidosis.