Effectiveness of the Stewart Method in the Evaluation of Blood Gas Parameters

Mustafa Gezer; Fatih Bulucu; Kadir Ozturk; Selim Kilic; Umit Kaldirim; Yusuf Emrah Eyi

doi:10.5505/1304.7361.2014.73604

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

Abstract

Objectives

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.

Methods

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.

Results

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.

Conclusions

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.