Strong ions, weak acids and base excess: a simplified Fencl-Stewart approach to clinical XXXX .

@entity1 @entity1372 @entity74 @entity2865 @entity2827
BACKGROUND: The Fencl-Stewart approach to @entity74 uses five equations of varying complexity to estimate the base excess effects of the important components: the strong ion difference ( @entity1372 and @entity2865 ), the total weak acid concentration (albumin) and unmeasured ions. Although this approach is straightforward, most @entity1 would need a calculator to use the equations. We proposed four simpler equations that require only mental arithmetic and tested the hypothesis that these simpler equations would have good agreement with more complex Fencl-Stewart equations. METHODS: We reduced two complex equations for the @entity2827 effect on base excess to one simple equation: @entity2827 effect (meq litre(-1))=[Na(+)]-[Cl(-)]-38. We simplified the equation of the albumin effect on base excess to an equation with two constants: albumin effect (meq litre(-1))=0.25x(42-[albumin]g litre(-1)). Using 300 blood samples from critically ill @entity1 , we examined the agreement between the more complex Fencl-Stewart equations and our simplified versions with Bland-Altman analyses. RESULTS: The estimates of the @entity2827 effect on base excess agreed well, with no bias and limits of agreement of -0.5 to 0.5 meq litre(-1). The albumin effect estimates required log transformation. The simplified estimate was, on average, 90% of the Fencl-Stewart estimate. The limits of agreement for this percentage were 82-98%. CONCLUSIONS: The simplified equations agree well with the previous, more complex equations. Our findings suggest a useful, simple way to use the Fencl-Stewart approach to analyse @entity74 in clinical practice.
