TY - JOUR

T1 - Strong ions, weak acids and base excess

T2 - A simplified Fencl-Stewart approach to clinical acid-base disorders

AU - Story, David A.

AU - Morimatsu, H.

AU - Bellomo, R.

N1 - Funding Information:
Funding was provided by the Research Fund, Department of Anaesthesia, Austin and the Repatriation Medical Centre, Heidelberg, Victoria, Australia.

PY - 2004/1

Y1 - 2004/1

N2 - Background. The Fencl-Stewart approach to acid-base disorders uses five equations of varying complexity to estimate the base excess effects of the important components: the strong ion difference (sodium and chloride), the total weak acid concentration (albumin) and unmeasured ions. Although this approach is straightforward, most people 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 sodium-chloride effect on base excess to one simple equation: sodium-chloride effect (meq litre-1)=[Na+]-[CI]-38. We simplified the equation of the albumin effect on base excess to an equation with two constants: albumin effect (meq litre--)=0.25×(42-[albumin]g litre-1). Using 300 blood samples from critically ill patients, we examined the agreement between the more complex Fencl-Stewart equations and our simplified versions with Bland-Altman analyses. Results. The estimates of the sodium-chloride 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 acid-base disorders in clinical practice.

AB - Background. The Fencl-Stewart approach to acid-base disorders uses five equations of varying complexity to estimate the base excess effects of the important components: the strong ion difference (sodium and chloride), the total weak acid concentration (albumin) and unmeasured ions. Although this approach is straightforward, most people 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 sodium-chloride effect on base excess to one simple equation: sodium-chloride effect (meq litre-1)=[Na+]-[CI]-38. We simplified the equation of the albumin effect on base excess to an equation with two constants: albumin effect (meq litre--)=0.25×(42-[albumin]g litre-1). Using 300 blood samples from critically ill patients, we examined the agreement between the more complex Fencl-Stewart equations and our simplified versions with Bland-Altman analyses. Results. The estimates of the sodium-chloride 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 acid-base disorders in clinical practice.

KW - Chemistry, analytical

KW - Complications, acid-base disorders

KW - Intensive care

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U2 - 10.1093/bja/aeh018

DO - 10.1093/bja/aeh018

M3 - Article

C2 - 14665553

AN - SCOPUS:0346336778

SN - 0007-0912

VL - 92

SP - 54

EP - 60

JO - British Journal of Anaesthesia

JF - British Journal of Anaesthesia

IS - 1

ER -