O. Siggaardandersen et N. Foghandersen, BASE EXCESS OR BUFFER BASE (STRONG ION DIFFERENCE) AS MEASURE OF A NON-RESPIRATORY ACID-BASE DISTURBANCE, Acta anaesthesiologica Scandinavica, 39, 1995, pp. 123-128
Stewart in 1983 (Coil J Physiol Pharmacol 1983: 61: 1444) reintroduced
plasma buffer base under the name ''strong ion difference'' (SID). Bu
ffer base was originally introduced by Singer and Hastings in 1948 (Me
dicine (Baltimore) 1948: 27: 223). Plasma buffer base, which is practi
cally equal to the sum of bicarbonate and albuminate anions, may be in
creased due to an excess of base or due to an increased albumin concen
tration. singer and Hastings did not consider changes in albumin as ac
id-base disorders and therefore used the base excess, i.e., the actual
buffer base minus the buffer base at normal pH and pCO(2), as measure
of a non-respiratory acid-base disturbance. Stewart and followers, ho
wever, consider changes in albumin concentration to be acid-base distu
rbances: a patient with normal pH, pCO(2), and base excess but with in
creased plasma buffer base due to increased plasma albumin concentrati
on get the diagnoses metabolic (strong ion) alkalosis (because plasma
buffer base is increased) combined with metabolic hyperalbuminaemic ac
idosis. Extrapolating to whole blood, anaemia and polycytaemia should
represent types of metabolic alkalosis and acidosis, respectively. Thi
s reveals that the Stewart approach is absurd and anachronistic in the
sense that an increase or decrease in any anion is interpreted as ind
icating an excess or deficit of a specific acid. In other words, a ret
urn to the archaic definitions of acids and bases as being the same as
anions and cations. We conclude that. the acid-base status (the hydro
gen ion status) of blood and extracellular fluid is described in terms
of the arterial pH, the arterial pCO(2), and the extracellular base e
xcess. It is measured with a modern pH-blood gas analyser. The electro
lyte status of the plasma is a description of the most important elect
rolytes, usually measured in venous blood with a dedicated electrolyte
analyser. i.e., Na+, Cl-, HCO3-, and K+. Albumin anions contribute si
gnificantly to the anions, but calculation requires measurement of pH
in addition to albumin and is usually irrelevant. The bicarbonate conc
entration may be used as a screening parameter of a nonrespiratory aci
d-base disturbance when respiratory disturbances are taken into accoun
t. A disturbance in the hydrogen ion status automatically involves a d
isturbance in the electrolyte status, whereas the opposite need not be
the case.