BASE EXCESS OR BUFFER BASE (STRONG ION DIFFERENCE) AS MEASURE OF A NON-RESPIRATORY ACID-BASE DISTURBANCE

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.