Summary
The concept of corrected chloride has been proposed to describe the net contribution of
chloride to acid-base disturbances in hypo- and hypernatremic states. Authors present a
graph to describe the relation between the water, sodium and chloride ions and to
determine the dysbalance of this relation. The aim is to classify hypochloremic and
concentrational alkaloses and hyperchloremic and dilutional acidoses, respectively, and
their combinations as significant contributors to acid-base disorders.
Introduction
Acid-base disturbances are caused by changes in so-called independent acid-base variables,
i.e., carbon dioxide partial pressure, strong ion difference and non-volatile weak acids
(1, 2). Among others, strong ion difference is disturbed by extracellular water content.
Dilutional acidosis is caused by extracellular water increased in relation to sodium
supply and is defined as hyponatremia. Concentrational alkalosis is defined, on the other
hand, as hypernatremia. Hyperchloremic metabolic acidosis is caused by increased chloride
concentration in normonatremic states, hypochloremic metabolic alkalosis by decreased
chloride concentrations. Nevertheless, these simple “net” disturbances are often combined
in critically ill patients (1, 3). It is therefore necessary to distinguish single and
mixed disturbances properly, not only for the understanding the acid-base status but also
for effective treatment.
Materials and Methods
Corrected chloride ([ Cl- ]corrected, mmol/L) has been recommended for
situations with abnormal concentrations of plasma sodium ([ Na+ ], mmol/L) and
calculated according to Fencl (1):
[ Cl- ]corrected = [ Cl- ]observed x
( [ Na+ ]normal / [ Na+ ]observed )
where observed chloride is corrected for dilution/concentration. Graph was constructed with
plasma sodium (mmol) on abscisa and plasma chloride (mmol/L) on ordinate with lines
representing respective values of corrected chloride inside graph.
Results
Graph is presented in
Figure 1.
Used reference range of plasma sodium ([ Na+ ]normal) was 140 - 144
mmol/L, reference range of plasma chloride was 104 - 108 mmol/L, reference range of
corrected chloride is identical with that of observed chloride (1). Nine sectors represent
the normal state, four simple disturbances (concentrational alkalosis, dilutional
acidosis, hypochloremic alkalosis, hyperchloremic acidosis) and four mixed disturbances
(concentrational alkalosis plus hypochloremic alkalosis, concentrational alkalosis plus
hyperchloremic acidosis, dilutional acidosis plus hyperchloremic acidosis and dilutional
acidosis plus hypochloremic alkalosis).
Conclusions
Authors evaluate the relation between [ Na+ ] and [ Cl- ] by graphical
interpretative tool. The concept of corrected chloride has been chosen as a basis for the
graphical description of the problem. Each laboratory can adopt reference values used in
the graph with respect to its own reference ranges . Graph enables to classify some of
acid-base disorders related to ions and water dysbalances even in situations where
investigation of acid-base status is not available. Request for acid-base investigation can
be a logical following step. Understanding to ion dysbalance enables the adequate
therapeutic proceeding. In complex disorders, treatment of only one cause can unmask other
pathologic condition and worsen patient’s outcome significantly. Authors believe that the
use of graph can reduce misinterpretation and incorrect treatment of critically ill
patients.
References
(1) FENCL, V., JABOR, A., KAZDA, A., FIGGE, J.: Diagnosis of Metabolic Acid-Base
Disturbances in Critically Ill Patients. Am J Respir Crit Care Med, Vol. 162,
pp. 2246 – 2251, 2000.
(2) FENCL, V., ROSSING, T.H.: Acid-base Disorders in Critical Care Medicine.
Ann Rev Med, Vol. 40, pp. 17 – 29, 1989.
(3) KELLUM, J.A.: Recent Advances in Acid-Base Physiology. In: Yearbook of Intensive
Care Medicine (ed. J.L. Vincent), Berlin, Springer, pp. 577 – 585, 1998.