Page 94 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

84 ELECTROLYTE DISORDERS

and in cats as: measure chloride. Direct potentiometry is commonly
used in blood gas analyzers and point-of-care electrolyte
þ analyzers, whereas indirect potentiometry is commonly
Cl correctedð Þ ¼ Cl 156=Na
used in the large chemistry analyzers located in the
Normal Cl (corrected) is approximately 107 to 113 central laboratory. Direct potentiometry reveals the true

mEq/L in dogs and approximately 117 to 123 mEq/L sodium concentration (activity), whereas in indirect
in cats. 17 These values may vary between different potentiometry, the concentration of the ion is diluted
laboratories and different analyzers. Newer analyzers to an activity near unity. 47 Because the concentration will
report higher chloride values unless the chloride calibra- take into account the original volume and dilution factor,

tion is deliberately changed. 102 Using the Cl (corrected) any excluded volume (lipids, proteins) introduces an
permits the division of chloride disorders into artifactual error (usually very small). However, significant
and corrected chloride changes (Table 4-1). In artifactual differences between point-of-care analysis and the central
chloride changes, changes in free water are solely respon- laboratory have been found clinically 69 for sodium and
sible for the chloride changes, whereas in corrected chloride concentrations, and these differences may be
chloride changes, chloride itself is primarily changed. worse in hypoalbuminemic human patients. 91 Some
Algorithms for the evaluation of chloride abnormalities laboratories measure potassium by enzymatic spectro-
are presented in Figures 4-1 through 4-3. photometry. This method is prone to interference by
hemolysis and hyperproteinemia. 5
CHLORIDE MEASUREMENTS
þ

Reference intervals for [Cl ] and [Na ] vary depending CLINICAL DISTURBANCES
on the analytical method and performing laboratory,
and these factors should be considered when interpreting DISORDERS ASSOCIATED WITH
and comparing clinical results. Breed-related changes for NORMAL CL (CORRECTED)
chloride concentration were not identified in dogs or Artifactual Hypochloremia and Artifactual
cats. 80,90 Chloride ions can be measured in plasma, Hyperchloremia
serum, or blood; serum is preferred because serum chlo-
ride is stable for months. Chloride concentrations most A change in the water content of plasma without an
commonly are measured by potentiometry, which is imbalance in the content of electrolytes dilutes or

based on ion electrical potential. When the ion electrode concentrates anions and cations. Consequently, [Cl ]
þ
is immersed in a solution containing chloride ions, an and [Na ] will change in parallel. These changes usually
electrode potential proportional to the logarithm of the are recognized by changes in sodium concentration
chloride ion activity is generated. Chloride ions then (hypernatremia or hyponatremia), and this ion (and
are measured by the chloride ion electrode based on this changes in osmolality) should receive primary attention
principle in combination with a reference electrode. (see Chapter 3).
Because of the much greater solubility of AgCl compared High chloride concentration with normal Cl
with AgI, the chloride electrode will be irreversibly dam- (corrected) (artifactual hyperchloremia) usually is
aged if immersed in solutions containing iodide ions, associated with pure water loss (e.g., diabetes insipidus,
resulting in a falsely increased chloride concentration. essential hypernatremia) or hypotonic losses (e.g.,
A high interference also is observed when bromide and osmotic diuresis). Patients with hypernatremia caused
cyanide ions are measured, and the chloride electrode will by sodium gain (e.g., hypertonic saline or NaHCO 3
only give reliable results if these ions are absent or in administration, hyperadrenocorticism) tend to have

minimal amounts when compared with chloride ions. abnormal Cl (corrected). Low chloride concentration

Care must be taken when using different analyzers to with normal Cl (corrected) (artifactual hypochloremia)

TABLE 4-1 Classification of Chloride Disorders

Disorder Cl Na þ Cl Corrected Associated Acid-Base Disorder

Artifactual hyperchloremia * * N Concentration alkalosis
Artifactual hypochloremia + + N Dilution acidosis
Corrected hyperchloremia *,N, + *,N, + * Hyperchloremic acidosis
Corrected hypochloremia *,N, + *,N, + + Hypochloremic alkalosis

Source: de Morais HSA: Chloride ion in small animal practice: the forgotten ion, J Vet Emerg Crit Care 2:11-24, 1992.
Cl , Chloride concentration; Cl corrected, corrected chloride concentration; Na , sodium concentration; *, increased concentration; N, normal

þ
concentration; +, decreased concentration.