Electrolytes and Blood Gases

Maintenance of water homeostasis is paramount to life for all organisms. In mammals, the maintenance of osmotic pressure and water distribution in the various body fluid compartments is primarily a function of the four major electrolytes, Na , K , Cl , and HCOi . In addition to water homeostasis, these electrolytes play an important role in the maintenance of pH, proper heart and muscle function, oxidation-reduction reactions, and as cofactors for enzymes. Indeed, there are almost no metabolic processes that are not dependent on or affected by electrolytes. Abnormal concentrations of electrolytes may be either the cause or the consequence of a variety of disorders. Thus determination of electrolytes is one of the most important functions of the clinical laboratory. Interpretation of abnormal osmolality and acid-base values requires specific knowledge of the electrolytes. Because of their physiological and clinical interrelationship, this chapter discusses determination. of electrolytes, osmolality, acid-base status, and blood oxygenation. 

Electrolytes are classified as either anions, negatively charged ions that move toward an anode, or cations, positively charged ions that move toward a cathode. Physiological electrolytes include Na , K, Ca , CT, HCO , H2PO4, 

and and some organic anions, such as lactate. Although amino acids and proteins in solution also carry an electrical charge, they are usually considered separately fi om electrolytes. Hydrogen ion (H ) concentration is routinely measured as pH, but its concentration is so low relative to other ions (10 versus 10 moI/L) in body fluids that it is not considered an electrolyte per se. The major electrolytes (Nab Kb CT, HCOa) occur primarily as free ions, whereas 

Determination of body fluid concentrations of the four major electrolytes (Na , K , CT, and HCO3) is commonly referred to as an electrolyte profile. Other electrolytes that have special functions in particular contexts are discussed elsewhere Ca b magnesium, and phosphates in Chapter 49 iron in Chapter 31 trace elements in Chapter 30 and amino acids in Chapter 20. 

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Scott MG, Heusel JW, LeGrys VA, Siggard-Andersen O (1999) Electrolytes and blood gases. In Burtis CA, Ashwood ER (eds) Tietz Textbook of Clinical Chemistry, 3rd edn. W.B. Saunders Company, Philadelphia, pp 1056-1092... 

Analyzers usmg ISEs capable of providing immediate whole-blood determinations of free calcium, electrolytes, and blood gases are now widely available. The free calcium analyzer consists of a system of pumps under microprocessor control that transport cafibration solutions, samples, and wash... 

Burrit ME Electrolytes and blood gases (ionized calcium). Anal Chem 1993 65 409R-11R. 

Electrolytes and Blood Gases Electrolytes and Blood Gases Appendix Physiology and Disorders of Water, Electrolyte, and Acid-Base Metabolism... 

Electrolytes and Blood Gases Electrolytes and Blood Gases Appendix... 

Beside these disposable systems enzyme-membrane-based devices (first-generation enzyme sensors) are working with a biological component that can be repeatedly used for thousands of measurements. The functional stability depends on the quality of the enzyme membrane material used. The autoanalyzer Stat-Profile 5 (Nova Biomedical, USA) and the lonometer (Fresenius, Germany) permit the analysis of metabolites, such as glucose and lactate, in addition to electrolytes and blood gases (see table 17.2). 

No standard reference material and procedure is actually available for molal ion activity assays. Calibration of the electrode is required. The calibration solution should match the mean sample composition as closely as possible. Addition of albumin to the calibration standard does not guarantee high accuracy of the results due to a shift of the assay standard potential that is different for plasma, serum, and albumin. Reports on comparisons of clinical analyzers show that interinstrumental deviations may be considerable. Recommendations for calibration and standardization by the IFCC Committee on Electrolytes and Blood Gases are in preparation. 

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