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A K Covington

Publications and source records attributed to A K Covington.

32 records · Page 2Linked to original sources
PubMed1989

IFCC document stage 3, draft 1, dated 1989 02 01. An approved IFCC recommendation. IFCC method (1988) for tonometry of blood: reference materials for pCO2 and pO2. International Federation of Clinical Chemistry Scientific Division. Committee on pH, Blood Gases and Electrolytes.

A reference method for tonometry of blood is described. The document covers the theory of tonometry, the materials and equipment needed, and essential aspects of the tonometry procedure for blood. The partial pressures of oxygen and carbon dioxide in tonometered blood are accurately known and therefore this blood is recommended for assessing the accuracy of blood gas analyzers. Tonometry of blood samples from patients may also be used in the determination of acid-base quantities and hemoglobin-oxygen affinity, e.g. p50.

Blood Gas Analysis↗
PubMed1989

Calculation of single-ion activities in solutions simulating blood plasma.

While, in principle, flame photometry of sodium and potassium measures substance concentration, and ion-selective electrodes (ISEs) measure ion activity, the situation regarding the comparison of results from the two techniques when applied to blood plasma is complex. The problem can be approached experimentally from the point of view of calibration of ISEs with concentration standards, and similar procedures are adopted for commercial ISE-based clinical analysers. Nevertheless, there is interest in the evaluation of single ion activities in blood plasma and solutions simulating its ionic composition. The theory of mixed electrolyte solutions developed by Pitzer has been applied to some solutions currently proposed for calibrating ISEs, and the results compared with the Stokes-Robinson-Bates hydration approach. It is recommended that the values from the Pitzer treatment be adopted, because, although this has some empirical features, it has a sounder theoretical basis than the Stokes-Robinson-Bates hydration approach.

Calibration↗
PubMed1989

International Federation of Clinical Chemistry (IFCC), Scientific Division. Committee on pH. Blood Gases and Electrolytes. IFCC method (1988) for tonometry of blood: reference materials for pCO2 and pO2.

A reference method for tonometry of blood is described. The document covers the theory of tonometry, the materials and equipment needed, and essential aspects of the tonometry procedure for blood. The partial pressures of oxygen and carbon dioxide in tonometered blood are accurately known and therefore this blood is recommended for assessing the accuracy of blood gas analyzers. Tonometry of blood samples from patients may also be used in the determination of acid-base quantities and hemoglobin-oxygen affinity e.g. p50.

Blood Gas Analysis↗
PubMed1987

pK1' and bicarbonate concentration in plasma.

Values for pK1' were determined from pH measured at 37 degrees C with three blood-gas analyzers and from calculated pco2 values in 443 freshly separated plasmas, tonometered at 37 degrees C. Plasma was taken from healthy volunteers, seriously ill patients, and hyponatremic patients. pK1' values varied by considerably more than 0.06 in healthy volunteers as well as in very ill patients, and bicarbonate concentrations ([HCO3]p) calculated by blood-gas analyzers based on the pK1' value of 6.1 could be in error by some +/- 60%. pK1' was similarly determined for tonometered (37 degrees C) replicate dilutions of plasma samples. By adding weighed amounts of dry NaCl and NaHCO3 to the diluted samples we increased the Na+ concentration to approximately 150 mmol/L and bicarbonate concentrations to values ranging from approximately 2.5 to approximately 52.5 mmol/L. pK1' values decreased when [HCO3]p was increased in dilutions of plasma kept at constant ionic strength. At any given [HCO3]p, pK1' values were higher at high than at low values of pco2.

Bicarbonates↗
PubMed1984

Simplified urinary oxalate determination using an enzyme electrode.

An enzyme electrode for urine oxalate measurement has been produced using acrylamide gel-entrapped oxalate decarboxylase retained over a CO2 sensor. Urine required pre-treatment with EDTA, but oxalate extraction was not necessary and inhibition by phosphate and sulphate was not apparent until after 10-14 days. The linear range was 0-0.2 mmol/l. Analysis of 50 urine specimens diluted 1 in 10 in pH 3.0 glycine buffer showed good correlation with a widely-used colorimetric method (y = 1.101x-0.018, r = 0.955).

Adult↗
PubMed1984

Bicarbonate or CO2?

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Acid-Base Equilibrium↗
PubMed1984

Simultaneous on-line measurement of blood K+, Ca2+, Na+, and pH with a four-function ChemFET integrated-circuit sensor.

On-line, simultaneous measurement of blood K+, Ca2+, Na+, and pH has been achieved by using a quadruple-function ChemFET (chemical-sensitive field-effect transistor) integrated-circuit sensor. Blood is withdrawn from the subject through an actively heparinized, dual-lumen cannula and passed into a flow-cell containing the sensor, in alternation with a calibration solution. A minicomputer controls the analysis system, logs data, and provides a continuous, graphic display of K+ and pH values.

Autoanalysis↗
PubMed1982

Interferent ion effects on the Orion SS-20 Calcium Ion Analyser.

Selectivity studies were carried out on bis-dialkyl phosphate and neutral carrier sensors available with the Orion SS-20 Calcium Analyser. Neutral carrier sensors showed better selectivity; changes of H+, Na+, K+ and Mg2+ within the physiological range produced no significant error in Ca2+ measurement. The Nicolsky equation, used as the basis of these studies, did not fully account for electrode response to mixed electrolytes. The importance of a check on the selectivity of sensors is emphasised.

Calcium↗