Biomedical subjects

A K Covington

Publications and source records attributed to A K Covington.

At least 19 recordsLinked to original sources

PubMed1997

International Federation of Clinical Chemistry (IFCC). Recommendation on mean molar activity coefficients and single ion activity coefficients of solutions for calibration of ion-selective electrodes for sodium, potassium and calcium determination.

In principle, flame photometry measures substance concentration, and ion-selective electrodes (ISEs) measure ion activity. However, 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 ion-selective electrodes with concentration calibrators, 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. Solutions are proposed for calibrating ion-selective electrodes for the determination of sodium, potassium and calcium. It is recommended that the values for single ion activities derived from the Pitzer treatment of mixed electrolyte solutions be adopted, because, although this has some empirical features, it has a sounder theoretical basis than the previously used Stokes-Robinson-Bates hydration approach.

Calcium↗

PubMed1995

International Federation of Clinical Chemistry (IFCC), Committee on pH, Blood Gases and Electrolytes: approved IFCC recommendation on definitions of quantities and conventions related to blood gases and pH.

Terminology in blood pH and gas analysis can be confusing, both because more than one name has been used for the same quantity, and because the same name has been used for more than one quantity. In addition, several calculated quantities are commonly used, but in some cases many different algorithms have been published for a single quantity. This document contains definitions of the most useful quantities in blood pH and gas analysis, and presents algorithms for the most useful calculated quantities. Use of these should lessen confusion among users and should also result in data that are more comparable among laboratories.

Algorithms↗

PubMed1995

International Federation of Clinical Chemistry (IFCC). Scientific Division. Committee on pH, Blood Gases and Electrolytes. Approved IFCC recommendations on whole blood sampling, transport and storage for simultaneous determination of pH, blood gases and electrolytes.

Pre-analytical variables, e.g., specimen collection, transport, and storage, can contribute significantly to inaccurate pH, blood gas, and electrolyte values. The International Federation of Clinical Chemistry (IFCC), through its Committee on pH, Blood Gases and Electrolytes, has developed specific recommendations to minimize the undesirable effects of pre-analytical variables. The Committee has drawn upon the experiences of its own members as well as published data by others. Specifically, the Committee has included pertinent guidelines and suggestions by the IFCC Working Group on Selective Electrodes (WGSE), the National Committee on Clinical Laboratory Standards (NCCLS), and the Electrolyte/Blood Gas Division of the American Association for Clinical Chemistry (AACC). This paper will familiarize the reader with the effect of different types of specimen containers and anticoagulants. It discusses important aspects of specimen collection procedures including patients status and special precautions during specimen collection from indwelling catheters or cannulae. The paper also identifies different requirements in storage and transport of specimens for blood gas and electrolyte analysis.

Anticoagulants↗

PubMed1994

Recommendations on whole blood sampling, transport, and storage for simultaneous determination of pH, blood gases, and electrolytes. International Federation of Clinical Chemistry Scientific Division.

Pre-analytical variables, e.g., specimen collection, transport, and storage, can contribute significantly to inaccurate pH, blood gas, and electrolyte values. The International Federation of Clinical Chemistry (IFCC), through its Committee on pH, Blood Gases and Electrolytes, has developed specific recommendations to minimize the undesirable effects of pre-analytical variables. The Committee has drawn upon the experiences of its own members as well as published data by others. Specifically, the Committee has included pertinent guidelines and suggestions by the IFCC Working Group on Selective Electrodes (WGSE), the National Committee on Clinical Laboratory Standards (NCCLS), and the Electrolyte/Blood Gas Division of the American Association for Clinical Chemistry (AACC). This paper will familiarize the reader with the effect of different types of specimen containers and anticoagulants. It discusses important aspects of specimen collection procedures including patient status and special precautions during specimen collection from indwelling catheters or cannulae. The paper also identifies different requirements in storage and transport of specimens for blood gas and electrolyte analysis.

Anticoagulants↗

PubMed1992

Dependence of measured ionized calcium on protein concentration as measured by three ion-selective electrodes.

A positive effect of protein on the measurement of ionized calcium in serum by ion-selective electrodes (ISEs) has been previously reported and the present study confirms this finding. Ionized calcium in serum was measured in the presence of increasing protein concentrations induced by venous stasis in 17 healthy volunteer subjects. Ionized calcium was measured using two commercial analysers, a Radiometer ICA2 analyser and a Baker Analyte+2 analyser, and a calcium cell devised by Covington for the calcium reference method (CRM). Both commercial analysers used charged ionophores and the CRM used a neutral carrier ionophore in the selective membrane. A small but significant rise in ionized calcium with increasing protein was measured on all analysers. Substitution of isotonic KCl for saturated KCl in the reference electrode of the CRM resulted in significantly reduced values for ionized calcium in paired serum samples when measured using the isotonic salt bridge. This study supports the premise that the positive effect of protein is related to the salt bridge concentration of the reference electrode rather than the ISE membrane composition.

Adult↗

PubMed1992

Recommendation on sampling, transport, and storage for the determination of the concentration of ionized calcium in whole blood, plasma, and serum. IFC Scientific Division, Working Group on Ion-Selective Electrodes (WGSE).

The substance concentration of ionized calcium (cCa 2+) in blood, plasma, or serum preanalytically may be affected by pH changes of the sample, calcium binding by heparin, and dilution by the anticoagulant solution. pH changes in whole blood can be minimized by anaerobic sampling to avoid loss of CO 2, by measuring as soon as possible, or by storing the sample in iced water to avoid lactic acid formation. cCa 2+ and pH should be determined simultaneously. Plasma or serum: If centrifuged in a closed tube and measured immediately, the pH of the sample will be close to the original value. If there has been a delay between centrifugation and measurement, causing substantial loss of CO 2, equilibration of the sample with a gas mixture corresponding to pCO 2 = 5.3 kPa prior to the measurement is recommended. Conversion of the measured values to cCa 2+ (7.4) is only valid if the pH is in the range 7.2-7.6. Ca 2+ binding by heparin can be minimized by using either of the following: 1) a final concentration of sodium or lithium heparinate of 15 IU/mL blood or less; or 2) calcium-titrated heparin with a final concentration of less than 50 IU/mL blood. Dilution effect can be avoided by use of dry heparin in capillaries or syringes.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Chemical Analysis↗

PubMed1991

International Federation of Clinical Chemistry (IFCC) Scientific Division. IFCC recommendation--recommendation on sampling, transport and storage for the determination of concentration of ionized calcium in whole blood, plasma and serum.

Explore the source record for details and available documents.

Blood Specimen Collection↗

PubMed1991

Comparative performance of 14-crown-4 derivatives as lithium-selective electrodes.

A series of neutral ionophore-based lithium-selective liquid-membrane electrodes have been prepared and the electrode performance compared with similar electrodes based on the lithium ionophores ETH 1810-ortho-nitrophenyl octyl ether (oNPOE) and ETH 2137-bis(1-butylpentyl) adipate (BBPA). By using a diamide substituted 14-crown-4 macrocycle, selectivities for Li+ in the presence of Na+ of log kpotLi,Na = -3.25 and -2.92 were obtained for diisobutylamide-oNPOE and di-n-butylamide-oNPOE derivatives. The di-n-butylamide-oNPOE based electrode functioned satisfactorily in serum, exhibiting a fast response time (10-15 s), an acceptable lifetime of 50 d and minimal protein interference.

Autoanalysis↗

PubMed1991

Guidelines for routine measurement of blood hemoglobin oxygen affinity. IFCC Scientific Division, Committee on pH, Blood Gases, and Electrolytes.

Two methods for the routine determination of blood hemoglobin oxygen affinity are described. Both methods use whole blood and do not require special equipment, tonometry, or special gas mixtures. The first method consists of a one-point determination of p 50, and requires only 200 muL to 400 muL of whole blood, therefore making it suitable for the pediatric population. The second method uses multiple points, thereby establishing both the shape and position of the hemoglobin oxygen equilibrium curve between 10 and 99% oxygen saturation. Interpretation of p 50 is discussed in relation to evaluation of patients with hemoglobinopathies and as a parameter in estimating availability of oxygen to the tissues.

Blood Gas Analysis↗

PubMed1991

International Federation of Clinical Chemistry (IFCC) scientific division IFCC recommendation. Recommendation on sampling, transport and storage for the determination of the concentration of ionized calcium in whole blood, plasma and serum.

The substance concentration of ionized calcium (cCa2+) in blood, plasma or serum preanalytically may be affected by pH changes of the sample, calcium binding by heparin, and dilution by the anticoagulant solution. pH changes in whole blood can be minimized by anaerobic sampling to avoid loss of CO2, by measuring as soon as possible or by storing the sample in iced water to avoid lactic acid formation. cCa2+ and pH should be determined simultaneously. Plasma or serum: if centrifuged in a closed tube and measured immediately the pH of the sample will be close to the original value. If delay has occurred between centrifugation and the measurement, causing substantial loss of CO2, equilibration of the sample with a gas mixture corresponding to PCO2 = 5.3 kPa prior to the measurement is recommended. Conversion of the measured values to cCa2+ (7.4) is only valid if the pH is in the range 7.2-7.6 Ca2+ binding by heparin can be minimized by using either of the following: a final concentration of sodium or lithium heparinate of 15 IU/ml blood or less, by use of calcium titrated heparin with a final concentration less than 50 IU/ml blood. Dilution effect can be avoided by use of dry heparin in capillaries or syringes. When heparin solutions are used errors due to dilution or calcium binding can be reduced using syringes with a heparin solution containing free calcium ions corresponding to the mean concentration of ionized calcium in normal plasma. Conditions for blood collection, storage, and transport to avoid preanalytical errors are described.

Blood Chemical Analysis↗

PubMed1991

International Federation of Clinical Chemistry (IFCC), scientific division: IFCC recommendation on sampling transport and storage for the determination of the concentration of ionized calcium in whole blood, plasma and serum.

Blood Coagulation↗

PubMed1990

International Federation of Clinical Chemistry (IFCC). Scientific Division. Committee on pH, Blood Gases and Electrolytes. Guidelines for transcutaneous pO2 and pCO2 measurement.

This document provides guidelines in the terminology, methodology, and in the interpretation of data obtained from the use of skin (transcutaneous) pO2 and pCO2 electrodes. The transcutaneous technique has found special application in newborn infants. The causes of analytical bias with respect to arterial blood gas values and imprecision obtained with transcutaneous pO2 and pCO2 electrodes are reviewed. Electrode temperatures above 44 degrees C should not be used routinely, and at a measuring temperature of 44 degrees C, the measuring site should be changed at least every 4 h to avoid skin burning.

Blood Gas Monitoring, Transcutaneous↗

PubMed1990

Guidelines for transcutaneous p O2 and p CO2 measurement.

This document provides guidelines in the terminology, methodology, and in the interpretation of data obtained from the use of skin (transcutaneous) p O2 and p CO2 electrodes. The transcutaneous technique has found special application for newborn infants. The causes of analytical bias with respect to arterial blood gas values and imprecision obtained with transcutaneous p O2 and p CO2 electrodes are reviewed. Electrode temperatures above 44 degrees C should not be used routinely, and, at a measuring temperature of 44 degrees C, the measuring site should be changed at least every 4 h to avoid skin burning.

Blood Gas Monitoring, Transcutaneous↗

PubMed1990

Guidelines for routine measurement of blood hemoglobin oxygen affinity. International Federation of Clinical Chemistry, Scientific Division, Committee on pH, Blood Gases and Electrolytes.

Two methods for the routine determination of blood hemoglobin oxygen affinity are described. Both methods use whole blood and do not require special equipment, tonometry or special gas mixtures. The first method consists of a one-point determination of p50, and requires only 200 microL to 400 microL of whole blood, therefore making it suitable for the pediatric population. The second method uses multiple points, thereby establishing both the shape and position of the hemoglobin oxygen equilibrium curve between 10 and 99% oxygen saturation. Interpretation of p50 is discussed in relation to evaluation of patients with hemoglobinopathies and as a parameter in estimating availability of oxygen to the tissues.

Abbreviations as Topic↗

PubMed1990

International Federation of Clinical Chemistry (IFCC). Scientific Division. Committee on pH, Blood Gases and Electrolytes. Guidelines for transcutaneous PO2 and PCO2 measurement.

This document provides guidelines in the terminology, methodology, and in the interpretation of data obtained from the use of skin (transcutaneous) P02 and PCO2 electrodes. The transcutaneous technique has found special application in newborn infants. The causes of analytical bias with respect to arterial blood gas values and imprecision obtained with transcutaneous P02 and PCO2 electrodes are reviewed. Electrode temperatures above 44 degrees C should not be used routinely, and, at a measuring temperature of 44 degrees C, the measuring site should be changed at least every 4 hours to avoid skin burning.

Bias↗

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.

Blood Gas Analysis↗