Definition, significance and measurement of quantities pertaining to the oxygen carrying properties of human blood.

A consistent set of definitions is given of the principal quantities pertaining to the oxygen transport by the blood, and of their mutual relationships, in relation to the methods used in their measurement. At the core is the correct definition of oxygen saturation, the deviation of which has recently been the cause of considerable confusion, especially concerning pulse oximetry. The occurrence, properties, determination, and pathophysiological and clinical significance of dyshaemoglobins, such as carboxyhemoglobin, methemoglobin, and sulfhemoglobin, are briefly described, together with possible consequences for diagnosis and therapy. In addition, attention is payed to the use of some haemoglobin derivatives, such as methaemoglobin and cyanmethaemoglobin, for clinical chemical and therapeutic purposes.

Simultaneous measurement of total hemoglobin and its derivatives in blood using CO-oximeters: analytical principles; their application in selecting analytical wavelengths and reference methods; a comparison of the results of the choices made.

Optical methods of quantifying total hemoglobin (tHb), applying the principles of the Lambert-Beer law, have been used both on untreated whole blood and on blood mixed with chemicals to form a stable chromophore, since the earliest days of laboratory medicine. The same principles may be applied for quantitation of the individual hemoglobin derivatives, such as oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb)1, as well as the non-oxygen transporting "dyshemoglobins", including carboxyhemoglobin (COHb) and methemoglobin (MetHb). The total hemoglobin measurement is typically carried out using a light source with a broad band of visible wavelengths. However, measurement of the derivatives requires using discrete, narrow bands of light in order to differentiate between the small differences of light absorbed by the individual derivatives. Either general-purpose, narrow band-pass spectrophotometers, or special-purpose photometers utilizing a set of fixed wavelengths, commonly referred to as "CO-oximeters" are suitable. Rapid, direct, photometric quantification of the derivatives, necessary in the clinical environment, relies on the specific light absorption characteristics of each hemoglobin derivative at the wavelengths selected, which in turn requires independent and exact knowledge of the concentrations of each entity in reference materials. This report examines the process involved in the selection of wavelengths and reference methods, contrasts the effects of the choices made and discusses some implications and limitations for routine measurement.

Comparison and assessment of blood gas related quantities including base excess, the gas exchange indices, and temperature corrected pH/PO2/PCO2, as defined in approved NCCLS standard C12-A, using a computer simulation of input variables.

Blood gases and related quantities reported to clinicians have, since the earliest days, included both directly measured as well as calculated or estimated quantities. Some developed as substitutes for quantities that were or are difficult to measure routinely, others to explain relationships between older, difficult to measure quantities and newly measureable quantities, and still others attempt to better understand the physiology of the acid-base process. The net result is a plethora of acid-base and related quantities that may be reported by different blood gas systems. In an attempt to address the issue of which quantities have stood the test of usefulness over time, and further, to examine the optimum algorithm for use in quantification, the NCCLS has developed, through its consensus process, a recommended set of quantities and their quantifying algorithms. We have studied these quantities and compared them with some other recognized approaches and present our analysis in this report. The major conclusion is that among those quantities recommended, the NCCLS algorithms present the most sensible overall approach and that we would recommend their use as described so that the quantities can be most effectively applied clinically, without differences in final values occurring due solely simple algorithm differences.

Biosafety implications in sample introduction: module design characteristics for discrete-sample systems used in critical whole blood analyte testing environments.

Systems designed for the measurement of pH/blood gases and expanded versions of these systems that include the ability to measure electrolytes or other related quantities, all incorporate one or more sampling modules that are limited in their ability to allow for the safe handling of potentially biohazardous blood samples. Systems that provide for injection of sample from a syringe use more than the required volume for sample testing and have the potential for causing splash-back of the sample if the introduction port is blocked. The probes of aspiration-based systems require manual dexterity by the operator and present the possibility of operator injury with a contaminated probe tip or the possibility of system damage as the probe extends and the operator moves the collection device into place. Some systems have the potential for both types of biohazards. This report describes the implications for system design of the sample collection devices commonly in use, and it offers a design solution that combines the ergonomics of an injection system and the operational advantages of an aspiration system, in combination, addressing the biosafety aspects in a unique fashion.

Total quality in blood gas analysis.

The critical nature of the clinical requirements when blood gas testing is ordered, coupled with the labile nature of the sample and rapidly changing patient conditions, make it imperative that the analyst be aware of more than just the analysis itself. This paper discusses the importance of the physiology of blood gas, the interpretation of basic blood gas results, the effects of the changing patient environment and the manner in which the sample was treated.