PH measurement of blood

The pH measurement of blood samples must be made at body temperature to be meaningful. 

Optical measurements of blood gases Available at bedside in the CCU Continuous readout of p02, pC02, and pH Rapid response and improved patient care No handling of blood by health care workers... 

Measurements on electrochemical cells Potentiometric titrations pH measurements ( 0.1 pH unit) pH measurements ( 0.01 pH unit) in measurement of blood pH and C02 tension... 

Electrode systems for the rapid measurement of blood pH, gases, and ions would be of great value in intensive care units where these analyses... 

Because an exact temperature of 37 "C is essential for the accurate measurement of blood gases and pH, state-of-the-art instrumentation is fiirnished with thermal sensors embedded in the heat sink around the measuring chamber and communicating to the microprocessor. Audible or visible alarms signal deviation of temperature outside of preset tolerances (usually 37 C + 0.1 °C). Also of value is to use temperature-sensitive buffers, such as HEPES or TES, in pH quality assurance procedures. 

Abnormalities of acid-base status of the blood are always accompanied by characteristic changes in electrolyte concentrations in the plasma, especially in metabolic acid-base disorders. Hydrogen ions cannot accumulate without concomitant accumulation of anions, such as CL or lactate, or without exchange for cations, such as or NaL Consequently, electrolyte composition of blood serum or plasma is often determined along with measurements of blood gases and pH and to assess acid-base disturbances. 

The paper by Van den Vlekkert et al. [120] presented the measurements of temperature dependence of the surface potential t/>o at the 7 AI2O3 electrolyte interface. According to these authors, such investigations are of a double significance. Firstly, because this device can be used as miniature sensors of pH measurements, e.g. in the clinical measurement of blood acidity. Secondly, the function has some relations to the thermal effects accompanying adsorption of one proton or two protons on the oxide surface. Knowing these values, one can determine indirectly the values of these heats. The heat values obtained in this way can be compared with those determined from suitable analysis of calorimetric experimental data. 

The hydrogen ion concentration in blood may not be indicative of that in other body compartments. For example, the pH within cells, within the cerebrospinal fluid, or on the surface of bone may all be altered without causing an alteration in blood pH. Recognizing this caveat, the acid-base status of the body is usually analyzed based on measurement of blood pH. Alterations in blood pH serve as the basis for the diagnosis of acid-base disorders. 

On-line Measurement of Blood Gases and pH in an Extracorporeal Loop 947... 

Insulin therapy is adjusted based on hourly measurements of blood glucose and - if possible -blood ketones, the overall aim being a gradual decline in both. The initial decline is to a large extent due to rehydration and expansion of the extracellular volume. Repeated analysis of arterial blood gases may be indicated but only in those patients with very low pH values and/or poor chn-ical condition. Measurements of ketone levels in urine is in general unreliable in this phase these methods measure acetoacetate, which is quantitatively of minor importance compared with... 

Frequent measurement of blood gases, that is, oxygen partial pressure (PO2), carbon dioxide partial pressure (PCO2), and pH, is essential to clinical diagnosis and management of respiratory and metabolic problems in the operating room and the ICU. Considerable effort has been devoted over the last two decades to developing disposable extracorporeal and in particular intravascular fiber optic sensors that can be used to provide continuous information on the acid-base status of a patient. 

Uses Diagnostic aid for measurement of blood volume indicator changing color at pH 10 dyeing textiles, leather, and paper useful in a simple double-labeling procedure for studying axonal branching... 

Low-dispersion flow injection techniques (dispersion values of 1-3) have been used for high-speed sample introduction to such detector systems as inductively coupled plasma atomic emission, flame atomic absorption, and specific-ion electrodes. The justification for using flow injection methods for electrodes such as pH and pCa is the small sample size required ( 25 pL) and the short measurement time ( 10 s). That is, measurements are made well before steady-state equilibria are established, which for many specific-ion electrodes may require a minute or more. With flow injection measurements, transient signals tor sample and standards provide excellent accuracy and precision. For example, it has been reported that pH measurements on blood serum can be accomplished at a rate of 240/h with a precision of 0.002 pH. 

Although blood sampling for measurement of pH and PCO is essential for the accurate interpretation of aJunormal muscle pH, when muscle pH monitoring is in effect, the need for frequent blood sampling is reduced. In practice, blood pH and gases are measured when an abnormal muscle pH is first noted, when an unexpected fall in muscle pH i reater than 0,05 occurs, or when therapy does not produce the expected improvement in muscle pH. When the muscle pH value is stable in the normal range, measurement of blood pH is usually not n( cessary. 

Expired carbon dioxide partial pressure is important because it measures the adequacy of ventilation and provides a measure of blood pH this is because expired gas from the lungs is in equilibrium with blood passing through the lungs. (Note that blood serves to carry CO2, produced from aerobic metabolism, to the lungs in the form of carbonic acid, H2CO3.) Since deviations of only a few tenths of a pH unit in blood pH can be either the cause or the effect of serious disease, you can imagine how this is useful information to... 

Immersion electrodes are the most common glass electrodes. These are roughly cylindrical and consist of a barrel or stem of inert glass that is sealed at the lower end to a tip, which is often hemispherical, of special pH-responsive glass. The tip is completely immersed in the solution during measurements. Miniature and microelectrodes are also used widely, particularly in physiological studies. Capillary electrodes permit the use of small samples and provide protection from exposure to air during the measurements, eg, for the determination of blood pH. This type of electrode may be provided with a water jacket for temperature control. 

Fouling of the pH sensor may occur in solutions containing surface-active constituents that coat the electrode surface and may result in sluggish response and drift of the pH reading. Prolonged measurements in blood, sludges, and various industrial process materials and wastes can cause such drift. Therefore, it is necessary to clean the membrane mechanically or chemically at intervals that are consistent with the magnitude of the effect and the precision of the results requited. 

Aperture impedance measurements of cell volume must take into account the osmolaUty and pH of the medium. A hypotonic medium causes cells to swell a hypertonic medium causes them to shrink. Some manufacturers of aperture impedance counters deHberately provide hypertonic electrolytic media for red blood cell measurements. The shmnken red cells not only become more nearly spherical and thus less affected by orientation, but also less deformable than cells in isotonic media and thus less affected by differences in hemoglobin content. 

Glass pH electrodes are simple to use and maintain. They respond selectively to hydronium ion concentration and provide accurate measurements of pH values between about 0 and 10. They can be small enough to be implanted into blood vessels or even inserted into individual living cells. In precision work, these electrodes are calibrated before each use, because their characteristics change somewhat with time and exposure to solutions. The electrode is dipped into a buffer solution of known pH, and the meter is electronically adjusted until it reads the correct value. 

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