Blood electrolyte measurement

The fact that 1 is fronting a host of molecular lumophore-spacer-receptor PET signaling systems appealed to Tusa, Leiner, and their collaborators at AVL Biosense Corporation, Atlanta, and Graz, Austria. Related sensory molecules now lie at the heart of blood electrolyte measurement in critical care units in hospitals [52], This is perhaps the clearest endorsement to date of the device capability of luminescent PET signaling systems. 

Figure 23. Measuring principle of a cartridge system using microsensors for the case of medical "point of care blood electrolyte measurements...

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. 

Miniaturized catheter-type ISE sensors, such as the implantable probe shown in Figure 5-20 represent the preferred approach for routine clinical in-vivo monitoring of blood electrolytes. For these intravascular measurements the reference electrode is placed outside die artery (in die external arm of die catheter), tints obviating biocompatability and drift problems associated with its direct contact with the blood. 

The properties of a pH electrode are characterized by parameters like linear response slope, response time, sensitivity, selectivity, reproducibility/accuracy, stability and biocompatibility. Most of these properties are related to each other, and an optimization process of sensor properties often leads to a compromised result. For the development of pH sensors for in-vivo measurements or implantable applications, both reproducibility and biocompatibility are crucial. Recommendations about using ion-selective electrodes for blood electrolyte analysis have been made by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) [37], IUPAC working party on pH has published IUPAC s recommendations on the definition, standards, and procedures... 

E 67. A 76-year-old male with a combined history of bronchiogenic carcinoma and CHF is maintained on a diuretic to control pulmonary and peripheral edema. Recent measurement of blood electrolytes reveals an elevated serum Ca2. ... 

The main challenge in designing clinically useful sensors is definitely the production of the electroactive element, i.e., the sensor membrane. The membrane is the place where the chemical recognition and discrimination processes occur. The membrane dictates, overwhelmingly, the quality of signal and durability of the sensor. Only a restricted number of membranes can be and are used in routine electrolyte and blood gas measurements ... 

However, in contrast to a direct measurement, where the analyte activity in the native sample is measured, in the indirect measurement (after dilution) this possibility is lost. In the latter case, only total concentration in a sample can be back-calculated . Additionally, because water plasma in a patient sample is not measured, the indirect method of measuring blood electrolytes in hyperlipemic/hyperproteinemic samples (i.e., in the cases of low plasma water vs. plasma volume) results in a negative bias compared to direct measurement (the bias is bigger with lower water content), while for samples with a high electrolyte content (i.e., high plasma water ionic strength) the indirect measurements will result in a positive bias. 

Measurement of ionized Mg + in human blood by ion-selective electrode in automatic blood electrolyte analyzer... 

Continuous hemodynamic monitoring is essential during all phases of hypothermia. Cardiac monitoring is necessary because of the increased risk of arrhythmias. Cardiac output is decreased 5% for every 1°C of body temperature reduction. This is thought to be secondary to bradycardia, which has been shown to occur with hypothermia (3). A pulmonary artery catheter may be placed if there is any question of hemodynamic instability. Arterial catheters are used for continuous blood pressure measurement, as well as for access to arterial blood for blood gas and electrolyte analysis. 

During each blood pressure measurement session, five measurements are recorded for each animal. The blood pressure is taken as the mean of the last 3 recordings. Urinary protein is determined by the Pyrogallol Red-molybdate method (RA-1000 Tech-nicon). Urinary sodium, creatinine and urea and serum electrolytes, creatinine, albumin, cholesterol and triacylglycerols are measured by a standard autoanalyser technique. Kidney samples are fixed in formalin and embedded in paraffin. Sections are stained with the periodic acid/Schiff technique. Focal glomerular sclerosis is scored semiquantitatively by light microscopy. 

Apart from specific antidotes (if they exist), the treatment of poisonings also calls for symptomatic measures (control of blood pressure and blood electrolytes monitoring of cardiac and respiratory function prevention of toxin absorption by activated charcoal). An important step is early emptying of the stomach by gastric lavage and, if necessary, administration of an osmotic laxative. Use of emetics (saturated NaCl solution, ipecac syrup, apomorphine s.c.) is inadvisable. 

The volume to be infused and rate of delivery are only part of the therapeutic plan for fluid therapy, albeit the most important in acute resuscitation. The electrolyte and acid-base status of the horse should also be considered and fluids chosen to help to correct physiological imbalances. Unfortunately, it is not possible to predict electrolyte and acid-base disturbances accurately based on clinical signs. Seemingly similar clinical presentations may have a quite different pathophysiology (Brownlow Hutchins 1982, Svendsen et al 1979). The recent availability of relatively inexpensive, portable blood gas and electrolyte measuring equipment (Grosenbaugh et al 1998) has made determining the acid-base status possible in ambulatory equine practice and allows the field veterinarian to monitor and treat these disturbances. As stated earlier, in the absence of specific laboratory information, fluid therapy should probably be limited to isotonic polyionic crystalloid fluids, possibly with the addition of 10-20 mEq/1 potassium chloride in the maintenance phase. 

In this section we review the current state of ISEs in connection with electrolyte and blood gas measurements including discussions on the specific membrane electrode systems used in electrolyte analyzers, the various approaches laken to incorporate the electrodes within biochemical instruments, and future prospects ft>r new ISEs in the area of clinical analysis. 

Within the next 5-10 years the use of ISE type devices for continuous monitoring during surgical procedures and at the bedside of critically ill patients should become commonplace. While there are still problems to overcome, recent experiments with animals have already demonstrated that such measurements are feasible. It is probable that biomedical instrument manufocturers will produce both extracorporeal (e.g., the Miles Biostator already mentioned) and catheter-type systems for continuous detection of blood electrolyte levels. The use of telemetry for monitoring ISE potentials will undoubtedly play a major role in the development of the catheter devices. Ideally, one can envision, in the near future, operating nrams equipped with in vivo or extracorporeal devices and video screens which continuously display the patient s electroijrte levels just as blood pressure and heart rates are currently monitored. 

Other Systemic Effects. Workers exposed for less than 5 years to TWA concentrations of 4.8-8 ppm had significantly elevated plasma sodium and chloride ions and decreased erythrocyte potassium and calcium (Pines 1982). However, the large variance in the electrolyte measurements among workers, the concomitant exposure to other chemicals, the fluctuating exposure concentrations, and the lack of a dose response for blood electrolyte alterations limit the value of this study. 

Chemical sensors have been developed by companies such as DuPont and Cygus Therapeutic Systems for the measurement of blood electrolytes and gases, and ion selective membranes are common in many clinical analyzer systems. While the use of chemical sensors for such determinations will continue to increase, sensor applications in clinical diagnostics will favor development and application of biosensors due to the high specificity residing in the biological component of these sensors. 

Table 24-2 shows the narrow concentration ranges of the major blood electrolytes. Therefore the demands for reliability and precision are extreme. The most frequent needs in the routine laboratory to assay for Na and in the same sample and to measure Ca are well-covered by the various devices on the market. 

Singh, R. and Roberts, M.S., Blood flow measurements in skin and underlying tissues by microsphere method—application to dermal pharmacokinetics of polar non-electrolytes, J. Pharm. Sci, 1993a, 82, 873-879. 

The second wave of electrochemical devices replaced flame photometry in many clinical laboratories by the ISE method in blood electrolyte (Na, K ) measurements. Improvement of electrochemical technologies played an important role in this development as well as safety considerations related to the use of flame photometry. The measurement of ionized calcium by potentiometry soon followed. The techniques for the potentiometric measurement of chloride, lithium, ionized magnesium, and total calcium are also available but need perfection mainly with respect to avoiding interferences. 

The CO2 content is an indirect measure of bicarbonate in the blood. Since most of the CO2 in the body is in the form of HCO3, the CO content indicates the status of base in the body. The venous CO level is commonly included when routine electrolyte levels are measured and should not be confused with the Pco that is found in arterial blood and measures respiratory acid. The normal range for CO content is 23-30 mEq/L (or mmol/L) for adults, 20-28 mEq/L (or mmol/L) for infants and children, and 13-22 mEq/L (or mmol/L) for newborns. The CO level, as an indication of the bicarbonate level, is regulated by the kidneys. An elevated CO2 level indicates metabolic alkalosis, whereas a decreased CO level indicates metabolic acidosis. 

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