Serum potassium, determination

Renai function impairment Perform periodic BUN and serum potassium determinations to check kidney function, especially in patients with suspected or confirmed renal insufficiency and in elderly or diabetic patients diabetic patients with nephropathy are especially prone to develop hyperkalemia. 

Fig. 13. (a) The cross section and chemistry of the Seralyzer reagent strip (Miles Ditignostic, Inc.) for serum potassium determination, (b) Comparison of strip and gravimetric analyses for potassium. 

Flo. 1. A control chart showing the results of serum potassium determinations performed daily on the same control serum (previously determined mean value, 4.40 mEq/liter). The warning and action limits are set at 2 SD and 3 SD, respectively. 

Fiq. 5. The effect on the coefficient of variation of continuous performance of serum potassium determinations carried out by one technician and assessed on the basis of duplicate determinations, performed in batches of six pairs of analyses [redrawn from Robinson (R6)]. 

Hypokalemia Hypokalemia may occur during therapy therefore, determine serum potassium levels frequently. 

Because indomethacin may increase serum potassium concentrations, indomethacin and spironolactone should be administered concomitantly with caution. Potassium-sparing diuretics should be used with caution, and serum potassium should be determined frequently in patients receiving an angiotensin-converting enzyme (ACE) inhibitor (e.g., captopril). Concomitant administration with an ACE inhibitor may increase the risk of hyperkalemia. The dosage of spironolactone should be reduced, or the drug discontinued, as necessary. Patients with renal impairment may be at increased risk of hyperkalemia [65]. 

Baseline ECG and serum potassium levels should be determined... 

Serum potassium concentrations were determined at the end of a 2-hour infusion of amphotericin deoxycholate (1 mg/kg/day) in a 2-year-old girl with systemic candidiasis receiving long-term hemodialysis for renal dysplasia (85). The potassium concentration was 6.7 mmol/1, despite dialysis against a 1.5 mmol/1 potassium bath just before the infusion. The next dose was given during dialysis, and the serum potassium concentration was 2.6 mmol/1 after the infusion. 

Other laboratory tests to assist in assessment and treatment include blood pH, serum C02, or PC02 (any 2) serum sodium serum potassium, BUN blood glucose and urine pH and sp gr. These determinations and the serum salicylate level should be followed serially during therapy (15). 

Procedure tlypokalemia must be corrected before starting this test and serum potassium monitored during the test. Fludrocortisone, 0.1 mg every 6 hours, is given for 3 days. Plasma is collected for aldosterone determination after a standing position has been maintained for 2 hours (for baseline measurement) and at the end of fludrocortisone administration. Twenty-four-hour urine collections for measurement of aldosterone are obtained 1 day before fludrocortisone administration is started and on day 3 of the test course. 

The kidney is the primary route of potassium elimination. Potassium is freely filtered with almost all of it being reabsorbed passively in the proximal tubule and the thick ascending limb of the loop of Henle. Therefore urinary potassium excretion is primarily determined by potassium secretion from the luminal cells of the distal tubule and collecting duct. The normal daily amount of potassium excreted in the urine is generally 40 to 90 mEq/L, but it can vary based on dietary intake, serum potassium concentration, and aldosterone activity. 

During the next 8 hours, the spontaneous ventricular rate (determined by briefly halting the transvenous pacemaker) progressively decreased to 33/min and then to 13/min. No atrial activity could he detected on the ECG. The QRS duration reached a maximum of 0.33 s (normal 0.1 s). Serum potassium increased to 8.7 meq/L (normal 3.5-5 meq/L). An antidote was administered. Serum potas.shmi rapidly fell to the normal range, and the patient made a complete recovery. 

Semm potassium is measured to determine if the patient has a normal range of potassium. The normal serum potassium is between 3.5 to 5.3 milliequiva-lents per liter (mEq/L). Caution Serum potassium less than 2.5 mEq/L or greater than 7.0 mEq/L can cause the patient to have a cardiac arrest. Diseases such as kidney disease can cause potassium to become imbalanced. When this happens, the patient will exhibit specific signs and symptoms and the serum potassium will be outside the normal range. 

Sodium and potassium in serum are determined in the clinical laboratory by atomic-emission spectroscopy, using an instrument designed specifically for this purpose [5]. Two filter monochromators isolate the sodium and potassium emission lines. A lithium internal standard is used, and the ratios of the Na/Li and K/Li signals are read out on two separate meters. The internal standard compensates for minor fluctuations in flame temperature, aspiration rate, and so forth. A cool flame, such as air-propane, is used to minimize ionization. Typically, the serum sample and standards are diluted 1 200 with a 100 ppm Li solution and aspirated directly. The instrument can be adjusted to read directly in meq/1 for sodium and potassium by adjusting the gain while aspirating appropriate standards. 

The treatment of hyperkalemia is to infuse slowly intravenous calcium gluconate (10 mL of 10% solution over 3 min). Soluble insulin (15 U intravenously) and 50 mL of 50% glucose solution should also be given intravenously [26], Plasma potassium should be determined hourly. Intravenous salbutamol also causes a reduction of serum potassium possibly by activating P-adrenergically stimulated membrane Na, K -ATPase [27). Longer term treatment might involve hemodialysis. 

Practical Example of the Addition Method Sodium and Potassium Determination in Blood Serum... 

To evaluate the precision for the determination of potassium in blood serum, duplicate analyses were performed on six samples, yielding the following results. 

FIGURE 5-17 Flow injection potentiometric determination of potassium in serum. (Reproduced with permission from reference 47.)... 

The above discussion does not mean that the use of urease and subsequently the use of an ammonia electrode is not practicable for a urea determination. Unfortunately, the commercial company that produced the urea analyzer, chose a conductivity procedure, which happens to be unsuitable for the laboratory of Neonatology. Had they chosen the ammonia electrode, which happens to be a relatively good electrode, and is especially specific, since only ammonia and not potassium can pass an air space, then the instrument could have been made highly specific for urea. In this case an ammonia determination would be done initially and then subtracted by the computer, from the amount which has been generated subsequently. In any case, with present technology, sensitivity is not adequate to use less than approximately 15fil of serum. 

Ng R.H., Sparks K.M., Statland B.E., Colorimetric determination of potassium in plasma and serum by reflectance photometry with a dry-chemistry reagent, Clin. Chem. 1992 38 1371. 

Several recent determinations of the alkali and alkaline earth metals in serum or urine have been reported. Barrett 29) determined potassium, sodium, and calcium in semm by diluting the samples with lanthanum chloride solution. Suttle and Field 3°) used atomic absorption spectroscopy to determine potassium and magnesium in sheep plasma. 

Table 3 summarizes those elements determined at levels exceeding the physiological concentrations. Bowman 96) determined 0.3 ppm lithium in serum by 1 10 dilution, and by adding sodium and potassium to standards. The concen-... 

This method is used to determine sodium and potassium in food, water and blood serum. The flame can be hydrogen/oxygen, methane/ oxygen or methane/air fueled. Wavelength selection can be by filter, prism Fig. 9.2 or grating and by either one or two detectors. 

In this case, sodium emission is monitored at a wavelength of 589.6 nm and potassium at a wavelength of 769.9 nm. The intensity of emission is calibrated with appropriate standards for the samples to be analyzed. In this way it is possible to automatically determine 100 values of sodium and potassium for 100 samples/h using modern clinical instruments. Limits of detection are sub-ppm and for serum values 140 mg/m the range of reproducibility is on the order of 2-3%. 

Distribution. Cyanide is rapidly distributed by the blood throughout the body. In a study using orally administered radioactively labelled potassium cyanide, radioactivity detected in whole blood or plasma decreased rapidly within 6 hours. Of the low levels of radioactivity detected in the red blood cells, about 94% of the radioactivity recovered was found in the hemolysate of which 70% was detected in the heme fraction, 14-25% in globin, and only 5-10% in cell membranes (Farooqui and Ahmed 1982). Yamamoto et al. (1982) determined that the pattern of distribution of cyanide did not vary with the concentration used. Ballantyne (1983b) observed higher cyanide levels in whole blood than in serum in rabbits exposed dermally to hydrogen cyanide, potassium cyanide, and sodium cyanide. See Section 2.3.2.1 for specific studies on cyanide tissue distribution. 

Examples of the use of FIA with ISE detection involve the determination of nitrate and total nitrogen in environmental samples [48, 49, 125, 166], potassium, sodium [125], calcium [51] and urea [124] in serum or major nutrients in fertilizers [73]. An interesting combination of an ISFET sensor with the FIA principle [52] is shown in fig. 5.17. This is a simultaneous determination of potassium, calcium and pH in serum during dialysis on an artificial kidney. 

Fig. 5.17. (a) A combination of FIA with ISFET detection [52]. For a description, see the text, (b) A recording of simultaneous determination of potassium, calcium and pH in serum by FIA with ISFET detection [52]. A - potassium standard B - calcium plus pH standard 0 - baseline values in the carrier solution (physiological... 

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