Serum potassium

Glucose Lactic dehydrogenase (LDH) Phosphorus Potassium Serum glutamic-oxaloacetic transaminase (SGOT) Serum glutamic-pyruvic transaminase (SGPT) Sodium Total bilirubin Total cholesterol Total protein Triglycerides White cell differential count ... 

Pharmacology Potassium participates in a number of essential physiological processes, such as maintenance of intracellular tonicity and a proper relationship with sodium across cell membranes, cellular metabolism, transmission of nerve impulses, contraction of cardiac, skeletal, and smooth muscle, acid-base balance, and maintenance of normal renal function. Normal potassium serum levels range from 3.5 to 5 mEq/L. 

Hypersensitivity to these agents depressed sodium or potassium serum levels marked kidney and liver disease or dysfunction suprarenal gland failure hyperchloremic acidosis adrenocortical insufficiency severe pulmonary obstruction with inability to increase alveolar ventilation since acidosis may be increased (dichlorphenamide) cirrhosis (acetazolamide, methazolamide) long-term use in chronic noncongestive angle-closure glaucoma. 

Potassium, serum digoxin level prior to therapy... 

Higham PD, Adams PC, Murray A, Campbell RW. Plasma potassium, serum magnesium and ventricular fibrillation A prospective smdy. Q J Med 1993 86 609-617. 

ACE inhibitors are well tolerated in most patients but are not absent of side effects. ACE inhibitors decrease aldosterone and can increase potassium serum concentrations. Usually the increase in potassium is small, but hyperkalemia is possible. It is seen primarily in patients with chronic kidney disease or diabetes mellitus and in those on concomitant ARBs, nonsteroidal anti-inflammatory drugs, potassium supplements, or potassium-sparing diuretics. Judicious monitoring of potassium and serum creatinine values within 4 weeks of starting or increasing the dose of an ACE inhibitor often can identify these abnormalities before they evolve into more serious complications. 

Conversely, metabolic alkalosis results in hypokalemia as a result of a net loss of hydrogen ion in the serum. In response, the body releases intracellular hydrogen ion into the serum to increase the acidity of the blood in exchange for extracellular potassium ions. This creates a relative deficiency of serum potassium. Serum potassium falls approximately 0.6 mEq/L for each 0.1 unit rise in blood pH. Similarly, this is frequently termed false hypokalemia because there isn t a true deficiency in total body potassium. 

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

Methyl-2-propen-l-ol, purchased from Aldrich Chemical Company, was distilled from anhydrous potassium carbonate. It was added directly to the n-butyllithium solution using a long needle. The checkers quickly replaced the pressure-equalizing dropping funnel with a serum cap to carry out this addition. The funnel was fitted to a small dry flask to prevent the introduction of moisture during the addition period and replaced on the reaction flask immediately afterwards. 

Agents acting in the proximal tubule are seldom used to treat hypertension. Treatment is usually initiated with a thiazide-type diuretic. Chlorthalidone and indapamide are structurally different from thiazides but are functionally related. If renal function is severely impaired (i.e., serum creatinine above 2.5 mg/dl), a loop diuretic is needed. A potassium-sparing agent may be given with the diuretic to reduce the likelihood of hypokalemia. 

Diuretics (see Chap. 46) may be ordered for some patients receiving a cardiotonic drug. Diuretics, as well as odier conditions or factors, such as gastrointestinal suction, diarrhea, and old age, may produce low serum potassium levels (hypokalemia). The primary care provider may order a potassium salt to be given orally or IV. 

B. has the laboratory draw blood for a serum potassium level... 

POTASSIUM-SPARING DIURETICS. Ratients taking the potassium-sparing diuretics are at risk for hyperkalemia Serum potassium levels are monitored frequently, particularly during initial treatment. 

The drug is discontinued and the primary care provider is notified immediately if the patient experiences these symptoms or if the serum potassium levels... 

Adverse reactions observed with the administration of terbutaline include nervousness, restlessness, tremor, headache, anxiety, hypertension, hypokalemia (low serum potassium), arrhythmias, and palpitations. A serious, but rare, adverse reaction is pulmonary edema... 

Mild (5.S-6.5 mEq/L) to moderate (6.5-8 mEq/L) potassium blood level increases may be asymptomatic and manifested only by increased serum potassium concentrations and characteristic BOS changes such asdisappearance of P waves or Rereading (widening) of the QRS complex. 

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. 

Sodium and Potassium. For the electrolytes, sodium and potassium the flame pho meter is the instrument of choice (29). This instrument permits readily the dilution of the serum 200 fold, for analysis, using an internal lithium standard. Most instruments require 1 ml for analysis. It is therefore practicable to measure out 3pi and dilute it to 1 ml. This is best done with a sampler-diluter of high precision. The tip of the diluter needs to be a drawn out polyethylene tip, or the 5 pi will not be measured with any degree of accuracy. 

At present, calcium and magnesium are estimated almost exclusively by atomic absorption (36). Present instrumentation permits the dilution of the specimen to approximately 1 - 100 for calcium and even higher for magnesium. For many instruments, the two elements are not read out simultaneously such as is practicable for sodium and potassium with the flame photometer. The lower limit of serum volime at present, for the practical assay for calciim and magnesiim in the laboratory of Neonatology, is approximately 10 ul The instruments are very readily automated, and it is not uncommon for results to be available at the rate of 240 per hour in the routine laboratory, where a typical atomic absorption instrument such as a Perkin-Elmer has been attached to an automatic feed system. 

In the Phadebas TM amylase test (72) (Pharmacia Labs) the substrate was a water insoluble cross-TTnked blue starch in tablet form which also contains some inert ingredients, sodium and potassium phosphate buffer salts and sodium chloride. This polymer was hydrolyzed by amylase into water soluble blue starch fragments. After centrifugation the absorbance of the blue supernatant was proportional to the activity of amylase present in the test samples. The day to day variation on a quality control serum had a coefficient of variation of 2.7% based on 30 days of data in our laboratory. The method is simple, reproducible and uses microquantities of serum. 

Serum potassium concentration Is Increased by the concurrent administration of Intravenous potassium penicillin 6. The penicillin preparation contains 1.7 mmol of potassium per million units. Thus, a patient receiving 10 million units of the antibiotic receives 17 mmol (m q.) of potassium. 

Although rum ammonia levels are not routinely measured, it is a useful indicator of Reye s syndrome and should be monitored in newborns at risk of developing hyperammonemia Ammonia is produced in many analytically useful enzyme reactions and the ammonium ISE has been used as the base sensor in several enzyme electrodes (see next section). In addition to valinomycin, other antibiotics such as the nonactin homalogs and gramicidins also behave as ionophores. The nonactin homolo were originally studied for their ability to selectively bind potassiiun ions It was then discovered that ammonium ions were preferred over potassium ions, and the selectivity coefficient Knh+ = 0.12 was reported. Since ammonia is present at fairly low levels in serum, this selectivity is not sufficient to to accurately measure NH4 in the presence of K. An extra measure of selectivity can be gained by using a gas permeable membrane to separate the ammonia gas from the sample matrix... 

Contraindications include serum potassium >5.5 mEq/L at initiation or a creatinine clearance <30 mL/min. 

Repeat as necessary until serum potassium normalizes ° Electrocardiogram monitoring is indicated when infusion rates exceed 10 mEq/h... 

Treatment depends on degree of hyperkalemia and presence/severity of signs and symptoms (sometimes irrespective of actual serum potassium level). Mild 5.5-6 mEq/L—furosemide and sodium polystyrene sulfonate. Moderate 6.1-7 mEq/L—insulin, glucose, sodium bicarbonate,... 

Monitor serum potassium levels every 2 h until normalizes. 

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