Potassium balance

Aldosterone, the most potent of the mineralocorticoids (Figure 25.43), is involved in the regulation of sodium and potassium balances in tissues. Aldosterone increases the kidney s capacity to absorb Na, Cl, and HgO from the glomerular filtrate in the kidney tubules. 

Til tee successive tubule portions contribute to the ASDN the late portion of the distal convoluted tubule, the connecting tubule, and the collecting duct. The recent observation that collecting duct-specific inactivation of aENaC in the mouse kidney does not impair sodium and potassium balance, suggests that the more proximal nephron segments (late distal convoluted tubule, connecting tubule) are mainly important for-achieving sodium and potassium balance. 

Potassium homeostasis refers to the maintaining and regulating of a relatively stable and mostly internal (intracellular) potassium balance (concentration), although more generally it refers to the maintenance of potassium balance in any compartment (e.g. in the blood). 

Potassium balance is also primarily regulated by the kidney via the distal tubular cells. Reduction in nephron mass decreases tubular secretion of potassium, leading to hyperkalemia. Hyperkalemia is estimated to affect more than 50% of patients with stage 5 CKD.28... 

For this reason, spironolactone is not the diuretic of choice for long-term treatment of hypertension. Its major use appears to be in combination with other diuretics for the purpose of maintaining potassium balance. 

Potassium balance The effect of quinidine is enhanced by potassium and reduced if hypokalemia is present. The risk of drug-induced torsade de pointes is increased by concomitant hypokalemia. 

In the case of digoxin we can visualize what is happening. The site of action and binding site of digoxin is to tissue Na+K+ATPase. This enzyme is distributed very widely in tissues, and particularly in excitable tissue, which depends on it to restore sodium/potassium balance to resting levels after excitation. Digoxin preferentially distributes therefore to these tissues, and a disproportionately small component is left in the plasma compartment from which we sample. 

Adverse effects Renal function may deteriorate with the decreased circulating fluid volume, especially after the addition of another diuretic drug acting on the RAAS system, and careful monitoring of serum creatinine is essential. Serum potassium should be monitored within one week of initiation and at least every four weeks for the first three months and every three months thereafter. It should also be monitored at any dose change in spironolactone or if there is a change in concomitant medications that affects the potassium balance. The spironolactone dose (standard 25 mg per day) should be reduced if potassium levels are <5.4 mEq/L, and treatment should be discontinued if painful gynecomastia or serious renal dysfunction or hyperkalemia result. 

Disequilibrium in the eleetrolyte balanee ean provide diagnostic clues. For example, hyperkalemia causes tail T-waves in leads II, III, V2 to V4, when the potassium balance exceeds 5.5 mmol/1. In conjunction, the amphtude of the P wave is reduced and QRS is widened. Hyperkalemia is usually present when the amphtude of the T-wave is higher than that of the R-wave. With increasing potassium concentration, P-waves widen and eventually disappear. Accentuated hyperkalemia results in asystole. 

Control of potassium balance is particularly important if the patient is also taking digoxin (hypokalemia potentiates the action of digoxin). Because of the risk of hyperkalaemia, amiloride should usually be avoided in patients taking ACE inhibitors unless renal function is normal. 

Direct estimation of aldosterone in blood and urine shows a marked rise after injury (Zl). The secretion rate can be measured with a double isotope dilution technique, and increased amounts have been found in the adrenal vein blood and in the urine (Dl, Ul). The pattern of aldosterone release follows that of cortisol and is related in time and extent to changes in sodium and potassium balance and the severity of the injury (C5). 

The mean value of the aldosterone secretion rate in newborn infants is significantly less than in older infants (W4). Careful monitoring of sodium and potassium balance is required in the neonatal period because of a potential insufficient secretion of aldosterone. 

Supetoxide disnrutase, 626, 802,805 Sweating, sodium and potassium balance and, 726 728 Syneresis, 107... 

If there is an increased risk of toxicity (for example because of renal impairment or if potassium balance is difficult to maintain) careful withdrawal of digitalis may be worth attempting. 

Reactions that parallel those observed with penicillins include local reactions to parenteral administration, epi-leptogenicity, effects on sodium and potassium balance. 

The loss of potassium caused by diuretics is their most intensively debated adverse effect, and the extent and significance of the problem has long been disputed. The effect of diuretics on potassium balance and their chnical consequences have been reviewed extensively (50-52,65,100-102). The risks of diuretic-induced hypokalemia have been greatly exaggerated (50,65,102). A fall in plasma potassium is common, but sound studies have consistently showed that diuretics do not deplete body potassium or cause potassium deficiency during longterm therapy in hypertensive patients (50). 

Hyperkalemia is an occasional complication of heparin therapy. It has been attributed to hypoaldosteronism, and fludrocortisone has been used to treat it (12). It has been suggested that marked hyperkalemia is only likely to occur in the presence of other factors that alter potassium balance (13). 

Potassium penicUhn G can significantly alter potassium balance when given in very high doses 20 mUhon units of potassium penicUhn G contains about 30 mmol of potassium, and in patients with renal insufficiency this amount can decisively aggravate potentially lethal hyperkalemia. Similarly, large doses of sodium penicillin G, carbenicil-lin, or ticarcUhn can cause hypernatremia (29,30). 

Alpha epithelial sodium channel (aENaC) Collecting duct No effect on sodium and potassium balance [193]... 

The regulatory action of tbe renin-angiotensin system in controlling. sodium and potassium balance and anerial blood pressure is modiHed by va.sodilators called kinin.. Proteolytic en /.ymes tbal circulate in the pla.sma form kinins. Kalli-krein is activated in plasma hy noxious influences to act on... 

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