Hyperkalemia decreased renal potassium excretion

Hyperkalemia Associated with Decreased Renal Potassium Excretion... 

The exact mechanism of the pentamidine-induced hyperkalemia has not yet been defined. Many different mechanisms can impair the renal handling of potassium and thus favor hyperkalemia in patients with AIDS. These include decreased renal function secondary to volume depletion, presence of under-lying renal disease, including tubular dysfunction with the possibility of hyporeninemic hypoaldos-teronism, hypoadrenalism, and the administration of drugs with potential for impairing renal potassium excretion (nonsteroidal anti-inflammatory agents, ACE inhibitors, potassium-sparing diuretics. 

Potassium-sparing by diuretic agents, particularly spironolactone, enhances the effectiveness of other diuretics because the secondary hyperaldosteronism is blocked. This class of diuretics decreases magnesium excretion, eg, amiloride can decrease renal excretion of potassium up to 80%. The most important and dangerous adverse effect of all potassium-sparing diuretics is hyperkalemia, which can be potentially fatal the incidence is about 0.5% (50). Therefore, blood potassium concentrations should be monitored carehiUy. 

As nephron mass decreases, both the distal tubular secretion and GI excretion are increased because of aldosterone stimulation. Functioning nephrons increase FEK up to 100% and GI excretion increases as much as 30% to 70% in CKD,30 as a result of aldosterone secretion in response to increased potassium levels.30 This maintains serum potassium concentrations within the normal range through stages 1 to 4 CKD. Hyperkalemia begins to develop when GFR falls below 20% of normal, when nephron mass and renal potassium secretion is so low that the capacity of the GI tract to excrete potassium has been exceeded.30... 

Hyperkalemia poses an immediate threat to the life of the uremic patient. Although potassium excretion decreases with increasing nephron loss, hyperkalemia occurs infrequently in stable chronic renal failure when the glomerular filtration rate exceeds 10 ml/minute. Serum potassium, however, may rise sharply if renal function deteriorates suddenly or if an excessive potassium load enters the extracellular fluid space. The latter event may result from dietary indiscretion extracellular shift of potassium by acidemia potassium release by hemolysis, rhabdomyolysis, or tumor lysis, or administration of potassium-containing drugs. 

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