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Diagnosis and treatment of hyperkalemia

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Decreased distal delivery of sodium

Under normal circumstances, potassium is freely filtered across the glomerulus and then mostly reabsorbed in the proximal tubule and thick ascending limb. Potassium secretion begins in the distal convoluted tubule and increases in magnitude into the collecting duct. Tubular secretion is the component of potassium handling that varies and is regulated according to physiologic needs.

In acute kidney injury, the rapid decline in glomerular filtration rate and reduction in functioning nephron mass lead to decreased distal potassium secretion.

Hyperkalemia is a frequent problem when oliguria is present, since the reduction in distal delivery of sodium and water further impairs potassium secretion. Patients with oliguric acute kidney injury are more likely to have a more severe underlying disease state, and therefore tissue breakdown and catabolism further increase the risk of hyperkalemia.

In contrast, in nonoliguric patients, the renal injury tends to be less severe, and enough sodium and water are usually delivered distally to prevent hyperkalemia.

In chronic kidney disease, nephron dropout and reduction in collecting tubule mass also lead to a global decline in distal potassium secretion. However, this is countered by an increased capacity of the remaining individual nephrons for potassium secretion. High flow, increased distal sodium delivery, and increased activity and number of sodium-potassium ATPase pumps in the remaining nephrons account for this increased secretory capacity.14 As renal function declines over time, colonic potassium secretion progressively increases.15

These adaptive changes help to keep the plasma potassium concentration within the normal range until the glomerular filtration rate falls to less than 10 or 15 mL/min. Development of hyperkalemia with more modest reductions in the glomerular filtration rate suggest decreased mineralocorticoid activity or a specific lesion of the tubule.

Mineralocorticoid deficiency

Pharmacologic agents and conditions can interfere with renin-angiotensin-aldosterone system

Figure 1. A number of pharmacologic agents and conditions can interfere with the renin-angiotensin-aldosterone system, altering renal potassium excretion. Reabsorption of sodium in the collecting duct increases the luminal electronegativity, providing a more favorable gradient for potassium secretion. Aldosterone is critical for this reabsorptive process. A number of drugs and conditions interfere with the production of aldosterone and, as a result, reduce renal potassium secretion. In some patients, more than 1 disturbance may be present. NSAIDs = nonsteroidal anti-inflammatory drugs.

Decreased mineralocorticoid levels or activity due to disturbances in the renin-angiotensin-aldosterone system will impair renal potassium secretion. Such disturbances can be the result of diseases or drugs (Figure 1).13,16,17

Aldosterone deficiency can occur alone or in combination with decreased cortisol levels. Destruction of the adrenal glands is suggested when both hormones are reduced. Enzyme defects in cortisol metabolism can result in either isolated deficiency of aldosterone or adrenogenital syndromes associated with decreased mineralocorticoid activity.

Heparin administration leads to a reversible defect in adrenal synthesis of aldosterone. Drugs that block the stimulatory effect of angiotensin II on the zona glomerulosa cells of the adrenal gland will lower aldosterone.

Renin-angiotensin-aldosterone system blockers. Angiotensin-converting enzyme inhibitors block the formation of angiotensin II, whereas angiotensin II receptor blockers prevent angiotensin II from binding to its adrenal receptor. The direct renin inhibitor aliskiren lowers angiotensin II levels by blocking the enzymatic activity of renin and lowers the circulating levels of both angiotensin I and II.16

The syndrome of hyporeninemic hypoaldosteronism is a common cause of hyperkalemia in patients who have a glomerular filtration rate between 40 and 60 mL/min. Diabetic nephropathy and interstitial renal disease are the most common clinical entities associated with this syndrome.10 Other causes include analgesic nephropathy, urinary tract obstruction, sickle cell disease, systemic lupus erythematosus, and amyloidosis.

Nonsteroidal anti-inflammatory drugs can cause hyperkalemia by suppressing renin release and reducing delivery of sodium to the distal nephron.18

Calcineurin inhibitors impair potassium secretion by suppressing renin release and by direct tubular effects.19

Beta-blockers. Beta-1 and to a lesser extent beta-2 receptor blockade can also result in a hyporeninemic state.

Distal tubular defect

Hyperkalemia can result from interstitial renal diseases that specifically affect the distal nephron. In this setting, the glomerular filtration rate is only mildly reduced, and circulating aldosterone levels are normal.

Renal transplant, lupus erythematosus, amyloidosis, urinary obstruction, and sickle cell disease are conditions in which an impairment in renin release may coexist with a defect in tubular secretion.

Potassium-sparing diuretics impair the ability of the cortical collecting tubule to secrete potassium. Specifically, amiloride and triamterene inhibit sodium reabsorption mediated by the epithelial sodium channel located on the apical membrane of the principal cell. This effect abolishes the lumen’s negative potential and thereby removes a driving force for potassium secretion.

Trimethoprim and pentamidine cause similar effects.

Spironolactone and eplerenone compete with aldosterone at the level of the mineralocorticoid receptor and can result in hyperkalemia.

Drospirenone, a non-testosterone-derived progestin contained in certain oral contraceptives, possesses mineralocorticoid-blocking effects similar to those of spironolactone.

The plasma potassium level should be monitored when these drugs are prescribed in patients receiving potassium supplements, renin-angiotensin-aldosterone system blockers, or nonsteroidal anti-inflammatory drugs.20

CLINICAL FEATURES OF HYPERKALEMIA

Neuromuscular manifestations of hyperkalemia include paresthesias and fasciculations in the arms and legs. Severe elevation in potassium can give rise to an ascending paralysis with eventual flaccid quadriplegia. Typically, the trunk, head, and respiratory muscles are spared, and respiratory failure is rare.

Cardiac signs

Electrocardiographic signs of hyperkalemia

Figure 2. Electrocardiographic signs of hyperkalemia

Hyperkalemia has depolarizing effects on the heart that are manifested by changes in the electrocardiogram (Figure 2). The progressive changes of hyperkalemia are classically listed as:

  • Peaked T waves that are tall, narrow, and symmetrical and can occasionally be confused with the hyperacute T-wave change associated with an ST-segment elevation myocardial infarction.21 However, in the latter condition, the T waves tend to be more broad-based and asymmetric in shape.
  • ST-segment depression
  • Widening of the PR interval
  • Widening of the QRS interval
  • Loss of the P wave
  • A sine-wave pattern—an ominous development and a harbinger of impending ventricular fibrillation and asystole.

The plasma potassium concentration often correlates poorly with cardiac manifestations. In a retrospective review, only 16 of 90 cases met strict criteria for electrocardiographic changes reflective of hyperkalemia (defined as new peaked and symmetric T waves that resolved on follow-up).22 In 13 of these cases, the electrocardiogram was interpreted as showing no T-wave changes even when read by a cardiologist. In addition, electrocardiographic criteria for hyperkalemia were noted in only 1 of 14 patients who manifested arrhythmias or cardiac arrest attributed to increased plasma potassium concentration.

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