Chapter 046. Sodium and Water (Part 14)

Liddles syndrome is a rare familial (autosomal dominant) disease characterized by hypertension, hypokalemic metabolic alkalosis, renal K + wasting, and suppressed renin and aldosterone secretion. Increased distal delivery of Na+ with a nonreabsorbable anion (not Cl–) enhances K+ secretion. Classically, this is seen with proximal (type 2)renal tubular acidosis (RTA) and vomiting, associated with bicarbonaturia. Diabetic ketoacidosis and toluene abuse (glue sniffing) can lead to increased delivery of β-hydroxybutyrate and hippurate, respectively, to the CCD and to renal K+ loss. High doses of penicillin derivatives administered to volume-depleted patients may likewise promote renal K+ secretion as well as an...
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Chapter 046. Sodium and Water (Part 14) Chapter 046. Sodium and Water (Part 14) Liddles syndrome is a rare familial (autosomal dominant) diseasecharacterized by hypertension, hypokalemic metabolic alkalosis, renal K + wasting,and suppressed renin and aldosterone secretion. Increased distal delivery of Na+with a nonreabsorbable anion (not Cl–) enhances K+ secretion. Classically, this isseen with proximal (type 2)renal tubular acidosis (RTA) and vomiting, associatedwith bicarbonaturia. Diabetic ketoacidosis and toluene abuse (glue sniffing) canlead to increased delivery of β-hydroxybutyrate and hippurate, respectively, to theCCD and to renal K+ loss. High doses of penicillin derivatives administered tovolume-depleted patients may likewise promote renal K+ secretion as well as anosmotic diuresis. Classic distal (type 1) RTA is associated with hypokalemia dueto increased renal K+ loss, the mechanism of which is uncertain. Amphotericin Bcauses hypokalemia due to increased distal nephron permeability to Na + and K+and to renal K+ wasting. Bartters syndrome is a disorder characterized by hypokalemia, metabolicalkalosis, hyperreninemic hyperaldosteronism secondary to ECF volumecontraction, and juxtaglomerular apparatus hyperplasia. Finally, diuretic use andabuse are common causes of K+ depletion. Carbonic anhydrase inhibitors, loopdiuretics, and thiazides are all kaliuretic. The degree of hypokalemia tends to begreater with long-acting agents and is dose-dependent. Increased renal K+excretion is due primarily to increased distal solute delivery and secondaryhyperaldosteronism (due to volume depletion). See also Chap. 278. Clinical Features The clinical manifestations of K+ depletion vary greatly between individualpatients, and their severity depends on the degree of hypokalemia. Symptomsseldom occur unless the plasma K+ concentration is with profound K+ depletion increase the risk of rhabdomyolysis. Smooth-musclefunction may also be affected and manifest as paralytic ileus. The electrocardiographic changes of hypokalemia (Fig. 221-16) are due todelayed ventricular repolarization and do not correlate well with the plasma K +concentration. Early changes include flattening or inversion of the T wave, aprominent U wave, ST-segment depression, and a prolonged QU interval. SevereK+ depletion may result in a prolonged PR interval, decreased voltage andwidening of the QRS complex, and an increased risk of ventricular arrhythmias,especially in patients with myocardial ischemia or left ventricular hypertrophy.Hypokalemia may also predispose to digitalis toxicity. Hypokalemia is oftenassociated with acid-base disturbances related to the underlying disorder. Inaddition, K+ depletion results in intracellular acidification and an increase in netacid excretion or new HCO3– production. This is a consequence of enhancedproximal HCO3– reabsorption, increased renal ammoniagenesis, and increaseddistal H+ secretion. This contributes to the generation of metabolic alkalosisfrequently present in hypokalemic patients. NDI (see above) is not uncommonlyseen in K+ depletion and is manifest as polydipsia and polyuria. Glucoseintolerance may also occur with hypokalemia and has been attributed to eitherimpaired insulin secretion or peripheral insulin resistance. Diagnosis (Fig. 46-3) In most cases, the etiology of K+ depletion can be determined bya careful history. Diuretic and laxative abuse as well as surreptitious vomiting maybe difficult to identify but should be excluded. Rarely, patients with a markedleukocytosis (e.g., acute myeloid leukemia) and normokalemia may have a lowmeasured plasma K+ concentration due to white blood cell uptake of K+ at roomtemperature. This pseudohypokalemia can be avoided by storing the blood sampleon ice or rapidly separating the plasma (or serum) from the cells. Figure 46-3