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At a glance

Inherited renal tubular defect resulting in urinary loss of magnesium, sodium, potassium, and chloride with otherwise normal kidneys. Hypokalemic metabolic alkalosis along with hypomagnesemia and hypocalciuria represent the most important features. A prolonged QT interval with possible “torsade de pointes” must be considered as part of serious anesthesia considerations.

Synonym

Primary Renotubular Hypomagnesemia-Hypokalemia Hypocalciuria Syndrome.

Genetic inheritance

Autosomal recessive renal disorder caused by mutation of genes encoding the thiazide-sensitive sodium-chloride cotransporter gene (SLC12A3 gene) and magnesium channels in the distal convoluted tubule. More than 100 different mutations distributed throughout the whole protein have been reported. Gene locus is 16q13.

Pathophysiology

Alteration of the thiazide-sensitive sodium chloride transporter impairs sodium and chloride reabsorption and stimulates renin and aldosterone secretion, resulting in hypokalemia and metabolic alkalosis. Reasons for renal magnesium wasting are unknown.

Diagnosis

Made by biochemical changes (alkalosis, hypokalemia, hypomagnesemia, hypocalciuria). Although some features overlap with Bartter Syndrome, in contrast to ☞Bartter Syndrome, Gitelman Syndrome patients present later in life with hypomagnesemia, high fractional excretion of magnesium, and low calcium excretion, but no overt hypovolemia.

Clinical aspects

Late childhood presentation with hypokalemic metabolic alkalosis and hypomagnesemia. Either asymptomatic or occasional mild episodes of muscle weakness are often observed. Symptoms are precipitated by nonspecific illness and may consist of tetany. Patients are neither polyuric nor polydipsic, but they have hypocalciuria, renal magnesium wasting, and absence of nephrocalcinosis. Chronic dermatitis, skeletal problems with growth retardation (as a consequence of rickets), and chondrocalcinosis; rarely rhabdomyolysis (secondary to severe hypokalemia) can be observed in some patients. Long-term prognosis is rather good, especially when potassium losses are corrected. Treatment with oral magnesium corrects the magnesium deficit but not the metabolic alkalosis. The relationship of these skeletal abnormalities to magnesium wasting and hypomagnesemia is not clear.

Precautions before anesthesia

Obtain history of frequency and severity of tetany and muscle weakness as an indicator of disease severity. Obtain electrolyte levels (potassium, magnesium, calcium) and arterial blood gas analysis. Correct electrolyte abnormalities preoperatively. Hypokalemia, hypomagnesemia, and baseline QTc prolongation, corrected preoperatively in our patient, are all risk factors for drug-induced torsades de pointes (TdP) and sudden death.

Anesthetic considerations

Anesthetic management in our patient aimed at preoperative correction of electrolytes and acid-base disturbances and avoidance of drugs and events that prolong QT interval. Laryngoscopy and endotracheal intubation, noxious surgical stimulation, and stormy extubation may aggravate QT prolongation and favor dysrhythmias. Maintaining adequate depth of anesthesia is mandatory to limit the effect of nociceptive stimulation. Respiratory alkalosis from hyperventilation may acutely exacerbate hypokalemia and should be avoided. The catecholamine stress response associated with direct laryngoscopy and tracheal intubation further exacerbates hypokalemia (intracellular entry). The arrhythmogenic potential of hypokalemia is thought ...

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