11. Bartter Syndrome
Definition
Bartter syndrome is a form of hyperaldosteronism that results from hypertrophy and hyperplasia of the juxtaglomerular cells, with normal blood pressure and hyperkalemic alkalosis without edema, increased renin concentration, angiotension II, and bradykinin. It is the manifestation of one of three genetic expressions: neonatal Bartter syndrome, classic Bartter syndrome, and Gitelman syndrome.
Incidence
Bartter syndrome is extremely rare. The precise incidence is not known. The disease process is seen worldwide, with no exclusion of race and approximately equal occurrence in both sexes. The neonatal form is typically known before birth, whereas diagnosis of the classic form is typically made within the first 2 years of life.
Etiology
Bartter syndrome predominately occurs as neonatal or classic forms. Neonatal Bartter syndrome (NBS) is subdivided into two types: type I NBS comes from a mutation in the sodium chloride/potassium chloride co-transporter gene; type II NBS comes from mutations in the ROMK gene. Classic Bartter syndrome develops as a result of mutation(s) in the chloride-channel gene (CIC-kb).
In each of these three subtypes a large volume of urine that is high in sodium, potassium, and chloride is delivered to the distal segments of the renal tubules. In that area only sodium is reabsorbed while potassium is secreted.
The characteristics of the disease are hypokalemia, hypochloremia, metabolic acidosis, and hyperreninemia (while the blood pressure remains normal). In both types of Bartter syndrome, classic and neonatal, the sentinel histologic finding is hyperplasia of the juxtaglomerular apparatus. Other histologic findings are listed in the box on the following page.
Histologic Findings in the Patient with Bartter Syndrome
• Apical vacuolization of proximal tubular cells
• Glomerular hyalinization
• Interstitial fibrosis
• Juxtaglomerular apparatus hyperplasia
• Medullary interstitial cells hyperplasia (infrequent finding)
• Tubular atrophy
Signs and Symptoms
Neonatal Bartter Syndrome
• Maternal polyhydramnios
• Neonate with massive polyuria (12 to 50 mL/kg/hr)
• Preterm delivery
• Secondary fetal polyuria
Classic Bartter Syndrome
• Constipation
• Cramps
• Developmental delays
• Failure to thrive
• Fatigue
• History of maternal polyhydramnios
• Linear growth retardation
• Minimal brain dysfunction
• Muscle weakness
• Nonspecific electroencephalographic changes
• Polydipsia
• Polyuria
• Preterm delivery
• Recurrent carpopedal spasms
• Salt craving
• Volume depletion
• Vomiting
Medical Management
Correction of dehydration is important, along with “realignment” of electrolyte values. The patient with NBS is frequently treated with indomethacin combined with potassium supplementation. The patient with classic Bartter syndrome is treated with potassium supplements, which are frequently insufficient; potassium-sparing diuretics may be added with only transient effects. The best method for correction of hypokalemia is administration of prostaglandin synthetase inhibitors. The patient, no matter what age, is encouraged to take in food and drink rich in potassium, such as bananas, citrus fruits and juices, tomatoes, and skim milk. The patient’s activity level is typically not restricted; however, the possibility of dehydration must be closely monitored. Strenuous exercise should be avoided because of the increased probability of dehydration, exacerbation of potassium loss created by the dehydration, and the increased potential for functional cardiac dysfunction/dysrhythmias secondary to the excessive potassium loss.
Complications
Failure to thrive, growth retardation, and developmental delays occur in pediatric patients (neonatal or classic Bartter syndrome) if symptomatic treatment is not instituted. Dehydration can exacerbate electrolyte imbalances and produce cardiac dysrhythmias and/or sudden cardiac death. Chronic hypokalemia progresses over time to culminate in chronic renal insufficiency and/or renal failure.
Anesthesia Implications
For the anesthetist the primary focus for a patient with Bartter syndrome should be on the fluid status and electrolyte levels, particularly in procedures with expected large volumes of blood loss, insensitive fluid losses, and third-spacing of fluids. The patient with Bartter syndrome is particularly prone to dehydration and hypokalemia. A good recommendation would be to place a second, large-bore intravenous line to facilitate rapid fluid administration if necessary. Also, a secondary infusion containing supplemental potassium chloride (KCl) may be appropriate.
Chronic hypokalemia may contribute to delayed gastric emptying, so it should be assumed that the patient has a full stomach at the time of induction. The patient with Bartter syndrome is more prone to develop an ileus, therefore gastric evacuation may be appropriate after the airway is secured. To help minimize the potassium losses from this source, it may be more appropriate to allow gastric fluids to drain via gravity rather than external suction. The best course of action might be to leave the nasogastric tube in place without suction or gravity drainage until a need is indicated by a feeling of nausea and/or very slow to absent bowel sounds.
Chronic hypokalemia can have an impact on the patient’s response to and recovery from neuromuscular blocking agents. It may also contribute to the presence of cardiac dysrhythmias and alter the activity of baroreceptors.
Hyperventilation may exacerbate both the hypokalemia and metabolic acidosis already present.
Because the patient with Bartter syndrome often has a history of treatment with prostaglandin inhibitors, the patient may be resistant to the effects of vasopressors.
