From the Guidelines
Metabolic alkalosis should be managed by addressing the underlying cause, correcting fluid and electrolyte imbalances, and using treatments such as oral or intravenous normal saline and potassium supplementation, as seen in the context of Bartter syndrome, a rare genetic disorder that can cause metabolic alkalosis 1.
Causes and Presentation
Metabolic alkalosis can occur due to various causes, including prolonged vomiting, excessive use of diuretics, hypokalemia, and certain endocrine disorders. In the context of Bartter syndrome, it is characterized by hypokalemic and hypochloremic metabolic alkalosis, often presenting with polyuria, hypochloremia, and hypokalemia 1. The disease can be confused with congenital chloride diarrhea, which also causes pronounced hypokalemic and hypochloremic metabolic alkalosis secondary to watery diarrhea.
Diagnosis and Differential Diagnosis
The differential diagnosis for metabolic alkalosis, especially when presenting with hypokalemia, is wide and includes distinguishing renal from gastrointestinal potassium loss and potassium shifts. In Bartter syndrome, fractional chloride excretion is usually elevated (>0.5%), which can help in distinguishing renal from extrarenal salt losses 1. Genetic analysis has become the preferred method for diagnosis, making diuretic tests obsolete due to their potential risks and uncertainties about their diagnostic value.
Treatment Approach
Treatment of metabolic alkalosis focuses on correcting the underlying cause and the associated fluid and electrolyte imbalances. For mild cases, oral rehydration with normal saline and potassium supplementation may be sufficient, while severe cases may require intravenous normal saline and potassium chloride supplementation. The goal is to expand the extracellular fluid volume and promote bicarbonate excretion, thereby normalizing the acid-base balance. Monitoring of electrolytes, especially potassium, calcium, and chloride, is crucial during treatment to avoid complications such as arrhythmias.
Specific Considerations for Bartter Syndrome
In the management of Bartter syndrome, it is essential to consider the specific type and the associated complications, such as nephrocalcinosis and urolithiasis. The use of genetic analysis for diagnosis allows for targeted treatment approaches, and the avoidance of diuretic tests due to their potential risks, especially in infancy, is recommended 1. The treatment should be tailored to the individual's needs, taking into account the potential for severe volume depletion and the need for careful monitoring of electrolyte levels.
From the Research
Definition and Characteristics of Metabolic Alkalosis
- Metabolic alkalosis is defined by an increase in plasma HCO3- level (>26 mmol/L) and blood arterial pH (>7.43) 2.
- It is characterized by a primary elevation of serum bicarbonate and arterial pH, along with a compensatory increase in Pco2 consequent to adaptive hypoventilation 3.
- Metabolic alkalosis results from alkali accumulation or acid loss, and it is associated with a secondary increase in carbon dioxide arterial pressure (PaCO2) 4.
Pathogenesis of Metabolic Alkalosis
- The pathogenesis of metabolic alkalosis involves either a loss of fixed acid or a net accumulation of bicarbonate within the extracellular fluid 3.
- Generation of metabolic alkalosis may be due to excessive hydrogen ion loss by the gastrointestinal tract (e.g. vomiting) or by the kidney (e.g. use of loop diuretics) or may be due to exogenous base gain 2.
- Maintenance of metabolic alkalosis reflects the inability of the kidney to excrete the excess of bicarbonate because of hypovolemia, chloride depletion, hypokalemia, hyperaldosteronism, renal failure or a combination of these factors 2.
Treatment of Metabolic Alkalosis
- The cornerstone of treatment is the correction of existing depletions and the prevention of further losses 2.
- In vomiting-induced chloride depletion alkalosis, infusion of potassium chloride restores the excretion of bicarbonate by the kidney 2.
- Acetazolamide is an effective and safe form of therapy for metabolic alkalosis, with a quick onset and long duration of action 5, 6.
- A single dose of acetazolamide effectively corrects metabolic alkalosis in critically ill patients by decreasing the serum strong ion difference (SID) 6.