What causes contraction alkalosis during diuresis?

From the Guidelines

Contraction alkalosis occurs during diuresis primarily due to the loss of fluid volume without a proportional loss of bicarbonate, as evidenced by the use of diuretics which can cause electrolyte and fluid depletion, as well as hypotension and azotemia 1. When diuretics promote excessive urination, they cause sodium and water excretion that reduces extracellular fluid volume. However, bicarbonate ions are not excreted at the same rate, leading to their relative concentration in the remaining blood volume. This creates a higher bicarbonate-to-fluid ratio, raising blood pH and causing metabolic alkalosis. Some key points to consider include:

• The loss of electrolytes, such as potassium and magnesium, which can predispose patients to serious cardiac arrhythmias, particularly in the presence of digitalis therapy 1.
• The risk of electrolyte depletion is markedly enhanced when 2 diuretics are used in combination 1.
• Volume depletion triggers increased aldosterone secretion, which enhances hydrogen ion excretion and sodium reabsorption in the kidneys, further worsening the alkalosis.
• Potassium depletion, which commonly accompanies diuretic use, also contributes by promoting hydrogen ion movement into cells in exchange for potassium moving out, raising blood pH even more. Treatment involves addressing the underlying volume depletion with isotonic saline and potassium replacement if needed, which dilutes the concentrated bicarbonate and corrects the alkalosis. The use of ACEIs alone or in combination with potassium-retaining agents can prevent electrolyte depletion in most patients with HF who are taking a loop diuretic 1.

From the Research

Causes of Contraction Alkalosis

• Contraction alkalosis is a condition that occurs when there is a decrease in the volume of fluid in the body, leading to an increase in the concentration of bicarbonate ions in the blood.
• Diuresis, or the increased excretion of urine, can lead to contraction alkalosis if not properly managed 2, 3, 4, 5.
• The use of diuretics, such as loop diuretics and thiazide diuretics, can enhance the renal excretion of sodium and water, leading to diuresis and potentially causing contraction alkalosis 2, 3, 4, 5.
• The mechanism of action of diuretics, including their effects on sodium and chloride transport, can contribute to the development of contraction alkalosis 4.
• Factors such as the dose and mode of delivery of diuretics, as well as the patient's underlying clinical condition, can impact the risk of developing contraction alkalosis 5.

Relevant Studies

• A study published in 2014 discussed the mechanism of action and effects of loop diuretics and potassium-sparing agents, including their potential to cause electrolyte imbalances and contraction alkalosis 2.
• A 2023 review summarized the therapeutic roles of thiazides and loop diuretics in blood pressure control and renal protection, highlighting the potential benefits and risks of diuretic therapy in patients with chronic kidney disease 3.
• A 1987 study examined the effects of thiazide diuretics on salt and water excretion, including their inhibition of sodium and chloride transport in the distal convoluted tubule 4.
• A 2015 article reviewed the clinical practice of using loop diuretics, including their dosage, mode of delivery, and potential side effects, such as contraction alkalosis 5.

Note: The study published in 1979 6 is not relevant to the topic of contraction alkalosis and diuresis.