Metabolic alkalosis - causes, symptoms, diagnosis, treatment, pathology

Summary

Metabolic alkalosis occurs when blood pH rises above 7.45 due to increased bicarbonate concentration. It can result from loss of hydrogen ions through vomiting or excess aldosterone, or from primary bicarbonate gain via kidney reabsorption or antacid ingestion. Hypokalemia often accompanies it, affecting the body's compensatory mechanisms, including cellular ion transport and respiratory rate adjustments. The kidneys eventually correct the imbalance by retaining hydrogen ions and reducing bicarbonate reabsorption.

Takeaways

• 📝 Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate (HCO3-) concentration.
• 📝 Blood pH is maintained between 7.35 and 7.45, and deviations indicate an imbalance in the body's acid-base regulation.
• 📝 The condition can arise from two main causes: loss of hydrogen ions or gain of bicarbonate ions, often a combination of both.
• 📝 Loss of hydrogen ions can occur through the gastrointestinal tract, such as during vomiting, or through the kidneys.
• 📝 Excess aldosterone, possibly due to an adrenal tumor, can lead to increased reabsorption of bicarbonate and loss of hydrogen ions in the urine.
• 📝 Primary gain of bicarbonate can be caused by increased reabsorption from the kidneys, stimulated by factors like volume contraction or hypokalemia.
• 📝 Hypokalemia, or low potassium levels, can trigger the renin-angiotensin-aldosterone mechanism, leading to metabolic alkalosis.
• 📝 Excess bicarbonate ions can also come from external sources, such as the ingestion of large amounts of antacids like sodium bicarbonate.
• 📝 Metabolic alkalosis often leads to hypokalemia, as the body tries to maintain pH balance by shifting potassium and hydrogen ions.
• 📝 The body compensates for increased bicarbonate levels by using ion transporters in cells and adjusting respiratory rates.
• 📝 If not caused by renal issues, the kidneys can eventually correct the imbalance by retaining hydrogen ions and reabsorbing less bicarbonate.

Q & A

What is metabolic alkalosis?

Metabolic alkalosis is a condition where blood pH is raised above 7.45 due to an increase in bicarbonate (HCO3-) concentration in the blood.

What is the normal range for blood pH?

The normal range for blood pH is between 7.35 and 7.45.

How can loss of hydrogen ions lead to metabolic alkalosis?

Loss of hydrogen ions, which can occur from the gastrointestinal tract during vomiting or through the kidneys due to excess aldosterone, leads to a relative increase in bicarbonate ions, thus causing metabolic alkalosis.

Why does vomiting lead to loss of hydrogen ions?

Vomiting leads to loss of hydrogen ions because gastric secretions, which are acidic and rich in hydrogen ions, are expelled from the body. Additionally, the pancreas may not secrete bicarbonate to neutralize the acid in the intestines, leading to a buildup of bicarbonate in the blood.

How does aldosterone contribute to the loss of hydrogen ions?

Aldosterone stimulates the kidneys to excrete more hydrogen ions and reabsorb more bicarbonate, leading to a more acidic urine and a more basic blood pH.

What is the role of diuretics in causing metabolic alkalosis?

Diuretics, especially loop and thiazide diuretics, can cause volume contraction and excessive loss of extracellular fluid, which can stimulate the kidneys to reabsorb more bicarbonate, leading to metabolic alkalosis.

How does hypokalemia (low potassium levels) relate to metabolic alkalosis?

Hypokalemia can trigger the renin-angiotensin-aldosterone mechanism, leading to increased reabsorption of bicarbonate by the kidneys and thus contributing to metabolic alkalosis.

What is contraction alkalosis?

Contraction alkalosis is a type of metabolic alkalosis that occurs due to volume contraction or excessive loss of extracellular fluid, often as a result of diuretic use or severe dehydration.

How do antacids contribute to metabolic alkalosis?

Antacids, such as sodium bicarbonate, are used to neutralize stomach acid. Excessive use can lead to an excess of bicarbonate ions being absorbed into the blood, increasing the blood pH.

What are the body's mechanisms to counteract metabolic alkalosis?

The body counters metabolic alkalosis through cellular ion transporters that exchange hydrogen for potassium ions, respiratory adjustments that retain carbon dioxide, and renal mechanisms that retain hydrogen ions and reduce bicarbonate reabsorption.

How does hypokalemia act as both a cause and a result of metabolic alkalosis?

Hypokalemia can be both a cause, by triggering increased bicarbonate reabsorption, and a result of metabolic alkalosis, as aldosterone can cause potassium excretion in the urine.