From the Guidelines
Bicarbonate is lost from the body through several key pathways, including renal excretion, gastrointestinal losses, respiratory compensation, sweat, pancreatic fistulas, certain medications, and lactic acidosis. The main ways bicarbonate is lost include:
- Renal excretion: The kidneys can excrete excess bicarbonate in urine, particularly in conditions like renal tubular acidosis or during metabolic alkalosis, as noted in the management of individuals with chronic renal failure 1.
- Gastrointestinal losses: Diarrhea is a major cause of bicarbonate loss, as bicarbonate-rich intestinal secretions are lost, and severe vomiting can also lead to loss of gastric secretions containing bicarbonate.
- Respiratory compensation: In cases of metabolic alkalosis, the body increases respiratory rate to blow off CO2, effectively reducing bicarbonate levels.
- Sweat: During intense exercise or in hot environments, small amounts of bicarbonate can be lost through sweat.
- Pancreatic fistulas: These can lead to significant loss of bicarbonate-rich pancreatic secretions.
- Certain medications: Carbonic anhydrase inhibitors like acetazolamide can increase renal bicarbonate excretion.
- Lactic acidosis: In conditions causing lactic acid buildup, bicarbonate is consumed to buffer the excess acid, as seen in hyperglycemic crises in patients with diabetes mellitus 2. Understanding these pathways is crucial for managing acid-base balance in various clinical scenarios, from simple dehydration to complex metabolic disorders, and correcting metabolic acidemia by maintaining serum bicarbonate at or above 22 mmol/L should be a goal of management, as suggested by the clinical practice guidelines for nutrition in chronic renal failure 1.
From the Research
Mechanisms of Bicarbonate Loss
- Bicarbonate (HCO3-) can be lost through various mechanisms, including: + Severe vomiting, such as in pyloric stenosis, resulting in metabolic alkalosis and hypokalemia 3 + Diarrheal conditions, where sodium bicarbonate is lost in large amounts, causing metabolic acidosis and hypokalemia 3, 4, 5 + Gastrointestinal bicarbonate loss, which is a common cause of hyperchloremic metabolic acidosis 4 + Renal tubular acidosis, where the kidneys are unable to reabsorb bicarbonate, leading to its loss in the urine 4, 6 + Certain diseases, such as hepatic failure, which can induce respiratory alkalosis, although the mechanisms are not fully understood 3 + Excessive loss of gastrointestinal secretions, which can disturb electrolyte balance and lead to bicarbonate loss 5
Renal Regulation of Bicarbonate
- The kidneys play a crucial role in maintaining acid-base balance by regulating bicarbonate levels 6
- The renal process of bicarbonate reclamation prevents the loss of bicarbonate in the urine, while bicarbonate regeneration replenishes the body's supply of bicarbonate 6
- However, certain conditions, such as parathyroid hormone excess, can limit renal bicarbonate reabsorption, leading to acidosis 7