Bicarbonate is a chemical compound that helps maintain the body’s pH balance. It acts as a primary buffer in the bloodstream, neutralizing excess acids and bases to prevent significant pH shifts. When the body’s pH deviates too much, various physiological processes can be negatively affected. Renal failure, also known as kidney failure, is a condition where damaged kidneys lose their ability to filter waste and maintain chemical balance. This decline in kidney function significantly impacts bicarbonate levels, leading to an acid-base imbalance.
The Kidney’s Role in Acid-Base Balance
Healthy kidneys play a central role in maintaining the body’s acid-base balance. They do this by excreting excess acids and regulating bicarbonate levels in the blood. The body constantly produces acids, such as hydrogen ions, which must be efficiently removed to prevent their accumulation.
The kidneys secrete hydrogen ions into the urine, primarily in the renal tubules. This process helps rid the body of acidic waste products and is crucial for keeping blood pH within a narrow, healthy range. Concurrently, the kidneys reabsorb bicarbonate from filtered blood back into the bloodstream.
Most filtered bicarbonate is reabsorbed, ensuring this buffer is not lost in the urine. Beyond reabsorption, kidneys also generate new bicarbonate, often coupled with hydrogen ion excretion. These combined actions of acid excretion and bicarbonate regulation are fundamental to preserving the body’s acid-base equilibrium.
How Kidney Failure Leads to Low Bicarbonate
In renal failure, kidneys lose their capacity to perform acid-base regulatory functions effectively, directly contributing to decreased bicarbonate levels. Damaged kidneys have a reduced ability to excrete the daily load of acids produced by metabolism. This means the body cannot eliminate these acids efficiently, leading to their accumulation in the blood.
This buildup of acids consumes available bicarbonate, causing levels to drop. For instance, kidneys in chronic kidney disease (CKD) become less efficient at producing ammonia, which helps neutralize acids and facilitate their excretion. This reduced ammonia production means fewer acids are effectively removed from the body.
Furthermore, damaged kidneys struggle to regenerate new bicarbonate or reabsorb it from the urine. While healthy kidneys reabsorb most filtered bicarbonate, impaired renal tubules in kidney failure cannot perform this function adequately. This diminished capacity for bicarbonate reabsorption and regeneration further depletes the body’s bicarbonate stores, resulting in metabolic acidosis. The severity of this metabolic acidosis often increases as kidney function declines.
Consequences of Low Bicarbonate
Chronically low bicarbonate levels, a hallmark of metabolic acidosis in kidney failure, can have widespread physiological impacts. Individuals might experience symptoms such as fatigue, weakness, nausea, and loss of appetite. The body may also attempt to compensate for increased acidity by increasing breathing rate, leading to deep and rapid breaths.
Over time, this persistent acid imbalance can accelerate the progression of kidney disease itself, creating a cycle where declining kidney function worsens acidosis, which in turn further damages the kidneys. Metabolic acidosis is also linked to bone demineralization, potentially increasing the risk of fractures as the body uses bone as a buffer to neutralize acid.
Additionally, low bicarbonate levels can contribute to muscle weakness and loss, sometimes referred to as “muscle wasting.” Metabolic acidosis is also associated with an increased risk of adverse outcomes, including death. These systemic effects underscore the importance of understanding and managing bicarbonate levels in renal failure.