What is the role of the bicarbonate (HCO3-) buffer system in maintaining acid-base balance in the blood?

From the Guidelines

The bicarbonate buffer system plays a crucial role in maintaining acid-base balance in the blood by neutralizing excess acids or bases to keep blood pH within the narrow normal range of 7.35-7.45. This system consists primarily of carbonic acid (H2CO3) and bicarbonate ions (HCO3-), which work together as a chemical pair, as described in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. When excess acid enters the bloodstream, bicarbonate ions act as a base and neutralize the acid by accepting hydrogen ions, forming carbonic acid. Conversely, when the blood becomes too alkaline, carbonic acid releases hydrogen ions to neutralize excess base. This system is particularly effective because it can rapidly respond to pH changes and because the components can be regulated by both the lungs (through CO2 elimination) and kidneys (through bicarbonate reabsorption or excretion) 1. The lungs can quickly adjust blood pH by altering the rate of breathing to control CO2 levels, while the kidneys provide a slower but more sustained regulation by controlling bicarbonate levels. Some key points to consider include:

• The bicarbonate buffer system helps to maintain acid-base homeostasis in the human body, protecting cellular functions that depend on stable pH conditions.
• The system can be affected by various conditions, such as respiratory acidosis, which can occur when the pH of the blood falls below 7.35 in the presence of a raised CO2 level 1.
• The kidneys play a crucial role in regulating bicarbonate levels, and renal compensation can occur in response to changes in CO2 levels 1.
• In patients with chronic kidney disease (CKD), oral bicarbonate supplementation may be necessary to maintain serum bicarbonate within the normal range, unless contraindicated 1. Overall, the bicarbonate buffer system is essential for maintaining acid-base balance in the blood, and its regulation by the lungs and kidneys makes it a critical mechanism for protecting cellular functions and maintaining overall health.

From the FDA Drug Label

CLINICAL PHARMACOLOGY Intravenous sodium bicarbonate therapy increases plasma bicarbonate, buffers excess hydrogen ion concentration, raises blood pH and reverses the clinical manifestations of acidosis. Bicarbonate (HCO3-) is a normal constituent of body fluids and the normal plasma level ranges from 24 to 31 mEq/liter Bicarbonate anion is considered "labile" since at a proper concentration of hydrogen ion (H+) it may be converted to carbonic acid (H2CO3) and thence to its volatile form, carbon dioxide (CO2) excreted by the lung Normally a ratio of 1:20 (carbonic acid: bicarbonate) is present in the extracellular fluid.

The role of the bicarbonate buffer system in maintaining acid-base balance in the blood is to buffer excess hydrogen ion concentration and raise blood pH. The bicarbonate buffer system works by converting excess hydrogen ions (H+) into carbonic acid (H2CO3), which is then converted to carbon dioxide (CO2) and excreted by the lungs. This process helps to regulate the pH level of the blood and maintain acid-base balance 2.

• The bicarbonate (HCO3-) ion plays a crucial role in this process, as it is the primary buffer against excess hydrogen ions.
• The kidney also plays a role in regulating the plasma concentration of bicarbonate by acidifying or alkalinizing the urine as needed.
• In a healthy adult with normal kidney function, the glomerular filtered bicarbonate ion is almost completely reabsorbed, with less than 1% being excreted in the urine.

From the Research

Role of Bicarbonate Buffer System

The bicarbonate buffer system plays a crucial role in maintaining acid-base balance in the blood. Key aspects of this system include:

• Regulation of pH levels: The bicarbonate/carbon dioxide buffer system helps to maintain acid-base homeostasis by regulating pH levels in the blood 3.
• Measurement of acid-base status: Measurements of pH, PCO2, and HCO3- are used to estimate the severity of metabolic and respiratory disturbances 3.
• Compensation for acid-base disturbances: The lungs and kidneys employ compensatory mechanisms to minimize changes in pH caused by various physiologic and disease disturbances 3.

Mechanisms of Acid-Base Balance

The bicarbonate buffer system helps to maintain acid-base balance by:

• Regulating the levels of bicarbonate (HCO3-) and carbon dioxide (CO2) in the blood 3.
• Compensating for primary respiratory acidosis and alkalosis, as well as metabolic acidosis and alkalosis 3.
• Using the concept of the anion gap to categorize metabolic acidoses, and urine chloride excretion to define metabolic alkaloses 3.

Clinical Significance

Understanding the role of the bicarbonate buffer system in maintaining acid-base balance is essential for:

• Recognizing and treating acid-base disorders 3.
• Correcting the underlying cause of acid-base disturbances and associated hemodynamic and electrolyte derangements 3.
• Implementing specific therapies, such as renal replacement therapy, mechanical ventilation, and inhibition of specific enzymes in intermediary metabolism disorders 3.

Note: The study 4 does not provide relevant information on the role of the bicarbonate buffer system in maintaining acid-base balance.