Respiratory Acidosis and Hypercapnia

pH Control and Buffering Mechanisms

• The body has sophisticated buffering mechanisms to maintain a stable pH, with three main buffer systems: bicarbonate, proteins (mainly hemoglobin), and phosphate systems.
• These buffer systems mop up excess hydrogen ions produced by cells.

Bicarbonate Buffering System

• The bicarbonate buffering system is the most important, making up approximately three-quarters of the body's buffering capacity.
• Hydrogen ions combine with bicarbonate ions to form carbonic acid, which dissociates to water and carbon dioxide.
• The reaction is driven to the right, meaning that hydrogen ions produced in cells and buffered by the bicarbonate system generate carbon dioxide and reduce available bicarbonate.

Control of pH

• Two organs control the pH of the body: the lungs and the kidneys.
• The lungs excrete carbon dioxide, and the kidneys remove hydrogen ions from non-volatile and organic acids into the urine.
• The blood transports acidic waste products from the site of production in the tissues to the site of excretion, namely the kidneys and lungs.

Acid-Base Balance

• The normal pH of the body is 7.4, which is maintained by the balance between the respiratory and metabolic components of acid-base metabolism.
• The respiratory component is controlled by the lungs, and the metabolic component is controlled by the kidneys.
• The lungs and kidneys interact and balance to control the pH of the body.

Disorders of Acid-Base Balance

• Disorders of acid-base balance can be divided into acidosis (low pH) and alkalosis (high pH), each having a metabolic and respiratory origin.
• Metabolic acidosis is characterized by a low bicarbonate concentration and can be caused by increased acid production, decreased acid excretion, or excessive loss of bicarbonate ions.
• Respiratory acidosis is characterized by a high pCO2 and can be caused by decreased respiration rate or lung disease.
• Metabolic alkalosis is characterized by a high bicarbonate concentration and can be caused by loss of hydrogen ions or administration of alkalotic agents.

Compensation Mechanisms

• Compensation for metabolic acidosis occurs through the respiratory pathway, where the lungs remove more carbon dioxide through hyperventilation.
• Compensation for respiratory acidosis occurs through the kidney, where more acid is excreted and more bicarbonate is generated.
• Compensation for metabolic alkalosis occurs mainly in the lungs, which retain carbon dioxide through slower breathing or hypoventilation.

Diabetic Ketoacidosis (DKA)

• DKA is a potentially life-threatening complication of diabetes mellitus, characterized by a lack of insulin and corresponding elevation of glucagon.
• It leads to increased release of glucose by the liver, high glucose levels in the urine, and dehydration.
• The absence of insulin also leads to the release of free fatty acids from adipose tissue, which are converted into ketone bodies, causing metabolic acidosis.
• The body initially buffers the change with the bicarbonate buffering system, but this system is quickly overwhelmed, and other mechanisms must work to compensate for the acidosis.