Pathology of Acidosis and Fistulae

Non-Respiratory Acidosis

• Characterized by high [H+], low pH, low PCO2, and low [HCO3]
• Compensation occurs through hyperventilation, which increases removal of carbon dioxide and lowers PCO2
• Hyperventilation is a direct result of increased [H+] stimulating the respiratory center
• Respiratory compensation cannot completely normalize [H+] since it is the high concentration itself that stimulates compensatory hyperventilation

Clinical Effects of Acidosis

• Compensatory response is hyperventilation, leading to Kussmaul breathing
• Increased [H+] leads to increased neuromuscular irritability, risking arrhythmias and cardiac arrest, especially with hyperkalaemia
• Depression of consciousness can progress to coma and death

Metabolic Alkalosis (Non-Respiratory Alkalosis)

• Characterized by primary increase in ECF bicarbonate concentration and reduction in [H+]
• Normally, an increase in plasma bicarbonate concentration leads to incomplete renal tubular bicarbonate reabsorption and excretion of bicarbonate in the urine
• However, in non-respiratory alkalosis, high renal bicarbonate reabsorption occurs due to factors such as:
  • Decrease in ECF volume
  • Mineralocorticoid excess
  • Potassium depletion
• Massive quantities of bicarbonate must be ingested to produce a sustained alkalosis

Causes of Metabolic Alkalosis

• Loss of hydrogen ion in gastric fluid during vomiting
• Ingestion of absorbable alkali as sodium bicarbonate
• Severe potassium depletion
• Consequences of diuretic therapy, leading to 'paradoxical' acid urine

Clinical Effects of Alkalosis

• Hypoventilation, confusion, and eventually coma
• Muscle cramps, tetany, and paraesthesia due to decrease in unbound plasma calcium concentration

Correction of Non-Respiratory Alkalosis

• Reversal of both primary cause and mechanism for its maintenance is required

Disorders of Hydrogen Ion Homeostasis

• Acidosis and alkalosis define primary acid-base disturbance, even when [H+] is within the normal range
• Definitions:
  • Non-respiratory (Metabolic) acidosis: Decrease in bicarbonate concentration
  • Non-respiratory (Metabolic) alkalosis: Increase in bicarbonate concentration
  • Respiratory acidosis: Increase in PCO2
  • Respiratory alkalosis: Decrease in PCO2
• Primary mixed acid-base disorders: Disorders of combined respiratory and non-respiratory origin
• 'Acidemia' and 'alkalaemia' refer to whether [H+] in blood is higher or lower than normal

This quiz covers the characteristics of non-respiratory acidosis, including biochemical changes and compensation mechanisms, as well as pancreatic, intestinal, and biliary fistulae and drainage.