ChemPath: Acid-Base Handling
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What is the normal range for H+ concentration?
35-45 mmol/L in ECF
What equation links H+ concentration to pH?
pH = log1/[H+]
What are the three main physiological buffers?
• Bicarbonate • Haemoglobin • Phosphate NOTE: also protein and bone
What is the rate of production of H+ ions per day?
50 - 100 mmol/day
Describe how the kidneys excrete H+ ions.
Bicarbonate is regenerated through the production of carbonic acid
Describe how H+ ions pass through the renal epithelial membrane.
H+ ions cannot pass through the membrane itself so a transport system is necessary (Na+/H+ exchange)
What is the rate of production of carbon dioxide per day?
20,000-25,000 mmol/day
Describe the respiratory control over carbon dioxide.
• Respiratory is controlled by chemoreceptors in the hypothalamic respiratory centre • An increase in CO2 will stimulate an increase in ventilation which then brings down CO2 concentration (because CO2 increases pH)
What information is provided by ABGs?
• pO2 • pCO2 • pH
What is the primary abnormality in metabolic acidosis? List three causes with examples.
Primary abnormality is increased H+ (with decreased bicarbonate) Caused by: • Increased H+ production (e.g. DKA) • Decreased H+ excretion (e.g. renal tubular acidosis) • Bicarbonate loss (e.g. intestinal fistula)
What is the primary abnormality in respiratory acidosis? List three causes with examples.
Primary abnormality is increased CO2 (therefore, increased H+) and a slight increase in bicarbonate Caused by: • Decreased ventilation • Poor lung perfusion • Impaired gas exchange NOTE: metabolic compensation is slower than respiratory compensation
What is the primary abnormality in metabolic alkalosis? List three causes.
Primary abnormality is decreased H+ (with increased bicarbonate) Caused by: • H+ loss (e.g. pyloric stenosis) • Hypokalaemia • Ingestion of bicarbonate
What is the primary abnormality in respiratory alkalosis? List three causes.
Primary abnormality is reduced CO2 If prolonged, this can lead to reduced renal H+ excretion and reduced bicarbonate generation Can be caused by hyperventilation due to: • Voluntary • Artificial ventilation • Stimulation of the respiratory centre
What derangement of acid-base balance would be caused by pyloric stenosis?
Metabolic alkalosis due to loss of H+ from profuse vomiting
Which condition classically causes a mixed respiratory alkalosis and metabolic acidosis?
• Aspirin overdose • Aspirin stimulates ventilation and reduces renal excretion of H+