ChemPath: Acid-Base Handling ✔️ Flashcards
What is the normal range for H+ concentration?
35-45 mmol/L in ECF
What equation links H+ concentration to pH?
pH = log1/[H+] OR pH = -log[H+]
What are the three main physiological buffers?
- Bicarbonate (H+ + HCO3- –> H2CO3) in kidneys
- Haemoglobin (H+ + Hb –> HHb) in RBCs
- Phosphate (H+ + HPO4- –> H2PO4)
NOTE: also protein and bone
What is the rate of production of H+ ions per day?
50 - 100 mmol/day
How is bicarbonate regenerated?
Bicarbonate used up as it buffers H+ forming CO2+H2O
As bicarb must be regenerated, it then forms carbonic acid (H2CO3)
From the carbonic acid, H+ is excreted in the kidneys
Bicarbonate is reabsorbed in proximal convoluted tubule (AKA leads to regeneration of bicarbonate)
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
The 4 types of acid-base abnormalities:
- Metabolic acidosis
- Respiratory acidosis
- Metabolic alkalosis
- Respiratory alkalosis
- What is the primary abnormality in metabolic acidosis? List three causes with examples.
Primary abnormality = increased H+ (with decreased bicarbonate)
Caused by:
- Increased H+ production (e.g. DKA, lactic acidosis)
- Decreased H+ excretion (e.g. renal tubular acidosis)
- Bicarbonate loss (e.g. intestinal fistula)
1.1. How is metabolic acidosis compensated?
Stimulates respiratory centre –> decreased PCO2
H+ returns towards normal
Click to look at arterial [H+] against arterial pCO2 (kPa) plotted on a graph:
- What is the primary abnormality in respiratory acidosis? List three causes with examples.
Primary abnormality = 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
2.1. How is respiratory acidosis compensated?
Over few days, increased renal excretion of H+ and generation of bicarbonate
H+ returns to normal but pCO2 and bicarbonate remain elevated
- What is the primary abnormality in metabolic alkalosis? List three causes.
Primary abnormality = decreased H+ (with increased bicarbonate)
Caused by:
- H+ loss (e.g. pyloric stenosis)
- Hypokalaemia (e.g. diuretics)
- Ingestion of bicarbonate
3.1. How is metabolic alkalosis compensated?
Inhibit respiratory centre to increase pCO2 = increase [H+]
- What is the primary abnormality in respiratory alkalosis? List three causes.
Primary abnormality = reduced CO2 via lungs
Can be caused by hyperventilation due to:
- Voluntary (e.g. anxiety hyperventilation)
- Artificial ventilation
- Stimulation of the respiratory centre
4.1. What is the metabolic compensation for prolonged respiratory alkalosis?
If prolonged, this can lead to reduced renal H+ excretion and reduced bicarbonate generation
H+ returns to normal but PCO2 and bicarb remain low
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
What information is provided by ABGs?
- pO2
- pCO2
- pH
Steps to read ABG to assess acid-base status?
- H+/pH –> to determine whether acidosis or alkalosis
- pCO2 –> determine respiratory disturbance (primary or secondary)
- Bicarbonate –> determine compensatory mechanisms etc.
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+
