ChemPath: Acid-Base Handling Flashcards
What is the normal range for H+ concentration? What is normal pH
35-45 nmol/L in ECF
pH 7.35-7.45
What equation links H+ concentration to pH?
pH = log1/[H+]
What are the three main physiological buffers?
- Bicarbonate (ECF, renal tubular fluid)
- Haemoglobin (RBC)
- Phosphate (renal tubular fluid/intracellular)
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. Where does this occur?
Via bicarbonate through the production of carbonic acid
Occurs in proximal tubules
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+ transporter)
What is the rate of production of carbon dioxide per day?
20,000-25,000 mmol/day
Describe the relationship between CO2 and repiratory rate
- Respiration 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
What are 3 mechanism of metabolic acidosis?
Caused by:
- Increased H+ production (e.g. DKA)
- Decreased H+ excretion (e.g. renal tubular acidosis)
- Bicarbonate loss (e.g. diarrhoea)
Describe the ABG results in a metabolic acidosis
- Low pH / increased H+
- Low pCO2
- Low HCO3-
What are 3 mechanisms of respiratory acidosis?
Caused by:
- Decreased ventilation
- Poor lung perfusion
- Impaired gas exchange
E.g. chronic lung disease (COPD), opioids, sedatives, neuromuscular weakness
NOTE: metabolic compensation is slower than respiratory compensation
Describe the ABG results in a respiratory acidosis
- Low pH / increased H+
- High pCO2
- High HCO3-
What happens in chronic respiratory acidosis?
Metabolic compensation will drive H+ down to near normal range, however pCO2 and bicarbonate will remain elevated
What are 3 mechanisms of metabolic alkalosis?
Caused by:
- H+ loss (e.g. pyloric stenosis)
- Hypokalaemia
- Ingestion of bicarbonate